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Stretch bolt theory discussed


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Complaints of MBE 4000 cylinder heads leaking

 

MBE4000 Cylinder head Bolts and stretch bolts generally
The MBE4000 head bolts, because there are stretch bolts, loose their clamping force on reuse, and unless they are strictly within the manufactures stretch limits, should not be used again otherwise leaks will occur.

Stretch bolts, when properly torqued, loose some of their diameter to the stretch, but are elastic, and if variations in the gasket material or other things occur they keep their clamping force by varying their diameter slightly, but frequently, like breathing. The clamping force of stretch bolts is necessary to retain the inevitable variations of cylinder head composite gasket material deformations due to heat etc. and they automatically keep the necessary clamping force on the head gaskets for them not to not leak.
Steve, BDC, Nov 2017

stretch bolt image #1
stretch bolt image #1


Cylinder Head Stretch Bolts v Non-Stretch Studs and Nuts

 

Replacing Stretch Bolts with standard (non-stretch) studs and nuts

  Non-Stretch Studs
Not withstanding the above technical information provided concering strecth bolts, some owners have nevertheless chosen to replace the stretch bolts with non-stretch studs and nuts, which I am told, are doing a good job resulting in a leak-free engine.
Steve, BDC, April 2018

Feedback on Replacing Stretch Bolts with standard (non-stretch) studs and nuts

  Greg updated us a year after doing the job on his MBE4000 as follows:
I had the valve covers taken off a month or so ago and according to the very experienced mechanic who did it, there was no evidence whatsoever of coolant leakage. Furthermore, I don't recall having to add any coolant in the past year, and if I did it would have only been a minor amount once, but I don't recall for sure at the moment.
Steve, BDC, December 2018




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