Broken Stud...Grrrr

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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AGoodfellow
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Broken Stud...Grrrr

Post by AGoodfellow »

On replacing the cylinder head on my G12 the two studs on the head that hold the inlet manifold broke.. well one did.

Anyone know what thread the stud is on the end that screws into the head please, so i can tap it back out. Also i take it the spares have new studs.

Many thanks

Andrew
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1608
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Re: Broken Stud...Grrrr

Post by 1608 »

I'm very surprised that the steel stud has broken considering it bolts two aluminium parts together. Could be that its been overtightened in the past to overcome an air leak. When re-built the manifold should only be finger-tightened before the heads are tightened, to prevent a bias btn the two faces. Sorry this doesn't help with the thread sizes, shouldn't need ''Tapping out' anyway'.
ajsph
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Re: Broken Stud...Grrrr

Post by ajsph »

The thread is 1/4 withworth
Poul
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Stuoyb
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Re: Broken Stud...Grrrr

Post by Stuoyb »

Sorry Poul, AMC used bsf into alloy, not whitworth.
Andy51
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Re: Broken Stud...Grrrr

Post by Andy51 »

Hi, don't know about G12s but 1/4 in stud on my alloy top yoke is 1/4 whitworth - 1/4 bsf is 26 tpi like bsc except thread angle is 55 degrees., and a bit fine for alloy. Does spares list help? They often give thread sizes on studs and bolts. Andy
ajsph
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Re: Broken Stud...Grrrr

Post by ajsph »

Have checked the threads in the cylinder heads I have and they are 1/4 withworth, and the studs have 1/4 withworth on one end and 1/4 cycle on the other end, I think AMC never used 1/4 bsf, as Andy says bsf and cycle both have 26 tpi but different angle,but when you buy new studs and bolts there should be 1/4 cycle, they are very often 1/4 bsf.
Poul
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Janet
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Re: Broken Stud...Grrrr

Post by Janet »

Andy51 wrote:Hi, don't know about G12s but 1/4 in stud on my alloy top yoke is 1/4 whitworth - 1/4 bsf is 26 tpi like bsc except thread angle is 55 degrees., and a bit fine for alloy.
Apparently so. It has been discussed on the forum in the past and I recall that most people thought it was a silly idea but, as Stuart said, AMC used it for alloy anyway.
Does spares list help? They often give thread sizes on studs and bolts. Andy
Most of the spares lists I've seen for AMC bikes don't give the sizes of nuts, bolts and studs. Perhaps The Club could compile a register of sizes in its spare time. (Sorry, Stuart :rofl: )
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Rob Harknett
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Re: Broken Stud...Grrrr

Post by Rob Harknett »

Janet wrote:
Andy51 wrote:Hi, don't know about G12s but 1/4 in stud on my alloy top yoke is 1/4 whitworth - 1/4 bsf is 26 tpi like bsc except thread angle is 55 degrees., and a bit fine for alloy.
Apparently so. It has been discussed on the forum in the past and I recall that most people thought it was a silly idea but, as Stuart said, AMC used it for alloy anyway.
Does spares list help? They often give thread sizes on studs and bolts. Andy
Most of the spares lists I've seen for AMC bikes don't give the sizes of nuts, bolts and studs. Perhaps The Club could compile a register of sizes in its spare time. (Sorry, Stuart :rofl: )
Re a Register.

I made an excel file about 3 years ago. The content mentioned at the end of this posting.
However there are books that give this information, so no need to make a register, AMC first did it in 1954. see below.

Actually there are more AMC parts list that do give dimensions, than those that do not. ( First 18 years of AMC had dimensions, post 1950 AMC, 17 years? did not. ) However, this only applies to parts up to approx. 1950 and parts still in use thereafter. Parts used from approx. 1950 onwards only, may not show a dimension. You should find dimensions in all pre AMC parts lists. In all cases dimensions & thread sizes will only be for fittings and few other parts like pistons and rings.

So for post circa 1950 dimensions you need to do a bit of detective work. It was at about this time AMC introduced a NEW part numbering system. The new part numbers omitted dimensions. The best single book to refer to, to discover dimensions is the April 1954 old/new part number conversion list. So check for the new post circa 1950 part number in this book. If its listed then the part was used pre 1950.

Owners of pre circa 1951 machines will also find this book handy to discover if their old pt. no. has a new part number. By using the new part number they may be surprised to find, the club has the part in stock. This applies to some parts that date back to the late 1920's. Four years ago I listed all parts the club had in stock at that time, that fitted bikes dating back to the late 1920's. I found there were over 300 parts stocked.
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AGoodfellow
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Re: Broken Stud...Grrrr

Post by AGoodfellow »

Guys,

Thanks for the info. the stud is 0.250" and 26TPI on the manifold side the head side looking at the picture on the spares page. I'm guessing its 20TPI which is whitworth form.
so i think i will go with that.

http://www.amoc-parts.com/store/comersu ... duct=20914

Away to machine up a short stud.

Thanks for the info

Andrew
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Rob Harknett
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Re: Broken Stud...Grrrr

Post by Rob Harknett »

Using my method above to discover dimensions will find stud 010635. 1 11/16" X 1/4" by 26 & 20 TPI. this being the twins short stud.
No need to guess Andrew.
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