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Stickolip

Starter motor studs

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Hi,

 

I have a Lister sr2 and I need the three studs that hold the starter motor in place. Does anyone know what studs they are? Thanks. 

Edited by Stickolip

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59 minutes ago, Tony Brooks said:

Message @RLWP aka MES Midlands

Thanks very much. 

50 minutes ago, Tracy D'arth said:

Have you not got one as a sample?

TD'

Unfortunately I don’t, thanks though

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From distant memory.

 

I think the studs are 3/8" in diameter.

 

The vital thing is the thread in the engine back plate that I think is cast iron and in cast metal a course thread is often used. If its  a post WW2 engine my guess would be 3/8 UNC but I think up to 3/8 the BSW (Whitworth) and UNC threads are the same pitch so will fit in each others threaded holes.

 

The other end of the stud is normally where the nut goes is normally a fine thread so 3/8 UNF or 3/8 BSF but that does not matter so much because you can always get nuts to suit your stud.

 

See if you can get hold of a 3/8 UNC or BSW  bolt and try it in a stud hole

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6 minutes ago, Tony Brooks said:

 

 I think up to 3/8 the BSW (Whitworth) and UNC threads are the same pitch so will fit in each others threaded holes.

 

I'd be a bit wary of mismatching threads,  even those with the same pitch,  (Thread Per Inch or tpi).

There are subtle differences the most important is that Whitworth threads have a flank angle of 55 degrees while UNC and UNF threads are 60 degrees.

As said do try something with a good thread of a known type in the holes, the correct one should then reveaal itself.

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21 minutes ago, Tony Brooks said:

From distant memory.

 

I think the studs are 3/8" in diameter.

 

The vital thing is the thread in the engine back plate that I think is cast iron and in cast metal a course thread is often used. If its  a post WW2 engine my guess would be 3/8 UNC but I think up to 3/8 the BSW (Whitworth) and UNC threads are the same pitch so will fit in each others threaded holes.

 

The other end of the stud is normally where the nut goes is normally a fine thread so 3/8 UNF or 3/8 BSF but that does not matter so much because you can always get nuts to suit your stud.

 

See if you can get hold of a 3/8 UNC or BSW  bolt and try it in a stud hole

I concur with Tony.

Threads into castings are practically always coarse and the age would suggest UNC, 3/8" being the likely size. Measure the holes in the starter for size.  3/8" UNC and 3/8" Whit BSW are the same pitch threads but the thread form is slightly different, not a good idea to mix them. 

If you find another bolt in the engine casting that has a 9/16" across flats measurement, it will be 3/8" UNC possibly, try it in the thread where you want the starter.

Rather than studs you could buy just bolts, preferably machine screws because they are threaded up to the head, bolts have a plain shank. Ensure that they thread in deep enough, there is a considerable load on them when cranking.

TD'

 

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Looking at some SR2 starter motors the bolt holes appear to be outside the flywheel starter ring? The SR2 manual also mentions 7/16 unified threads are used on this engine.

 

https://www.ebay.co.uk/i/392815175778?chn=ps&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&itemid=392815175778&targetid=908661247816&device=c&mktype=pla&googleloc=9045364&poi=&campaignid=10199631013&mkgroupid=105678538687&rlsatarget=pla-908661247816&abcId=1145987&merchantid=7298464&gclid=EAIaIQobChMI6JqO0-i96gIVArDtCh1PzAMyEAQYAyABEgJB9fD_BwE

 

Our much larger HA2 has blind holes hence the shimming washers.

IMG_1836.jpg

Edited by OptedOut
Added info

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We can't argue with the manual as long as 7/16 refers specifically to the starter motor studs. I think the threads on those engine ranged from 3/16" up to about 1/2" depending upon the location.

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Thanks everyone for your input. It’s an engine I have been given by a local farmer. My friend has sent me a pic of his sr2 starter motor bolt.  

112609D0-A1AA-4C56-B2A5-6695EE901CBD.jpeg

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I don't think that is a proper stud, I think its a cut off length of studding. It also looks too course to be UNF.

 

Not sure how you can ascertain the diameter unless the friend measures his or tells us the spanner size that fits properly.

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24 minutes ago, Steve56 said:

The studs will be 3/8 UNC/UNF from memory 

That is three of us that have suggested those sizes.

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Hi guys, thanks for all the advice and help. The thread is indeed 3/8 unc, I will now get some shouldered studs made. 

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6 minutes ago, Stickolip said:

Hi guys, thanks for all the advice and help. The thread is indeed 3/8 unc, I will now get some shouldered studs made. 

Remember the nut end is usually UNF, but its up to you, Not sure if UNC nuts may not have greater tendency to work loose.

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13 minutes ago, Tony Brooks said:

Remember the nut end is usually UNF, but its up to you, Not sure if UNC nuts may not have greater tendency to work loose.

Never use UNC nuts, hard to find, will work loose.  Bad engineering to do that.

Studs need to be 3/8" UNC one end, UNF t'other. spring washers or self lock nuts too.

 

TD'

 

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1 minute ago, Tracy D'arth said:

Never use UNC nuts, hard to find, will work loose.  Bad engineering to do that.

Studs need to be 3/8" UNC one end, UNF t'other. spring washers or self lock nuts too.

 

TD'

 

Agreed.

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12 hours ago, Tracy D'arth said:

Never use UNC nuts, hard to find, will work loose.  Bad engineering to do that.

Studs need to be 3/8" UNC one end, UNF t'other. spring washers or self lock nuts too.

 

TD'

 

Never reuse a 'nyloc' locking nut - new every time.  If you do use them ensure that at least two full threads show above the fitted nut.

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3 hours ago, Grebe said:

Never reuse a 'nyloc' locking nut - new every time.  If you do use them ensure that at least two full threads show above the fitted nut.

Depends on if its been used again before and if the studs thread is clean and rust free,  If they meet stiff resistance when the tip of the stud starts to poke through the nylon bit of the nut then ok. If the studs thread is rusty it'll probably tear the nylon on a new nut.

Edited by bizzard

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