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Old 11-16-2015, 01:43 PM
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dbhill916 dbhill916 is offline
Join Date: May 2013
Location: Westerville, OH
Posts: 166
Default can you substitute class 12.9 for 8.8 bolts?

Hi all,

Is it safe to use bolts that are stronger than specified by Rotax, or will there be an unintended consequence (e.g., damage to the internal threads, etc.)?

I over torqued the metric bolts on my water pump housing and will be pulling the engine to remove & replace the affected bolts. Unfortunately, LEAF is quoting 6 weeks to get replacement M6x90 bolts. I have located a domestic source of M6x90 bolts, but they appear to be considerably stronger as they are Class 12.9, vs Class 8.8 as found on one of the ruined bolts in my possession.

A quick internet search shows that Class 8.8 has a yield strength of 660 MPa while Class 12.9's yield strength is 1100 MPa. Is it possible to do damage using bolts that are too strong? Will the torque specifications be the same? If not, is there a known conversion? If not, then I will not use them and will just wait for Christmas.

thanks in advance,
David B. Hill
RV-12 #0760
Dues paid through 6-2022
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