Compression Test a new Engine

hey Guys, I know how to do the compression test while th engine is wired, etc in the bike, but is there a way to do this while the engine is sitting on my workbench? I just picked up an engine with 5k on it and want to make sure this thingw orks before I go through the effort of putting it into the frame.

Thanks Again!:whistle:

Clamp it down.
Pull the plugs.
Open up the carbs.
Hook up your guage.
Jumper cables to starter and case.
Complete circuit at battery end and she'll spin and hopefully pump up your guage.

-Duck

Modified to say...clamp it down good . Opposition to the inertia the starter is overcoming will want to spin the whole motor in the oppisite direction around the crank axis.

Post edited by: Duck, at: 2006/02/26 10:15

You would think that the inertia would try and flip the motor over, but in the case of the KZ four cylinder motors it tries to turn the motor over backwards against the full length of the crankcase and trans and it can't do it.
I did a compression test on a KZ650 motor sitting on the floor of the garage and that's what happened anyway, no problem at all. It had about 130k miles on it and averaged 30 psi of compression in all four cylinders

If it was not for the fact that it was a freebie I would have been depressed

Thanks Duck, it worked well to get the girl to turn over. The question I have now is though,, the PSI came out to be on average 230, ha...So Clymer says it should be 130-160, is this just because I have the carbs off and it is just allowing so much more air flow? It just seems odd to me that it would be 100 more than it should be...:pinch:

230:woohoo: wow thats a lot. I dont think having the carbs off will give you 230 something is wrong or done to the engine. Normall comp. test is with the throttle open all the way anyway. It will allow more air in easier with the carbs off yes but not 230psi. Mines about 170 and the head has been milled. With the throttle open all the way.

must be one hell of a starter youve got!:ohmy: is your gauge set at zero when you start?:whistle:

ha, yeah it is definately synched to Zero...I did do a wet test on this and I am wondering if the exhaust valves could be sticking or if I put too much oil into the sockets, would that cause a limited air to gain pressure? Any ideas on how this is possible would be appreciated, ha:pinch:

try it again with no oil and see what you get.

does the motor turn over really hard?exhuast valve sticking could definately cause higher compression,but all the exhuast valves would have to be hanging up though.pop the valve cover off and check your camshaft on the exhuast side if it seems to be ok check your clearances on the exhuast side ,if they are all real loose that could be the problem or maybe someone snuck some 13.5:1 pistons in there :whistle: goodluck,happy wrenching!

Too much oil will give you a much higher compression reading, there is no reason to do a wet test unless a dry test indicates a problem

I ran the wet test because I was scared about the cylinders not having any oil whatsoever because of the engine has sat for 20+ years...The engine turns over very easily, so I am thinking that I will have to try the test again to see if the oil has subsided and try it from there and after that will have to check the exhaust valves, but hoping it was just too much oil:S

sneak a peak and see if the pistrons have carbon build up on top.

Post edited by: nads.com, at: 2006/02/28 14:26