discomania
Well-Known Member
Where did you get the bolts? I have seen cheap bolts which were shockingly deformed, if that was what I was able to detect with my bare eye then what chances do we have that the bolts were made of the correct metal as prescribed in the specification?
All bolts are theoretically stretch bolts, thats how they work, but bolts known as "stretch bolts" are bolts that have a carefully calculated yield point they will then stretch and then continue to exert the same clamp force even after heating and cooling. A bolt on your chassis doesn't need to withstand heating and cooling so it will stretch out and exert clamp strength but doesn't need to be dead on accurate for every bolt.
If they use a cheap metal, with too low a tensile strength and therefore a lower yield point, the bolt will experience plastic deformation much sooner than it ought too and stretch further than it is meant to which will allow the head to lift.
If they made them with too high a tensile strength, then they may not have stretched enough given the torque applied, and like years ago, actually do need retorquing as the gasket compressed and settled with the hot/cold cycles.
I personally would try to retorque them a little, you may even find the ones at the leaking end turn much easier (clear indication of a bolt issue - unless you forgot to torque them)however, bear in mind that stretch bolts will exert the same clamp force even if its turned up to another 1/2 turn more, then going beyond this can enter into the point at which the already yeilded bolt could shear...
All bolts are theoretically stretch bolts, thats how they work, but bolts known as "stretch bolts" are bolts that have a carefully calculated yield point they will then stretch and then continue to exert the same clamp force even after heating and cooling. A bolt on your chassis doesn't need to withstand heating and cooling so it will stretch out and exert clamp strength but doesn't need to be dead on accurate for every bolt.
If they use a cheap metal, with too low a tensile strength and therefore a lower yield point, the bolt will experience plastic deformation much sooner than it ought too and stretch further than it is meant to which will allow the head to lift.
If they made them with too high a tensile strength, then they may not have stretched enough given the torque applied, and like years ago, actually do need retorquing as the gasket compressed and settled with the hot/cold cycles.
I personally would try to retorque them a little, you may even find the ones at the leaking end turn much easier (clear indication of a bolt issue - unless you forgot to torque them)however, bear in mind that stretch bolts will exert the same clamp force even if its turned up to another 1/2 turn more, then going beyond this can enter into the point at which the already yeilded bolt could shear...
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big ad
Active Member
well i have spent all day on teh old girl and it turned out to be the dowel on the front of the engine had twisted - not sure how but it was - will post a picture later, put a new head gasket on and put her back together and took her for a spin and she seems ok, but she was ok last time!!!!
