BSA A10 rocker box heli coil size’s

[mario medeiros]

I know it’s not right but I have a endless supply of regular 5/16-18 and 5/16-24 heli coils at work and I need to thread the cylinder head where the long rocker box bolts thread into. Should I use course or fine thread coils in the aluminum head? Thanks

[mario medeiros]

Hey Portuguese? Me too, yes they are a bronze or brass insert which I was going to drill then tap for the heli coil I hope it will work, also was wondering if I should use a course or fine heli coil, seems like what I have read is course is better to prevent stripping in aluminum.Just wanted to see if anyone else has done what I’m about to try. Thanks

[muskrat]

G'day Mario.
Facing the same problem back in the 90's with the A7 racer I just re-tapped 3/8" bsw. Still working on the A7 plunger.
In your situation I'd helicoil to 5/6 bsw and make/get new bolts (grade 8 or better).
Cheers

[Swarfcut]

 Reserve the coarse Whitworth system for threads directly into alloy, this thread form gives good support to  components mounted in a relatively soft casting. However in alloy it will will not support the loads exerted by head bolts*, hence the use of inserts to spread the forces.

 For Alloy heads, preserve the original cast in insert if you can. For a  Helicoil type re-thread, choice at 5/16" is CEI  at 26 TPI, BSF (22 TPI) or UNF at 24 TPI. So with the Helicoils available 5/16UNF would be a reasonable choice. You'll need bolts to suit, but these should be easy to source, and take care with those blind holes, a little customising may be needed for the correct bolt length to prevent bottoming. Are you sure the bolts you have are correct and unworn? A new set of bolts to fit the existing inserts may be all you need.

 Swarfy.

[mario medeiros]

Are the bronze factory inserts replaceable? where would you buy them and how would they come out if i was to replace them? All of my 5 long bolts thread into them but the bolts even half way into the inserts seem very loose and sloppy and i am afraid they will strip or pull out once i torque them.

[mario medeiros]

Will do, thanks to all.

Mario

[chaterlea25]

Hi Mario and All
The bronze inserts are cast into the alloy,
They have 2 hexagon sections to prevent them moving.
There is enough metal to accept a helecoil
Its best to set the head up on a milling machine or  very rigid pillar drill

John

[bikerboy]

I assume you are talking about the rocker box bolts not the cylinder head bolts? Mine are helicoiled and they are fine

[Swarfcut]

 Oh, Silly Me!..... Yes it is Rocker Box bolts. which are doing the job of holding down the cover as well as carrying the load of pushrods acting against the valve gear, requiring the need for good support for the threads in a light alloy casting..*

 Swarfy.

 "Original post done in a sober moment, hence the error.