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post #1 of 10 Old 06-14-2009, 12:47 AM Thread Starter
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LT1000 Briggs idle knock

Was wondering if any can help me with this.. I have an lt1000 tractor with a 17hp briggs intek single OHV. I got the tractor used, and dont know much about the maintence history. The engine starts right up and runs great, but when you idle it, there is a noticable knocking sound. I figured it was probably rod knock, so I removed the engine and replaced the rod, rings and gaskets. I also cleaned all the carbon off the head and piston, lapped the valves and re-adjusted them. I put it all back together and the noise is still there. I tried running the engine off the tractor and it makes the sound, so its nothing something on the craftsman doing it. I measured the crank and it is within spec according to my briggs book. What else can it be? I am thinking the balancer, but didn't notice any play in it. Thanks!
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post #2 of 10 Old 06-14-2009, 01:03 AM
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Re: LT1000 Briggs idle knock

Piston slap? Did you check the clearance between the piston and cylinder wall?

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post #3 of 10 Old 06-14-2009, 09:58 AM
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Re: LT1000 Briggs idle knock

End play in the crank??..that can cause a knock at idle and seem to dissapear at higher rpms..
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post #4 of 10 Old 06-14-2009, 12:40 PM Thread Starter
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Re: LT1000 Briggs idle knock

How do I check the end play on the crank? My manual gives me tolerances, but not how to actually check it.
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post #5 of 10 Old 06-14-2009, 12:54 PM
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Re: LT1000 Briggs idle knock

"he engine starts right up and runs great, but when you idle it, there is a noticable knocking sound."

Most likely thing is the counterweight bushing, probably top one. These commonly wear out partly from people idling the engine so slow it does not get proper lubrication. Really nothing practical you can do about it if that is what it is as the bushings are not replaceable and half the wear will be in the eccentric which is cast into the crankshaft. Eventually they let go wiping out the engine but that may be a long ways down the line with proper maintenance.

Too bad you didn't know about this so you could have checked it when the sump was off. As I said, nothing you could have done anyway only you would have known.

Well let me back up here a little bit. You didn't post the engine model number and they made drastic changes in the counter weight system in that hp range, the hp range overlapping different series of engine.

Again, you didn't post model number but most likely this is an engine with a vertical crankshaft. IF so, the odds of crankshaft end play causing this is very slim because it would have to lift and drop a heavy flywheel to have end play knock. This is common to engines with horizontal crankshafts. Piston slap, maybe but here again the likely hood of this depends on the model number.


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Last edited by Walt 2002; 06-14-2009 at 01:49 PM.
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post #6 of 10 Old 06-14-2009, 10:04 PM Thread Starter
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Re: LT1000 Briggs idle knock

The model is 311707-0123. It looks to be the older design balancer (like the L-heads). I checked the end play and it was within spec. I had a little time today to work on it so I pulled the sump and checked the crank eccentric and balancer and the crank was in spec, but the balncer was slightly off (.002) smaller than the book listed. I had a spare one from another engine and installed that one which was within spec. I put it back together and tested it off the tractor on the bench and it still knocks at low idle. I think I'll check the piston next time I get a chance. If it is piston slap, would I have seen anything on the cylinder walls? The walls were in excelelnt shape on this engine.
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post #7 of 10 Old 06-15-2009, 01:05 AM
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Re: LT1000 Briggs idle knock

I'm not sure if you would have been able to see anything or not - probably not. The cylinder (I assume) is cast iron, the piston is aluminum. Did you notice any scuffing on the piston? In cars, the pistons are slightly oval to allow for heat expansion, so you need to check at 90* axes on the piston. I would suppose your piston would be the same, but someone else would know, I hope....

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post #8 of 10 Old 07-15-2019, 02:28 AM
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Re: LT1000 Briggs idle knock

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Originally Posted by moldymac View Post
The model is 311707-0123. It looks to be the older design balancer (like the L-heads). I checked the end play and it was within spec. I had a little time today to work on it so I pulled the sump and checked the crank eccentric and balancer and the crank was in spec, but the balncer was slightly off (.002) smaller than the book listed. I had a spare one from another engine and installed that one which was within spec. I put it back together and tested it off the tractor on the bench and it still knocks at low idle. I think I'll check the piston next time I get a chance. If it is piston slap, would I have seen anything on the cylinder walls? The walls were in excelelnt shape on this engine.
I wish I had your time and motivation...I could get some things done around here.
I had an old ohv I think 31series but maybe smaller (did they make ohv smaller 28??) one with the metal shroud on a 1992 or 94 toro wheel horse.
It had a knock. Sounded like it was about 2.5 inches past the valve or rocker arms.
A harder knock and not a rocker rattle. Valve adj made no difference.
It was in pristine condition and the guy that bought it had engines to go on it if it blew. Will never know what it was.
I wasn't even away they had a a balancer at that point in my mower career.
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post #9 of 10 Old 07-15-2019, 08:45 AM
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Re: LT1000 Briggs idle knock

Most times you will notice piston slap when the engine was cold. As the engine warms, the piston expands a bit, and closes up the cylinder wall to piston clearance, so the sound should diminish a bit as the engine warms.
I would suggest using some multigrade oil, hopefully extending the usable lifetime. B&S has finally approved that for use, though suggesting oil consumption may increase. I would consider 15W40 and 20W50, personally, though others may disagree.
I would also not run the engine at idle as each noise indicates a collision of internal parts hitting each other, and the increased rpm will increase lubrication, and perhaps allow the plain bearing to float on the oil 'wave' rather than be metal-to-metal.
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post #10 of 10 Old 07-15-2019, 05:48 PM
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Re: LT1000 Briggs idle knock

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Originally Posted by Tractor-Holic View Post
End play in the crank??..that can cause a knock at idle and seem to dissapear at higher rpms..
If it's a briggs engine with the counterbalance it's most likely crankshaft end play. (if all else is correct)
Quite common in both the OHV and the old L head briggs single cylinders with the counter balance system.

Very true: You need to check the crankshaft end play while the engine is fully assembled and take the crankshaft end play to the very minimum specs. In your re-build kit if you got the gasket set, the extra sump gaskets are different thickness so as to adjust crank end play. You can find the specs for end in the service manual.

I've had to actually make a metal shim washer and install it on either end of the crankshaft. Briggs has metal shim thrust washers. Easier to install the shim on the inside of the sump pan. Briggs usually suggests installing the shim on the flywheel end of the crank which results in having to pull the crankshaft completely out of the block. I'm not sure why Briggs installing the shim on the flywheel end of the crank, MAYBE because the sump end of the counter balance has a raised groove at the sump end and the grooved mating surfaces of the counter balancer will have less play. (pay attention to your paper gasket thickness when doing the metal shim)


I have a steel plate that I bolt to bottom of the engine and rig a magnetic base dial indication so I can get the crank end play down to minimum specs.

You can usually see slight wear marks on the mating groove at the end of the counter balance. (sometimes you will still have a very slight noise at idle even after shimming but not a knock that sounds like a rod)

If you will post up a model, type, and complete engine info we can be more helpful. (with specs, etc.

That is a aggravating noise, even upsets gophers when on a mower.

Last edited by Forest Gump; 07-15-2019 at 05:54 PM.
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