have a b&s model 44u877-0005-g1 serial number 180123yg : owner said was running good then heard a pop stopped mowing parked, did a compression check found both cylinders were 60 psi, one plug had a little moisture on it other was dry. i believe that the compression should be over 90 psi is that correct, did not do a leak down test, so do i have a rings problem or valves, wanting any feed back to see where to start
#2
StarTech
Depends on how well the valves are adjusted and if the engine is using the newer ACR camshaft or the older non ACR camshaft. BTW the newer camshaft is only available as a replacement part.
Don't forget sealing of the valves and several others. Most people never de-carbon the cylinders. Most will have an iceberg of carbon on the back side of the intake valve. That can hold the valve open. Valve seat might of came out. Head gasket?? Put shop air into the cyls. Listen for air leaking out the air filter or muffler at TDC on compression stroke.
Since that is a OHV Twin Intek and when doing a compression test I set both intake valves at approx .010-,012 and re-test compression and compare one cylinder to the other. (make sure the ex valve lash is not too tight if you see the compression still low on either cylinder. Should be around .005. What this does is take the camshaft ACR out of the loop. The ACR is for the intake valves on that engine.
I would expect both cylinders to be with 5-10 lbs of each other and close to 90 or more.
The previous owners description of what happened (a pop and stopped) and what you see is iffy?? (not quite adding up)
See if it's getting fuel to the carb or give it a little prime gas into the carb throat.
I've seen them engines at least try to run on even one cylinder and at 60 psi the plugs should have been really black/oily.
Before I loosed the valves for another compression test I would check for spark on each cylinder and then if spark give it a prime of fuel and crank to see if you get any promise of a pop/run.
Depends on how well the valves are adjusted and if the engine is using the newer ACR camshaft or the older non ACR camshaft. BTW the newer camshaft is only available as a replacement part.
You will always have air out of the oil fill tube. Cylinders are never 100% sealed. What percentage leakage matters. High amount does point to cylinder problems. Normally you are looking for 20% or less leakage. One thing you particularly checking is the valve sealing or if you air escaping around the cylinder head or between the cylinder and the push rod galley which why when I doing a leak down test I remove the rocker covers. Especially important on the Briggs single 21,28,31, and 33 series Intek engines as they are bad about blowing the head gasket between the cylinder and push rod galley.
Air does leak pass the ring end gaps so even the positioning of rings can affect the leakage rate. Otherwords if all the rings end gaps are nearly inline more air will pass then when they are all equally spaced apart. Also the amount ring end gap affect the leakage rate. This why we shoot for a 20% or less rate.
