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Discussion Starter · #1 ·
Hi all, I have an '86 300zx na. My motor bit the dust and so I bought a jspec motor to swap in. The motor is in great shape and had low miles but my mechanic tells me that the old motor was a v-belt configuration and the new motor is a serpentine belt configuration and that the crank is about 3/4" longer. He thought it was some difference between being initernally and externally balanced. Does this sound right? Should I tell him to swap things out to make the new one like the old one, or is it that big of a deal. And just get a longer tensioner. TIA
 

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Swap on the old one if it fits and solves the problem.

I know that the early n/a z31's (84-86) had an all v-belt system while the later z31's (87-89) and I believe all turbos (?) had 2 vbelt's and one serpentine belt. The serpentine driving the waterpump and alternator. There may be some chance of getting a crankshaft pulley off the correct year and swapping it onto your set up.
 

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my 88 n/a engine has all serpentines , but if you dont have the accesories then you should change the balancer for the one that has the correct balt config , you can get the belt at any auto parts store (serpentine or vbelt).
 

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Discussion Starter · #5 ·
My only question is that since the crank pully isn't the same-The one that came with the car had the pulleys bolt on to it, and the one that came with the motor is all one vulcanized piece, will this mess up my balance? There is more of a gap with my old crank-pulley(v-belt) then there is with the new micro-v serpentine belt. Usinge the old pulley system gives me about 3/4" extra because the new setup was moulded with a longer snout. So I'd have to use a spacer or have extra bolt hanging around. Are all the pre-90 300z's externally balanced or not? I'd hate to take a balancing pulley off of my motor that needs it or have two balancing pulleys on there if it doesn't? Does this sound right. I know others have swapped a J-spec motor in but I wasn't sure of the year.
 

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Discussion Starter · #7 ·
I don't seem to bexplaining myself well enough-hang with me and I'll get there. My accessories are the v-belt style. My new motor has the micro-vbelt style crank pulley/harmonic balancer that is all one moulded piece. My old motor had the harmonic balancer that had the pulleys bolt to it. The spacing is a little off because of how the one piece harmonic balancer is moulded. The old balancer with the pulleys that bolt onto it will fit but there is a gap or extra bolt that will have to compensated for with some sort of spacer. My question is will using my old style one(which is in better shape as well) throw off the balance of the new motor which used this one-piece style. if I spaced if so the pulley was sitting on the crank in the same place as the moulded one piece sat. They don't appear to be that much different other that the one piece is all vulcanized together and has a longer moulded snout. But I'd hate to be wrong just because i don't want to go through the trouble of finding and swapping belts and pulleys after going through all the trouble of finding the motor.
 

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Discussion Starter · #9 ·
This link was extremely helpful to me. N ow all i have to do is figure out the parts microfiche so i can see if the part number given to use is the new or the old one. Does the microfiche give diagrams?
 
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