OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines B&S 12.5 HP I/C Quiet, exhaust valve retainer.

I am optimistic that we will see some rain at some point and am getting my ride on's up to scratch.
This engine has done a lot of work, and I have at times overworked it on hot days as well.
Its symptoms were, once at operating temperature, would run rough & was missing quite a lot.
Also wouldn't idle - just stall. You could still mow with it.
I had cleaned the carb, changed plug and magneto, with no change.


I am trying to remove the exhaust valve and haven't come across this type of retainer, how do I get it off?



The bore is scored and I can just pick up the largest scratch with my fingernail.


I have already got the parts list and manual from the BS site.


As usual, all comments are appreciated
from Mark

It looks as if it may have a valve rotator, which would be unusual for a side valve engine. I can only recall three types of retainer Briggs used on the old side valve engines: the keyhole type, which we are all used to on the small engines, and can be seen on your inlet valve; a lateral pin through a hole in the valve stem; and an automotive-type split cotter. In your picture it looks like the valve has the groove for a split cotter, but I don't see the cotter.

The easy way to clear up all these mysteries is if you just post the Model, Type, and Code and we'll have a look at the Illustated Parts List. We'll also be able to look it up in the Briggs repair manual.

Yep thanks Grumpy, it does have the split cotters on the exhaust valve only.
When I flexed the spring with my screw driver I didn't see them as they where stuck inside.
I got the valve out using an 18mm open end spanner as a fork and tapped the valve head until the cotters where visible, then using a small flat tip screwdriver was able to get them out.
I can move forward now, many thanks.

Another question: why are Briggs rings so expensive? You can pick Honda parts up at a more reasonable price.

Hi Mark and Grumpy, that valve retainer should have pins in it and is pretty tricky to get back in. This is a good time to use a valve compressor tool if you have one. Although I can't see the pins from the angle of the photo . When you compress the retainer you should be able to see the pins and they will either fall out or they should be easy to remove hence you might need a little grease to hold them in place to re-install. Go slow with the valve compressor so you can see how the pins sit , sometimes the pins can stick and ride up with the retainer when compressing, so you may have to spray a tiny bit of degreaser.

Mark, I don't really know what forces are driving the prices for spare parts, but I can make a blind guess. Honda parts, in my experience anyway, are expensive from Honda dealers. Non-genuine Honda parts are around half of Honda's prices or less, on ebay. This happens because they are made by the people who supply the parts for chondas. The result, in my experience anyway, is good parts at low cost. (I'm not saying there aren't any bad parts being sold, of course: you have to know what you are buying.)

There are non-genuine Briggs rings being sold on ebay, but by American sellers, so the postage cost makes them over-priced here. My guess is there aren't many local sellers of non-genuine Briggs rings because Briggs engines are mostly side-valve with aluminium bores, and don't have their rings replaced all that often because the bores are too worn to make that worthwhile. Now that the side valve Briggs engines are all made in China, I'm guessing that non-genuine spare parts for them will become as cheap as Honda ones, but the aluminium bore engines still won't be worth re-ringing, because of the bore wear. It may not be worthwhile selling the rings just for the relatively few which (like yours) have cast iron bore liners. It may be a while before this situation resolves itself anyway because the large side valve engines were only moved to China about 2 years ago, much later than the small side valve engines. The local ring producers there may still be getting up to speed at this stage.

Thanks Rob, they ended up being the cotters, glad it wasn't the pins by the sound of it.
I will use grease to hold the split cotters when I put it back together, good tip.
I don't have a compressor tool.

Grumpy that makes sense, supply and demand for the BS rings. I must admit that my starting point for the small Briggs engines is good compression, otherwise it is a waste of effort.

I have some images: Not exactly sure how to proceed from here.


Carbon found in the intake port.


Not sure what to make of this, casting broken away around exhaust valve guide.


Scoring around the top of the piston, on the valve side that matches scratching in the bore. No scoring found on rings.



With timing marks aligned piston was travelling back down the bore. Bit different to what Ive seen with the smaller engines.

The Briggs engines use a key on the crankshaft to locate the small timing gear rotationally. I have always assumed, on the basis of no evidence, that the camshaft and its timing gear are in one piece. If that latter point is true, I don't see how the valve timing could be wrong when the timing marks are aligned.

I can't understand your pictures of the ports and valve guides, so I don't know what problems you are seeing in those pictures.

From the marks on the piston above the top ring, and the stripes down the bore, it looks as if there has been foreign matter in the cylinder and that is the resulting damage.

Yes I didn't explain enough, The top image above shows carbon found under the inlet valve head, in the port. Does this mean the inlet valve was leaking?

The 2nd image above shows underneath the exhaust valve head, you can see where the muffler screws in. It has a broken casting at the front of the valve guide. I think it will be fine.

I have honed the bore, this is how it came up.


I buffed the scoring on the piston on my buffing wheel, not to get rid of the scratches, but to smooth them out.

My ring end gap for the compression ring was 0.8mm.

I am putting it back together with the existing rings. I know it is far from perfect.

If an engine has leaky piston rings, it is likely to finish up having a black, oily intake port. There will be blow-by (gas leakage past the rings), which means a high volume of gas passing through the breather. When much gas goes through the breather the amount of oil mist and droplets it carries with it, becomes substantial. Additionally, engines with blow-by inevitably have dirty oil, so the oil passing through the breather is dirty too. The result is a dirty intake tract. Furthermore, the dirty oil carries dirt into the combustion chamber, causing wear to the bore and piston. Note that the wear to your piston occurred above the piston rings, not below them, indicating that it came through the intake pipe, not from the oil splashing from the sump. The wear is pretty bad on that engine: it may have had a leaky air cleaner as well as the dirt that came through the breather. Imperfect air filtering is a leading cause of bore wear.

It is better to do a more complete job of honing the scratches out of the bore: scratches provide a passage for blow-by, and perpetuate the problem. However it is not necessary to fully remove the scratches from the outside of the piston above the top ring. If you measure the piston diameter there, and compare it with the bore diameter, you'll find there is considerable clearance up there, even with a new bore and piston. That is not a sealing surface or a bearing area. Further down the piston it does have to be a close fit, to prevent piston slap.

The honing process is supposed to produce helical marks in the bore, not circumferential ones. You need to run the hone slowly and pump it up and down the bore as fast as you can. The bore should look like a whole lot of intersecting helixes, crossing each other at 30 to 45 degrees.

Well Grumpy that has given me something to think bout. This is always the hardest part for me, deciding on a repair option at the pointy end.
Your post above is very well written.

I can do a bit more honing, at a slower speed this time and replace the rings to extend its life.
Then next time get it bored out oversize.
This what I would like to do

A lot of my hard slog mowing around here is done now, the grass is under control, plus we have four legged lawn mowers wandering around to help save on fuel.

Boring engines is a complex process Mark, and not remotely worthwhile unless you are a hobbyist and enjoy the job, or you are working on an irreplaceable collector's piece. Note that the Briggs in that video has an aluminium bore, making the job even less justifiable than it would otherwise be. He also glosses over a couple of difficult points, which I won't go into or this thread would be doomed to be transferred to Tech Talk. I'll just say this: I have a slightly better milling machine than he does, but I've never bored an engine in my life.

I have known it to be done, for example on small single motorcycle cylinders, on a decent vertical mill though.
That was a setup that a well-qualified old mate put together some years ago, for a trailbike rides operation.
The most critical bit was the precision adjustable boring head he used, which wasn't cheap. Certainly not worthwhile for doing only one or two!

Another alternative [to rebore/hone out to oversize] traditionally used for Briggs engines with up to 0.005" bore wear was to fit a 'chrome ring set', with a 3-piece oil control ring. Briggs has obsoleted the chrome rings [P/No 392331] for Mark's engine, but they are still available aftermarket, through GA Spares and Stens/Bynorm.
Bruce has them listed in the ODK Online Store here.

While a bit of a 'patch-up', these rings do usually work to extend the engine service life a bit.

As grumpy says, imperfect air filtering is the most common cause of this problem. The old all-foam Briggs filters were particularly bad if they weren't serviced - once the foam was clogged, the engine would run very rich, which greatly accelerated the bore wear.

Back in the days when car parts were expensive and labour was cheap, one common alleged solution was "reboring in the chassis". This involved removing head, pistons, and sump, then bolting a crude portable boring machine to the block, using adjustable clamps attached to the head studs. The results varied from poor to worse.

Achieving a decent reboring job (to a toolroom standard, approaching production line quality) required two things: a full-sized (at least a Cincinnati No. 3, but preferably bigger unless the engine had a rather low deck height) vertical mill in excellent condition, and a qualified and experienced A grade machinist. In reality commercial reboring jobs were done on well-worn mills by people who were "qualified by experience".

Gadge, relatively small precision boring heads are pretty cheap these days (I think mine cost a hundred and fifty-something dollars including half a dozen different carbide tipped boring bars) but it doesn't have the rigidity to hold center when the bore has worn both oval, and off-center. It is much the same as this:
http://www.ebay.com.au/itm/50MM-PRE...DefaultDomain_15&hash=item462a04e059

To do the job properly takes a truly massive head, in a truly massive mill.

Gadge, thanks for looking those part no.s and rings up.

Could I use my drill hone to hone it out oversize? Sounds like a lot of honing, I think I would like to practice that on a small engine first.

I have done some more work on the bore with my battery drill on 1st speed, here are some shots.




With a worn bore plus my honing could I go up a ring size?

The valves are lapped and came up well, here is how I put them in, not having the compressor tool.




Just have to wait for gasket kit and rings now.

He he, that might have been appropriate in the days of steam engines. In fact it was; as 'in situ' reboring was the only way the big [bores measured in feet, rather than inches, weren't uncommon on the Low Pressure side] horizontal stationary steam engine cylinders could be done [steam powered boring rigs!]; it was also sometimes done that way on steam locomotive cylinders. But any further discussion on that theme belongs in its own off topic thread...

No, forget about using a handheld drill/hone to resize a bore! Briggs did once suggest [in my 1981 Repair Manual] that it could be done with a stone hone and drill press, for alloy bore engines <shudder>.

Those shots look OK; a 45� crosshatch honing pattern is supposed to be 'ideal'. No, I don't think enough metal would have been removed, to go to oversize rings. Ordinary cast iron rings are fairly easy to fit to a bore by filing back the ends, but chrome rings are not.
Yup, good way to do it.
Just FWIW; as an amateur mechanic, my own 'rule of thumb' is that any special tool needs to pay for itself [in terms of avoided cost, compared to getting a pro to do the job] in two uses at most.

Mark, that trick of using two cable ties as a valve spring compressor for Briggs engines was introduced to Outdoorking by Joe Carroll several years ago, and has been recommended here since then. I've never found any need for a spring compressor on OHV mower engines, since low speed engines have very weak springs, and you can easily use your fingers. However side valve engines are another story, because of limited space, and even most commercial spring compressors won't fit in there. A simple forked lever can work pretty well, especially for the stronger springs found in side valve car engines, where the use of fingers or cable ties is not a realistic option.

Its good to see that Joe's method is still being used by some, it works quite well, sometimes the retainers or collets may drop out while trying to release the spring but 2 cable ties sure beats a expensive tool...

Joe is going to be doing a video for youtube soon on a briggs valve job, as this morning I dropped off a 3.5hp sidevalve briggs with valve issues (no compression at all) that should make for an interesting vid on the findings.

Thanks for the tip-off MrMckay - please make sure we hear about it when the video is up on youtube. Eventually maybe it can be linked to an Outdoorking thread, so we can discuss it?

Thanks fellas with all comments to date,
This engine is awaiting parts.
I am feeling more confident about this engine now.
So I have ordered a new piston with cast iron rings, plus a gasket & seal set.

I was told by the supplier that I didn't have any choice with switching to chromed rings. The chrome rings do not fit the piston and if your engine didn't use them at the beginning, then you can't switch. And also that the cast iron rings will "break-in" the walls faster than the hard chrome, which take longer.

I haven't done any experiments to know any difference here, so decided that by not changing from original was best.
Thanks again.

If Briggs used different piston ring groove dimensions with the chromed rings, it sounds as if they specifically didn't want people to fit them interchangeably with the plain cast iron rings. This may perhaps have been because they wanted to be fairly sure nobody would fit chromed rings, or steel rail oil rings, to an engine with an aluminium bore. I've certainly never been prepared to do so myself.

I remember the days when most car engine rings weren't chromed (yes, I'm pretty old) but the better grades of replacement rings were chromed. Most cars used to have their rings replaced once or twice before they were scrapped, in those days. Some models of engine tended to use more oil after re-ringing with chromed steel rail oil rings, compared with putting in a new set of original plain cast iron rings, but most models didn't. I haven't heard a convincing explanation of why this is so. Some of the old hands put it all down to break-in procedure when the new rings were fitted. (Back in those days, cars with plain iron rings always required a fairly complicated "running in" process to keep them from scuffing their new rings and performing poorly thereafter. Even now, it is possible to scuff modern rings, though it's more difficult than it was then.)