Does anyone have an XK8 with a NCA7739AC tensioner and are willing to measure the pulley? My pulley broke and I bought a new replacement (P/N ALT04144) which has a 3.0" (76mm) diameter, when I put it on the belt felt really tight. I'm wondering what was the original diameter. BTW the bearing in this pulley is P/N 6203RS. Thanks.

 

i'll get one from my box of pulleys in a second. i'm pretty sure they're the same diameter.

never had a problem swapping to metal idlers on these but i think the bolt is different between the metal and plastic wheel tensioners

 

Within reason, does the diameter of the pulley make much difference? The spring in the tensioner is designed to apply a suitable tension over a fairly wide range of belt lengths as the belt stretches over its lifetime. A slightly larger or smaller pulley would surely look like a slightly more or less worn belt as far as the spring is concerned. Provided the tensioner is within it's proper operating range (I think there are two marks on the body of the tensioner to indicate the upper and lower limits) then it should be fine.

Richard

 

I used the same Dayco 89016 pulley for both the idler and the tensioner some time back with no issues. It is 76mm diameter metal with no flanges.

Has the serpentine belt been replaced with, possibly, a slightly shorter one? As Richard says, there's some latitude in belt length that can be accommodated by the tensioner.

See the pics in this post from DaveInVA for the belt stretch markings on the tensioner body:
https://www.jaguarforums.com/forum/x...2/#post1196718

There's a post somewhere here that explains the marks, but they're basically new-ok-replace

 

This is the belt I used recently. It fits fine. Is your belt the equivalent size?

 

^^ I fitted the same belt with no problems.