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Jubilee Deluxe Head Bolts

Submitted by andy_riley on Wed, 11/11/2020
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Light Twins

My Lockdown / Winter project just got more interesting !

Armed with my brand new torque wrench I read an earlier forum topic and set about to torque up the cylinder head to the required 15IIb,  one of the studs didn't even take 5llb before pulling out from the crankcase ouch !

I suspect a previous owner ran it with this bolt loose, as its clear I didn't strip it, and looking at the stud, its been done a while.

My question is: what's the chances of heli-coiling and fitting a new stud?  and is it possible to do this without splitting the crankcase  ?, 

Is the stud a cycle thread for the nut and a coarser BSW thread into the crankcase ?

Any help appreciated    Andy Riley 

Submitted by peter_holland1 on Wed, 11/11/2020

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Hi Andy,
5/16 BSW at the crankcase and 5/16 BS Cycle at the other end, as you suggest.
It depends on your confidence and experience regarding the helicoil. The helicoil must be put in vertically, as the stud will need to be dead vertical.
Is it a blind tapped hole in the crankcase? Or will the aluminium swarf fall into the crankcase? 8 holes are blind, 4 holes are through holes.
Peter

Submitted by dan_field on Thu, 12/11/2020

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If there’s room, (I can’t see my crankcases from the warmth of the kitchen!) Id get a threaded insert fitted, nothing wrong with a helicoil - Tracey Tools will send you the kit, but an insert is better!  No problem doing it without splitting the engine, just tape up any holes to stop swarm getting inside. 

Submitted by andy_riley on Thu, 12/11/2020

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Thanks:

Looked on the Tracey website, I can see the Heli~coil kit,  where would I get an insert from ?

Never used an insert 

Hi Andy, 

If Tracy tools are advertising a ‘kit’ it should include an oversize drill, a tap which has the same pitch as the thread you are repairing but with an oversize outside diameter, a wrench for winding in the insert and, usually, several inserts. I should imagine you will require an Imperial repair kit and companies such as Cromwell Tools may not stock them.

Each kit normally only repairs one thread size so be certain to order the correct diameter and thread form. i.e. 5/16” BSCy.(if that is what you want)

lots of modern engines have helicoil inserts fitted during manufacture where aluminium components are used. They increase the pull-out strength of the fasteners, reduce friction and corrosion and allow finer pitches than Whitworth, for example, giving greater torque/nip force ratios.

Happy Tapping

Dick

Submitted by paul_reynolds on Thu, 12/11/2020

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Heli-coils are common in the aircraft industry. I suggest buying from an engineering tool supplier, like Cromwell. You need a slotted T-Bar to wind the insert in to half a turn below the crankcase surface, then reverse direction to break the little tang off. You will also need the correct size drill. I usually turn a piece of inch steel bar with a drilled hole the size of the drill first to use as a guide to drill the hole square to the flange surface.

Submitted by andy_riley on Sun, 15/11/2020

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Thanks to all for the information supplied , I have found a local supplier of the kit and I should be in a position tap it out  next week.

Having spoken to 'experts'  inserts are not  available for BSW threads and the Heli~coil is an industry tried and tested method to repair threads in aluminium casings.

It doesn't appear to be the massive issue I first thought it was when the thread pulled out and the tea cup smashed against the wall !

Thanks 

Andy 

Submitted by andy_sochanik on Sun, 15/11/2020

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You will NOT be able to do it without first stripping the engine, as :

1) You have to drill a larger hole first, before adding insert/helicoil.

2) It has to be dead vertical, in exactly the right place.

In addition, there will be swarf created from the drilling AND the tapping - unless its one of the blind holes Peter alludes to.

Submitted by george_farenden on Sun, 15/11/2020

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Any 'expert' who says they aren't available isn't much of an expert in my eyes. 

RGM certainly stock them, and so do many other Brit bike dealers/spares suppliers.

If the original thread was Whitworth,  stay with that or you have to venture into the world of one-off studs.

As to swarf, if you are redoing one of the blind holes, lots of grease on drill and tap, and masking tape over any uncovered engine openings should keep the panics at bay.

Regards, George

 



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