Head bolts and head gasket crush

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.
 

Fast Eddie

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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.
 
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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).
180160261_10220701470546274_2237793095709442891_n.jpg


The reduced shank head studs also help prevent stud thread pull out.
SS-tri-stock-or-FA-head-w-Maney-cyl-Whit-324x467.jpg
 

jaydee75

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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,
What kind of head gasket on your 920?
Jaydee
 

Fast Eddie

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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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YING

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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
 

Fast Eddie

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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.
 
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