Snapdragon engine HELL(P)

[Stemar]

Having suffered from low power, getting gradually worse, last season, I had the pump and injector on my MD1 serviced and things are no better. It started fine even on a brass monkey day like today and runs fine in neutral, it's just that there are no revs in gear. When we first turned her over ther was no compression at all, but this came back reasonably quickly. Oil pressure was a problem. we had to pull the pump and prime it by hand to get the light to go out, but seemed OK afterwards.

Any ideas anyone? Is it worth spending any more on this or will I be throwing good money after bad?

Alternatively, what replacement engine would you suggest as a good secondhand buy? It has to fit in the same length as the MD1, though width isn't too much of a problem.

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[chippie]

I had a similar problem with a different brand of engine . The problem in my case turned out to be drag inside the gearbox caused by too thick an oil.
Your problem seems gearbox caused to me. One other possibility is that the timing for the injectors is out and wont develop full power under load.

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[JSB]

Hi
Have a look at this Website if you don't find what you are after, email Tony who is very helpful. http://www.canaljunction.com/boat/faultfinding.htm

John

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[oldharry]

Power loss on an engine that starts and ticks over happily: Engine timing = injector pump and valve gear are first suspects as you have had things to pieces. But increasing power loss with lack of compression: Valve problems (burnt bent, maladjusted); head gasket problems = blowing due to warped or cracked head; Piston problems = worn or broken rings, bore glazing or wear (these faults will also create high crankcase compression - block the breather for 30 seconds and see if pressure builds up. Oil will be blown out of the breather when the engine is running fast); Cracked head or block; Crank problems = tight or damaged bearings, main bearings shot. External problems = blocked air intake, drag in the drive train (gearbox, prop shaft tight, prop fouled). Fuel supply = blocked breather in the fuel tank, partial blockage in filters or lines preventing sufficient fuel from reaching the engine.

So its down to you: some of these things are simple to rectify, others are major issues.

2 things you say that do not bode well: 1: lack of compression. Even dry there should be compression. Compression ignition engines depend on good compression (!) and if there is little or none on turning it over then you need to know why. Compression loss will cause power loss - if the engine starts at all. 2: the oil pump had to be hand primed. This suggests a badly worn pump, which will not be delivering enough oil to lubricate things adequately. The light only warns of complete failure coming on when the pressure drops effectively to zero. Low oil pressure is almost as bad as none at all. Unless the oil pump is damaged some way it should self prime (unless it has been cleaned and reassembled dry - it needs to be liberally oiled on reassembly to creat a seal). A worn oil pump suggests a worn engine as a rule, it being the best lubricated part of the whole thing.

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[Stemar]

Thanks for the advice.

I think I can eliminate a problem with the gearbox, because it's lubricated by the engine oil, and if the engine was trying and failing, rather than just not trying very hard, I'd expect lots of black smoke.

I'm reluctantly coming to the conclusion that given the low compression when dry and the problems priming the oil pump, anything I do now would only prolong the life of this engine for another season or two at best, and, if my oil pressure's low, the likelyhood of a horrible crunch followed by silence must be significant, It's bound to happen just when I really don't need it (lee shore or something expensive close by...)

Next question - suitable replacements. I've seen a YANMAR YSM8 for sale. Does anyone have any thoughts on this engine? Is it likely to fit? Are parts easily available/very expensive? Etc.

Would I do better going for a 1GM for not a great deal more?


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[TonyBrooks]

Don't you dare - lost of contraindications and prtial info hear.

1. Starts easily when very cold = compression OK, so bores, rings, valves should be OK - especiallya s this appears to be a single cylinder.

2. Injector pump timing - if memory serves me the injector pump is driven directly by cams that are part of the engine - so timing is not likey to be wrong unless something has badly worn.

3. I understand that at least some of the MD range are equiped with a "grease nipple" for priming the lubrication system after standing for a long period, so there may not be a lubricating pump problem at all - I am still not sure exactly what the comment about the pump means.

I think the MD range is very robust, so (hoping I am not satating the obvious) I would be looking at things like fouled prop, alternator partially siezed (supprising the difficulties that causes), overtightened stern gland, and gearbox problems.

Is it possible to undo the shaft coupling and try running it in gear, but with shaft disconnected. If so, that should show if there is a problem in the box or in the shaft/prop.

Tony Brooks

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[dickh]

Re: Snapdragon engine HELL(P)-EXHAUST ELBOW??

What has not been mentioned yet is a nearly blocked Exhaust elbow. This will produce the symptoms you talk about. This has happened on both mine and a friends engine. To check it you need to remove the elbow COMPLETELY and inspect on the bench. Mine had only a contorted 5/16" hole down the centre and my friends was similar. Replacing the elbow produced miraculous results! - just like a new engine!
Mind you, I discovered this after checking and changing all the fuel filters and having the injectors anf injector pump overhauled......

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif