# Aluminum bore Briggs engines



## mopar4u (Jul 14, 2006)

what is everyone's thougts on putting new rings (properly gapped) into a briggs aluminum bore engine where the cylinder is oversized (worn beyond spec)? Will you get piston slap? Shouldn't be a problem?


----------



## mopar4u (Jul 14, 2006)

top, any opinions or facts?


----------



## paulr44 (Oct 14, 2008)

Piston slap and ring end gap are two different animals. Even if ring end gap is set perfect, if the piston skirt clearance is out of spec. you can have piston slap. If the bore isn't too far oversize, B&S used to make .003" oversize rings. You'd need to mic things up, or at least put the piston in without rings and check skirt clearance with a feeler gauge. And if the bore is tapered badly, oversize rings may help but not for long. When a piston starts to rock, the sealing quality of the rings can be lost or diminished, resulting in loss of compression, and possibly combustion gasses/pressure getting past them resulting in flame wrap. Bottom line...engines are designed to work with proper tolerances, when they are "worn beyond spec." as you mention, if it runs it's on borrowed time.


----------



## mopar4u (Jul 14, 2006)

Thanks Paul, I believe the .003" rings your refering to are the chrome rings, I've also read they can potentially be used when the cylinder bore is slightly overisized. So if the cylinder bore is .003" oversized, your skirt clearence will be large, that leaves me to assume by Briggs offering these rings that it is safe to do this and piston slap shouldn't be an issue. Depending on the application I would think you could get several years of borrowed time. Yes/No? 

Although seeing a bore this oversized probably means other items in the engine are just as worn. Crankshaft pin where the rod rides comes to mind.

Just trying to avoid throwing out motors if you can get a little more reliable life out of them at the cost of a set of rings, then it seems like a viable choice. Machineing just isn't a cost effective fix.


----------



## paulr44 (Oct 14, 2008)

I put chrome rings in my mini-bike engine, a Tecumseh H35 plain-bore (aluminum cyl.)(okay, I bought them and my older brother put the piston in), and they wore the bore oval in about a year. Chrome rings are designed for cast bores, as they have higher wall pressure. I know what you mean about keeping things going, plus there's a satisfaction to making something broke or condemned work again.
A fresh set of rings can often get a worn engine to work again, but for how long is the question. Knurling the piston skirt would also buy some time, but not much.

You point out something often overlooked...if the bore is worn, then the rest of the moving parts are probably too. I will take one exception to that, and I base it on first hand experience. Had a 5hp B&S I/C (big block) come in on a mower, smoking a lot. Guy ran it without an air filter. The rings were toast, but the the cast bore was actually in decent shape. New rings, a valve job and it ran just fine. Seems like when a lot of dirt is ingested in a short period of time, the rings take the big hit, as opposed to what we usually see when there's no cross-hatch left: often a nice ridge at the top of the cyl., piston skirts with >20% wear pattern, etc. etc.


----------



## 30yearTech (Sep 14, 2006)

Chrome rings are available for most kool bore (aluminum cylinder) Briggs engines. They are for engines with cylinder wear of up to .005". Look at the IPL for your engine to see if chrome rings are available.

Download a service manual for your engine at www.mymowerparts.com

They list the specs and rejects for engines.


----------



## paulr44 (Oct 14, 2008)

I stand corrected. Chrome rings by B&S are intended for aluminum bores too. I do know they have higher wall pressure, and assumed they were intended for cast bores only. You know what happens when you assume...
Paul


----------

