Briggs Knocking?

[lefty]

Briggs engine: 31C707 0230 E1
Craftsman Tractor

I know this may be tough to hear through video but thought I'd give it a try. I noticed a neighbor struggling with their tractor after hearing a bang and stall. He was going down a hill and told me that it had done it a few minutes before. The bang and stall were accompanied by smoke. This time, it wouldn't start again.

My first thought was either the hill caused oil to roll up into the cylinder or maybe a head gasket issue. So I rolled it to my house and let it sit for a couple of days. Oil level looked good, however, he told me he had changed it and used 5w-30. He had also mowed a few times since then in 90 degree weather. About and hour each time.

After the few days, I started it and it ran fine for about 30-60 seconds at which time it would start surging a bit. I also think I was hearing a knock so I thought I'd post this video. I can't imagine running 5-30 in 90 degree temp did much good for it. It was a piece of crap to start with that he got for free.

Another piece of info: The first time he mowed with it I happened to be outside and it sounded like the RPM was too high. I took a look and noticed the governor linkage to the carb was disconnected. There wasn't enough bend to keep it in the hole on the carb. So I fixed that for him and sent him on his way.

Does anyone hear a knock here?
https://photos.app.goo.gl/dVBEgCRrq7jLWvLL9

Thanks

[KE4AVB]

If the link was off I surprised as it would would ran at any speed.

As video I don't hear anything abnormal here.

Since the 31 series are bad about blowing head gaskets you should had done a leakdown test with the valve cover off. Also this engine has a counterbalance system and one of the links might have broken. From your description of the problem reported a simple two minute test is not enough. This one sounds like an engine pull and internal inspection is needed. Might even an ACR failure where broken pieces got into gear train, temporary jammed the engine, and then fell to bottom of sump.

[38racing]

i was thinking acr but op didn't indicate any slow crank issue. I was looking at old slinger bent when acr wet in my neighbour's. all the little teeth were gone. hadn't noticed before.

[lefty]

I haven't had a chance to dig into it yet. I still have to touch base about whether or not he'd be willing to fund the operation.

[Arkie]

Your description appears they guy needs to keep a eye and ear open for a donor engine if the tractor mower is worth such type repairs.

BUT
ABOUT the knock and what I have done to cure such in several models of Briggs and that model also even though the specs for crankshaft end play is up to .030. The counterbalance is especially prone to produce a knock if the end play is .015 and up to the max specs.
Before I DIG INTO ONE as you say I always VERY CLOSELY check the crankshaft end play especially if I'm hearing the knock and ALSO even if I do not hear a knock BECAUSE I shim the crankshaft end play for the very minimum of not over .005 when assembling. I always check the crank end play before removing a sump for other issues such as replacing a sump gasket, etc. I also mic the thickness of the sump gasket after I have removed the sump, most will check close to .015 but I want to make sure of such since about 3 different thickness in some gasket kits.
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Hard to believe but I've heard them Briggs OHV and L-heads with a severe knock and by shimming the crank to minimum of .005 max end play the knock would go away due to the counterbalance being the source of the knock. Sometimes on the vertical engines you can see bright grooves in the sump plate where the counterbalance is wearing due to too much end play.

By getting a precise check of the crank end play BEFORE I remove the sump or side plate I know what shim thickness I need without having to do several trial and error sump installs then test during assembly.

I would suggest using a straight 30W oil in his engine. (and stay off of severe slopes especially if it's not pressure lubed type engine.

[lefty]

Thank you. I don't currently own a dial indicator, which I think is the necessary tool for such a measurement. I'd like to pick one up and like any tool, there is a wide price range and I'm sure quality/reliability. Do you have any recommendations? I haven't had the need up until this point but have been thinking about it for a while.

Thanks.

[Arkie]

Just some hints, no specific tool recommendation.
I've got two and the one I use the most is the least expensive type and I got it off of flea bay few years ago.
Both of mine have the magnetic base stand and one I can also clamp on the adjustable base ARM clamp but prefer the magnetic base most generally and I made a bolt on metal plate that I can bolt to a aluminum engine to get a steady rest for example.
I also use them for checking backlash and run out when setting up automotive differentials and other things.
Just do a on-line search for clamping type dial indicators.
I do not like to recommend HF tools but HF has a magnetic base one that is around $20 that works if you are tender with it and store properly when done. The knobs on the magnetic base type is to release the magnetic when it's stuck to metal.
A adjustable dial indicator holder arm magnetic base type is user friendly. (the base and arm adjusts every which way when the magnetic base is stuck to metal so as to get the dial indicator into position to adjust for zero.
A $25 magnetic base type one will do a good job of reading crankshaft end play and is easy to set up after you have done one. With a good steady set-up you can get the end play to minimum more easily by getting the end play reading before and using a dial indicator to check the thickness of the old and the new sump plate gasket.

[lefty]

I was able to get to it last evening. I did a leak test and the head gasket is gone in the usual spot, next to the valves. So there's that for starters.

[lefty]

I fixed the head gasket and still had an intermittent surge but I no longer had hard hot restart. I held the throttle and it indicated fuel issue. So I cleaned the carb and all is well now. The engine sounds a bunch better too. Thanks for the help.