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I found a replacement magneto-side bushing for my 124T02-3853-B1 Briggs and Stratton engine in the parts list for that engine. (The part number 796961.) However, when I disassembled the engine, I saw that the bearing was integral with the casting. The manufacturer's manual for the 120000 series engine does not provide information on how to install the bushing on engines that did not originally come with one. What is the procedure for doing this?

The tool kit (PN 19158) used to do this from Briggs NLA. So if anyone know what reamer was used please post its size. Otherwise a machine shop would the line ream bearing for a press fit of the bushing.

know a good machinist take it to them Briggs use to make a cutter to do it but have discontinued it. probably could have it done cheaper than you could have bought the cutter anyway

Thanks for the information. I did find the 19158 tool listed in a B&S Service Tool Catalog uploaded 7 years ago at https://www.yumpu.com/en/document/view/23866457/briggs-stratton-service-tools-catalog where it lists the kit as being for engine models 6, 8, 6B, 8B, N, 90000, 100700, 110000, 120000, and 130000.

Can anyone suggest a good amount of interference between the bushing and the block if the block is reamed to accept the bearing?

Having done this many, many, many years ago when teaching, I would recommend that you rethink about attempting this repair without the full kit. You must remember that you are not just inserting a new bushing in the magneto side of the crankcase, but you must make sure that the new bearing is inline with the bearing on the crankcase cover. If it is not in alignment you will be wasting a lot of time as one of the two bearing surfaces is going to wear out very quickly, because the crankshaft is going to try to run true. A tilt of 1 degree between the two bushings 8” apart is going to put a lot of pressure on the bearing surfaces and this will mean it is going to be extremely hard to turn the crankshaft when you reassemble the engine. Take a look at Sec. 11 pages 5-6 of this manual to see how the kit is used and the procedure is done. Just my experienced opinion, which won’t buy you a beer. https://docs.google.com/open?id=0B6NaqjIxWV1ycG8wd0s3Z2Q2X00

Having rebushed at least 300 BSA engines the advice Rivets is giving is spot on.
We spent $ 800 ( Aus) to get a piloted reaming tool to do the final ream on BSA timing side bushes then had a dozen dummy bearings turned up in 1/2 thou increments to make sure the crankshaft ran dead true and in out case, the other end runs in either a roller or ball so we had a bit of wriggle room.
This is a high precision machining job & not something to be tackled at home with the Black & Deckers.
Which is why no mower shops do it any more & the kit got dropped.
The labour cost setting up the mill would be almost the cost of a new short block and definately more than a set of cases .

Thanks again for all of the information. I was thinking of using a piloted reamer with a new sump for alignment. That should hopefully provide sufficient accuracy. The mag-side journal is 0.874" while the ID of the 796961 bushing is 0.878" (and 1.001" OD). Journal bearing clearances are 1.5 mils per inch of diameter as a rule of thumb. Typically bushings in this diameter are made about 2 mils oversize. Unfortunately the amount that the bushing will reduce in diameter due to an interference fit is difficult to calculate, but 70-100% is typical, giving a clearance of somewhere around 2 mils or a bit more. All of this seems about right, but it would still be nice to know what size B&S decided to make the reamer in the 19158 tool.

If you go ahead on this, look at costs closely.. you can get a brand new short block from $99 depending on where you look.

jdtm said:

Thanks again for all of the information. I was thinking of using a piloted reamer with a new sump for alignment. That should hopefully provide sufficient accuracy. The mag-side journal is 0.874" while the ID of the 796961 bushing is 0.878" (and 1.001" OD). Journal bearing clearances are 1.5 mils per inch of diameter as a rule of thumb. Typically bushings in this diameter are made about 2 mils oversize. Unfortunately the amount that the bushing will reduce in diameter due to an interference fit is difficult to calculate, but 70-100% is typical, giving a clearance of somewhere around 2 mils or a bit more. All of this seems about right, but it would still be nice to know what size B&S decided to make the reamer in the 19158 tool.

Click to expand...

After sleeping on it a bit, it seems possible that the bushing was intended to be installed with a 1 mil interference fit. Perhaps it was made 1 mil larger than 1 inch so that a reamer with a standard dimension of 1 inch could be used.

That sounds reasonable considering the bushing has to be staked after installation.