XJ XJ6 / XJ8 / XJR ( X350 & X358 ) 2003 - 2009

smaller pulley, belt slipping: 4080525 vs 4080521 vs 4080515

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Old 12-27-2014, 08:04 AM
Matei Dima's Avatar
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Default smaller pulley, belt slipping: 4080525 vs 4080521 vs 4080515

Hi all,
Finally got my car back after 7 months at the Jag dealer, and I noticed serious belt slip over 5000rpm, and a squeal on cold start.

The car originally had a Phoenix Coachworks 2.5# pulley, and the belt replaced with the Gatorback 4080525. It worked fine. When the car was at the dealer, the S/C had to be off to change the dreaded hose from under it, so I had it sent to Powerhouse to be rebuilt and ported. They had to cut my pulley off because it was on too tight, and they installed their own free of charge, however it caught on my previously filed-down snout. They filed the snout some more, and it spun freely.
This has lead me to believe the Powerhouse pulley is smaller in diameter.

Trouble began when the dealer reinstalled the eaton and pulley, they said the tensioner is all the way, and the belt has a squeak on a cold start, which goes away when it warms up. But the real problem is that when I drove it yesterday, when I got to 5000rpm at WOT, I had a chirping sound along with no blower noise increase, even though rpms were increasing. Does anybody with a Powerhouse pulley and 4080525 belt also have this problem??

And why is it 52.5" long? As I understand, stock lenght for the 4.2 is 52", so at most a gatorback 4080521 would be suited. And if you take into account the smaller diameter of the +10% pulley, we have approx. a half an inch difference:
delta between the stock and smaller pulley's diameter is about 0.26 inches, 2.6 vs 2.86. the wrap from around the pulley is about 190 degrees from what I understand, so you have 190/360 * 2.86*pi - 185/360 * 2.6*pi = 4.74 - 4.195 = ~ .545 inches. For the smaller pulley I put 185 and not 190 degrees because the angle is a bit more shallow, but the difference is almost unmeasurable.

In conclusion, from what I calculated, when going for the 2.5-3# pulley, you would need a belt about half an inch shorter than stock (52") to compensate. Doesn't it mean that a 4080515 belt would be suited for this setup? If I am mistaken, please correct me. Especially if there are folks with the Powerhouse pulley / 525 belt combo that is working. And if anybody has other thoughts on the matter, please chime in.

 
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