OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines When to leave alone

I am cleaning up a 3HP Brigg Model 92502.
When I took off the head I found quite a build up of sticky black residue. The valve seats were quite clogged up.
The unit had also been burning oil recently.
With the valves lapped in there is some compression but it's not great (can't measure it).

I was not intending on opening the crankcase so I don't know of a way to check out the condition of the piston rings. The piston bore is not scored.

My question is when do you leave something alone and when do you investigate further? I don't have a good track record of getting piston rings out undamaged and checking the piston rings is the only reason I would open the crank case.
Does the 3HP tend to wear its piston rings or do they go on forever?

Sorry this is so vague but I'd appreciate some views on whether you would leave alone or check the rings.

Hi there

All engines will wear piston rings if not maintained correctly, especially small engines like this, oil was probably never changed, nor the air filter

The biggest problem with going deeper with little engines these days is cost. The bore may not be scored, in 4 strokes it rarely is, it is probably well glazed (shiny) though and will no longer retain oil. If it has been burning oil, most likely it will have been coming from the rings, due to the side valve design it wont have been coming up through the valves. Depending on just how much carbon it has around the piston, another check you can do is put the piston at TDC and see if you can rock it back and forth in the bore, a good telltale that the rings are worn out.

It is entirely up to you, but just remember you are up for a head gasket anyway, you will also need a crankcase gasket and ringset if you go further, you will also need to hone the bore if you want to do it properly. All up parts will most likely cost more than the engine is worth.

Good Luck!

Many thanks.
The aim was just a quick clean up rather than a complete rebuild. If I stop now I can always go back a do a proper rebuild later when I have a bit more money to spend. Re-seating the valves, freeing the governor flap and replacing the plug will probably give me another years smokey service without doing any permanent damage to the unit.
Mean while I'll pick up the parts over the coming months so I can hide them in the monthly outgoings.

Duncan I guess the real question is what is the purpose/reason for wanting to repair this motor, is it for restoring some machine to original or is it for something you intend to use?

Well that why you do lead down tests as it is none invasive and give you a good idea what is going in the cylinder without even pulling the head. Based on the results you would have a good idea where the problem lays.

Anyways since you have the head off check the valve guides for excessive wear as a worn will lead to excess oil in the cylinder and an exhaust will cause a lot of smoking but no excess oil the cylinder. Even the cylinder is not scored you should still mic it at top, middle, and bottom on the ring travel; twice at each level 90 degrees of each other. This will check for overall wear, tapering, and ovaling. I seldom see worn cylinders without worn rings. If you have less .005 of overall wear then you should re-ring with standard rings once you break the glaze.

Nath, I do see quite a bit scored cylinder in 4 cycles too. Operators thinks air filters are unnecessary at times.

Matter of fact I got a log splitter that I just did the above tests on which just be kill it as I can't oversize beyond .020 over and it has all the above problems including heavy scoring of he cylinder walls. I got fairly good idea once ridge hone the cylinder I going to go pass the .020 over before removing the scoring. Initially I had 30 psi compression and 60% leakage rate which a good portion was the intake valve seating but once I pulled the head I found the exhaust valve guide worn out and the cylinder scoring.

Too bad Briggs no longer sells the .030 over pistons and rings or the .010 over sets. There are a lot of savable engines if they did. I reckon their logic is it is worn enough to oversize you go to .020 right of the bat and if too worn to go to .020 it is a waste of time and you should just replace the engine if a replacement is available or kill off the equipment.

NormK
It's a second mower, (Mountfield Emblem 14" cut) which I quite like because it's so light and manoeuvrable.

I guess that is probably the answer right there. I do like it and I don't need it back immediately so why not take the time to do it properly!

I already bought the complete set of gaskets so there is nothing to stop me opening the crankcase and checking the piston rings (except a very stubborn bolt on the blade). I've not checked the rings on an engine yet so it would be a good thing to do to expand my education.

Its got the plastic Auto choke carburettor bolted to the fuel tank. I can't see many spares for these and its been working ok so that is one thing I will leave well alone.

If nothing it will be a good learning experience and can be invaluable at times. Heck that the way I learned a lot my repair knowledge which was tearing into engines no one else could or was willing to fix. It doesn't hurt though to have the service manual handy for reference.

Hi Duncan, no problems with doing the repair if you like the mower. As for the bottom bolt, some are extremely tight, I had the side of a socket break off recently getting one of them undone

Standard or el cheapo impact socket? With the impact sockets I have I normally shear the screw/bolt before I bust a socket.

AVB it was obviously an el cheapo impact socket that could not handle the 1150nm of torquue

There not many sockets that can handle 848 Ft-lbs. If you indeed put the much on the bolt it should had shear well before that. I don't much of anything above 300 ft-lbs. Although my impact is capacable of 900 ft-lbs working torque and 1300 ft-lbs loosening if right hand threads are involved. Most blade bolts here are 7/16 or 1/2.

AVB, I have only come across a couple of Briggs that my 320nm rattle gun couldn't handle, it is the Victa 2 stroke ones that really test things, they are a nut on the end of the crank, the thread gets damaged and also the can rust up pretty hard

When come to engines I seldom need an impact but it is the large riders, zero turn, ATV/UTV equipment that I need more power for. I had several zero turn deck spindle bolts that I was having to use a 5 ft cheater on my pull bar, place my feet on the deck and row boat them loose. On an ATV I was having jump on end of the same setup to break free the axle nuts. At the time I weighed 260 lbs, now I down to 245 lbs and hopefully still dropping toward my target of 220-230 lbs. My pre-old age weight. Oh I not that old just 59, just learning to live the single life and cooking smaller meals and not for a family of three. I got as terrible habit if the food is there I will eat it. Boy my chickens are liking me lately.

My Campbell Hausfeld rated at 250 ft-lb which equals 320 nm wouldn't even touch them. I actually gave it away. I had only one item that my Air Cat couldn't free that was because it overcame the engine compression too easily. That was a Stihl backpack blower. It just took a piston stop and a pull bar to remove the fan. Just shows that you must use the correct tool for the job.

Now I did have air supply problem but even with it resolved the old 250 ft-lb still wasn't doing the job. The main problem with the air supply was those couplers and plugs causing a major restriction. I still have a slight problem on the 125 ft run of 3/8 air line but that is a CFM restriction at the air compressor that I can't resolve without replacing the whole compressor setup. Most times I just need to bump the trigger to loosen a fastener. Actually I can carry a 10 cu ft air tank to the field along with the impact and loosen most fasteners on riders to replace blade or pull an electric PTO clutch. That because the Air Cat beak away power uses less air.

Now why I need such a powerful impact. The nuts on zero turns transaxles that torqued to 300 ft-lbs. Those nuts are the type that destroy the threading due the metal locking design. You actually need to replace the axles because of this but I found it just easier the disassemble the transaxle and pull the compete axle if I need the replace the seals. On ATVs it is because these things are constantly being submerged in nasty water.

Oh I twisted a few cheap adapters and extensions in two. They were some I brought at a flea market. The last one I twisted in two using a torque wrench and it snap at 150 ft-lbs. I call HFT about the spec on theirs 1/2 to 3/8 and it is 350 ft-lbs so I just chalk it to a defective adapter but I have replace that socket with a 1/2 drive version. For some reason I have never busted a socket.

Now we got to back topic here so Duncan have you figured out what you are going to do with the engine. I know it is a lot the take in if your experience is low but if you are getting into repairs might as well get your hands dirty and we will try are best to help out.

I attempted to use my $24.00 air rattle gun on a Victa crank nut on a mower that had sat in a partially exposed rusty chook shed for many years and for the first time, this cheap and cheerful tool couldn't budge one. I fetched my 12 volt car lug nut remover kit I keep in the boot which works with a slow series of heavier hammer blows, once per second, and it started to move it after about ten hits.
It has a claimed rating of 500nm from memory.
Whenever I have loosened lug nuts for people at the side of the road, they are always impressed . It plugs into a 12v power socket or direct to the battery via alligator clips. Not bad for $50.00.

I found one of those several years ago. You're right they are slow as Christmas but actually works very well if you are patient enough. I had paid about 50 usd for the one I gave away and about 170 usd for my current one.

My go to rattle gun is my Workzone lithium battery powered model I bought last year for $105. It has fulfilled it's purpose of removing and fitting the blade boss nuts on my mowers very satisfactorily so far. Very noisy hammer action though. Hearing protection is preferable.