QuestionWhat is a general cause of low engine compression. I have triumph tr 7 w/aluminium block and head. Engine starts up easy and runs good up to 13-1500 rpm. No power-compression 80-100. No water in oil. Liqiuids level constant for both oil and coolant. Some backfires. Could engine been overheated? How to fix, new gaskets?
please advise,
thanks,
gary
Answergary:
It seems you have two questions, which may or may not be related. 1.) cause of low compression; and 2.) No power. My questions: You didn't say what happens after 1,300-1,500 rpm? Also, you seem to think it maybe overheated- does it overheat?
Your compression figures do seem somewhat low at 80-100 psi.
I generally take out all the spark plugs first, then using a good (screw-in) compression gauge (and holding the throttle open) test each cyl in turn. No one cyl should be greater than 10% lower than the highest pressure. If one (or more) cyls are low, try squirting in a bit of engine oil from a squirt can and retry. If pressure increases this means time for piston rings. If no increase, likely a bad valve (most likely exhaust)- which means a cyl head rebuild job.
If you have low compression on two adjacent cyls, it could indicate a head gasket problem - in which case you'd have to pull the cyl head and replace the gasket. This type of head gasket failure might not mix your coolant and oil and might not show up that way.
Lastly, IF your overheating and backfire and have low power, I would also check your fuel/air mixture to be sure it is right- sounds like it could be running lean.
A backfire- if it happens often also indicates to me that the engine timing might need to be checked to make sure it is in spec as well.
