Head bolts and head gasket crush

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Fast Eddie

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I just gave the 920 a once over, ain‘t gonna use it much this year me thinks but def got some plans.

Anyhoo, it’s not done much mileage since the 920 build, about 1,500-2,000 I guess, but it has gotten a few track sessions under its belt now.

Firstly, the head fixings had not lost ANY torque. I cracked ‘em back, then torqued ‘em up and they were in exactly the same place.

Tappets hadn‘t moved at all either.

Given this is a relatively recent build, and it has an alloy barrel (Maney) I was very pleasantly surprised.

The reason for posting is this: I credit this lack of crush / movement to the wasted stem head fasteners. I’m convinced the ‘give’ they have prevents excess crush on the clamping faces and that when things heat up / expand and cool / contract, the fasteners yield and return.

Well worth considering IMHO.
 
Well, on the 850 motor I’m using the cNw kit. But I’m using Maney barrels on the 920 which have different requirements to stock. So on that Ken (lcrken) helped me out A LOT as a one off job, but now JS stocks all that’s required.
 
The reduced shanks are especially important in a large displacement high compression motors. Below is what happened to a 920 alky burner - the original through bolts actually broke from the strain (causing the cases to fail).
Head bolts and head gasket crush


The reduced shank head studs also help prevent stud thread pull out.
Head bolts and head gasket crush
 
I just gave the 920 a once over, ain‘t gonna use it much this year me thinks but def got some plans.

Anyhoo, it’s not done much mileage since the 920 build, about 1,500-2,000 I guess, but it has gotten a few track sessions under its belt now.

Firstly, the head fixings had not lost ANY torque. I cracked ‘em back, then torqued ‘em up and they were in exactly the same place.

Tappets hadn‘t moved at all either.

Given this is a relatively recent build, and it has an alloy barrel (Maney) I was very pleasantly surprised.

The reason for posting is this: I credit this lack of crush / movement to the wasted stem head fasteners. I’m convinced the ‘give’ they have prevents excess crush on the clamping faces and that when things heat up / expand and cool / contract, the fasteners yield and return.

Well worth considering IMHO.
Eddie,
What kind of head gasket on your 920?
Jaydee
 
Copper. It’s the only option with a 920. I used the 0.005” copper wire and Pliobond as per JS recommendation.
 
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I just gave the 920 a once over, ain‘t gonna use it much this year me thinks but def got some plans.

Anyhoo, it’s not done much mileage since the 920 build, about 1,500-2,000 I guess, but it has gotten a few track sessions under its belt now.

Firstly, the head fixings had not lost ANY torque. I cracked ‘em back, then torqued ‘em up and they were in exactly the same place.

Tappets hadn‘t moved at all either.

Given this is a relatively recent build, and it has an alloy barrel (Maney) I was very pleasantly surprised.

The reason for posting is this: I credit this lack of crush / movement to the wasted stem head fasteners. I’m convinced the ‘give’ they have prevents excess crush on the clamping faces and that when things heat up / expand and cool / contract, the fasteners yield and return.

Well worth considering IMHO.
Eddie,
Is it standard practice to back off the head bolts before re-torquing? I have always just checked them in the proper sequence. I am using the CNW kit that have been waist cut and at my 2,000 mile check,everything is good.
Thanks,
Mike
 
Eddie,
Is it standard practice to back off the head bolts before re-torquing?
AFAIK, if the fasteners have been in a while then yes, they need backing off to free up any ‘binding’ of the fasteners. Do them one at a time in the correct sequence there‘ll be no negative effect on the joint at all.
 
I don’t understand what AFAIK means
 
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