Low Compression on Briggs and Stratton Platinum

[primerbulb120]

I've got a Briggs and Stratton Platinum Series engine on a Craftsman push mower. The mower is a trash pull, but it's nearly new. The compression was at 10 psi when I got the mower. The valves look okay, but I took them out and cleaned them to be sure. I didn't see oil leaking into the cylinder so I don't think it has bad rings. I have a new head gasket on order in case the old one was blown. If you have had a similar experience with one of these engines, I'd appreciate it if you could tell me what was wrong with yours.

 

[7394]

Personally, I'd say you jumped the gun on the tear down, a simple 'leak-down' test would have pinpointed the exact area that needed addressed. It would have told you if it was intake valve, or exhaust valve, or rings. Compression is usually low at starter engeged speed, so the compression releases allow the engine to spin easy with out overwqorking the started. But 10 psi is extremely low. Was this on a cold engine ? Was the throttle WFO while testing ?

 

[primerbulb120]

I agree. I don't have a leakdown tester and don't want to purchase one, but I could have put compressed air in through the spark plug hole and listened to see where it came out. The engine was cold. I don't know what you mean about the throttle, but it was attached to the governor and the governor seems to be working.

 

[7394]

Yes adding air on a compression stroke (both valves closed) would have been helpful for a direction to pursue.

Throttle open is helpful on comp test as it allows engine to inhale as much air as possible, for true comp test.