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The art of bolt tightening

January 29, 2011

For some this might be obvious but for those who dont know this will save you alot of headache in the future, tightening bolts properly is essential to seal gaskets properly to distribute the tightening pressure so you dont get leaks; in most cases if you dont tighten in the proper order the gasket will usually seal because its new, but almost always will fail before a properly installed gasket as it starts to degrade.

If your working on something that has multiple bolts, the key is to tighten the opposite bolt to the one you just finished tightening.

Lets take for instance the cylinder head bolt tightening sequence for m20 6 cylinder engine in an e30.

You can see by the sequence of the numbers that starting from the bottom center you go opposite then as you go towards the outsides you follow the same process, and intuitively I think you can understand that the head will tighten evenly across if you follow this process.

But thats not where it ends, you still dont want to over tighten any one specific point before you tighten the others equally. Thats why in a lot of applications the bolts must be tightened in stages. Lets take the same m20 here are the stages:

Pre 1989 m20’s were assembled with Hex bolts, thereafter torx bolts where used, if your doing engine work you should replace the hex bolts with torx bolts (the hex bolts and all head bolts are one time use anyways). The tightening procedure explains the for the first stage you follow the sequence for tightening seen in figure 1 and tighten all bolts to 22ftlb, then you start the sequence all over again starting at position 1 and do stage 2 by turning each bolt 90 degree’s, finally the third stage is again starting from position 1 you tighten each bolt 90 degree’s again. so at the end of tightening all bolts each bolt will be tightened 22ftlb+180 degree’s, but in a manner in which it was applied evenly.

This does not only apply to e30’s, m20’s or just engines, this applies to anything that has multiple points of anchoring ranging from transmissions to thermostats.

To simplify even further here is how everyone should be tightening their wheel nuts/bolts.

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