View Full Version : Honda bf40 compression range

08-06-2009, 04:17 AM
I testing the compression on my Honda bf40.
I cannot find in any manual what range the compresssion should be?
My compressions are reading
1- 70 2- 75 3- 80.
Are these in line? The engine seems to be running very smooth.

08-06-2009, 10:11 PM
"Compression is supposed to be 199psi at 500 rpm. Cranking is not close to 500 rpm, so this number probably not realistic.
When you take compression, the engine throttle should be at full throttle. If you take it in idle setting, the numbers will be low like yours.

You are probably fine..."

08-06-2009, 10:17 PM
"Let me modify my last statement... The compression numbers do vary quite a bit and it might be helpful to take another reading at full throttle.

If there is still a variation, the valve clearances may need some adjustment."

08-06-2009, 11:25 PM
Thanks Honda Dude. Thats great info.
I will test it in the am.

08-07-2009, 11:03 AM
"Yes, best with engine warm and full throttle, you must have ignition off (to protect ignition electronics), use the lanyard safety switch.

Squirt some fairly heavy oil into the low cylinder and test again, if the compression improves you will know that it is a Ring issue and if not, a Valve problem.

Operation without adequate valve tappet clearance will burn the valve, they should be a regular maintenance check item."