Couldn't start the 2gm diesel, 55 degrees outside. Mechanic checked fuel supply, injectors and compression. Compression starts at 200psi and gets to 400psi after about 6 revolutions, he said it should get there in 2. After about 10 tries, when engine is a little warm, it starts and seems to run fine. It will restart when warm but not when cold. Preliminary thoughts are worn rings, cracked piston, valve not seating, all of which require pulling engine. Engine has about 1,000 hours on it. anyone experienced a similar problem or can think of some other cause for lack of compression.
low compression-engine rebuild?
- Thread starter dfriha
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I'm waving the BS flag here.
ALL diesels are recalcitrant when cold without preheaters. It's the nature of the beast.
I've never heard about a compression test only taking two revolutions to achieve the 'actual' number.
My 2gm(f), when it's cold outside, wants the throttle opened about 20% for starting.
hth,
Rich
ALL diesels are recalcitrant when cold without preheaters. It's the nature of the beast.
I've never heard about a compression test only taking two revolutions to achieve the 'actual' number.
My 2gm(f), when it's cold outside, wants the throttle opened about 20% for starting.
hth,
Rich
Compression tests are normally done on a warm engine. i.e. with plenty of oil round the pistons and rings etc.
If yours didn't start the readings are questionable but look good anyway. 1,000 hours is a relatively young diesel.
Also make sure to test both cylinders, and with both injectors removed - and you need a really lively battery; not one that has been flogged to death in trying to start a dead engine.
Pre heating and/or a little squirt of ether (or WD40?) should help to get it going.
This is not recommended by the makers because they fear the solvent will wash the oil from the cylinder walls. IMHO an occasional small squirt would cause very little additional bore wear.
If yours didn't start the readings are questionable but look good anyway. 1,000 hours is a relatively young diesel.
Also make sure to test both cylinders, and with both injectors removed - and you need a really lively battery; not one that has been flogged to death in trying to start a dead engine.
Pre heating and/or a little squirt of ether (or WD40?) should help to get it going.
This is not recommended by the makers because they fear the solvent will wash the oil from the cylinder walls. IMHO an occasional small squirt would cause very little additional bore wear.
Readings do not sound bad.. Lots of hard starting problems can be traced to a tiny air leak between the hp pump and the outlet of the lift pump.. Check all the &#$^%$ Banjo connections and be careful not to strip 'em. when ya put the wrench on and give them a little bump. don't forget the secondary fuel filter bowl gasket and the bleed screws..
Hit the compression release lever and crank the engine for about 10-20 seconds. This will get lubrication going. Close the compression release lever. Place the battery switch on "both". Open the throtle to around 3/4 the transmission in neutral and cranck away, it should start. The problem may not be so much the loss of compression but the slow cranking when the engine is cold. Help it along by providing maximum starting battery power and more volume of the fuel air mixture by opening up the throtle. Hold the throtle lever as when the engine catches you need to reduce RPM. If once the engine warms up, it runs well and will easily restart then I would not worry about the condition of the engine. It sounds fine. Some folks will use a small space heater to warm up their engines in extreme cold weather and you could try and use one to see if it will help. Check the state of charge and condition of your batteries as cold weather also affects their performance.
Thanks for the replies but all suggestions have been done. At 60 degrees the engine should fire right up on the first or second try. The Yanmar mechanic is not sure what the problem is and arrived at his (somewhat reluctant) conclusion by eliminating all others.
Just like any medical procedure, get a second opinion from a different mechanic..one who would know they are only performing a diagnostic analysis. I think those reasons the mechanic has given would be so serious that the engine wouldn't run at all no mater what amount of cranking was done. The fact that is does run and doesn't emit a ton of smoke or steam or sound like a tin can full of rocks means it is something less serious. It could have something to do with the fuel metering (shim pack). Or maybe the injectors were damaged if an excessive amount of water got into the fuel and has impacted their operation.
Compression testing is tricky. The fact that it does build up is a good sign. I would question the test.
Good luck.
Compression testing is tricky. The fact that it does build up is a good sign. I would question the test.
Good luck.
It can be done in the boat but the engine must be moved. To get the rod bolts and end caps off the oil pan has to be removed. If you lift the engine high enough I suppose that could be done in the boat. But everything is loose, might as well take it out and save the mess.
It sounds to me like the symptoms are consistent with a small air leak in the fuel system. It could very well be that engine temperature is incidental to it being at rest or running. A small amount of air in the fuel sytem will cause a hard start condition but once the engine fires it will clear out the air and continue to run and restart well until it is put to rest for hours or days which will again allow air to enter system. The usual suspects would be the lift pump, banjo connectors or fuel filters. If the engine was real low on compression it would be smoking hard when running. Addying an oil additive to increase viscocity would reduce the smoking and increase compression. Good luck and let us know the outcome. Definitely get a 2nd opinion before major work.
Update. I have talked with 2 other mechanics and they both tend toward loss of compression possibly due to a bent connecting rod. In the Yanmar service manual there is a test that can check for a bent rod by removing the injectors. Also before that the engine can be turned over to check if the injector pump emits the same amount of fuel to both injectors. That will be the next step.
Just a data point for you. On my 3GM, before its rebuild (after 26 years), when it was cold (<60) I always had to set the engine throttle high to get the engine to start. The boat I used to race on which also has a yanmar is the same way.
I suspect you're going to be VERY disappointed when that engine is torn down and nothing is bent. In order to bend a rod you'd have to have hydraulic locked the engine and that's not likely.
In fact, you'll be even more disappointed when you find that it's STILL hard starting when the temperature is low.
Run it.
Rich
In fact, you'll be even more disappointed when you find that it's STILL hard starting when the temperature is low.
Run it.
Rich
bent rod
Low compression on a 1000 hours motor...my guess would be a slightly bent rod due to a hydro lock. Not all that unusual or hard to do.
Usually goes like this:
Air leak in the fuel system so engine wont fire right up
someone keeps cranking the engine hoping it will start (without turning off the intake water)
muffler fills up, water flows into the manifold and through the exhaust valves
hydo-lock....bent rod...low compression
Low compression on a 1000 hours motor...my guess would be a slightly bent rod due to a hydro lock. Not all that unusual or hard to do.
Usually goes like this:
Air leak in the fuel system so engine wont fire right up
someone keeps cranking the engine hoping it will start (without turning off the intake water)
muffler fills up, water flows into the manifold and through the exhaust valves
hydo-lock....bent rod...low compression
OK, Another data point. On my 3GM one of the rods was bent & the engine was still running just fine. While rebuilding the engine my mechanic said that one piston was about an 1/8 of an inch shy of where it should be at the top of its stroke. No idea if I did it or a previous owner. The engine was rebuilt because I had fried the piston ring on one piston (overheating). Yes I do hang my engine key on the raw water intake valve now.
I'm gonna place my horse bet on a fuel supply issue.
Good luck,
Brian
I'm gonna place my horse bet on a fuel supply issue.
Good luck,
Brian
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