BS Compression

[bh357]

What is a normal compression for a BS mower engine, model 110900 (single cylinder, vertical shaft, 4hp)? I measured 90psi, but the guage I used was one you had to hold pressed to the plug hole (does not screw in). Also, I had to pull the starter rope with one hand while trying to hold the guage with the other. The true reading may be a bit higher. The engine seems to run good.<br />Thanks.

 

[SlowlySinking]

Re: BS Compression

Some mower engines have an easy start feature that reduces the compression while cranking, this makes it tough to get an accurate reading.<br />If it runs good why are you concerned?

 

[walleyehed]

Re: BS Compression

That engine has a compression release and it can't be done in that manner...it has to be a leak-down tester, BUT, if you still show 90psi, you don't have any ring to cylinder problems.

 

[bh357]

Re: BS Compression

Thanks. I forgot to mention that the reason I decided to check compression was that I get a bit of a puff of smoke when I go from idle to WOT. It seems to accelerate nicely, just a little puff of smoke.

 

[Pascal]

Re: BS Compression

90 psi on a pull start compression test is excellent.<br /><br />The manual says that the testing the compression is done with all the shrouds removed and you are to flip the flywheel backwards on the compression stroke. If the flywheel bounces "sharply back" compression is good. There is no spec compression number in the manual for those engines.<br /><br />Have done several comparisons tho and 60 psi will give a sharp bounce <br /><br />What color is the smoke?? blue = oil & black = fuel. is the oil livel too high?? What's the air filter like?? <br /><br />JD