I finally bought in! You can only read so much and then you have to BUILD something.
After reading for hours about all of the options to consider when building a Diesel motorcycle, I spent my mad money on the following parts.
1. Donor bike - 1974 Motoguzzi GT800. Why? It has a Huge hole where the engine can go. Heavy frame (over built). It was inexpensive($2000). Shaft drive.
2. Engine - Kubota D902 - $1700. Why? Super mini series. Small foot print engine. 892 cc, 160 lbs , 22 hp, 3600 rpm. Might need turbo..
The new engine is hanging in the frame.
Hurdles
1. CVT or Harley gear box. The stock gear box is to long.
2. Calculating the proper gear ratios. I would love to speak to someone the understand gear ratios. I have all of my number.
3. The never ending question.. What gear box? I spent hours looking at various ATV, snow mobile and Harley transmissions..
ALL of them have too large of a gear reduction to accommodate the diesels like of RPM..
I would love to speak to someone about plotting the optimal gear box.. ratios.
I am excited about this process and look forward to speaking with this group..
Your affliction seems to be quite advanced Kenneth. And the prognosis suggests a permanent condition. That said, great to see you diving right in. I agree the 902 is an excellent choice given the power-to-weight ratio. BTW, great price for that engine. And while there are turbo plug-and-plays, don't rule out the Aisin supercharger option (personal bias rooted in laziness). I've got a 902 in reserve waiting for the next build.
I suspect you've looked at Garbs 722/cvt combo in a CX500. Would be down-sized version of what your building. However, he was able to shoehorn the Comet 40 in since, with the 18 hp rating, it would handle his 722. Not so for you. Nonetheless, it's a good study in engineering.
And then here's a discussion to puzzle out what you're pondering utilizing a Harley box with limited space. You do appear to have a good bit of space topside.
Good choice of engine and donor but you are going to run into the same problems as me with my D722 and Dnepr donor.
If it is at all possible keep the original gearbox, (and its location!), and see if you can change the gear ratios.
Some ways I used to achieve this is:
-Bigger rims to fit larger tyres, great advantage of spoke wheels.
-Bigger final drive ratio
-Changing the actual gear ratios in the gearbox
-Machining the clutch-flywheel package to be as small as possible to create more room in front of the engine
-Modify front suspension to make room for the engine sticking out (I'm putting in an leading link fork).
-Put the engine in at an small angle leaning to the left, you'll clear the injection-pump-rail and you can relocate the alternator and oilfilter.
1. Ron- Turbo and super charging - Hopefully by going with the larger displacement of the D902 force air will not be needed. This will avoid expense, complexity and promote longevity.
2. Ron- Have I seen Garbs 722cvt CX500?.. YES..Amazing work..I would love to speak to him about the end result.
His set up is the way I am leaning...right now..
3. Ron - A Harley Gear box.. Because of the numerous aftermarket providers, custom gear ration can me bought.. Pricey tho..
3. Ron - Gear box or CVT - I think I prefer the CVT. But tuning the slow speed characteristics of a cvt can be difficult.. With a conventional clutch you can slip it until you pull away.. CVTs do not like to slip.. The CVTs critical issues will be over deceleration braking and the slow speed to neutral release point..
4. CVT negatives.. People, we love to hear the sound of our engines.. I had a CVT- Ridley mini harley. The sound of the 700 v twin was amazing.. It also made one hell of a sound when my friend reached over to blip the throttle.. Just as the word "NO" left my mouth the bike went through the garage door. Live and learn.. yes I know put it on the side stand..
5. Ron- Frame modification- Nothing is off the table.. The Guzzi group will disown me with they find out I am butchering a running Guzzi.. Shhhhh
6. Tet - Using the Stock gear box.. yes that is an option.
Pros: 1. it matched the Drive shaft input.
2. mounts are inplace
Cons 1. large, heavy
2. Custom gears sets are EXPENSIVE. No other stock gears are available that I have found
7. Tet - Bigger final drive ration - Bigger the final gear ratio is already to tall for the diesel engine. ??
8. Tet - Putting the engine in at an angle.. That is one option I am looking at to allow the CVT room..
Thanks for all of the great input..
I would LOVE to have a Final Gear ration conversation.. I have read so much about ratios.. I have confused myself.
Primary ratio? I can not figure out my stock primary ration.
Gear box ratio? The goal is to find a CVT that can create the same range.
Final drive ratio? I might have to switch to chain drive to compensate for the lower rpm of the diesel.
In the 2nd pic with the engine across the frame does it not have to be round the other way to get the correct rotation?
In the inline position it looks as if it will go further forward if you eased out or fabricated some bowed out down tubes.
However you are still left with the fixed ratios if using the standard gearbox.
Going across the frame would allow a Harley or other gearbox but you would then require some sort of 90 degree drive if keeping the shaft drive.
You might get an inline engine with chain drive gearbox in there but you would have to lift the gearbox up with a chain/belt drive to gearbox from flywheel then another chain/belt to the drive shaft which would need a small jackshaft to mount a sprocket and outrigger bearing.
The beauty of adding in a chain or belt will instantly give you an easy and cheap way of altering gearing.
A lot depends on your fabrication skills and available machinery. The simplest way would be across the frame with a Harley box and possibly a small jack shaft to bring the final drive/gearbox in line.
klwinter2 wrote:
6. Tet - Using the Stock gear box.. yes that is an option.
Pros: 1. it matched the Drive shaft input.
2. mounts are inplace
Cons 1. large, heavy
2. Custom gears sets are EXPENSIVE. No other stock gears are available that I have found
7. Tet - Bigger final drive ration - Bigger the final gear ratio is already to tall for the diesel engine. ??
You´re putting an really heavy cast iron diesel engine into your bike, those few pounds won´t make much of a difference.
I doubt that the current FD ratio is to tall for your diesel but if its really that high up, don´t change anything.
klwinter2 wrote:
Thanks for all of the great input..
I would LOVE to have a Final Gear ration conversation.. I have read so much about ratios.. I have confused myself.
Primary ratio? I can not figure out my stock primary ration.
Gear box ratio? The goal is to find a CVT that can create the same range.
Final drive ratio? I might have to switch to chain drive to compensate for the lower rpm of the diesel.
How do I confirm the ratio number?
Kenneth
The numbers from your gear commander screenshot seem off but you can count your gear ratios and calculate it yourself.
The ways to do that is as follows:
I'm using the final drive unit for my Dnepr as an example
#1 Counting teeth
I know its an 35/10 set.
Meaning that the Pignon (INPUT) gear has 10 teeth
and the Crown (OUTPUT) has 35 teeth
Simple devision:
OUTPUT devided by INPUT = Final Drive ratio
35/10=3.5
For this gear set the INPUT (Final drive shaft) will have to turn 3.5 times to turn the OUTPUT (Wheel) once.
#2 Counting revolutions
This once is easy but not as accurate
Turn the INPUT untill the OUTPUT has turned once, whilst counting the rotations of the INPUT.
So for my Dnepr FD unit I'd turn the Drive shaft (INPUT) 3.5 times before I have turned the wheel (OUTPUT) over once.
Using this you can calculate just about any gear ratio be it final drive or gearbox
Can you tell me how many rip-ems (RPM) the bike did when traveling lets say 60 MPH. If its below 3600 rip-ems I'd, REALLY advice you to stick with the stock gearbox.
"...the fearless Dutchman..." -Stuart
"...the mad Dutchman..." -Diesel Dave
Honda VT600 C Shadow
H̶o̶n̶d̶a̶ ̶C̶B̶R̶6̶0̶0̶F̶2̶
Mercedes-Benz W123 300D Sedan
CVTs aside, your primary drive ratio on a straight through transmission is 1:1. And in light of the available torque, my belief is that gearbox ratios are a moot point given that the top gear (be it a 4 or 5 speed) ratio is always 1:1. At that point it's all about final drive. The exception are those few (Royal Enfields and Suzuki LS650s as several examples) where final drive is sometimes set up (not by the factory) to run one gear down in the box to allow the top gear (1:1) to function effectively as an overdrive. Not ideal as you want to spend much of you time running 1:1 through the mainshaft to reduce friction losses and heat imposed by the countershaft (our UK chaps might prefer layshaft).
That said, here's a study in shaft-drive offsets that might be of interest.
gilburton
"In the 2nd pic with the engine across the frame does it not have to be round the other way to get the correct rotation?"
Maybe.. the engine turns anti-clock wise ( looking at the flywheel). The drive shaft turns clockwise ( from the engine side).
"In the inline position it looks as if it will go further forward if you eased out or fabricated some bowed out down tubes."
Correct. I can get about 5" more with a frame modification
"However you are still left with the fixed ratios if using the standard gearbox.
Going across the frame would allow a Harley or other gearbox but you would then require some sort of 90 degree drive if keeping the shaft drive.
You might get an inline engine with chain drive gearbox in there but you would have to lift the gearbox up with a chain/belt drive to gearbox from flywheel then another chain/belt to the drive shaft which would need a small jackshaft to mount a sprocket and outrigger bearing.
The beauty of adding in a chain or belt will instantly give you an easy and cheap way of altering gearing.
A lot depends on your fabrication skills and available machinery. The simplest way would be across the frame with a Harley box and possibly a small jack shaft to bring the final drive/gearbox in line."
Good Idea.. This is what I am thinking after studying it last night. .THANKS for the ideas!!
TET
"I doubt that the current FD ratio is to tall for your diesel but if its really that high up, don´t change anything."
It is this assertion that has me confused.. This is why I am trying to pin down the drive line gear ratios"
klwinter2 wrote:
The numbers from your gear commander screenshot seem off but you can count your gear ratios and calculate it yourself.
I will redo the gear chart.. I am going to start with the Stock motorcycle with stock gearing.. And the try to back in my application.
From a layman perspective.. it appears that since the diesel engine runs at 1/2 the RPM as the Stock engine, I simple need to Double my input speed into the drive line to maintain the same final ground speed.. MAYBE that is OVER SIMPLIFIED????
The stock bike engine had an RPM range of 0-7000 rpm for a ground speed of 100mph...
IF my diesel engine only spins at 3500 rpm - I will need to over-drive the stock trans/final drive to maintain the same ground speed?? AM I wrong with this logic ??
#1 Counting teeth
I know its an 35/10 set.
OUTPUT devided by INPUT = Final Drive ratio
35/10=3.5
I have a 8/37 ring and pinion. Stock Guzzi Gearing.
Thus a 1 : 4.625 ratio.
One rotation of the wheel takes 4.625 of the engine ( with no transmission)
Can you tell me how many rip-ems (RPM) the bike did when traveling lets say 60 MPH.
If its below 3600 rip-ems I'd, REALLY advice you to stick with the stock gearbox.
The number I have right now say 60mph at 3300. If this is true.
This is not the proper top gear ratio for touring?? I have the engine specs for the D902.
Based on the HP, fuel consumption and Torque Curves it would appear I should target 3000 rpms at 75 mph.
This will should put me in the sweet spot of the engine and limit the engine vibrations???
This machine will have to run on the US interstates. 75 mph is needed.
PLEASE Point out the ERRORS in my logic.[/color][/color]
I have the Specs for the stock motorcycle gear ratios.
Do most motorcycle transmissions run greater than 1:1 in the highest gear?
Click to zoom in..
4 gear is 1 : 0.0869
5 gear is 1 : 0.0750
If I am reading them correctly 4 and 5 gears are greater than 1:1.
Meaning over drive - output shaft spinning faster than the input.
This is correct?
If it is correct I am surprised to see a bike of this era (1974 Guzzi) running over square in the transmission.
Are you?
CVT considerations ..
I dont think a CVT can recreate the hi and low gear range.?? Low 1:2 Hi 1: 0.75
Everything I have read indicates 1 : 1 to be the HI on the CVT..
klwinter2 wrote:
"I doubt that the current FD ratio is to tall for your diesel but if its really that high up, don´t change anything."
It is this assertion that has me confused.. This is why I am trying to pin down the drive line gear ratios"
What I meant is; gasoline engines normally run higher rip-ems than diesel engines. Thus, if anything, the gearing will be to low for your diesel to attain the speeds you want. (See further explanation below)
klwinter2 wrote:
From a layman perspective.. it appears that since the diesel engine runs at 1/2 the RPM as the Stock engine, I simple need to Double my input speed into the drive line to maintain the same final ground speed.. MAYBE that is OVER SIMPLIFIED????
The stock bike engine had an RPM range of 0-7000 rpm for a ground speed of 100mph...
IF my diesel engine only spins at 3500 rpm - I will need to over-drive the stock trans/final drive to maintain the same ground speed?? AM I wrong with this logic ?? [/color]
You are talking maximum rip-ems. To attain the same speed with less rip-ems you will need to LOWER the gear ratio of the entire drive train. So you will have to put in less rip-ems for the same speed.
klwinter2 wrote:
I have a 8/37 ring and pinion. Stock Guzzi Gearing.
Thus a 1 : 4.625 ratio.
One rotation of the wheel takes 4.625 of the engine ( with no transmission)
Can you tell me how many rip-ems (RPM) the bike did when traveling lets say 60 MPH.
If its below 3600 rip-ems I'd, REALLY advice you to stick with the stock gearbox.
The number I have right now say 60mph at 3300. If this is true.
This is not the proper top gear ratio for touring?? I have the engine specs for the D902.
Based on the HP, fuel consumption and Torque Curves it would appear I should target 3000 rpms at 75 mph.
This will should put me in the sweet spot of the engine and limit the engine vibrations???
This machine will have to run on the US interstates. 75 mph is needed.
If that's what you want, go for it. Don't let me stop you.
But keep in mind that these engines were designed to run at 3600 rip-ems all-day.
klwinter2 wrote:I have the Specs for the stock motorcycle gear ratios.
Do most motorcycle transmissions run greater than 1:1 in the highest gear?
Nope. Most run higher, because rip-ems are fun.
klwinter2 wrote:
If I am reading them correctly 4 and 5 gears are greater than 1:1.
Meaning over drive - output shaft spinning faster than the input.
This is correct?
Eh, kind off? But I think you're using the terminology wrong here.
When we talk overdrive for vehicles it means that the engine rip-ems is lower than drive wheel rip-ems.
So you need to calculate your total drivetrain gear ratio for each gear.
Here's your top gear:
(Final drive ratio) Multiplied by (Gearbox ratio for that gear) = Total drive train ratio
4.625 * 0.750 = 3.469
Which is nowhere close to overdrive.
For each turn of the wheel the engine will turn over 3.469 times.
"...the fearless Dutchman..." -Stuart
"...the mad Dutchman..." -Diesel Dave
Honda VT600 C Shadow
H̶o̶n̶d̶a̶ ̶C̶B̶R̶6̶0̶0̶F̶2̶
Mercedes-Benz W123 300D Sedan
My apologies for the earlier reference to traditional automotive transmissions driven through the mainshaft at 1:1. Typical constant mesh boxes like the Guzzi in fact utilize the countershaft as the output shaft allowing for output ratios of the designer's choice.
For the sake of a common language, let's agree on certain terminology as there indeed may be some international differences. Let's see if I get this right.
1. A "high" ratio final drive is in regard to the ratio (e.g. 1:5). The RPMs delivered to the wheel are 1/5 that of the engine RPMs. A high ratio final drive should not be confused with thus producing a "high" speed. Quite the opposite. It will result in a much lower speed than a "low" ratio final drive for the same engine RPM.
2. A "low" ratio final drive (e.g. 1:3) will produce less torque but potentially a higher speed for the same engine RPM
3. Here in the colonies, the term overdrive has historically meant that the RPM delivered to the final drive is greater than that of the engine and separated from any reference to the final drive ratios. That is, the output shaft is spinning faster than the engine. The "overdrive" is attained by way of countershaft ratios, an integral overdrive unit or an auxiliary overdrive box. Not to confuse further, but final drive ratios can be such that a vehicle will be referred to as being "overdriven" while in the absence of a gearbox related overdrive.
Are the above assumptions correct? We all singing off the same sheet of music?
If so, and to summarize, given the limited RPM range of the Kubota, Kenneth's options would seem to be as follows.
1. Achieve the requisite overdrive via custom gearbox ratios (sell a kidney or two for this one)
2. Achieve the requisite overdrive via custom final drive ratios (see cost above plus the first-born)
3. Achieve the requisite overdrive via an intermediary jackshaft between/above the gearbox and shaft drive utilizing belts or chains (belts preferred)
4. Achieve the requisite overdrive via a chain final drive
5. Secure the holy grail of CVTs and live happily ever after
To your earlier point Kenneth, I would agree that 3,000 RPM is a reasonable target for cruising. You don't want that little Kubota at full cry just to achieve 75.
I clearly have too much time on my hands tonight..................
If you have the space and the skills to use them , A set of "quick change" gears for an automobile diff go for app $200 and range from 1:1 all the way to 5:1 ! more durable than a chain drive and cheaper than a shaft !
1. A "high" ratio final drive is in regard to the ratio (e.g. 1:5). The RPMs delivered to the wheel are 1/5 that of the engine RPMs. A high ratio final drive should not be confused with thus producing a "high" speed. Quite the opposite. It will result in a much lower speed than a "low" ratio final drive for the same engine RPM.
2. A "low" ratio final drive (e.g. 1:3) will produce less torque but potentially a higher speed for the same engine RPM
You are correct.. I was incorrectly swapping terms.. HIGH GEAR does NOT equal High ratio. My bad..
3. Here in the colonies, the term overdrive has historically meant that the RPM delivered to the final drive is greater than that of the engine and separated from any reference to the final drive ratios. That is, the output shaft is spinning faster than the engine. The "overdrive" is attained by way of countershaft ratios, an integral overdrive unit or an auxiliary overdrive box. Not to confuse further, but final drive ratios can be such that a vehicle will be referred to as being "overdriven" while in the absence of a gearbox related overdrive.
Correct.. I speaking of the gear box.. I was surprised that the 4th and 5th gear were Greater than a 1:1 output.. ie overdriven
Are the above assumptions correct? We all singing off the same sheet of music? MEEEE MEE MEEE . We are good here..
If so, and to summarize, given the limited RPM range of the Kubota, Kenneth's options would seem to be as follows. Options: I am targeting these two for now..
3. Achieve the requisite overdrive via an intermediary jackshaft between/above the gearbox and shaft drive utilizing belts or chains (belts preferred)
5. Secure the holy grail of CVTs and live happily ever after
I clearly have too much time on my hands tonight...... I am thankful you are here to bounce ideas off of.!!!
IF I can find an appropriate CVT for my application, I have a question about How the CVT works..
Constraints:
1. My nal rear end ratio is set at 1 : 4.625 . Shaft drive.
2. Diesel engine rpm is 1/2 the gas engines rpm.
3. Due to the lower rpm of my diesel engine I calculated I will need increase/over speed the output to the final drive by 1.28:1.
Ie 1 engine rpm makes 1.28 trans output to the rear end.
With these constraints, based in HOW a CVT works..
Should I building my rpm increase into the system BEFORE or After the CVT.. Load sensing and rpm are the fundamental forces that are tuned in a CVT to establish performance characteristics.
From the archives............... another study below of a project that shares some features with yours. While it's a snowmobile, it's using the D902 and a CVT. Noteworthy is the power and torque. Using a turbo and D1105 pump parts, they dyno'd at 55 hp and 78.4 ft. lbs. of torque at 3900 RPM. That should get you your 75 mph with no problem. Curiously, using a CVT their final drive number ended up at 1.48:1. But on a sled that's really the primary drive ratio of the CVT since there is no "final drive". Just an interesting read.
Great minds think alike.
I was studying snow machined.
Snow machines have had CVT for years and there seems to be MANY more after market parts for them.
Here in TN... I have never seen one...
No wait.. we had a neighbor moved to TN from MI..
They had a snow blower and a snow machine for sale in the middle of summer, 5 years after they move down here.. No one bought them...
It appears the snow machines have a chain reduction to the drive belt just like a motorcycles final drive..
Photos are hard to see the parts.. But here is what I found..
The green circle is where the Secondary clutch mounts. The Jack shaft includes the Brake, Then to the chain drive to the belt..
I'm steel looking for the ration in the chain case.
RON.
From the archives............... another study below of a project that shares some features with yours. While it's a snowmobile, it's using the D902 and a CVT. Noteworthy is the power and torque. Using a turbo and D1105 pump parts, they dyno'd at 55 hp and 78.4 ft. lbs. of torque at 3900 RPM. That should get you your 75 mph with no problem. Curiously, using a CVT their final drive number ended up at 1.48:1. But on a sled that's really the primary drive ratio of the CVT since there is no "final drive". Just an interesting read.
with a shaft bike you have another option... Chain AND CVT. Run a chain up to one side of the bike.... and a CVT down back to Shaft. This gives you adjustable ratios by changing sprockets. Few diesel ATV's went this route. The chain in their case was done to increase RPM at the first CVT pulley so it fell better with in the specs of the CVT they were using.
Course I guess one could do opposit....... and do CVT up to one side and chain and sprocket down to other side to spin the shaft. Not sure which is best.
Apparently these guys have some sort of Dual CVT as well though I suspect it is a CVT per track and not like the one in the trike in linked video above.
Klwinter2 I have responded to your other posting but I believe it is applicable here as well so I will cut and paste my responses to this thread as well
If you can get clutches that are tuned for use in diesel application you can worry about the rpm shift after the cvt. However most likely any off the shelf clutches you get will be designed for gas engine use and therefore higher rpm ranges. These clutches can be modified to function at lower rpms (heavier weights in the primary clutch, weaker spring in the secondary) but id recommend against that as rpm is your friend in order to generate the forces needed to keep enough pressure on the belt. What tappy said was spot on, increase the rpm before the cvt. Cvt sheave and belt size are incrimental with power increase but what it boils down to is torque, how much input in ft/lbs a cvt can handle throughout the designed rpm range before the sheaves lose grip on the belt will determine what size of cvt you need. A cvt spinning faster (rpm increased before it) will see less torque and therefore can be smaller. Gearing up after the cvt will have the cvt seeing more torque and will need to be larger to prevent slip. Every cvt system I have ever seen had the secondary clutch larger than the primary and it worked out that the belt traversed the entire face of the secondary when rpm was maxed out. This will only occur if the clutches are tuned for the used rpm range however. Also having the wrong size belt will prevent this. Cvt sets are designed/tuned as a set. They are tuned to work together, swapping around primary or secondary clutches could work but they will need to be retuned to work together. This is simple in principal but cvt tuning can be wizardry in my opinion especially in high hp applications. For your application what it boils down to is the faster you can have your cvt spinning, the smaller it can be and still handle the torque input without slipping. I had the same issue you are having with my build. Search cx500 Kubota. There are two threads on it. For my build I used a comet 40 series clutch witch based on comets rating of I believe a 16hp engine max (I figured for a gas engine the torque would be about 25 ft/lbs) would not be able to handle the torque output of 45 ft/lbs for my d722 engine. But I have an 8 inch htd pulley which drives a 4 inch pulley, doubling the rpm, and halving the torque. My primary clutch is then driven by the shaft that the 4 inch pulley is on. Theoretically the max torque it will see is 22.5 ft/lbs which I figured it could take without slipping. I did all this in order to use the comet 40 series (fairly small) as opposed to a much larger cvt I would normally need to run which I had no room for.
My system actually spins my primary clutch too fast. With stock tuning it was trying to drive at idle and opening up to max ratio far too fast. In order to fix this I lightened the weights in the primary until I could spin it up to about 2000 rpm on a digital rpm readout drill press without it opening. This way I could idle at about 1000rpm before the primary clutch started grabbing the belt (due to 2:1 ratio).
Also to add. The maximum speed that we can get out of our bikes is based on our power figures. You can generally get so much speed fro so much hp. In my original configuration (d722, now a z482 for ease of maintenance and radiator relocation) I Set a desired achievable max speed that I thought my engine could give and designed my transmission system, taking into account my fixed shaft final drive, to give me that speed near maximum engine rpm. To do this you need to know the final drive ratio of your cvt system. These ratios are available online for all comet cvts. You could get all the rpm issues figure out to use a certain cvt function properly but if it is trying to drive your bike at a speed that you don't have enough power to achieve, it wont work. Start with desired attainable speed at one end and max cruising rpm at the other, then calculate for everything in between to make the numbers match up. My transmission is slightly different as it has another step after the cvt before the shaft drive in the form of a sprocket on the secondary cvt shaft driving over to a sprocket on a stub shaft driving the shaft to the diff at the wheel. For me the calculation included engine rpm at max speed (3600), 2:1 ratio of the htd pulleys, max drive ratio of the cvt, sprocket to sprocket ratio after the cvt, then the fixed final drive ratio. My system is to be honest overly complex but the added step of the chain drive after the cvt allowed me to do my final tuning to get all my numbers in line. I believe I have a 1:1.5 ratio there, slowing the rpm input back down a bit. You should be able to get everything to work fine without this step. Basically my system over compensates for my cvt size (too fast) and the chain drive corrects this. This could have been avoided by overdriving my cvt less, maybe a 1.5:1 ratio instead of 2:1 but I had to use the 8 and 4 inch pulley sizes for different alignment reasons and was stuck with the 2:1 ratio.
IMHO the best/easiest option for you to do is to see if you can swap the shaft drive swingarm out for a chain driven style. This seems like an extra step but it will make the build much simpler overall. Then you could mount the engine sideways, drive to a Harley or similar tranny or mount a cvt modified to work at lower rpm right to the flywheel with a stub shaft, then chain drive to the rear wheel. I have plans to in the future use a guzzi frame but with a Kubota z602 which will hopefully bolt to the stock transmission and fit. Obviously that is maybe not an option for you as your engine is much larger.
Some details about my diesel Moto-Guzzi project that might answer some of your questions: the engine is a 3 cylinder Diahatsu 950, bought new. The tranny is the stock 1978 Moto-Guzzi Convert unit, which uses a hydraulic torque convertor to connect to the flywheel, making adaptation easier than fitting a Moto-Guzzi clutch. The Convert has a 2-speed tranny behind the torque convertor with a dry clutch in-between. High gear is for highway use, while low is used in town as it gives a bit better acceleration but limits top speed. There’s no neutral, so you only shift while stopped. Two speeds work fine in combination with a torque convertor, other than the torque convertor output rpm is always lower than the engine rpm. This is sometimes called “slippage”, and soaks up some of the engine power, which also means poor fuel economy compared to the other models. To make up for the slippage in the torque convertor the Convert final drive “differential” has taller gearing than other models; 9/34 (3.778:1) vs 8/37 (4.714:1). But, it isn’t easy to swap; the drive shaft and rear housing/swingarm are unique and won’t fit other transmissions unless the front input shaft from a 4 or 5-speed tranny is used, and the u-joints are also different, requiring some machining. Obviously if you’re starting with a 5-speed then you’ll need to find a complete Convert rear drive if you want to go this route to get 25% taller gearing. It’s worth noting that the Eldorado tranny has a slight overdrive in 5th (1.079:1).
The Convert rear end has a single brake disc but two brake calipers – a primary hydraulic one, and a cable operated parking brake that operates when the kickstand is down, preventing the bike from moving when the engine is started. Remember that the Convert tranny has no neutral, so it’s always in gear – don’t goose the throttle unless you want to start moving with the kickstand up. There’s a learning curve with Converts.
With my stock Convert tranny and stock final drive, 3600rpm gives about 64mph. That’s not fast enough for USA highways and freeways. I’m modifying the Convert tranny for taller gearing by changing the input shaft “primary” gear from the stock 19-tooth to a 24- tooth gear, which also means moving the intermediate shaft about 5mm. This will give it 80 mph at 3600 rpm, and obviously lower rpms at lower speeds, which should help fuel economy. I’ve already machined off the old gear and welded on the new one, and am in the process of relocating the intermediate shaft bearings to make everything line up properly. A 24 tooth gear is from a spare output shaft, or used parts places, or NOS.
I also have a T-3 5-speed tranny and the matching front drive shaft, in case I can figure out how to fit a clutch to the diesel flywheel that will work with the Guzzi tranny input shaft and clutch release mechanism, but that’s harder than modifying the Convert tranny gearing.
The original stock Convert with gas engine got around 35 mpg on the highway, somewhat better at lower speeds. If you have to deal with stop and go traffic, especially if traffic is creeping along, the Convert is great, since you don’t use the clutch at any speed. That saves your left hand. With the Daihatsu diesel the mileage went up to 45 mpg or so. Adding the Vetter streamlined nose increased that to about 65 mpg. The next step is to fabricate the tail, which is as important for proper aerodynamics as the nose, and should bump the mileage up even more, with a slight increase in top speed at 3600rpm, but probably not enough to keep up with freeway traffic, so the tranny mod is still necessary.
The Daihatsu engine is longer than the stock engine, and has a cooling fan and water pump on the front, so the chassis has been stretched about 5 inches. The taller engine also required different frame geometry to clear the valve cover. The stock fuel tank would no longer fit, so I made a new one that kept the angular lines of the original one – keep that in mind, it took one whole winter the way I work. YMMV.
The torque convertor generates heat so there’s also an oil cooler and pump in addition to the engine radiator. I kept the mechanical radiator fan for simplicity. The 30psi oil pump is driven directly by the crankshaft at the front. The Daihatsu exhaust manifold points straight out to the side, about where my knee would be. I fabricated a new one that points back, tucked in close to the chassis, like a real motorcycle. The tail pipe was originally a stainless steel bathroom grab handle ($5). The muffler is a chrome reproduction Triumph unit from Bent Bike. The stretched chassis require a longer speedometer cable, which isn’t like any other until I tried one from a snowmobile! The bike now weighs about 500 lbs, or about the same as the police version with all its equipment, or riding two-up. It also feels top-heavy, which isn’t surprising with the taller and heavier engine and the larger fuel tank (8 gallons when full). The longer wheelbase changed the handling, but on the road it feels solid and tracks like it’s on rails. At parking lot speeds the top-heaviness takes getting used to.
I’m very happy with the linked-brake system that came stock on the Convert. Also the floorboards. When I modified the chassis to fit around the fatter diesel engine I didn’t want to lose cornering ground clearance, which was also reduced by stretching the wheelbase, so the floorboards are a bit higher.
I’ve run out of ideas to offer. Ask questions and I might have an answer.
Very nice build GuzziJohnO. IMO stretching the frame to enable the engine to fit while using the stock transmission is the best route to go. I would have loved to do this with my build but the cx500 transmission is part of the engine case/block, it is not a seperate unit.
I had hoped to avoid cutting the frame for the diesel install.
That is not going to work, so I will modify as needed..
Right now it appears if I moved the whole engine forward 6 inches, I could use the CVT system.
It would require removing and modify the front two down tubes.
This will allow me retain the stock bike length..
My question are about CG affect of moving engine forward and crash bar strength.
1. By Moving the engine forward towards the front fender I can get the engine and CVTs into the frame. But it will change the balance of the machine.. Do you think moving the engine 6" forward would upset the CG too much???
2. Are the crash bars structural? ie are they strong enough to hold the frame shape while I build the engine mounts and come back with new front down tubes? red and yellow circles.
Before you start cutting metal just check that the front wheel and fender will clear the engine when fully compressed.
You could use a ratchet strap to pull it together.
Gilburton's point is well taken. Clearance at the front wheel appears to be at a premium. And if a no-go, would mean a frame stretch instead. But, before you resort to the blue tipped chisel (isn't that the proper British term for the torch? Or more commonly referred to here in the states as the "fire axe") are you certain that engine can't be nudged further forward. It can be narrowed considerably. The alternator does not have to be mounted where it sits. A local Amish machine shop modifies the front crank pulley to drive additional hydraulic pumps. And their modification could instead mount a pulley forward of the downtubes to drive the alternator off to the side. Doing so would allow you to drive only the water pump vertically from the crank utilizing a tensioner.
Interference by the oil filter could also be addressed with the front cover in the pic below that offers either left (with red cap) or right filter mounts. The unused base is then capped off. There's an accompanying option of a right angle filter base that allow you for a full 180 degree orientation including tucking it back along side the engine under the injection pump.
The oil filler casting on the pump side can also be unbolted and capped off with a plate, narrowing the engine even further up front. And the oil filler tube/cap can be repositioned to either the pan or valve cover. But, still not sure it would get you a full 6 inche.
As an aside, the other benefit of choosing this engine is that when it comes time to mount your sidecar, your reverse can be driven by the hydraulic or power steering pump that bolts to the back of the injection pump cam. No doubt that's what Kubota had in mind when they designed it.
If you haven't done it already, do read Russell's Kubota/ BMW build as it shares many parts with your engine, save that extra cylinder.
