compression test on motor that hasn't ran for years? ADVICE!

[NJPCRX]

I wanna do a compression test on my atc 90 that hasn't ran for YEARS. It turns over freely by hand. I was gonna fill the cylinder with marvel mystery oil and let it sit for a couple days, but I don't wanna get a false compression reading. I also don't wanna pull start a dry cylinder and do damage. What should I do? What reading am I looking for? Also, can I take the tappet covers off and spray some lube in the head before I get to pullin on it? I just wanna make sure its lubricated and maybe hydrate the valve seals and everything a little before I try to test it. Its got full oil in it now, but its probably 20 years old. What should I do?? Drain the old oil first? Douche it with clean oil?

[dougspcs]

Change the oil with a good 10w40 ATV/motorcycle oil, get a can of engine fogging spray used to winterize outboards and spray it into the intake while pulling the engine over slowly with the plug in a few times. This will get some good lubrication to the cylinder, rings, and valves.

Then continue to pull it over slowly with the plug OUT 20-30 times to get oil circulating thru the top-end.

Adjust the valves, fresh gas, carb cleaning and a new plug and fire it up.

Get a bit of running time on the engine before worrying about compression tests..

[DohcBikes]

Doug nailed it and the only thing I might add is a gas tank flush and an inline fuel filter to be sure you don't get any solids through the carb.

[sanchez]

Because real fogging spray is the only stuff for this (wd40 is not) and I cheep I just use ATF, fill the cylinder at tdc, makes bit of a mess when u spin the motor loads exhaust with oil which smokes
Mix in acetone or drygas with the ATF as a soak for seized stuff {used ATF works if u really cheep)

[dougspcs]

Because real fogging spray is the only stuff for this (wd40 is not) and I cheep I just use ATF, fill the cylinder at tdc, makes bit of a mess when u spin the motor loads exhaust with oil which smokes
Mix in acetone or drygas with the ATF as a soak for seized stuff {used ATF works if u really cheep)

The reason I suggest fogging spray is because it won't make it hard to get to run after and create a huge smoke cloud as you try to burn it out of the exhaust..less is more sometimes..

Also when it comes to doing it right..CHEAP isn't in my vocabulary!!

[tomlbby]

according to my clymers honda service manual for a 1970 to 1987 atc 90,
its says compression should be between 142-170 psi.
I agree though,you should get it running right and then check compression if concerned.Too many things could give you a bad reading on a motor that hasnt been run in awhile.also these readings seem on the high side to me,if she starts and runs compression is good(enough)

[NJPCRX]

Ok, where do you find the fogging spray? Is that the technical name for it?

[DohcBikes]

The common name is fogging oil, and you can find it at you local boat dealer more than likely, or you can order on the net. Depending on your locale, some hardware stores and other places that carry automotive products will carry it as well. CRC and Stabil are two common brands.

[dougspcs]

This is the stuff I use:

http://www.amazon.com/gp/aw/d/B001KYH6BQ

Its great stuff..I use it for lots of things from prepping motors for storage to coating cables, bolts and adjusters on my machines before I put them away. It's better than WD40!!