Jackshaft Endfloat - how much?

[marshman]

Hi Guys,

I'm still trying to stop the knocking noise from the front end of the engine. I've checked the jackshaft for sideways movement and ease of rotation - both ok but there is around 15 thou of end float. Is this acceptable?

Thanks in advance

Roger

[flying farmer]

imported post

I have a engine in bits ready to go back together, I have just measured the clearance of the unworn part of the keep plate in the groove of the very low milage jackshaft, and it is 10 thou.

Neil

[marshman]

imported post

Thanks for that info Neil, that gives me a bit of reassurance and something else I can cross off the list. I've just rechcked mine and its 12 thou, and I measured only 2 thou of run out on the sprocket as you rotate the whole assembly.

Roger

[MLCstag]

I have a engine in bits ready to go back together, I have just measured the clearance of the unworn part of the keep plate in the groove of the very low milage jackshaft, and it is 10 thou.

Neil

I appreciate this is an old post, but I have some end float and was wondering how the measurements should be made for the crank shaft shims. Should the jackshaft be pushed fully in or pulled fully out for the shimming of the sockets? Pushed in, the existing shim looks good, pulled out and it needs a thicker shim. The end float makes the shimming pointless, yet it's a critical task according to the ROM?

Cheers Brian

[flying farmer]

I appreciate this is an old post, but I have some end float and was wondering how the measurements should be made for the crank shaft shims. Should the jackshaft be pushed fully in or pulled fully out for the shimming of the sockets? Pushed in, the existing shim looks good, pulled out and it needs a thicker shim. The end float makes the shimming pointless, yet it's a critical task according to the ROM?

Cheers Brian

This is a damn good point, and to be honest not one I had ever given any thought to.

I have just nipped out to the shed and had a quick look at the engine. The old worn jackshaft keeper plate has all the wear on the back side.

A look at the teeth would confirm that the thrust due to the angle of the teeth would be outwards, therefore the shaft should be pulled outwards
when measuring the alignment of the sprockets, as this is where it will be when the engine is running.

This is very fortunate for me as initial measuring made it look like I was going to have to take 10 thou off the back of the inner crank sprocket
to get the alignment right, now it all looks good as it is.

A well timed question Brian!

Thanks, Neil

[Stagdad]

Interesting point Brian/Neil ,hope I remember all these little gems of information when I next rebuild.
cheers Steve

[MLCstag]

Thanks Neil,

Ok, Jackshaft thrust out during motion and my sprockets are lined up with the existing shim in this scenario. I stated it incorrectly in the above post and would have needed to remove the existing shim (or machined off few thou) to line the sprockets up with the jackshaft pushed in as there was a 4 thou gap. Guess that means about 4 thou wear in the keeper plate/grove> However, all is now well if I check whilst pulling the jackshaft out.

Brian

[wilf]

Can the keeper plates be reground flat to remove the wear? Or does this effectively remove depth from the oilway groove? (is there an oilway groove?).

Not had this bit off mine yet.

[flying farmer]

Can the keeper plates be reground flat to remove the wear? Or does this effectively remove depth from the oilway groove? (is there an oilway groove?).

Not had this bit off mine yet.

Regrinding it flat wouldn't help as the keeper plate sits in a groove on the jackshaft, it would just increase the endfloat.

That said, when the engine is running, the jackshaft will be pressed up against the keeper plate, and the only time the end float will make any difference is if the engine is turned backwards.

Neil

[wilf]

Thanks Neil, these plates seem different from the cam thrust plates I am used to on yank V8s. Must have a look at the ROM again.