OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Briggs and Stratton Model 90302

Delving into a lawn motor motor for the first time and this is what I find on the pistons and valves. Is all that carbon build up normal or does it indicate an oil problem? Well, the engine does seem to have an oil problem because oil was draining out of the breather assembly pipe (don't know its real name) that plugged into the carby.



Would the gasket being broken on the breather assembly cause oil leaks? Trying to isolate the problem.

The easiest way to check the condition of the rings on a Briggs is to do compression tests with and without a teaspoon of engine oil put in through the spark plug hole immediately before you do the test. If the pressure is 15 psi or more higher with oil in there, you need new rings.

Oil in the breather tube is often an indicator of worn rings, but it is an even better indicator of an over-filled sump.

Very worn rings, to the point where the engine smogs out the neighbourhood, result in liquid oil in the combustion chamber, which you do not seem to have. Beyond that I can't tell: black deposits are normal, and in the pictures they do not seem heavily caked up. How much blue smoke was it blowing?

It wasn't starting. It seemed very hard to turn. I did a compression test and it came out 65 psi. Not sure the test is too accurate as, like I said, it didn't turn very easily.

There is a rattle in the engine like something small is loose too, so I'm trying to find that.

Worn engines normally turn more easily than new ones. If it is more difficult to pull the starter than on other similar Briggs engines, and it has nasty internal noises, it sounds like it has a serious mechanical fault. The 65 psi compression test result would be within the common range for a well-worn Briggs, but unless you repeat the test with the teaspoon of oil added, that's all it tells us.

I suggest you remove the starter and rotate the engine by the flywheel fins (with spark plug lead disconnected, of course). See if you can find out more about this clunk. Also watch the piston while you rotate the engine slightly backward and forward. See if there is any lost motion when the piston is in the middle of its stroke.

Thanks Grumpy

I found the rattle, its in the starter clutch. I'm assuming a rattling starter clutch might make it hard to turn the motor?

And this exploration has probably gone further than it needed. I'm probably gonna pull the whole thing apart now so I know where everything belongs, not confident I'll get it back together again but I'll have fun trying . The mower is a throwaway, so no great loss.

I'll have more questions I'm sure as I dive in further.

I don't see an immediate connection between the starter rattling, and it making the engine hard to turn over, but it is possible of course that it causes both problems. You can find out simply by removing the starter and seeing if the engine is easy to rotate by turning the flywheel.

There is a lot to be learned by dismantling an old engine that is probably beyond its use-by date. However you learn much more if you do it carefully, one step at a time, and review what you learn at each step. We are here to help if you choose to do that.