Head Bolt Torque

"Using clean lightly oiled head bolt threads and the OEM steel washers, with the machined flat side toward the head, TQ the bolts following the sequence found in the service manual, with a final torque of 43 ft lb (yes that is higher then what the service manual says, we believe the misprint in the manual of 34 ft lb is just another mistake found and uncorrected in the written service manual)"

 

Can someone tell me why they suspect that 34 ft-lb is a misprint?

How did they verify that 43 is the correct spec?

 

Thanks,

TD
 

This torque was proposed by Eddie Sisneros years ago when he was developing DZ motors with more displacement and was has having head gasket problems.  I don't think the misprint idea was ever verified and the official service manual has not been changed.  The 43 foot pounds has been in use many years by TT readers and motor builders here with good success.

 

In many cases there is no logic where the torque values in a service manual come from.  It would be nice to think they were developed by engineers with valid testing . But I think many of the values a tech writer got from a standard handbook with no verification.  There are examples of tech manual torques both too high and too low.

The only thing verified is that when 34 ftlb is used, on motor builds there is a common failure of head gaskets.

 

When 43ftlb is used on these same builds there is much less instance of head gasket failure.

 

Service manual typo, misprint or value set without R&D, or just a value found to commonly get a stock motor past the warranty period..who knows...

 

43ftlb works well... so it is what is recommended. 

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