Setting water pump belt tension question

That's how they do it on spacewalks outside the spacestation... They have two different people at ground control to help count your rotations too. Of course when not in the vacumm of space you get dirt and grime and belt wear which can slightly change the number of rotations you need. Also a brand new belt will stretch a little and so a tiny bit tighter would be better than a tiny bit looser.

 

The short answer is NO. The old belt is worn and stretched and your assuming the new belt is within millimeters of length of your old belt. Tension the replacement belt per OEM manual/procedures. Don't over-tighten them or your going to have bearing and bushing issues.

 

I wonder what the manufacturing tolerance is on the length from one new belt to another.

I'd probably just set the tension per the instructions and move on to life's next question.

 

Info:

 

Because there's not a belt adjustment process in the maintenance instructions for modern cars it's safe to assume that there's a wide range a variability for belt tension without issue. And clearly too loose you'll get belt noise and too tight you could get damage parts.

And clearly, you can always count on someone sitting at home in front of their computer convincing you something irrelevant is really important.

Kind of like proper torque on on a bolt. Majority of bolts will not be an issue at all if the torque is off... But if you're talking about headgaskest bolts or cam or crankshaft bolts you're gonna want those to be as accurate as possible because doing those wrong can't be easily fixed.

In other words just go with counting rotations on the tensioner and make it a little tighter than before after you've matched up the two belts to confirm how much tighter than before.

 

There's no belt tension adjustment on most modern cars because, they use a spring tensioner on one of the idler pulley.
You over-tighten a belt, the car won't stop running. Your just going to have to replace your water pump or alternator or whatever that belt is driving a few hundreds or thousands miles down the road. Because your placing an excessive load on those bearings or bushings. If you trash an idler pulley and it seizes up, your going to snap that new belt anyways. Things will last a long time, WHEN properly maintained and kept within specs......

Generally, you should be able to get anywhere between 1/2 to an inch deflection between your longest pulley runs... That's better than counting bolt rotations and praying that the belt you bought is the EXACT length of the OEM belt - NOT a generic belt that will fit your make and model if properly adjusted.

Again; your car your money - do whatever you like.....

@PriusCamper; I'm surprised at your answer since you claim to repair cars for a living. Then again, I guess if it isn't an immediate failure, that's more repeat business for you.....

 

Here’s the specifics, the deflection test option, seems fairly typical:

 

It's mostly rubber and subjected to a very harsh environments in a longitudinally mounted engine - behind the radiator, condenser, turbo cooler and possibly transmission cooler. The transverse mounted engine environment is a lot easier on belts, away from all that heat being blown onto them. Since the belt manufacturers don't know where that belt is going to be placed, it's engineered to withstand the harsher climates; so heating them up will seat/settle them into the pulleys. Then a final adjustment can be made. Not as important on a transverse mounted engine, but a requirement on a longitudinally mounted engine; IMHO. If you want to do it correctly.

Just my 2-cents.....

 

If you mean in the 2006 RM floating around, then no, it isn't. I posted about that quite awhile ago. I have corrected it in my copy: