Who makes high grade 26 tpi allen head bolts?

marshg246 said:
Wow! In other words, they were BSC/CEI diameter and threads per inch but cut at 55 degrees? Was there ever a named standard for that?
Click to expand...

Known as Whit Form. The rear head (and pre-Unified base) nut is apparently Whit Form so the head studs ought to also be Whit Form (and pre Unified base studs?) which suggests the head bolts could also be Whit Form.
andover-norton.co.uk

Andover Norton - CYLINDER BASE/ HEAD NUT 3/8

CYLINDER BASE/ HEAD NUT 3/8
andover-norton.co.uk
 
marshg246 said:
Yes!

I've had a couple of heads where the stainless hex heads were smaller than usual, and the dummy didn't use washers. This caused the aluminum to collapse in on the bolt. They were hard to get out and I had to re-open them to the right size before assembling. There's no doubt in my mind that Allen cap screws must have tight-fitting washers to prevent this as their heads have even less bearing surface normally.

Even the 850 through bolts into cast iron can have that trouble. I recently took a set off where the prior guy apparently got confused and had 1 bolt with two washers, 1 with none, and 2 with one. Again, very tough to get the one with no washer out due to the top edge of the cast iron collapsing in on the bolt.

I'm sure Jim knows this, but worth mentioning.
Click to expand...
The std washers (01.6213) are not big enough, or thick enough. I make mine from s/steel, sized to fit the counterbore recess and 4mm thick. Depending on the condition of the counterbore, i sometimes have to kiss the recess with a counterbore tool to re-establish a decent seat for the washer. The earlier twins had head bolts with bigger heads and washers and don't suffer this problem as much.
850 through bolts, a recent head and barrel job i found 5 washers, one recess with two, the other three one each. It amazes me how people can overlook things like that. It was obvious that something was amiss as the two washer bolt was nearly level with the gasket face. I think that must have been done at a dealer years ago as the Diy home mechanic won't have a stock of washers available.
 
Back
Top