16hp cast iron 326437 Briggs compression spec.

[90cummins]

I just rebuilt my old 16hp cast iron briggs with a 0.010 over piston, rod & valve job.
And it runs fantastic.
I performed a compression test after break-in and recorded 125psi hot and cold.
Does anyone know the actual spec or range for this engine.

Thanks
90cummins

 

[rangerfredbob]

I wouldn't get too caught up in the compression, small engines are strange in that department, most are low compression ratio with strange cam profiles that occasionally have a bump to reduce cranking compression... Generally the low point on a running small engine is 90psi so anything over that is fair game...

 

[90cummins]

I am not caught up in details.
I like info even when there is no specific info available.
This engine was rebuilt as a replacement for the original 10hp Tecumseh on my log splitter.
I also installed a 28 gpm pump in place if the original 22gpm pump.
I recorded these data points for future reference.
Final setup after break-in and 3 oil changes with 15w40.
Compression cold 125 psi
Compression hot 125 psi
Rpm 2956 no-load
Rpm 2763 @ 2000 psi
Rpm 2631 @ 2500 psi
Rpm 2345 @ 3000 psi
Max psi = 3200
Cycle time no load 7 seconds @ 2956
Alternator output 46 volts ac

Cycle time 7.5 seconds @ 2785 rpm
Cycle time 6.75 seconds @ 2980rpm
This is what happens when I have time on my hands.

90cummins

 

[flyerdan]

It seems that a lot of air cooled engine makers are vague on actual compression readings - the Briggs book for that series calls for a special tool that uses compressed air at 70 psi, quite similar to the aircraft compression tester, except the Briggs one uses color codes on the dial instead of actual numbers for their results table.
125 sounds pretty good for that, it would be about a 77/80 or better.

 

[rangerfredbob]

Ok, I guess I could have worded it better, what flyerdan said is more of what I was trying to get at... you will likely not find a compression spec for anything small... from what I've read over the years it's mostly observation not numbers... on some of the smaller mower engines with the pull start off the spec had something to do with turning the engine backward by hand toward compression to see if it bounced off compression or went through...

 

[RandyT]

Ok, I guess I could have worded it better, what flyerdan said is more of what I was trying to get at... you will likely not find a compression spec for anything small... from what I've read over the years it's mostly observation not numbers... on some of the smaller mower engines with the pull start off the spec had something to do with turning the engine backward by hand toward compression to see if it bounced off compression or went through...

Briggs doesn't public compression readings for their engines stating that with compression release there is no accurate way to measure it. but will use compression on twins for comparison between cylinders. The early Briggs used the rotate backward to check compression for bounce, or thumb over the spark plug hole to see if it blew your finger off the hole. The early Briggs engines used a modified camshaft lobe that held one valve open longer than it should to make starting easier but gave up power in the mix. Honda on their small push mower type engine have a published reading of 71, and Kohler with the Command twins since they don't use compression release have a minimum reading of 160.

For Briggs at least the old L head engines I always like to see 90 psi or above. That is with 40 some years of tinkering and 23 of those as a professional small engine tech.

 

[RandyT]

It seems that a lot of air cooled engine makers are vague on actual compression readings - the Briggs book for that series calls for a special tool that uses compressed air at 70 psi, quite similar to the aircraft compression tester, except the Briggs one uses color codes on the dial instead of actual numbers for their results table.
125 sounds pretty good for that, it would be about a 77/80 or better.

What you describe is a cylinder leakdown test. It uses compressed air at TDC to check the amount of bypass the rings, head gasket, and valves. Same principle is also used on automotive engines also. My tester calls for 100 psi input for accurate readings. Some of the newer testers don't require that high pressure. Just for comparison I worked on a generator a couple years ago that had 5 psi compression and put the leakdown tester on it to find where I was loosing compression and to my surprise the leakdown was only 10% which didn't make sense. The is the power of a compression release mechanism. Ended up having a blocked exhaust was the reason it wouldn't start.