Disassembling a 12.5 Briggs IC

.080"??? Wow...thats super loose!

Id like em ot be around .015"

I took a little more apart after Church and lunch. When I got the crank-balancer assembly out I noticed some movement in the bearings. I checked both sides and got .016 on the flywheel side and .014 on the sump end. I haven't found what the tolerance is but I doubt it's that much. I took an 11hp apart a few years ago that had the oil thinned with gas and it's balancer bearings were bad to. I may put it back together with a set of rings and see what happens, I already have the gaskets.
Cannon

I decided to check the piston clearance in the bore today, I can get .008 in on the top 90 degrees to the pin and .005 at the piston skirt on the bottom. I removed the valves, the intake seat and valve are both shinny but the exhaust is darker. Should the exhaust be bright like the intake? I ordered some cheap ring yesterday. http://tewarehouse.com/7-03525 and am going to hone it a little and put it back together. I have an old snapper I might try it out on. If it ever runs again.
Cannon

How wore is the bore itself? Oversize, taper, out of round? Briggs used to offer Chrome "Saver Rings" that were like 0.002" oversize to tighten up an older engine. And, on engines that were wore oversize (up to say 0.008") but still within acceptable limits for taper and round I have in the past acquired 0.010" over rings and filed them down to get the correct end gap to tighten one back up if the customer did not want to spend the money on a bore or it was not economically feasible to do so. This is not a good repair, it is a patch at best, but it will usually get a few more seasons out of an old engine before it starts to blow oil.

Joe

The exhaust valve & seat will not be shiny like the intake after it has been used for a while. The intake is washed, sort of, with filtered air and fuel on every intake stroke. The exhaust does not get such clean stuff flowing by, and it is a lot hotter. All that causes the valve and seat to be darker in color. As long as you have a clean seat & valve, and they meet equally all around the circumference you should be ok. You can use grease or compound or toothpaste .. or whatever ... as a check. Dab some on the valve, on the area that contacts the seat. Insert the valve into the guide, seat it gently, and remove. If the 'stuff' you used has a good, common separation line all the way around the valve, it will work fine. The 'stuff' will try to stick together as the valve is removed, but fail. If the surfaces are concentric & parallel, you will get a very even separation line more or less in the center of the seating area. If not, some cleanup would be in order.
The piston gaps mentioned do not seem at all extreme to me. Have you inspected the bore/cylinder walls for scoring or other damage? In a lot of cases, you can still see the original cross-hatch, indicating there's not a lot of wear. The ring gap I don't know beans about. Maybe just breaking the glaze, installing new rings, and setting the valve lash will make it work better.
I do not think the plug wire is up to what you need. Maybe you can buy a replacement, and glue it into the coil. I do not think it is 'brain surgery' to install, just sort of difficult to get it to cram into place as the new insulation will not be as squeezed by time as the one you remove.
tom

In my opinion that engine is toast. I don't know the specifics about the proper clearances for 12.5hp but that one is beyond "loose". It has run with thinned oil and that balancer is way too loose, that thing will knock and rattle like crazy when you put it together. The rings tend to go in these situations the bore might not be that bad, but you can't tell until you put new rings in the bore and gap them. You can slide the rings down the bore and see how the gap changes to get an idea of the taper in the cylinder.

Seeing how common these engines are you might have better luck finding a different engine. To do that one the right way you need to inspect the crank to find out if the crank or the balancer or both need to be replaced (I would be the balancer bearing surfaces are toast), bore it oversize and put new rings in it. From the looks of things .010 might not be enough, that one could easily end up .020 or even .030 over. You need to inspect the bore.

It depends on what you want to do, if you just want to make the mower run as cheaply as possible, finding a new engine is the way to go. If you want to mess with making that one run just to see what happens then go for it. If you want a useable mower, I would recommend going further into the rebuild rather than just a patch job. I don't think I am alone on the forum making this recommendation either.

Onan 18, I did check the ring gap in 3 places down the bore and the gap was close to the same. Other than that I don't have any way (that I know) to check the bore.
Tomw0, I'll check the valve seat like you said. The cross-hatch is only visible below where the rings travel and a lip that will just catch my finger nail on top. The coil was running the engine with half the wires chewed in two in one place and an extension put on with a wire nut in another. I was going to solder a new piece of wire on to the chewed place if I can find some solid core wire.
NDwrench, This engine came on a $30 yard sale Murray, I kept the engine and wiring harness for parts and have sold the frame and mowing deck for $25. If the balancer assembly were tight I would bore it and do a better rebuild but as it is I am just going to throw $20 of rings and gaskets at it to see what happens. I'm retired and this is how I entertain myself.
The rings shipped today and I am wondering how much the ring gap will be in the worn cylinder. Thanks for the input.
Cannon

Entertainment you say? Well in that case let her rip. Its kind of fun to see what happens in situations like this. I don't doubt it will run, the question is how well will it run?

You don't have use for this engine other than just to mess around with it?

NDwrench said:

Entertainment you say? Well in that case let her rip. Its kind of fun to see what happens in situations like this. I don't doubt it will run, the question is how well will it run?

You don't have use for this engine other than just to mess around with it?

Click to expand...

I would probably put it on something and use it but no I don't need it. I have plenty of mowers.
Cannon

I wouldn't be too concerned about the clearance on the synchro balance. Due to surface speed, they need more clearance than a rod or main bearing. If the bearings look OK, and the eccentrics don't show any wear, put it back together. It's not an Indy car engine, it's a low-budget Briggs. With new chrome rings, you will be surprised how well it will run. I've saved many of those engines that instinct would have told you to throw away.

From ignorance, how do you check the clearance on the balance shaft bearings? I know how to do rod & main bearings, is it the same process?

I have a I/C Quiet Model 287777 that seems to run pretty well, but kind of has a 'chunking' sound when it is put under full load, i.e., cutting heavy grass where you can hear the throttle go wide open. Could that be balancer shaft bearings? Seems to me that they are given a different 'load' pattern than rod bearings, for example.
tom

Since the balancer halves slip on the crank you can't use palstigauge. You have to measure the crank with a micrometer and use a snap gauge or small bore gauge to measure the balancer bearing surface. The method Cannon51 used with the dial indicator is a simple way to do the same thing, however the B&S manual lists reject sizes not clearances. I would probably use the dial indicator as Cannon51 did.

On my 11hp I/C the balancer felt like a normal main or rod bearing, probably .001 to .002 thousandths clearance.

I repaired a chewed thru HV lead (only 1 thin wire remained) by cutting it in half, using a butt splice to put in a short extension piece, then soldered the whole thing up, then wrapped it in Skotch 88 electrical tape to more than the original wire diameter. Still running, 2 years after. Never done it before. If I do it again, probably it will fail.

Tomwo and NDwrench. I copied this page from an old Briggs manual. If I read it correctly there is .011 difference between the reject sizes of the crank and balancer. This is using the older model 11hp numbers but it looks the same. At .014 and .016 I'm outside that tolerance so one or both of my parts (crank and balancer) is bad but not as much as I thought it would be.
engine2quarters, I took a better picture of the coil. I plan to cut the wire at the chewed place and add a new wire and boot. I'll lap the wires about 1/4 inch, solder and use a piece of plug wire insulation over the gap. Maybe some shrink rap over that. So far I have not been able to find any wire at auto parts stores here so I may have to use some off a dead blower coil I have.
According to the tracking it looks like the parts are not arriving until Tuesday.
Cannon

This weekend I lightly honed the cylinder, lapped the valves and washed the block with soapy water. I checked my old Briggs book and it said to check the ring gap 1" down the bore. The new top ring is .019 there and .020 about 3/4" up from the bottom of the ring travel. I installed the piston and bolted the rod cap on. The torque spec on the rod cap bolts was a little less than 200 inch pounds but my 1/2 torque wrench only goes down to 20 ft lb so that's what I torqued it too. The exhaust valve gap was OK but I had to grind the intake valve to get .006 gap. I never got a valve spring compressor so after fighting them a while I clamped them in the vise and put 2 zip ties on them, need to buy a compressor. I got the flywheel back on, maybe I will get to crank it this week.
Cannon

Zip ties as compressor...really? LOL

I would mention loctite should always be used on those smooth flanged pan/sump bolts.

As for a bad coil wire, see if you can find another metal core spark plug wire, (I cut off and save all high tension leads from bad coils) and simply grab the high tension lead close to where it glues into the coil. (it would have to be from a twin cylinder to be long enough, an 8 hp. would not be long enough) Rotate and pull, till it rips out, dig out remaining glue and insulation, put some glue on the new lead and install. There is a metal spike/wood screw inside the hole that connects into the metal core.

wwxx

I got the engine back together today, just need to set it on something and add oil.
wwxx, I had this dead coil off a chainsaw. The wire was not long enough to go all the way to the coil so I spliced it with a small piece of crimp connector, covered it with a piece of fuel line and taped it up. We'll see. I used the other coil to be sure I had it long enough.
Cannon

I got it set on the Snapper today and started. It sounds a little clattery but is running and not smoking. It had run about 2 minuets when I started the video. After I stopped the camera I took the cap off the fuel tank and it smoothed back out. I think I spent about $35 on gaskets, rings, sticks with stoppers to lap the valves and some lapping compound. Thanks for all the comments.
Cannon

Cool, amazing how tolerant these engines are of loose bores. Interesting to see how long it runs. The rings are pretty stout in these engines. Is the old snapper a project, or just something to mount the engine to?