DDH Compression

[Ralphie]

Can someone please tell me what an acceptable compression reading is for a DDH with the Hercules 6 cylinder diesel engine.
 I posted a question in December about my non strarting DDH and had lots of suggestions - thanks guys.  The dozer has been sitting idle for 18 months and recently when I went to use it I couldn't get her fired up using the same technique I always have of a few squirts of ether, all I get is fumes out the exhaust.
 I have had the injectors out and established they are pumping plenty of fuel. I did a compression test on it today, the best cylinder was 170psi, four had 120psi and one 80psi. My question is, would the diesel fuel be actually combusting with these sort of compression readings?
 If it is the low compression causing it not to start it is hard to figure what would have created the problem by it just sitting idle for that time, as it worked fine the last time I used it.
Thanks for  a great website...!

[RAB]

Those values are for a gas engine and pretty poor at that (170 would be high, but the difference between cylinders is abysmal).
120 plus or minus 10 (with a max of,say, 10 range) would be typical for a low compression gas engine.
That would be nowhere near high enough to cause ignition of heavy oil, or even gas!
Try some oil into the ring area, but beware of hydraulically locking the engine.  May be valves are not seating properly for some reason.
Regards, RAB

[John Schwiebert]

Another thing to try would be to fashion an adapter that would go into the block in place of the injector that will alow you to pump compressed air into the cylinders. Never tried it ona crawler of that size but the ideal place it to hace the piston at exaclty TDC compression stoke as the piston will be straight up and both valves will be closed, if the piston is not in that position the engine may tend to rotate thus opening a valve and you loose all. Another way is to loosen or remove the rocker arm shafts and then pump air in the cylinders. Listen for leaks, at the exhaust, at the intake and  at the pan. You should have around 300 psi compression 350 is better yet but you will not see that on that engine I don't think. Questions?

[walter hudson]

how did you check the compression ? to get a proper reading you must remove all injectors ,remove the air cleaner hose and spin the engine at the proper speed for starting . when you tried to start the tractor what was the temp. ,old diesels are picky about temp. for initial start up. i have seen a 10 degree difference temp. cause one to just white smoke and not start .