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Help! Problem with serpentine belts, not tight enough! "New" J-spec engine.

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Old 07-15-10, 12:51 AM
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Help! Problem with serpentine belts, not tight enough! "New" J-spec engine.

Hi guys,

The FC I picked up about a month ago supposedly had much of the maintenance stuff replaced, along with the engine.

The engine was blown, so the previous owner replaced the engine with a J-spec engine. Along with the engine, he replaced the apex seals, silicone vacuum hoses, spark plugs, spark plug wires, cleaned the fuel injectors, among other things.

The main problem I am having though is with the belts. He replaced the belts with NAPA "premium" serpentine belts, and they have been rubbing like **** against the pulleys and creating belt dust, and quite a bit of it.

Even with the tension setting max'd out for the air pump and alternator, the belt has little to no tension in , but the other two belts on the other side of the engine bay (idler and p/s pump and a/c) I can properly tension.

I picked up some new belts at autozone today, and it seems to be about the same length as the NAPA ones, which is still too long! (little to no tension)

Can someone please advise with what size belt I need? What part number of what manufacturer?

Even with all the maintenance stuff done to my FC prior to purchase, I've still had to do quite a bit of work to it and it's still not done. /sigh

Any help would be much appreciative!

For reference here are the part numbers I have for my belts.

All Napa belts.

25-7315
25-7385
25-9380
25-9415

Last edited by 19rxseven87; 07-15-10 at 01:19 AM.
Old 07-15-10, 01:35 AM
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25-7315 (31.5 inches long)
25-7385 (38.5 inches long)
25-9380 (38 inches long)
25-9415 (41.5 inches long)

anyone suggest any other part numbers that would be a tad bit shorter?
Old 07-15-10, 06:01 AM
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try shorter belts, they are not serpentine belts, they are just v-belts.

if you have 31.5" and it is maxed out try 31 or even 30.75 or 30.5 depending on how much room you have, if they are too wide try a slightly narrower belt
Old 07-15-10, 08:04 AM
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The Dayco belts work fine. I get them from Advance Auto.
Old 07-15-10, 06:15 PM
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sorry, i meant v-belts.

though typically i refer to the belts on the engines, as serpentine belts.

i purchased shorter belts, so lets hope that works.
Old 07-15-10, 06:39 PM
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I had to modify my Power steering to get my IC pipes around it.SO I had to find a belt for the Power steering.
You take a piece of String and wrap it around the Pulleys.(think about it as: cutting the belt and then measuring it,sort of thing)Get the measurement of the String in inches or Cm's and take it to Napa,where they give you a Vbelt of the appropriate size.
The size was a bit off the first time(one of those DUH measurements!),But I got one that fit,and I am on my way.Power steering unit lowered 4 inches
Old 07-15-10, 08:43 PM
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25-7315 (31.5 inches long)>30.5
25-7385 (38.5 inches long)>37.5
25-9380 (38 inches long)>37
25-9415 (41.5 inches long)>40.5
:P
Old 07-16-10, 01:30 AM
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well, i just finished installing the new belts, nice and tight.

the alternator isn't charging anymore and i don't know why.

i just finished installing my electrical boost gauge and after that my alternator wouldnt charge? or according to autozone, it isnt charging correctly, and only charging at 12v..
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