Head torque specs

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David,

For a .90 size engine with 8, 8-32 head bolts passing through the cylinder's lip, 20 in/lbs is what I use. If the bolts are outside of the cylinders lip & do not pass through the cylinders lip, this amount of torque could bend the top of the cylinder outwards. You will be able to feel the loss of the piston's fit at TDC when this happens. With 8, 6-32 bolts I use 15 in/lbs. Remember that these numbers are only for assemblies with the bolts passing through the liners lip, not outside of the cylinders liip.

If you're using a minature type torque wrench, thread interference, any type of lubrication, dirt & different screw coatings or alloys can change the torque amount. The numbers given are for alloy steel screws used in aluminum crankcases.

JA
 
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Gutentight.........................................................
this^^^.. 38 years doing nitro engines and have never used a TQ wrench,even on my $650 On-Road Car engines...
yep. I use a long shank T-handle hex driver, and when the driver starts to twist, it's tight enough. I just tighten the head bolts in a cross (4 bolts) or opposing (6 bolts) in 2-3 stages.
 
The majority of the time when I receive an engine for repairs the 6, 6-32 head bolts have not been tightened down any where close to spec. This doesn't necessarily mean there is any leaking taking place. However, there could be some unwanted movement between the three pieces involved; the head button, the cyinder's flange & the top of the crankcase; especially if the bolts are outside the liner's lip. Imagine how much movement could be taking place when these three key pieces are not in direct contact with each other.

Jim Allen
 
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