The Chopper Compendium

Ran a compression test & not only is it low ( like 50lb) in 2 cylinders, but I can literally watch the gauge drop as soon as I stop kicking.

Top end rebuild time !!

most compression gauges have a schrader valve in the end of the hose where it threads into the spark plug home so that the gauge will hold the reading until you release the pressure.

Also on a big V twin, you need to hold the throttle wide open when cranking for a compression test, If you dont, you will get low readings.

was talking to someone who said if my rings werent seated it will read low. He also said it should start at 50lb. The carbs were removed so its getting plenty of air (To much?). He also seem to think I didnt lap the valves in well enough. Suggested I do it with a drill (reversing directions during process), with a couple grits of compound. Also something tells me my valve timing is still off. When all timing marks are in line, intake is still closing when piston is half way up on compression. I've since moved to 3 teeth past the mark so valves open sooner & looks better ,but think I will try another tooth or two to see what that does.

Turns out my gauge was bad....picked up a new one, ran a test & center cyl. read 90....l & r cyls. read 60. Shot a little oil in the cylinders & all 3 read over 120. Would this be normal for a motor that has never been run with the lack of oil being pumped throughout the motor?

What is the engine? I would try to find the compression specs in a service manual, or online and see how your compares

Jeff L wrote:Turns out my gauge was bad....picked up a new one, ran a test & center cyl. read 90....l & r cyls. read 60. Shot a little oil in the cylinders & all 3 read over 120. Would this be normal for a motor that has never been run with the lack of oil being pumped throughout the motor?

I Think that if it has never been run, that the rings are not seated. Adding the oil seals the ring area and increases compression.

Jim Sawyer wrote:What is the engine? I would try to find the compression specs in a service manual, or online and see how your compares

Its a BSA rocket 3 750. I was told on a british site that it should be like 120.

[/quote]I Think that if it has never been run, that the rings are not seated. Adding the oil seals the ring area and increases compression.

[/quote] Im hoping that is the case.

I shot a little starting fluid into the cylinders & kicked it over. It popped!!!!!!!!! Im sure it is going to run now. I have a little to do on the carbs (they were leaking), when they go back on I hope to report a running bike.......