dead B+S mower engine

First.......put in a new plug. Just because it fires, doesn't mean the plug is good. I have seen engines run (poorly) with a bad plug.

You say it has compression, but does it have enough. Just because the valve seats look good, doesn't mean the are closing all the way. Check the gap, should be approx. .04

Hank

Reply to
Hustlin' Hank
Loading thread data ...

One of the piston rings froze up?

Reply to
Oren

A compression gauge is cheap, maybe 15$ and will tell you all you need to know before wasting any time on a junker. I cant give accurate numbers but I will guess and say 130 is new, 110 its at half life and near 80-85 its not going to want to do anything. Try misting in gas with a hand spray bottle just as it starts.

Reply to
ransley

Which gap? Spark plug? Valves? Piston rings? or.... or.....

Reply to
Stormin Mormon

Yep, I thought the same thing.

OR A valve is sticking open.

Before ripping it all apart, pour some kerosene or diesel in the sparkplug hole. (bout a quarter cup) Put the plug back in finger tight, without the plug wire attached. Turn the engine over by hand. It will likely not turn all the way because of fluid lock when the piston comes to the top. Leave it sit like that for a day. If a ring is stuck, this may free it, as well as a stuck valve. You can always open a cover on most engines to see the valve stems move. You can always work them up and down with a plyers.

When you want to start it, remove the spark plug and spin it over to blow out the remaining kerosene, clean the plug and reinstall it, and try to start the engine.

Once you get it started, change the oil because the kerosene may have diluted it.

If the kerosene is gone after one day, you definately have a leaking piston ring.

Reply to
mister_friendly

The valve clearance. Over time the valve seats wear and the gap closes, not allowing the vlave to close completely. If the vlave clearance is less than .04, the valves MUST be removed and ground down to the proper clearance.

Hank

Reply to
Hustlin' Hank

How can you give a suggestion like that? Caustic (many oven cleaners have it) will eat die-cast (pot metal)! Moron, not Mormon!

Reply to
Bob Villa

When I took a small engine course, we learned that the intake valve clearance is .010 and the exhaust is .020 inches. That from memory, and it's been a lot of years since then.

Reply to
Stormin Mormon

It was very apparent what you meant...some people need to be hit with a 2X4!

Reply to
Bob Villa

How much time does it take to clean a carb, versus how long to eat potmetal? As I suggested, rinse well and dry. As someone else suggested, rinse promptly, and thoroughly. People (like you) who abuse exclaimation points can be helped!!!!!!

Reply to
Stormin Mormon

What you kinda remember is the 10-20-30 rule. .010" for mag/fly, .

020" for points, .030" for spark plug! (don't want to disappoint!) bob
Reply to
Bob Villa

Spark plug gap for BS engines is 0.035, so 0.040 isn't that far off. Some idiots need to stop embarassing themselves with clueless flames.

Reply to
Stormin Mormon

far off. Some idiots need to stop embarassing themselves with clueless flames.

Now you're saying you were right comparing a spark gap with a valve clearance gap...and you're NOT the idiot here!!!!!!!!!! You have waaaay too much time here giving bad advice that you can't keep straight in your head (age related).

Bob Villa

Reply to
Bob Villa

Yeah, I'll check them. Visually they look good (i.e. seating evenly and no other obvious major drama has occurred) but that's no guarantee that they're not worn so much as to be inefficient.

I've found the allowed clearances for that engine - 0.005 to 0.007" on the intake and 0.009 to 0.011" on the exhaust.

cheers

Jules

Reply to
Jules Richardson

Yeah, I'll give that a go; as it's a horizontal cylinder I'll have to pull the engine, or just stand the whole mower up on its butt :-) It seems like a worthwhile test, though - I really don't like how loose that piston is feeling compared to the "new" 11HP engine I got.

cheers

Jules

Reply to
Jules Richardson

Just for the record, 0.030" for this B+S engine according to their operating manual (just in case someone stumbles across this thread at a later date! :-)

cheers

J.

Reply to
Jules Richardson

Hmm, well it fails that test (or passes it, depending on how you look at it. I can keep my thumb there while it's turning over; I can feel it compressing, but it's not so much that I can't keep my thumb in place.

I've only worked with big multi-cylinder engines before, so messing with the small single-cylinder stuff is a bit of a (fun!) learning experience

- I'm not sure how good compression *should* be on such a small engine, but it sounds like this engine doesn't exactly have a lot :-)

(unfortunately I do have a compression tester, but it's 4000 miles away, which isn't much use right now! Maybe I should just cave and buy another one...)

cheers

Jules

Reply to
Jules Richardson

The small engines I've serviced. I've had to pull a rectangular cover from the side of the motor, which exposes the valve springs. The clearance is measured between the end of the valve stem, and the push rod. Have to turn the crank shaft so the lifting pressure is released. As the engine warms up, the valve stems lengthen due to temperature. So, there needs to be a gap, to compensate for the lengthening.

Reply to
Stormin Mormon

formatting link
bucks. You can likely find a 20% off coupons, too.

As to piston rings loosening. I'd consider diesel or WD-40 which at least have some lubricating value.

Thanks for the correction: Spark plug gap .030 sounds right.

Reply to
Stormin Mormon

OK, now sitting there with a gas/oil mixture (about 75% gas, 25% oil) in the bore - I'll see how that goes if I leave it overnight.

I checked the valve clearances - 0.005" on the inlet and 0.011" on the exhaust, so those are within spec.

I got the 11HP engine running earlier, borrowing the magneto and spark plug from the broken 10HP. That seems to rule those out as culprits on the 10HP. I still can't definitely rule out carb issues, although it's interesting that the 11HP ran with its carb, but that carb didn't get the

10HP going.

I've not checked the ignition timing yet as I didn't have a suitable wrench for the 1-1/4" bolt on the flywheel, but I suppose I can always compare the flywheel position on the 10HP at TDC relative to the 11HP.

cheers

Jules

Reply to
Jules Richardson

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.