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Rocker box stud

Submitted by george_phillips on Sat, 28/01/2017
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Hi Guys, I've found why there is a constant oil mist round the top of the engine. One of the rocker box retaining studs has shed its threads in the alloy head (55 ES2). It's the centre front one at the rear of the exhaust valve. Has anyone any idea what size/thread it is as i intend to fit a helicoil - unless someone has a better idea? George

Submitted by george_phillips on Tue, 31/01/2017

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Hi Baz - after a bit of research I find that the stud should be a 5/16" with a TPI of 26. Now I've got to find if Time Sert or Helicoil do that size. Thanks for your help - George

Submitted by ian_macdougall on Tue, 31/01/2017

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George, do these studs not have different thread form at either end? 26tpi (Cycle) for the rocker box nut, 18tpi (BSW) where it screws into the alloy head. My '56 19S alloy head is definitely 18tpi (just checked the head lying on the bench).

Ian McD

Submitted by ian_macdougall on Tue, 31/01/2017

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George, do these studs not have different thread form at either end? 26tpi (Cycle) for the rocker box nut, 18tpi (BSW) where it screws into the alloy head. My '56 19S alloy head is definitely 18tpi (just checked the head lying on the bench).

Ian McD

Submitted by george_phillips on Tue, 31/01/2017

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Now I'm getting confused Baz! Which chart are you referring to? I believe the threads are different at each end of the stud but I'm on about the end that screws into the alloy cylinder head. George

Submitted by george_phillips on Tue, 31/01/2017

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Doh! Just realised you're talking about the chart you attached earlier on. My apols. But that's Whitworth and I think the cylinder head thread is 5/16"BSC at - I thought - 26TPI? george

Submitted by george_phillips on Tue, 31/01/2017

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Oh well. Back to square one! I'll keep digging. I need to get it right so's I get the correct helicoil or insert. George

Submitted by george_phillips on Tue, 31/01/2017

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Don't know what that is, Dan. Mine has an alloy head. Is that a "Wellworthy"? Does this affect the thread - or rater, the TPI. George

Submitted by george_phillips on Wed, 01/02/2017

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Sorted! After an interesting and informative telephone chat with Ian I now know that the stud is a 5/16" with a Whitworth (coarse) thread into the head and a fine (26TPI) BSC thread for the nut. Now I can set about sourcing a Helicoil or insert set for the damaged thread in the head. Many thanks for all your help, Ian. George

Submitted by dan_field on Wed, 01/02/2017

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Previously George Phillips wrote:
Don't know what that is, Dan. Mine has an alloy head. Is that a "Wellworthy"? Does this affect the thread - or rater, the TPI. George
Hi GeorgeAs far as I know the alloy head on an ES2 of that era was a Wellworthy head, although the head is aluminium the combustion chamber is iron, hence the name "iron skull". Mine says wellworthy on the side, but am not sure if they all did.Anyway glad you got it sorted, it was always going to be a whitworth thread in my mind, I guess you know the front and rear studs are a smaller diameter than the others.Dan

Submitted by george_phillips on Wed, 01/02/2017

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Thanks Dan. Life is one great learning cycle! I'll check what's written on mine tomorrow. It certainly has an iron inner. I realise about the front and rear studs. the one last confusion is that then rocker box is held on with studs on my bike but RGM tell me it's a bolt. They don't do a stud. I'm trying to glean from them what the thread is so's I don't buy the wrong helicoil. And so it goes on........... George

Submitted by ian_macdougall on Wed, 01/02/2017

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The earlier iron head models have bolts holding the rocker cover, the alloy head models have studs. I guess the thinking was that bolts could be removed & replaced any number of times from an iron casting but with an alloy casting there would be a risk of damaging the threads so preferable to remove the nut from the stud. It also means that iron head rocker boxes can be removed with the head in situ so the RHS cylinder head sleeve nuts become more accessible. I have never removed a rocker box from an iron head - do the bolts have the same thread as the lower end of the alloy head studs? If not this may explain why George's research led to Cycle rather than BSW. Someone will know.

Ian McD

Submitted by george_phillips on Wed, 01/02/2017

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Once again Ian, that makes a lot of sense. problem is that at present I'm getting two different answers and both seem feasible. I may have to go down the bolt route as it seems the only thing available. Once RGM confirm the thread type/ size I can move. Thanks again. George

Submitted by albert_sheean on Thu, 02/02/2017

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Previously George Phillips wrote:
Hi Guys, I've found why there is a constant oil mist round the top of the engine. One of the rocker box retaining studs has shed its threads in the alloy head (55 ES2). It's the centre front one at the rear of the exhaust valve. Has anyone any idea what size/thread it is as i intend to fit a helicoil - unless someone has a better idea? George
Hi George,I had a similar issue with my 1958 Model 19S. The bolts were a 5/16" BSF (5/16"-22TPI) thread and I got a helicoil kit from Armstrong.Regards,Albert.

Submitted by george_phillips on Thu, 02/02/2017

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So grateful for all your inputs guys. Information overload! I've taken the plunge and ordered a 5/16 BSF bolt plus a helicoil kit from RGM. Total cost about £40. Expensive for what is effectively a stud replacement but there you go. Onwards and upwards! George

Submitted by george_phillips on Thu, 02/02/2017

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Just checked, Dan, and it is indeed a Wellworthy iron skull head. Also thanks for the tip. I've put a hold on my order as another query has arisen over the efficacy of changing what may well be a Whitworth thread in the head to a BSF. All good fun!!George

Submitted by george_phillips on Fri, 03/02/2017

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Just to tidy this up - I emailed Mike Pemberton and apparently it is quite OK to fit a 5/16 BSF helicoil in place of a 5/16 BSW socket thread. So a new 5/16 BSF bolt will do the job. Sorted - I think........George

Submitted by george_phillips on Fri, 03/02/2017

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Thanks Baz. Now why couldn't I find that! I may well get a stud and keep the bolt as a spare. Cheers, George

 


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