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TR7 & TR8 Forum

SPROCKET FIT ON JACKSHAFT

Moss Motors
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englishbob robert L
montreal, QC, Canada   CAN
hello fellow wedgers
stripping my motor for rebuild and have found the sprocket on the jackshaft was loose, and was probably part of the ticking noise from the front and the erratic running.
The slots in the sprocket are enlarged where it engages with the tab on the jackshaft, not bothered about the sprocket as it will be replaced, i am concerned however with the tab on the shaft itself, will this have worn? and will have a loose fitting sprocket on reassembly? If it is worn is this something that can be repaired, a I understand a new jackshaft is $$$
does anyone have a photo of sprocket and tab fitted together and am I correct in assuming that the fit should be snug?
thanks in advance
bob

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tirebiter Jeff Garber
Dighton, MA, USA   USA
I'm sure someone will correct me if I'm wrong but if memory serves me correctly (and I'm too lazy right now to consult the parts book) that tab is a half moon shaped woodruff key. Available at most hardware stores. If it's too thick file it to fit. Same with overall dimensions. File it to fit. Very useful with a worn shaft or sprocket slot. Buy extras and play with offset filing to try out different cam timing/fine tuning adjustments.

The sprocket to the jackshaft is not a press fit but it is a very close tolerance fit. Meaning both surfaces have to be 100% clean and with no damage to either. It goes together by hand ... barely. There should be no play or wiggle room. Some light tapping might be needed to get the sprocket on all the way once it gets to about halfway home, especially if the woodfruff key gets cocked a little as the sprocket goes onto the shaft.

englishbob robert L
montreal, QC, Canada   CAN
thanks Jeff
just ordered one locating dowel!
Was just wondering what the loose sprocket on the jackshaft would have done to the running of the engine! and what might have happened if it had let go!!
cheers

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tirebiter Jeff Garber
Dighton, MA, USA   USA
ok dumb me for not looking at the parts book first. Yes the jackshaft uses a dowel. Nothing you can do about the hole in the jackshaft or the sprocket, if either one is elongated. JB Weld would be worth looking into, though. Basically glue it all together with the new dowel. The sprocket at least has an alternative hole and I do not think it would upset the distributor timing.

Did you order a new lock tab also ?

Would have been a mess with bent valves at the least if it fell off.

Draegon Tim Barrick
Hamilton, ON, Canada   CAN
Last year I had my engine rebuilt, and after running for 10 minutes, it stopped.

Took the mechanics a few weeks to figure out the jackshaft had sheared the 2 locating pins, so the sprocket just spun, no distributor or waterpump running.

Jackshaft working properly is extremely important.

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