Author Topic: Start-o-Matic baseplate - thread type?  (Read 398 times)

Matt J

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Start-o-Matic baseplate - thread type?
« on: July 15, 2019, 07:23:29 PM »
Hello Everybody
I bought an early '50s (I think) 6/1 a few months ago, which at some point used to be most of a S-O-M. All the generator bits are gone though now.
I've had it running but would quite like to make it do some work, probably some form of generator.

It is mounted on a cast iron base plate - there is a machined flat section and four holes where the alternator would have sat. Please could somebody tell me what thread size these holes are? They're not 1/2" BSW or 1/2"BSF.

Many thanks,
Matt

glort

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Re: Start-o-Matic baseplate - thread type?
« Reply #1 on: July 16, 2019, 01:27:42 AM »

I believe I have seen plates on the engines saying they used UNF threads. The other likely candidate would be Whitworth.

ajaffa1

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Re: Start-o-Matic baseplate - thread type?
« Reply #2 on: July 16, 2019, 09:09:31 AM »
Hi Matt J, up until the 1950`s the Brits had a whole lot of different thread patterns and sizes, they then moved over to the Unified system. There were two types of threads: Unified Coarse and Unified Fine, generally speaking if the thread is into cast iron it would be UNC. This is almost indistinguishable from the earlier Whitworth thread system except that one has a 60 degree thread angle while the other is 55 degrees.

Bob

38ac

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Re: Start-o-Matic baseplate - thread type?
« Reply #3 on: July 16, 2019, 11:31:27 AM »
 They are very likely 1/2 UNC. Most of the Lister equipment of that vintage that I have been around was marked if manufactured with  Unified threads. I don't believe that the CS engine was ever changed but that is only based upon what I have had my fingers in. The UNC and UNF thread patterns follow the SAE(coarse) and USS(fine)  patterns of the United States with tolerances being the only difference. They are interchangeable other than critical applications.  The 1/2 UNC at 13 TPI does differ from BSW at 12. 
Thread gauges are cheap. Id bet that a 1/2 USS capscrew will thread right in.
« Last Edit: July 16, 2019, 04:51:14 PM by 38ac »
Collector and horder of about anything diesel

glort

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Re: Start-o-Matic baseplate - thread type?
« Reply #4 on: July 16, 2019, 12:08:10 PM »

Thank your preferred Daiety for metric.
So much simpler and practical that the 173 flavours of Imperial.

Matt J

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Re: Start-o-Matic baseplate - thread type?
« Reply #5 on: July 17, 2019, 06:08:10 AM »
Thanks all,
Having now spent a bizarre amount of money on four 1/2" BSW bolts (didn't fit), then four 1/2" BSF studs (didn't fit) I will treat myself to a UNC thread gauge and try that.

Will let you know...

Thanks,
Matt

Hugh Conway

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Re: Start-o-Matic baseplate - thread type?
« Reply #6 on: July 17, 2019, 08:31:20 PM »
Just checked my 1954 start-o base.
The bolts and base threads are 1/2" 12 TPI.
Your mileage may vary
Cheers
Hugh
JKson 6/1  (Utterpower PMG ) Off-grid
Lister 6/1 Start-O-Matic engine......running with PMG
1978 Royal Enfield (glutton for punishment by Indian iron)
1963 BMW R-27 project

Matt J

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Re: Start-o-Matic baseplate - thread type?
« Reply #7 on: August 28, 2019, 08:02:28 PM »
Hello All
Just thought I'd update on this rather mundane topic I started!

Confirm that the threads are 1/2" BSW. I just wasn't trying hard enough to get them in through the accumulated gunk previously.

Thanks for your assistance.

Matt