Briggs 12000 series with excessive compression

[wolfden793]

Hi All,

This community has been very helpful to me and I'm looking for some help with a Briggs 12H802 1752 B1 engine that has excessive compression. It pulls very hard on the compression stroke and is nearly impossible to turn the flywheel by hand. So far, I've checked the valve lash and the intake was very tight, exhaust was normal. Ground the intake per specs and reinstalled. While the head was off, I cleaned the head and cylinder along with removing all soot from the piston top. Also removed both valves and cleaned them along with reseating. Also re-torqued the connecting rod bolts thinking maybe they were too tight. Many articles on the ACR being the source of the problem, but I put a different cam in and no change. The original was undamaged, but given they are plastic, it couldn't hurt to switch them. Any thoughts appreciated!

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[RandyT]

Make me think that something is dragging like the flywheel brake preventing it from turning. Either that or some other internal engine damage like a seized rod bearing.

 

[wolfden793]

Hi Randy,

Thanks for your reply. The flywheel brake was the first thing I checked and made sure it was free of the flywheel. As to the rod bearing, I did remove the rod bolts and re-torqued, but no change there. I didn't inspect the bearing, though. I'm going to check the valve clearances again and see what difference that might make. Perhaps a bit more tweaking. I'll keep the rod bearing in mind. Thanks again!

Jim

 

[BravoXray]

Does it have the compression release system on it? If so, it isn't working. I saw a YT video recently where an engine was hard to crank, turned out the compression release mechanism on the camshaft was broken.
When working properly, early on the compression stroke the exhaust valve would be bumped open slightly to reduce the compression. Once the engine starts, centrifugal force deactivates the feature.

 

[wolfden793]

Good Morning,

Thanks for your reply. I did change the camshaft, but it not appear to have any damage to the CR. The metal wire on the shaft was intact. Hope to check the valves again today. Thanks for your input!

Jim

 

[IrishLoader]

Jim, check your gap on the coil, less than .006 could cause the issue. If you lack a feeler gauge a simple business card is about the right shadetree standard.

 

[wolfden793]

Hi There!

Thanks for your reply. This is one of the first things I checked, as I removed the coil and flywheel to clean them. That didn't seem to make a difference, but certainly worth checking again. As for the shadetree measurement, I use an index card with good success, but do have feeler gauges as well. Thanks again!

Jim

 

[sea2summit]

This is all by feel or you put a pressure gauge on and it’s out of spec?

 

[wolfden793]

Hello,

Thanks for your reply. I assume you're speaking of a leak down tester? If so, yes I did and it had no leaks. When air pressure was applied, it flywheel moved a bit. Hope this is what you were referring to.

Jim

 

[tomplum]

Did you look real close at the timing gear on the crank for problems? Or maybe confuse the key for a line up mark-( if that's even possible)?