SB20 - Oh Snap!

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Breaking a Drive Belt Tensioner

Adjusting SB20 drive belt tension is something your should consider performing every couple of years. Here's how:

Stages SB20 - Drive Belt Adjustments

The good news: A properly adjusted belt is quieter and extends the life of the drivetrain.
The bad news: The belt tensioners (one on each axle) can break if you over tighten them.



The tensioner bolt will typically snap next to the washer assembly 😖.

 

DIY Fix

Getting SB20 replacement parts is challenging these days. Here's how to fix a broken tensioner.



1. Drill out the broken bolt that is welded to the tensioner ring. 




2. Find replacement bolts. I recommend M5 x 1 with thread length of 30 mm. Use stainless steel if possible. If you have a hex cap bolt, you can use it directly.  If you have a round head, you will need to file one edge.  You will also need matching lock nuts.

You can also use SAE bolts.  A 10-24 or 10-32 bolt with 1-1/4" thread length works well.




Here's a closer look at the filed edge on a round head.

 

3. Here's a completed assembly compared to the original.



You can now reassemble.  The new tensioner uses an M5 bolt in place of an M4. It should be significantly stronger.

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FAQ

Q: Why does this part break so often?
A:  Here are a couple of reasons.  

1. The OEM M4 bolt is undersized. As little as 20 Nm of force can break it. Be gentle.
2. Many people forget to loosen the vertical hex bolt behind the axle when adjusting the non-drive side.



Tightening the belt tensioner without loosening the vertical bolt can snap the tensioner. 
You have been warned. 

(I forgot once.  That's why I know ðŸ˜€)











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