M500 engine knock that wasn't

I have had a engine knock in an old 500 for a while . Today I thought I would find out where . It sounded like it was in the front cylinder . I pulled the belt and the knock went away . OK its in the jackshaft or front pully or the chain cases . Pulled the wheels and opened the cases and started the engine . The left jackshaft sproket had .030 run out . Now I know where the knock is and I think the PO dinged the shaft under the block where it slides to change belts . So I guess I will run it till I find time to pull the motor so I can get to the shaft to clean it up and fix the wobble . Hope this helps someone else solve there problems .Gearbox

I am skeptical that it is that simple. I hope it is but I have never had noise coming from the jackshaft that was simply the result of runout. There are several things that could cause the knock…..while you are there, check the bushings in the jackshaft sheave itself (3 around pens & 1 on main shaft) to make sure they are not 'oval', also check the 'pillow block' bearings for starters. A word of caution…..running a failing variable speed sheave or jackshaft to total failure can be very dangerous and expensive. I'm not saying it isn't the runout……I just have my doubts.

6brnorma said:

I am skeptical that it is that simple. I hope it is but I have never had noise coming from the jackshaft that was simply the result of runout. There are several things that could cause the knock…..while you are there, check the bushings in the jackshaft sheave itself (3 around pens & 1 on main shaft) to make sure they are not 'oval', also check the 'pillow block' bearings for starters. A word of caution…..running a failing variable speed sheave or jackshaft to total failure can be very dangerous and expensive. I'm not saying it isn't the runout……I just have my doubts.

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.030 run out at the sproket end of the shaft = at least .150 at the block and thats a lot for that heavy a chunk of iron . Gearbox

gearbox said:

.030 run out at the sproket end of the shaft = at least .150 at the block and thats a lot for that heavy a chunk of iron . Gearbox

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Well an update . I got time today to get into this one . Pulled the block and found the PO must have run the block loose then turned the block around . Found a chewed up right shaft and badley damaged block . Ordered new shaft and block . I love these old friction drives . Just over $ 200 for parts from Bobcat be here on tuesday . Gearbox

gearbox said:

Well an update . I got time today to get into this one . Pulled the block and found the PO must have run the block loose then turned the block around . Found a chewed up right shaft and badley damaged block . Ordered new shaft and block . I love these old friction drives . Just over $ 200 for parts from Bobcat be here on tuesday . Gearbox

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Parts came in today chopped old shaft with the torch and a few wackes with a hammer and back together in 3 hours no more knock . Gearbox

gearbox said:

Parts came in today chopped old shaft with the torch and a few wackes with a hammer and back together in 3 hours no more knock . Gearbox

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Do you happen to have any pictures of the before and after?

thynes said:

Do you happen to have any pictures of the before and after?

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Sorry about no pics but I am still on dial up . Fiber optics are ran to the house but still not hooked up . SOON I HOPE Gearbox