Author Topic: Big end bolts too short?  (Read 933 times)

Offline nigeldtr

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Big end bolts too short?
« on: 11.11. 2010 18:05 »

Just putting my bottom end back together (1953 plunger A10) but just found that that the new big end bolts are shorter than the originals and leave me no room to do the nuts up -the new nuts are also shallower and sit too deep inside the big end cap (knackered now, no meat to grip the socket  *sad2*)  The old nuts are about 3mm thicker and have a shoulder of about 2.7 mm turned on them which means the hex head sat a little higher. The new nuts and bolts were from SRM (tried putting a washer under the new nuts but there was no thread left for the nut to "lock" onto.

Are there two different lengths? - old bolts 67.8 mm long, new 65 mm.


1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!

Offline a101960

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Re: Big end bolts too short?
« Reply #1 on: 11.11. 2010 19:24 »

I to had this problem with big end bolts supplied by SRM. I am surprised that SRM did not mention the fact that the bolts that they supply are Triumph items, and that you will need to have 1/8th" machined of off the caps. At the time that I bought my bolts the Triumph bolts were the only bolts of the correct specification available (forged with rolled threads). I think that bolts of the correct specification and the correct length are now available from Paul Goff. It is imperative that the bolts are forged with rolled threads. Machined bolts will eventually fail due stress risers caused by the cutting process. Another supplier of the correct grade bolts is Mike Cheyne who had a batch made in the USA because nobody in the UK was willing to make these bolts. I can put you in touch with Mike if you want to talk to him. As far as I am aware nobody else stocks big end bolts of the correct length and specification.


Online chaterlea25

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Re: Big end bolts too short?
« Reply #2 on: 11.11. 2010 19:39 »
HI All,
I know this was quite a while ago BUT I got the correct spec bolts/nuts from C&D Autos
John O R
1961 Super Rocket
1963 RGS (ongoing)