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 Briggs & Stratton Oppy Twin question

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CosmicArkie
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PostSubject: Briggs & Stratton Oppy Twin question   Briggs & Stratton Oppy Twin question Icon_minitimeMon Apr 01, 2019 3:04 pm

I've got a 42A707 1238 01 18.5hp oppy twin I've shoehorned into my JD 111H mower.  It runs but has a miss; sputters out the exhaust intermittently, just ain't "right".  New coil/plugs.  Went through the carb (3 screw).  Meh.

I noticed there is side play at the flywheel.  Not end/thrust play but side to side.  Hard to measure but noticeable.  Makes air gapping the ignition troublesome.

Is it conceivable that the play is the cause of the miss?  I've put a different 4 screw oppy carb and a side draft off an OHV single with a fabbed elbow on it and the miss is still there.

Now, the governor does vary a little at times and I've read a few threads suggesting that may be the cause, but it just doesn't seem like it is the source of the issue because the miss doesn't coincide with the variations.

Any suggestions/thoughts?

As a little further background, this engine didn't have much of any tar in the crankcase, much less oil when I got it.  I've flushed it out and put fresh dino's in it.  If the case bore is wallowed out, do any shops still line bore them and press in DU bearings?

Thanks.
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Crazy_Carl
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PostSubject: Re: Briggs & Stratton Oppy Twin question   Briggs & Stratton Oppy Twin question Icon_minitimeMon Apr 01, 2019 4:01 pm

I've had an ATC with a loose cam in a similar situation where the ignition pickup sensor is trying to read a magnet that is moving side to side a little. It didn't give me a ton of igntion problems really, but you're situation is a little different.

Did you check your spark plug gaps?
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prancstaman
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PostSubject: Re: Briggs & Stratton Oppy Twin question   Briggs & Stratton Oppy Twin question Icon_minitimeMon Apr 01, 2019 5:18 pm

I would pull the flywheel and look to see how much play is on the crank. It shouldn't move to the side any. Most likely that bearing is worn real bad. That would make it miss too, since the gap for coil is not constant but unstable and probably too far away to make spark at times..
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PostSubject: Re: Briggs & Stratton Oppy Twin question   Briggs & Stratton Oppy Twin question Icon_minitimeMon Apr 01, 2019 5:20 pm

I believe those engines have bearings for the crank, see if you can source a replacement
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AllisKidD21
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PostSubject: Re: Briggs & Stratton Oppy Twin question   Briggs & Stratton Oppy Twin question Icon_minitimeMon Apr 01, 2019 6:06 pm

Actually I think they are just a plain bearing surface that's part of the casting in the the block, which is unfortunate because if the bearings are worn that means the block is essentially no good.  I don't know if you could find someone who would bore it out and put bearing inserts in like you mentioned, but that might be an option.

If the crank bearings are chewed that bad though, your oil should look like glitter glue after some run time, so maybe check that out as well before you tear it down. Maybe there's a small chance the flywheel itself is loose on the crank taper.

It's also worth noting that the Briggs oppy's were sorta known for popping exhaust valve seats out of place, so that could possibly be the noise you're hearing at the exhaust.

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CosmicArkie
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PostSubject: Re: Briggs & Stratton Oppy Twin question   Briggs & Stratton Oppy Twin question Icon_minitimeMon Apr 01, 2019 10:28 pm

Plugs are new & gap was checked. I had a valve seat issue on a previous flatty single and it just made RUDE noises. And died. Dead.

I picked up the B&S shop manual for the oppy twins and it mentioned the possibility of line boring a plain bearing casing and inserting "DU" bearings with Tool #bla-bla-de-bla. Finding a shop with a tool might be problematic. And expensive.

Thanks for the inputs.
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prancstaman
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PostSubject: Re: Briggs & Stratton Oppy Twin question   Briggs & Stratton Oppy Twin question Icon_minitimeTue Apr 02, 2019 4:32 pm

Ask a regular machinist shop or tool and die shop. The work needing done, if that is the problem, would be a simple job to do as long as you tear down the engine and have the insert already. Probably cost like 10 bucks to do too.
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