Hi All, I'm currently stripping a manky, badly modified '96 Daytona for a CRK conversion. The engine in it has done at least 33k but was ok on the ride home in terms of temp, noise and smoke. I'm thinking of a compression test to make as sure as I can the head gasket is ok. Ive removed the tank and all gubins so access is ok except middle cylinder is under the frame. The access looks ok to remove plugs but wondering if people can confirm this? Thanks in advance, Dave.
Getting the middle plug out is quite possible if a wee bit awkward. Some silly bugger put a frame in the way! Someone previously asked what the readings should be - can't remember who. IIRC they should be around 130-140psi. Google is your friend in this instance. That's where I found the info.
Remember to turn fuel off and short the starter solenoid for cranking the engine over, No risk of fire starting !
That was another part of my question as no fuel left by the time I test. Also I was going to drop the oil but figured it's best to wait until after compression test?
Yes leave oils in, if the oil is old do oil change before testing ! As old stale oils can give lower than true readings ! Oil is thrown up onto bore's and improves seal on rings, best done on a hot/warmed up engine ! If done on cold engine and pressure's are low , but within 15 psi of recommended good figures, engine and rings should be considered as good/OK.
It's got a bloomin alarm fitted so I'm keeping that on until after the compression test so I can crank the engine. After that I will remove it.
Go on then, why? I've tried to think of a reason why the throttle position would make a difference but I can't think of one!!
It's been said that it helps get a full intake of air into the cylinder quicker... In theory it doesn't make much difference but helps if you get differing readings, mention not doing it, and get a million people telling you that's why To me it's one less thing to think could make a difference if you do it...
Yeah makes sense, cheers. I've removed the carbs now so full charge guaranteed!! I realise people have said engine should be warm etc but I'm hoping I'll get decent readings cold so will go with them. Time will tell eh?!!
If you've got one cylinder wildy different to the others then I'd be confident it'll be the same on a warm engine.... If all are the same but low then time to try warm engine
OK, doing test on cold engine ? Well expect engine compression readings to be lower than the recommended by about 5 psi but if greater than 15 psi lower then rings are worn, not worn out unless the readings got more than 25 psi below spec's, and centre cylinder should read lowest on cold test as on a hot running motor it gets heat from outer cylinders ! So rings and bore are set up to allow for the greater expansion from running in a hotter zone, used to be very noticeably different in the air cooled era ! Hope you get good readings when you take the above into consideration... Cheers capt.
Thanks capt, makes sense but I didn't know about the centre cylinder being different as I've not done this level of engine surgery before!
Ok after buying tester and adapting a spark plug tool I've got the results!! C 1, 68psi C 2, 75psi C 3, 71psi So plus 15 psi for cold gives a range 83 to 90 psi. This is with old oil, no carbs and stone cold.
Looks like it's low across the board then if 140-150 is ok range? Even if I take into consideration the fact engine is cold. Stupid question time but when I tested all 3 plugs were out. Can that make a difference. I can't see how but as I've said I don't mind asking stupid questions?!
