Starter motor speed

[stormcoat]

I have nearly finished the rewiring of my Petter powered Dnepr, but I am having a problem starting the engine. Once started, it runs smoothly and seems to have plenty of torque, however, it will only start if I connect up a jump lead to a car with the engine running at fast tickover and putting out 14 volts. Otherwise, it will start with a whiff of petrol in the air intake. (Loud bangs and possible harm to the engine.) The starter motor is new, but was made for a Ford Granada 2.8. It has no difficulty in turning the engine over, but just needs a few extra revs to make the engine fire. I am wondering if I need a starter which turns over faster. I should know (but I don't) if starters designed for diesels are wound to run faster than those for petrol engines, or perhaps they were when these old Lucas starters were made.

There is no problem with the battery, that has been tested. It is also bigger in cca than it needs to be, so the only other option, after this, will be to examine the engine itself to see if it needs adjustment to the timing, or possibly new rings etc.

Does anyone have any knowledge of this topic, please?

Regards, Stormcoat.

[andrewaust]

The extra compression might be making things tough for the starter to wind the engine over, some technical manuals state minimum rotation speed at start-up "cranking speed", like you said, if it is to slow the engine will not fire. Every engine is slightly different, but most smaller engines "of the top of my head" is 200 - 300 rpm.


A

[BHNZ]

Hi Stormcoat - I see you are using a starter from a Ford Grenada. Do you have an idea as to the diameter of the ring gear on the Ford engine? It occurred to me that if the ring gear on the Petter is larger in diameter then it will turn slower than the Ford engine. A possible cure would be to fit a larger pinion to the starter motor and re-position the starter to ensure correct gear meshing. Check the gear ratio on a Grenada and select a pinion to obtain the same ratio on the Petter. It might only require a pinion one tooth larger. Do you use a de-compressor to spin the Petter up or is it just 'normal', with no de-compressor?
Cheers, Brian

[stormcoat]

Thanks, I had wondered about the gearing. I will check, if I can get the data. I have spun it with the decompressor open, as suggested in the workshop manual, but it does not make any difference. The starter will turn the engine over comfortably on full compression, providing that the battery is at least 60% charged.
Petter's show that, for electric start, the engine should have heater plugs, but the manual makes no mention of where, in the cylinder head, they can be fitted. Neither does the spares list make any reference to them.

Then next thing to check is the injection timing, which the manual suggests checking when fitting variable speed control.

(Kick starting is impossible; there is far too much compression and not enough strength in the ratchet to take any more pushing. One tooth has already broken. Besides, I would have to remove the sidecar each time I wanted to start it. Imagine that in a traffic jam!)

Regards,

Stormcoat.

[XLerate]

An important consideration is that diesels require more amperage in starting circuit than a gasser to turn them over, because of higher compression. On a bike that was originally a gasser the mains wiring may be too undersized to handle the current. Best to upgrade to some real heavy cable. Some of the MIG welding cable is just perfect for this, often sold by the foot at welding shops. Super fine & flexible wiring in the bundle, plus more individual strands carries current much better.

Also all your terminals must be up to task, copper or brass if available and a good crimped & soldered connection. In addition your chassis ground needs clean bare metal connection. Good to insulate all metal to metal connections especially at chassis with either dielecric grease or other grease to prevent corrosion & cut down on electrolysis. Most corrosion deposits will migrate to grounds.

In addition switches may not be rated for the required amperage. Marine switches are usually the best you can get, designed for harsh environment & premium quality.

Adding all this together delivers a whole bunch more current to starter motor & shouldn't break the bank.

[tribsat100]

I agree with all of the above, its suprising how many people are left scratching their heads when the lights on their machines dont shine too brightly or the horn is weak when the earth strap goes from the battery to a point on the frame. The current then has to find its way throught the frame to the front end and this route is through the headstock and greasy headstock bearings with the inevitably variation in current supply.

A good piece of advice is all in the previous post and these points should be considered before beefing up the set up

[stormcoat]

Thank you for all your suggestions. I shall try some of these ideas. However, I have noticed that the exhaust is becoming very smoky after some minutes of running, so I shall need to investigate the condition on the bores and pistons at some time. A slight loss of compression may not make much difference at first, but if there is damage to the piston rings this will simply get worse.

I have connected the earth lead straight from the battery to the engine and the live starter lead is brand new, made up with proper connection by our local parts dealer. This did have a noticeable effect on the starter motor's performance, but not enough to get the engine going without further assistance.

Fortunately, spares are still available for these engines. They may be old fashioned. but they are straightforward to repair and service. They do not come up all that often on ebay, but there have been two recently. For anyone mad enough to use one for conversion, they are listed as Petter AD2. Advantages are:

A ready made bell housing which simply needs and adaptor plate to fix a gearbox to. (I have a spare adaptor plate, which simply needs drilling.)

Provision for electric start and internal alternator, if your engine does not already have one.

Spares and information readily available.

Light weight - alloy crankcase and heads

Drawbacks;

Largest engine only 14.75hp, 734cc

Twin cylinder has long PTO mechanism at the timing end, which means the Dnepr frame needs lengthening to clear this, although if the flywheel generator is fitted, unlike mine, it can project between the frame tubes, unlike mine which is fitted with and alternator from the PTO.

Series now obsolete, so secondhand is the only source.

Regards,

Stormcoat.

[XLerate]

I still see three possibilities in the electrical. Though the starter lead cable is new & even high quality it may not be of sufficient gauge to carry the current that is required. I was surprised how heavy the standard diesel cable was when I swapped in my 4 cylinder Cummins 4BT diesel in my truck. Almost twice as thick as the gasser V8 cable! It's about 2/0 wire gauge.

Also I've read many reports of recent date where folks have bought 'brand new' meaning freshly rebuilt starters that were bogus junk right out of the box. Country of manufacture can be a factor here, as well as quality standards of rebuilder.

Also there's a decided difference between 'Rebuilt' equipment and 'Remanufactured'. The Rebuilt may only receive a deep cleaning plus a bearing or two with new brushes. The Remanufactured unit may include a newly rewound armature, new field coils & new brush assembly in addition to new bearings. We know too that products from various 'Discount Auto Parts' chains must be saving money somewhere, and that may be in an area that directly effects quality of parts.

Before giving up I'd visit a breakers/dismantlers & grab a used original equipment starter, and also grab a heavy duty starter cable off a diesel vehicle. Any length would do on the cable for test purposes, but get a big fat one, as well as a heavy earth/ground cable.

Interesting that my Cummins diesel truck has a 'Brand New' ignition switch from a Discount Autoparts store. The engine will not even begin to turn over with it, just get a click. Another gentleman with same engine swapped into his truck experienced exactly the same! We're both accomplished electricians and all the rest is very heavy duty.

We both ended up using a very heavy duty [50 amp marine type] starter push button wired through a heavy duty [50 amp marine type] relay direct to starter and in both cases instant success. Now my ignition key only controls fuel solenoid. He later bought a premium quality ignition switch and reports that it works fine. These cheapo discount ignition switches just aren't built to carry the required amperage/current for a diesel starter.

I would first try bypassing the ignition switch [because it's cheapest!] and wire direct with a heavy duty relay carrying full battery current, actuated by a starter button. May make all the difference in the world. I believe you have a weak link such as this in the start circuitry. I tested mine before install by wiring starter direct from battery, with a hand held push button to starter solenoid, which told me I had to wire it that way permanently. We've lived happily ever after...

[Mouse]

Its also worth noting that a loss in compression will cause slow cranking and overload the starter motor. I've had this problem with the failed V twin diesel and my old R BMW that I ran on propane which gave it valve troubles. I've burnt out numerous starters and overloaded many batteries and damaged them thinking it was a battery+motor problem when for most of it my valve clearances had closed up (thanks propane) and simply needed adjusting.

I know its counter-intuitive to blame low compression but the starting cycle includes the 'spring' of the compressed but uncombusted chamber gas returning energy after TDC and helping spin the engine over. Worse is after TDC when the leaky uncombusted cylinder is then 'sucking' on the down stroke sapping even more starter power.
It's all to easy to blame the battery and starter for slow cranking when the problem can be elsewhere in the engine.