Small Engine Ring Gap - PeachParts Mercedes-Benz Forum

kknudson · #1 10-15-2010, 07:38 PM

After rebuilding my Lawn tractor last year, a neighbor asked me to help his son rebuild his lawn mower.
Dad's mechanical abilities are pushed changing a light bulb (really), but the kid is pretty handy. I've helped him a number of times, and he's helped me with a number of projects.

So the son decided he wanted to do what Uncle Kevin did, similiar mower setup.
Slightly newer B&S he picked up at a yard sale. Engine is bad, he ordered a +.020 ring set. He decided std wouldn't work and .010 isn't available.

Well we can't hone it to .020, but the cylinder isn't bad, so I figure we hone it nice and grind/file the ends of the rings.

What kind of ring gap should I shoot for, the manual he got says if over .030 replace. But doesn't show what to go for when installing, (Thanks B&S).
Other than direct replacement (cars) I've always had a recommended ring gap in the manuals.

We are doing this tomorrow, Saturday, so my guess is .005 to .010.

Any help is appreciated, Dad's buying me beer if we get it running.
He'll probably buy pizza for lunch, and a few beers anyhow.

Thanks

One of those Dads OK to a jerk, Kids got potential. I figure(Hope) I can help guide him a bit.

Chas H · #2 10-15-2010, 07:43 PM

I have always used 0.003" of gap per inch of bore. Since it's an aircooled engine maybe add an extra 0.001" to the total.

Matt L · #3 10-15-2010, 08:12 PM

.001/inch sounds like too little. It is very important to not make the gap too small. If the ring ends butt together, the ring will lock into the bore. The rest of the engine won't like it too much that the piston stopped moving or the land broke off, depending on the direction of travel.

I don't know how reliable this place is: http://www.aa1car.com/library/ring_end_gap.htm (first hit on
Google). They recommend .004/inch of bore. That sounds more appropriate.

You probably won't go wrong with .015 on that.

Chas H · #4 10-15-2010, 08:28 PM

Thankyou. I mispoke. I use 0.003" per inch of bore. Using 0.004" per inch isn't gonna make any difference in a small bore engine. Your link is to a performance oriented website where ring gaps are typically larger.

Matt L · #5 10-15-2010, 08:56 PM

That's for liquid-cooled performance engines.

Air-cooled engines also have larger gaps.

rscurtis · #6 10-16-2010, 04:38 PM

If this engine has an aluminum cylinder bore, you don't hone it. Get your hand on a Briggs chrome ring set and put it back together. If it's a flathead engine, adjust the valve clearance while you have it apart.

This is not a Mercedes or an Indy car engine. If it has .015-.030 ring gap, put it back together and don't worry about it.

kknudson · #7 10-16-2010, 05:50 PM

It's a cast Iron cylinder.

We honed it, put the new rings in, the old rings were shot.

Checked the valves, new gaskets etc.

Dang thing won't start.
Sounds like it wants to, exhaust gets hot, do have spark but it just won't run on it's own.

Really bummed, we worked hard on it this morning, kid learned a lot and was a big part of it. He didn't just watch he did much of the work, we cross checked each others work. After I put the bolts in the bottom case, he cross checked I got them all tight. We took turns doing the head bolts in order, one torqueing on one reading the manual.

Everything checks out, I'm baffled.
I figure it should at least start, even if it doesn't run right.
It's either something stupid, or something major.

Although I'm no pro at small engine repair.

May try and locate an old old friend who had a lawn mower repair business, haven't seen him for a few years. But I know he's stilling living a few miles away.

layback40 · #8 10-16-2010, 10:06 PM

Try a little starter fluid as a last resort.

Tomguy · #9 10-17-2010, 02:43 AM

Quote:

Originally Posted by kknudson

Dang thing won't start.
Sounds like it wants to, exhaust gets hot, do have spark but it just won't run on it's own.

Sheared flywheel key? Sure sounds like it. That's what happened to my go-kart engine when I didn't tighten the flywheel "Nut" enough.

BTDT on the ring issue on a B&S engine too. Did a rush repair job on my tractor some 15 years ago. Conn rod bolts came loose somehow & piston was slamming head. Piston was shot. Bore was OK, but a little worn. Put in the 0.020 piston with matching chrome rings. Didn't hone or anything since I put the chrome rings in. Lasted at least 8 years after that. I would assume it's still running for the new owner. It was a 12-month tractor, with a 48" mowing deck in summer & 48" blower in the winter.
http://jacqueslacasse.tripod.com/LesKreifels/Simplicity7016_2.jpg

kknudson · #10 10-17-2010, 03:49 AM

Quote:

Originally Posted by layback40

Try a little starter fluid as a last resort.

Tried that, thats what has me baffled. That started my tractor before I rebuilt in almost not matter what.

Quote:

Originally Posted by Tomguy

Sheared flywheel key? Sure sounds like it. That's what happened to my go-kart engine when I didn't tighten the flywheel "Nut" enough.

That would screw up the spark timing, hmmm I'll have to check that.
It's a ***** to remove, my good puller doesn't fit this flywheel. But I made one that worked on my tractor.
Hopefully it will fit this one, I don't what to make another.

FYI I did find out the kid bought the mower used with the extra rings.
Prior owner was gonna rebuild it and couldn't get it to start, so he decided to dump it.

Toomy, nice looking tractor, thats why I rebuilt mine. I have a 36" snow head for it, that thing was amazing even for a single stage the snow it would just walk through. And the snowhead won't fit any new tractors.

So my tractor really is year round to, I have the mower, plugger, aerator (Garbage picked), spreader, roller (rusted out I think), sweeper (rarely used, garbage picked like new) and the thatcher (front mount, so I can thatch, mow and plug at the same time) that also only fits this tractor.

kknudson · #11 10-17-2010, 08:57 PM

Well TomGuy, haven't fired it up.
But I pulled a cover off and the slots don't align !!!!
And it took nothing to remove the bolt.
Put my puller on and it popped right off, no key present, not even a damaged one.

We'll finish it tomorrow night.

BIG Thanks, if you're ever in my neck of the woods, just NW of Chicago, Beers on me !!!

I knew it was something simple, I wasn't great with small engine repair. Between these two I now think I have learned quite a bit. Mostly the things NOT to do, but the things to do as well

kknudson · #12 10-17-2010, 08:58 PM

I think I have a key for it handy too.

layback40 · #13 10-17-2010, 09:52 PM

sounds like some one had it to pieces before.
great that you found the problem.

Matt L · #14 10-17-2010, 10:49 PM

Don't put a steel key in there.

t walgamuth · #15 10-18-2010, 05:50 AM

I was going to say timing off....