OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines B&S Sprint 375 blows smoke

Dear All,
I got a lawn mower with a B&S Sprint 375 engine. The engine runs very well and it always starts first go but it blows a noticeable amount of smoke.
This is what I�ve done so far in order to isolate the potential cause of this problem:
- Replaced old fuel with fresh fuel: no difference
- Replaced fuel diaphragm on carby: engine runs better, but no difference on smoke
- Checked oil level: just below max. Oil looks old and black, but there is no water in it
- Run engine with oil breather tube disconnected from carby: no changes on smoke.
At this point would you consider to replace the rings or there is anything else I can do before taking the engine apart?
Thanks in advance for your comments.

Max

Is the smoke blue or black? If the smoke is blue I would be checking into condition of the rings, pcv valve, valve guides, etc

Hi Joe,
I would say white/bluish but definitely not black.

It does sound as if rings are the culprit, but there is a simple test you can do that will usually verify it. Do a compression test, put a spoonful of engine oil into the cylinder through the spark plug hole, and repeat the compression test. If the compression increases markedly, the compression rings are leaking. With Briggs engines especially, if the compression rings leak, chances are it will burn oil.

It is possible to have vast oil consumption and oil smoke you can't even see through, together with good compression and no oil going through the breather (happened to me yesterday with a Honda engine, it actually surprised me, it's been so long since I last saw it) but so far at least, I haven't seen that with a Briggs engine. If the oil test says the compression rings leak, you need new rings anyway, but you can be pretty confident it will fix your oil smoke as well. If the compression rings aren't leaking, it is still probably an oil ring problem, but please come back and tell us so we can talk about it some more.

Hi All,
I would definitely say that the rings are gone. Normal reading was 50 psi, pressure after pouring oil was 90 psi! I'll start looking for a 2nd hand engine because it will probably be cheaper than taking apart my unit. Gaskets, oil seal, rings etc. seem quite expensive compared to a 2nd hand engine..
Thanks for your comments!

The cost of parts depends on how you source them Max, and a second hand engine may have most of its life behind it. Anyway, that is your choice to make.

Thanks for telling us the outcome of your test. I'll close this thread.