Where to obtain a compression testing device for Yanmar 1GM10

[ianwoods]

Hi, I need help to find/borrow/buy a compression tester for my Yanmar 1GM10. It needs to be of the clamp type that will fit in the place of the injector. Your assistance is certainly appreciated and will help diagnosis of my engine starting problem.

 

[justdrifting]

Thats easy just pop along to a local garage if its more than a one man band they lend you one.Thats what i did.

 

[dickh]

Or buy one off eBay, use and then resell again - that's what I did - but make sure it's suitable.

 

[steve28]

The other thing to check is the piston height, this is done using a piece of lead solder in through the combustion chamber, then turn the engine by hand and it crushes the solder to a certain thickness, you will need to get this figure from the yanmarhelp.com website.
The three 1gm10 engines i have worked on all had good compression so much so that i could lean on the starting handle for some time before it went past compression.

 

[oldharry]

"...will help diagnosis of my engine starting problem."

I doubt it very much. If the engine starts at all then you have compression - and thats all a tester will tell you. Diesel compression is so high that minor leaks do not show up on compression test though they may be enough to cause poor starting.

If you suspect compression loss, then you need to do a leak down test. This pressurises the cylinder, then measures the rate at which the pressure drops. Also with a bit of luck it will show where it is leaking. A head gasket will leak into the cooling system, rings will leak through into the sump and out of the breather, valves will leak into the manifolds.

Compression testing tells you none of these things. The engine will show symptoms anyway of each of these faults: Bubbles in the coolant if the gasket's leaking. Blowby through the engine breather builds pressure in the sump if you block the breather with the engine running - indicative of ring, bore or piston wear.
Damaged valves can be diagnosed by turning the engine over by hand: while turning the engine over on the compression stroke pause momentarily. If the valves are leaking compression will drop rapidly. And you haven't spent any money on it yet!

Is the starter turning it over fast enough to allow it to start? Even a minor reduction of cranking speed can be enough to prevent starting. Look for poor connections, worn brushes, damaged windings, does it spin freely by hand (damaged bearings).

Poor starting is just as likely to be injection problems - injection timing, poor spray pattern, pump problems, fuelling problems, cold start procedure incorrect, preheat failure (if fitted) etc etc - nothing to do with compression!

Diesel compression testers are not cheap, are not easy to use correctly, and tell you nothing you cannot find out by using eyes and ears anyway (for free!)

 

[ianwoods]

Many thanks Old Harry; a very informative article.
Most of the advisers say "compression must be down or it would start easily". Ive done new powerful battery; injector cleaned and reset; load test on starter; earth lead on engine; reset valves; changed all filters; bled system several times; checked exhaust elbow; put thinner oil (engine oil) in the saildrive leg. Starting time increased throughout the summer.
Rack appears to open fully prior to starting. So what next?

 

[Haven't-a-Clue]

Ah, the old "squish band" two stroke technique, brings back memories of Stan Stevens!

 

[Tranona]

Ian

Have checked on the saildrive issue. Should not affect starting as the gearchange mechanism is in the box. Therefore nothing moves in the leg until you engage gear. Think, but not sure as don't have details in the manual, that there is an interlock mechanism that prevents starting in gear because of the potential drag of the leg.

Presumably you are starting in neutral with throttle half open. In which case my suggestion of turning over with the decompressor lever up to give the engine a chance to spin then dropping the lever should help when cold. Other than checking back pressure in the exhaust, no more ideas I am afraid.

 

[oldharry]

Unless theres a major drop in compression from a damaged valve or broken piston, I still think the tester wont tell you very much.

Have a look through the compression check problems: Blowby is an easy one - take the oil filler cover off when its warmed up - is it blowing fumes and oil out? If so the rings, piston, or bore are in trouble: broken/damaged/worn - the only way then is to strip it and see. Check first that the breather is working properly.

Head gasket - if its raw cooled its quite difficult to see gassing in the coolant, but taking the head off will tell you straight away. The gasket will either have a biut blown out of it, or will show a clearly darkened area where it has been blowing. If it is, get an engineering shop to check the head is not warped - surprisingly common in diesels. At the same time, the valves can be checked. If the valves are recessed inside the head, pour a little fuel round each valve. If its leaking the fuel will run through, and the valve either needs re-seating, or replacing depending on how bad it is. If you cant do it that way, pour a little fuel into the ports. Again any valve leakage will show up immediately.

A compression tester is expensive and will only tell you what you will find out anyway by taking the head off - which you would have to do anyway if the compression is down!

 

[cliffordpope]

I would have thought a tester is only giving you a number to hang on the knowledge you can already get just by swinging the handle. With good compression it should feel as if there were a large compression spring in the cylinder. You pull the handle slowly round, but if you relax it springs back again. It should do this endlessly, until eventually most of the compression has managed to leak away. But if you only get a dispirited hiss from the air intake, and the handle goes limp after a short movement, then the compression is poor.

If you can actually feel poor compression, the old trick is to pour some thick oil into the cylinder. If it temporarily makes an improvement, then the bore or rings are worn. But if it makes no difference then it suggests valve leakage.

 

[ianwoods]

Thanks for the onfo. The compression on the starting handle is fine: hard to turn over. I have another cats whisker of a tweek on the rack control screw and starting was within 20secs of cranking today - all be it milder weather. I spoke to Marine power who pointed to exhaust elbow - which I checked; to a weakspring on the governor arm - it operates fine; and to the height that the piston rises to. They also mentioned that the saildrive version doesnt start as well as the shaft drive 1GM10 and that the engine is not identically interchangeable. I was informed that I should be using engine oil in the saildrive leg rather than sae 90 which is marked on the leg as this reduces drag when starting up the engine. It was uggested by another that I replace the jubilee clips on the rubber fuel line with petrol line clips (eg of the side crimping variety) because the former are not the most reliable for air/fuel tightness. I have decided to put a nonreturn valve in the uel line just before the tickler pump to remove any chance of drawback of the fuel. So here we go again. I will keep you informed.