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Tallicia Tallicia is offline
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Join Date: Sep 2016
Car: E88
Exclamation Serpantine bypass A/C and PS belt length? - 05-23-2019, 09:31 AM

Does anyone by chance know what size serpentine belt would be needed to bypass the PS and A/C on the 135i N55 ( or other N55B30A with similar pensioner and pulley layout?

I'm replacing my tensioner and pulleys and A/C over running pulley and have a new PS pump and PS pulley as well to go on, but would like a quick way to verify where noise is coming from.

Running the engine without a belt, she runs great. the noises I'm getting when cold until temps are over 200'F I expect will be addressed by tensioner, deflection and Alternator pulley. While I am in there I will use a string to measure what length will work for bypassing the other two "non essential" pumps.

Basically I'm trying to have a good tool and info to debug and track down noises.

Picking up a $15 belt to swap on that can bypass some makes it much easier to determine the noise, plus in a bad situation pinch, it's nice to have an option such as bypassing the PS pump while parts are on order.

So I'll be measuring soon, but wanted to see if anyone else might have measured or used a belt shorter than the 7 groove 1860mm or 1855mm for testing/bypassing?

Side note: would some dyno queens or performance oriented builds not benefit from removing the bottom deflector pulley and running a belt direct between the tensioner, Alternator, one deflector and to the crank? I know it's minimal, but on track/strip, it's just two less bits getting spun around and worn out and eating up horsepower.
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