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Compression check
Remember these former post, well I did have water in the cylinders and I did not pull the heads, I did get the motor to turn over, I decided to wait on the carbs until I had a rebuild kit, So in the meantime I bought a compression gauge to check cylinder compression. And if I am using the tool right, and it seems pretty straight forward to me, you remove the spark plug thread in the proper adapter attach the gauge to the adapter and turn the motor over and what the gauge reads is the compression for that cylinder. First off is that right?
The manual says I should have 185 psi. Is that right?
So if I am using the gauge right and the manual is right then I have problems.
Number one cylinder reads "0" number two reads "15" number three reads "30" number four reads "15"
Numbers 2 & 4 being the left side front to back Numbers 1 and 3 being the right side front to back.
Please some one help me determine what the problem is.
Is it worn rings or because it sat with water in the cylinders for so long could it get better, blown head gaskets, cracked heads, valves, should I go ahead and pull the heads and have a shop do a valve Job or what ???
Any help or suggestions will be greatly appreciated
#1 12-03-2010, 10:49 PM,
To do a proper compression test you have to make sure your battery is fully charged. Take all the spark plugs out. Turn the motor over about 8 to 10 times on each cylinder check. Make sure you hold the throttle wide open when you turn the motor over. Then do the test again but do a wet test, put some oil in each cylinders through the spark plug hole just before you turn it over, if the readings get higher you then know the problem is probably in the cylinders.
Ride safe have fun and enjoy. Lane
1985 Aspencade
2002 Vulcan
#2 12-04-2010, 04:43 AM,
The engine should also be warm when you do a compression so that the pistons and rings fit properly otherwise the reading will be very low.

In your case it sounds like there is rust in the cylinders preventing the rings from sealing. Pull the heads or go in the spark plug holes to inspect the cylinder. You can rent a snake scope at a tools rental shop.

One other thing, do you know that your tester is reading OK? Borrow another tester and try again.
Ed (Vic) Belanger - 1954-2015
Founder of

#3 12-04-2010, 06:11 PM,
Did I mention she had been sitting out in the weather for three years with no plastic or cover? I pulled the valve covers and the valves are moving up and down when I turn her over by hand. So I figure to pull the carbs and clean them, clean the tank put a new filter and check the fuel pump put new plugs in and see if I can get her to fire up get her all warm and check the compression again. Does that sound like a plan?
The compression gauge is new bought just for this purpose, I guess it is possible to buy a new defective gauge.
#4 12-07-2010, 11:22 AM,

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