I’m currently putting together the timing chain assembly on 1987 4.2L engine. Having just replaced the bush in the idler sprocket (upper timing chain), I’ve found that it is undersized by a few thou, so I’ll need to ream it. Is there a clearance spec that I should target for this?
Unfortunately I didn’t measure the ID of the old bush while in place, but measurement after closing the shell suggests about .004" as found.
The bush for the intermediate sprocket hasn’t arrived yet, but I now expect to have to size this one as well…
Hi that’s me! We never simply replaced the white metalled bush always the complete assy.! As far as I can recall if you press in a new bush it shouldn’t reallly need to be reamed out! It’s a relatively big surface area bush so a 0.001” clearance should be fine.
Do you know if it fitted around the shaft easily before you pressed it into the sprocket?
Thanks - no I didn’t try closing the shell around the shaft before fitting. I’ll check this on the next one though. In the meantime I’ll shoot for .001".
Info on the interweb points to the self clearancing properties of Babbitt bearings…