The BSA A7-A10 Forum

Technical (topic titles must be descriptive) => A7 & A10 Engine => Topic started by: Dynamo Regulators Mike on 08.03. 2009 15:32

Title: A10 Alloy headbolts
Post by: Dynamo Regulators Mike on 08.03. 2009 15:32
Does anyone have the lengths of alloy head (67-1126) A10, 58-59 Super Rocket, headbolts to hand please?
Have a BSA service sheet with iron head lengths, but alloy ones definitely differ.
Also I have managed to screw a thread insert too far into the barrel in an attempt to clean up a sticking thread with a tap. I may be able to deliberately screw the insert further in and fit a second insert, but is there a trick or tool to remove an insert without damage?
Title: Re: A10 Alloy headbolts
Post by: trevinoz on 09.03. 2009 00:08
There is a tool but I have used a file tang in the past to remove inserts.
Title: Re: A10 Alloy headbolts
Post by: Brian on 09.03. 2009 06:25
Mike, here's a picture of the correct tool. The arrow shaped thing on the bottom. Trev's suggestion of a file tang is a good one though.
Title: Re: A10 Alloy headbolts
Post by: bsa-bill on 09.03. 2009 10:22
Presuming we're talking about a helicoil, if at all possible with a sharp instrument pick the end of the insert thread out enough to grab it with longnose pliers then it will easily come out by twisting the pliers anticlockwise and up . DAMHIK

All the best - Bill
Title: Re: A10 Alloy headbolts
Post by: Dynamo Regulators Mike on 09.03. 2009 10:44
Yes its a helicoil type insert Bill.
Thanks guys for the tips. I'll have to search my files. *smile*
Anyone know the head bolt lengths? The 1.5 diameters rule of thumb gives a thread depth of 9/16" for 3/8 BSF, but that seems barely enough for torqueing down headsbolts safely.
Title: Re: A10 Alloy headbolts
Post by: dpaddock on 09.03. 2009 14:21
Bolt lengths are 3-1/16" for the long bolts, 2-11/16" for the short ones. Thread length is 7/8".
Title: Re: A10 Alloy headbolts
Post by: Dynamo Regulators Mike on 09.03. 2009 19:41
Thanks David
That pretty well ties in with the bolts I had fitted.
Title: Re: A10 Alloy headbolts
Post by: BSA_54A10 on 11.03. 2009 21:02
Just on a slightly different tack here , what do you mean by screwed in the helicoil too far ?
They should be 1 to 2 turns below the top of the hole.
If you have yours in deeper than that you probably should have used a longer helicoil.
They come in 1/4" incriments and the insert should engage with the full length of the bolt thread, less 1 or 2 turns at the leading edge.
The ones that come with the kit are specifically for threads in cases which are quite thin but in your heat they are much longer.


If one is too short buy some longer ones.
I almost never use the inserts that come with the kits as with the exception of the primary cover all of them are too short for use on the Beesa's. Long ones can be cut down to fit correctly by carefully running a Dremel cut off wheel down from the top cutting off the excess length into little semi-circular rings. Don't try to cut them off across the threads ( as you would a bolt ) as the wheel will tend to slip and slide every where get stuck between the turns and either break the cut off wheel or bugger the insert. Also you end up with a taper on the  end of the insert which the bolt will tend to pick up and drive the insert deeper or push it out of the hole.

If you use solid inserts ( like time-serts ) then the opposite applies, they have to be cut off square across the thread at the leading end.

For removal of a failed insert I use a darning needle to lift the end of the wire then a pair of tweezers to unravel the wire from the hole, Once the end is clear of the hole I grab it with a pair of long nose vice grips and continue to unwind it. large insets where the needle nose pliers will fit in easily never seem to give me grief it is always the 1/4" or smaller ones that like to play up.
Bike Beesa