What needs to change to make Yanmar L engines do high RPM?

[bhtooefr]

So, there's a couple ways to attack the RPM problem.

One is to find an engine that does high RPM already. However, as most of the high RPM engines are for automotive applications, most aren't suitable for motorcycle applications - too heavy, too complex, too big, too expensive, etc., etc.

Another is to take an engine and make it do high RPM. That's what this thread is about. Similar threads can be made for other engines (the Ruggerini twins would be an interesting choice to cover,) but I thought I'd post one up for the Yanmar L-series engine, including Chinese clones, given their incredible availability, and low cost.

So, what are the Yanmar's mechanical weak points, when it comes to high RPM (4000-5000 RPM)? How can they be fixed?

Once the mechanical weak points are fixed, what can be done to tune it to run more optimally at high RPM? I'm assuming camshaft regrinding will be necessary, or at least modifications to the valvetrain. It's already a quite short stroke engine (186 diesels are either 86x70 or 86x72, depending on whether it's a 406 or a 418,) but what's the rod ratio? (Of course, going to a shorter rod ratio could hurt, when it comes to wear.)

I'll readily admit that I have no expertise in this area, but I thought it might be worth getting people thinking. If the mods to make these engines run reliably at high RPM are relatively cheap and practical, then it might just be worth doing them.

[Diesel Dave]

Not an easy one to answer....

1) Flywheel can explode - replace with steel version
2) Conrod stretch/fracture - replace with higher quality steel
3) Piston weight - Direct injection = combustion chamber cast into the piston, replace with flat piston and cast a new head with indirect injection chamber.
4) Crank failure - replace with forged version.

The stock bits would be Ok up to 10% overspeed, after this your in the hands of the gods.

BTW I have seen a flywheel explode on a lathe - it took out several bricks in the facing wall and a 3" chunk out of the beds, the bits would not even slow down if passing through a human leg/groin.........

[bhtooefr]

1 and 4. Are there upgraded versions of these available, or would they have to be made? Looking around and not seeing anything, but...
3. However, there are direct injection diesels that get well into 5000 RPM territory (mine, a 1.9L VW TDI, will do 5100, with stock peak HP at 4000.) So, that means that there are suitable pistons, no? If nothing else, use one of those suitable pistons, with a custom rod. That takes care of #2, as well.

And, yeah, I know flywheels aren't anything to mess around with.

[andrewaust]

Diesel Dave is on the money, I've taken and held the L100 at 4200rpm, factory max is 3800rpm, I wouldn't take my engine any further, indirect diesels tend to have high rpms in light commercials and cars, but these have big journals etc to handle the speed. Mechanical injected diesels tend to like lower rpms even though some will rev, the torque is still in the low 2000rpms. Most small direct injected diesels tend to be set around 4000rpm, with larger variants set lower.

I've found that the L100 tends to like low rpms "2200-2400" for delivering power/torque, short shifting tends to accelerate the bike just as quick as revving through the gears, I'm only using high rpms when I get stuck out on the highways.

One very important thing about the L100's and probably more so the clones, take the rpms past the nominated max rpm I stated and you will start to get piston to valve clipping, not good for any engine.

A

[bhtooefr]

indirect diesels tend to have high rpms in light commercials and cars, but these have big journals etc to handle the speed.

Ah, that'll be a major issue, if that's a weak point on the Yanmar design.

Mechanical injected diesels tend to like lower rpms even though some will rev, the torque is still in the low 2000rpms. Most small direct injected diesels tend to be set around 4000rpm, with larger variants set lower.

As I understand, the pump is one limiting factor in some designs... then again, the one on the Yanmars probably is one of those designs.

I've found that the L100 tends to like low rpms "2200-2400" for delivering power/torque, short shifting tends to accelerate the bike just as quick as revving through the gears, I'm only using high rpms when I get stuck out on the highways.

Regrinding the camshaft and adjusting any fuel plates may move that power band up, though, no?

One very important thing about the L100's and probably more so the clones, take the rpms past the nominated max rpm I stated and you will start to get piston to valve clipping, not good for any engine.

So that's indicating valve float... stiffer valve springs would help there, right?

[Diesel Dave]

Also note the simple jerk pumps don't like operating at high RPM.

My lombardini triple uses single pump injector units like the old VW Pump-deuze to overcome this problem but it's also indirect injection so the pistons are much lighter.

It might be easier to convert to 2 stroke, upen some ports at the barrel base and use the valves as exhaust. You will need a blower, either a crank driven fan or a Turbo. Twice the bangs = twice the HP, very little extra weight and all the power is within the engine tollerances, 3800 will be like 7600 rpm.

[kapis]

the two stroke conversion would be very interesting project anyone up to it?

[John]

So, there's a couple ways to attack the RPM problem. What are the Yanmar's mechanical weak points, when it comes to high RPM (4000-5000 RPM)? How can they be fixed?

Apart from extending the usable range of each individual gear, the other advantage of more revs, is potentially more available power. But with diesels there is a problem. In terms of combustion, many, if not most diesels could produce usable power up to possibly 5500. But because diesel is a slow burning fuel, the torque levels tend to drop like a stone after approx 3500. Even in turbocharged engines the torque begins to fall away from its peak after 3000. There comes a point, even with charged engines, where despite the rising revs, the falling torque level means the power is going to level out & then decline. With naturally aspirated engines this effect is even more pronounced.
As a diesel rises to peak power revs, the air/fuel ratio approaches stoichiometric levels, similar to a petrol engine. In other words, there is a much smaller difference between the fuel consumption of a diesel & petrol at power peak than at any other point in the range. With ecu control, & modern high pressure injection systems, (2100 bar) adjustment & multiple injection sequences can offset some of the disadvantages, but the simple (read primitive) mechanical pumps of Yanclones & the like (200 bar), have no such facillity. The injection timing is fixed for all engine speeds, which is why they are noisy at idle & run out of puff at high revs! Their area of 'expertise' is naturally confined within a narrow rev band. As regards higher revs for Yanclones are concerned with standard timing, there are 2 statistics that illustrate the point about falling torque levels making a natural ceiling for HP. At 2500 rpm the engine makes about 16 ft/lbs (7.6 bhp). At 8.8 bhp maximum @ 3600, it is making just under 13 ft/lbs. With standard injection timing, the engine would make less power at 4000 than at 3600, so there is no advantage in revving out. With advanced injection, the engine would make more power at higher revs, but produce less torque (& power) & be less fuel efficient at lower revs, so you have to decide which compromise you are prepared to make!

[bhtooefr]

Hmm, looking at how the injection system works, I wonder if some sort of cam phasing system could be done. The problem would be phasing just the injection lobe, and not the intake or exhaust lobes, but if you can pass that hurdle, it could be phased off of the governor, so fully mechanically...

[Byrdman]

I've seen an L100 run at 9000rpm for a little while! Had a big, fat turbo bolted on it.

Bot much left afterward but she screamed for a bit.

[andrewaust]

John I've never taken the engine to 4900rpm where did you get that figure from (you've said it 4 times doing a search and must bring it to both your attention and others as running the Yanclone so high will explode the engine which could cause personal injury), max rpm is 4200rpm, compression 22:1 "yes not standard for UK and other countries it seems" and yes injection timing is set for high rpm, but it's doesn't seem to display anymore diesel knock then some of the other diesels. The Yanclones display a degree of diesel knock, even my gen set is loud and I have never touched it from new except for general maintenance. The Yanclones in Australia seem to be set for 10hp, not the 8.8.

John! If I have mistyped the rpm somewhere please let me know what thread it is and I'll correct it. If you take a Yanmar clone any further then 4400 you will get valve clipping "valve bounce hitting piston".

The engine has now done a considerable amount of kilometers with no hint of valve or piston problems, also remember John I had assistance to achieve 120khr . In ideal conditions 110 can be achieved, 100Khr is easy as long as it's not windy, flat road and under 30C. Also remember I am 73kg not using a large battery, only kick start and a solo saddle seat, I've stripped as much weight off the bike I possibly could. I also stated in this thread https://www.dieselbikeforum.com/view ... 2Fhr#p9903 "The bike will not do those speeds every day of the week either, but impressive when it does"

Thought I'd better clear that up.


A

[coachgeo]

To be honest with you.... and maybe this is for another thread... but why the need for increased RPM. Isn't it more logical to go with completely different gearing to go along with the inherint nature of the diesel engine? I dont know much about all this but I suspect Petrol bikes developed into RPM monsters cause its the nature of the petrol engine and the designs of trannies, gear ratios etc etc that are out there have simply grown to harness an RPM beast.

Diesel Beast is a torque monster. Design around that inherint nature seems the best route IMHO.

I may be WAYYYYYYYY off due to lack of knowledge though???

[Sphere]

400 cc yanclones are not torque monsters.

[coachgeo]

400 cc yanclones are not torque monsters.

equivilant to 400cc petrol in torque? Margionally better orr?

[Sphere]

The Enfield 350 develops 32Nm my 462 Hatz 26 ish I think. Should be similar for the yanclones.

[big al]

Some of the responders to this post are on the right track.Forget about over revving these diesels the cam grind and injection timing won't let you gain much of anything Well they will fall flat on their face as far as torque and horsepower's concerned at high revs.Your 10hp Yanmar and clones are designed with a governed speed of 3,600rpm and are made to run 24 hours a day at 3,000 rpm maybe 3,200 .So with my past experience with hopping up diesels in highway tractors i'll tell you what i'm planning with my build wich i've acquired all the parts for.
I'm using an actual Yanmar L series and hooking it up to a CB350n Honda tranny and gearing the primary to give me 85mph at 3,600 rpm in 5th gear wich leaves me with 70mph at 3,000rpm
Granted it probably won't have the power to pull 5th gear to 70mph untill i add my little mra300 supercharger and bring the boost to somewhere between 3 to 7 lbs wich i hope will give it enough torque to pull 5th gear to 3,000rpm giving me a cruising speed on the highway of 70moh wich is enough to make me happy.
My point is i'm going after more power at a rpm where that engine is happy not at 4,000 or more where it will definetely self destruct in short order.I welcome people's comments on my reply.
And don't wait to hear how this will turn out as i won't be putting it together untill this fall and next winter.

[bhtooefr]

To be honest with you.... and maybe this is for another thread... but why the need for increased RPM. Isn't it more logical to go with completely different gearing to go along with the inherint nature of the diesel engine? I dont know much about all this but I suspect Petrol bikes developed into RPM monsters cause its the nature of the petrol engine and the designs of trannies, gear ratios etc etc that are out there have simply grown to harness an RPM beast.

Diesel Beast is a torque monster. Design around that inherint nature seems the best route IMHO.

I may be WAYYYYYYYY off due to lack of knowledge though???

ft-lbs torque*RPM/5252=hp.

So, assuming torque can be maintained at higher RPM, horsepower will increase as well. More horsepower means more speed.

[big al]

Those formulas look real good but don't really apply to diesel engines as well as to gas engines .Just compare the dyno torque and horsepower curve for the two and you'll see where thay differ.The curves for the gas engine are your typical bell curves where the diesel engine horsepower is pretty much an ascending straight line from 0 to its maximum rpm where its torque curve is pretty much a flat line from 1200rpm to it's rated maximum rpm.
Having said all that i agree with you that if you rev it higher there will be a return but it'll drop off very suddenly as the camshaft grind is not designed for high rpm and the inability to alter fuel injection timing is the most deciding factor.
Take your Gas engine the ignition curve has to change constantly with rpm the faster you twist that engine the more ignition advance you need .The same goes for the injection of fuel in a diesel engine .
Your car diesels have that feature built in their design wich is why they're able to run much higher rpm's.
The stationnary type diesels most of us use in these conversion such a the Yanmar have fixed injection timing events wich granted can be altered for more advance but that would make it nearly impossible to start as it would ignite before reaching tdc and it would also knock twice as hard at low rpm.
I'll stay the course and supercharge mine and make use of its normal rpm range.

[bhtooefr]

Yeah, that's one side of the problem - getting the torque curve to not fall off, while keeping it usable at low RPM, without ending up redesigning the whole thing.

(The other side is the mechanical integrity of the engine, when it was never designed to really exceed 3600 under a load, and maintaining that without ending up redesigning the whole thing.)

[John]

John I've never taken the engine to 4900rpm where did you get that figure from? The Yanclones display a degree of diesel knock, even my gen set is loud and I have never touched it from new except for general maintenance. The Yanclones in Australia seem to be set for 10hp, not the 8.8.
Thought I'd better clear that up.
A

Hi Andrew. My sincere apologies for any misunderstanding, offence or error on my part. You haven't typed any rpm mistakes in any of your posts that I'm aware of, - the 4900 rpm figure was mine alone. I had been calculating gear ratios & speeds for my own bike, using the gear/sprocket calculator from http://www.rbracing-rsr.com. In one of your posts you said you were using a 17T gearbox sprocket, which was the one I was contemplating for my bike. The calculator gave a figure of 55.07 mph (88.1 km/hr) @ 3600 for this sprocket size. Assuming the 120 km/hr figure was by gps rather than speedo, I extrapolated from that figure, that it would require 4900 rpm to reach a genuine 120 km (75 mph)
The possible extra noise from advanced timing, was I admit, & apologise, a bit of poetic licence from me, based upon one of your posts where you said that the low rpm noise was perhaps louder than standard.
I am happy to put all this right, & edit out all errors, or unintended misleading statements in my posts. Please rest assured that no offence was intended, or implied, & that with regard to speed & rpm, my understanding was genuinely based upon the figures from the gear/sprocket calculator. Sorry Andrew.
The 8.8 bhp figure came from the quoted figures printed on the air deflector plate of my own Yanclone. 6.6 KW @ 3600. John

[John]

.Your 10hp Yanmar and clones are designed with a governed speed of 3,600rpm and are made to run 24 hours a day at 3,000 rpm maybe 3,200 .
I'm using an actual Yanmar L series and hooking it up to a CB350n Honda tranny and gearing the primary to give me 85mph at 3,600 rpm in 5th gear wich leaves me with 70mph at 3,000rpm
Granted it probably won't have the power to pull 5th gear to 70mph untill i add my little mra300 supercharger and bring the boost to somewhere between 3 to 7 lbs wich i hope will give it enough torque to pull 5th gear to 3,000rpm giving me a cruising speed on the highway of 70mph which is enough to make me happy.

Hi Al. I don't forsee any reliability issues of running any industrial diesel at full rated revs of 3600. I used to operate a professional ride on rotary mower for my local council. It had a little 3 cylinder kubota diesel of around 670 cc, & would be held at 3600 for at least 7 hours a day 5 days a week over a period of years, with no engine issues whatsoever. If a manufacturer didn't think their engine could take sustained running at full speed, they would limit the revs to sustainable levels, which is effectively why they give a 3600 power ceiling.
A genuine Yanmar is an expensive way of discovering if it is up to the demands of supercharging. Good luck with that!
A small business in Wales once developed a supercharger specifically for diesel singles, & if anything, it was too successful. They found that the big ends gave out on the smaller capacity engines, & on the larger capacity ones over 400 cc, the injection pressure of the fuel pump was insufficient to effectively atomize the fuel at high revs.
Even if the outcome is successful, you will need at least 12.5 bhp at the rear wheel to see 70 mph on the dead level on a calm day, meaning that the engine torque will have to rise to 22 ft/lbs @ 3000 in order to generate it. That's an increase of 48% over standard output at those revs, & more torque than a 350 petrol Enfield develops anywhere in its rev range! With a standard Yanclone, you will generally see a cruising speed of between 45 & 55 mph depending on road conditions. Even when the engine is geared for 58 mph @ 3600, you will still experience plenty of downchanges to maintain speed on any kind of undulating terrain. Put another way, the 500 EFI petrol Enfield, which has 3 times the bhp of a Yanclone (27 bhp) & double the torque, tops out at 84 mph, @ 5290, & at no point on the dynamometer hits 20 bhp at the rear wheel. At 70, the 500 engine is doing 4430 rpm, & producing a net power of 19.4 bhp & 23 ft/lbs at full throttle, AFTER transmission losses & rolling resistance have been deducted.
Forget the revs, the capacity, & the torque, the only relevant factor is the HP. Once you know what the engine produces at 3600, then deduct at least 15% for transmission losses to get rear wheel power. Find the cube root of the rear wheel HP, & multiply it by the constant of 30.2. This will give you the speed in mph that the bike should reach on the dead level in calm conditions. It doesn't, however, take into account rolling resistance, hills & headwinds! Then you can gear the engine according to its needs, rather than a desired abitrary figure. Good luck!

[John]

400 cc yanclones are not torque monsters.

equivilant to 400cc petrol in torque? Margionally better orr?

A 406 Yanclone is basically equal to a soft tune 280 cc petrol single in terms of peak torque, or approximately similar peak torque to a good 250 jap single. At 3600, the Yanclone develops a tad more than my old kawasaki 200 single 4 stroke. 12.8 ft/lbs. (Kawa 12)
The 462 cc Hatz develops 19.4 ft/lbs peak compared to the 350 Enfield petrols 19.7. Although at 3600, the Hatz has dropped to 15.6 ft/lbs, to the 350's 19. Which is why it is self defeating to overgear them.

[big al]

Thanks for your input John.First let me say i got a great deal on two actual Yanmar engines one with electric start and one without so if i blow one i have a spare plus i have a clone available also.If my way of thinking is correct i suspect the Yanmar quality is far greater than the clones in the way of metallurgy ie stronger pistons rods crank etc.I don't plan on going farr even if i get it to 70mph and all the roads in my area are fairly flat.I have a CB100 Honda that produces 11hp and has a top speed of 68mph so this is why i'm thinking 13 hp would give me what i want.If i can't pull 5th gear then i'll drive it on secondary roads in 4th gear and i think a modest boost of say 3 to 6 pounds should give me what i want without compromising that genuine Yanmar.

[andrewaust]

Hi John


No harm done, just needed to pull you up before things get out of hand and people thought I was quoting something I wasn't. Yes I am using a 17t sprocket, but I'm also using Dunlop tyre on the rear with a lot more rollout "larger profile" then the standard Avon tyre that I think the Enfield came out with which will change gearing ratio to the Kilometer.

To answer some of the other posts asking why increase the RPM !!
You will never get a power beast from using a Yanmar or Yanclone 406, but you can do a few things to make them rev a little more "and that is being asked by bhtooefr in this thread". It depends on where you live, terrain, idiots in cars with no patience and the list goes on why you might want a little more rpm from the bike.

If I were to use a 19T sprocket for example, acceleration would be to slow meaning I'd have some idiot up my arse trying to push me along, might only happen here in Australia? Hill starts would be hard etc - so when I built the bike I looked at the power figures, searched for a Yanclone with as much Hp in the single 406cc variant as possible and matched up the gearing to suit. What I ended up with was a fairly usable bike which will sit on 100khr most of the time and not exceed the 3800rpm that was written in the manual not to go over.

The accuracy of the Tinytac tachometer and the Enfield speedometer could be brought into question, the RTA speed awareness signs seem to display an accurate speed, I'm not that worried to go to the trouble of GPS speed logging, long as its doing close to the displayed speed I'm happy.

Big Al mentioned boosting! Some small boost shouldn't be a problem, I spoke to my local Yanmar distributor and repairer who owns the business and also has substantial qualifications in mechanical engineering. One thing he did point out, the oil pump system has no relief valve, so whatever pressure it produces that's what you get, so when cold and if you're thinking of using a Turbo charger you might look into building some kind of relief valve system if using bronze cartridge type bearings as the extra pressure when cold might mean oil getting into the inlet or exhaust side of the turbo. I cannot see a problem if using a ceramic bearing turbo as they're usually meant to run a restrictor jet/valve in the inline feed pipe "check this though".

I have a turbo and intercooler here, tossing up whether to use it on the yanclone or not, I'm happy with what I have so sometimes it's better leaving well alone. The beauty of building these Diesel bikes comes down to the unique imagination of the one who is building it, there is no right or wrong way of doing it, long as it's safe and won't cause personal injury to you or others.



A

[big al]

No turbo for this guy .I adhere to the kiss principle .I purchased an AINSI AMR300 supercharger from someone in Australia and had it shipped here and plan on using that.It carries its own lubrication and won't heat the intake charge as much and provide positive pressure from idle all the way up the rpm range .We'll see what happens i also have a pyrometer and boost gauge going on it to keep track of things.If nothing else it should be an interesting piece of engineering when i'm done.

[snoopy]

You don't need to do 3800rpm with this engine, the torque comes much lower down and as one previous poster has said you get the same acceleration at 2500rpm ish then peak. On mine I run a 18t rear and I'll be fitting a 19t on return as its at peak revs at 60mph (I have a 18" rear though).

The engine does not like running at idle and I do a lot of clutch slip to maintain low traffic speeds. It's not good for this but loves to sit all day at 50mph (3k rpms).