jackshaft

[Stagjag]

I have a nocking noise from the front of the engine I thought it might be the timing gear, I took the plunge and got stuck in but all timing gear was in good nick as I changed it about 8000 miles ago but I noticed the jack shaft had a bit of play in it, I took the shaft out and could not see any were on the block and it’s hard to tell if the shaft is worn , the fixing plate had some marks ,worm gear for the water pump and distributer looks good,

[barkerwilliams]

Are the teeth on the sprocket in the last two photos worn. The tooth above the white mark in both photos - is the tip of the tooth missing?

Alan

[flying farmer]

It looks like the end of one of the jackshaft sprocket teeth is missing in the 4th picture, and the teeth look like they have a bit of a slope on them. I wonder how good a fit the new chain is in the worn sprocket?

If the jackshaft or block are worn on the front bearing, it can be measured by pushing a feeler gauge between the block and shaft. Don't know the proper figures, but an unworn block and shaft will be in the region of 1-2 thou, most are in the 3-4 thou region and I have had a knackered one with about 8 thou. Since the front jackshaft bearing is fed directly off the main oil gallery a large clearance will significantly drop the oil pressure.

[Stagjag]

Thanks for the reply ,the block looks fine thank god I tried to put a video of me rocking the jackshaft in place but could not work out how to do it,I’ll put the shaft back and measure up the play ill have a closer look next week as I’m not at home just now, thanks John

[Stagjag]

Ok the jackshaft end float is .012 in or 0.30 mm is this acceptable ? The fixing plate is slightly worn on one side, and I would change the sprocket anyway

[flying farmer]

The jackshaft will be pushed towards wherever the wear has occurred on the retaining plate, can't remember offhand whether this is towards the front or rear of the engine, but bear in mind the alignment of the sprockets has to be correct in the running position.
This means that if the wear allows the sprocket to move forward, you need to check the alignment with the sprocket pulled forwards, not pushed back or the chains will be running at an angle which will increase wear.
Don't know if I have ever measured the end float on a jackshaft, but I have swapped a few worn retaining plates for better ones.

[Stagjag]

Ok thanks I can see now the importance of being aligned properly ,I have slight worn plate but not that bad ,I’ll change the sprocket and see if I find a better retaining plate thanks John

[Mark Serj]

Just for clarity, as regards alignment of the sprockets, Neil is referring to vertical alignment of the drive sprocket on the crank with the jackshaft sprocket. You can see this referenced in the owners manual

Cheers