Lucas Magneto Repair - 1/4 BSW LH thread required!

[puffernutter]

I'm fixing up a Stuart Turner P55 marine engine and it has been missing the magneto until now. I have just sourced a Lucas SR2, but it has a damaged cover (I'm hoping I can repair that) but the impulse body (that takes the drive from the engine) is held on with a key and a rh threaded nut. Through the centre of that nut, into the magneto drive shaft is a threaded hole which I think may be a 1/4 BSW but LH thread. Any suggestions of a source of a screw, or can I borrow a 1/4 BSW LH die from somebody (if there is such a thing!) and I'll have a go at making one!

I have tried all the usual sources, but I stand more chance of finding a unicorn!

Cheers

Peter

 

[brightspark]

tracy tools may have carbon steel ones

 

[Brad93]

will
check
tomorrow

 

[6ply]

I'm fixing up a Stuart Turner P55 marine engine and it has been missing the magneto until now. I have just sourced a Lucas SR2, but it has a damaged cover (I'm hoping I can repair that) but the impulse body (that takes the drive from the engine) is held on with a key and a rh threaded nut. Through the centre of that nut, into the magneto drive shaft is a threaded hole which I think may be a 1/4 BSW but LH thread. Any suggestions of a source of a screw, or can I borrow a 1/4 BSW LH die from somebody (if there is such a thing!) and I'll have a go at making one!

I have tried all the usual sources, but I stand more chance of finding a unicorn!

Cheers

Peter

Peter, Sure it's not 5/16 BSW/ BSF left hand? Only asking as I have taps.

 

[willie.macleod]

Would the P5 version be likely to have the same bit, I know of a complete unit about to go for scrap due to cracked block and could speak with owner to salvage bits if required.

 

[m_c]

Tracy tools have them listed - https://www.tracytools.com/product/1-4-x-20-tpi-bsw-l-h/

 

[Agroshield]

...I think may be a 1/4 BSW but LH thread.

Would it not be prudent, instead of just thinking it is 1/4 BSW LH, to confirm it is so?

Whittle a piece of dowel down to exactly 6.35mm diameter and insert it into the hole, turning in an anticlockwise manner as you do so.

Withdraw by turning clockwise and measure the distance between the oily grooves on the dowel. If ten grooves span 1/72 of a yard, your thinking is correct.

Edit:

RDG have the die a bit cheaper than Tracy.

If it is not critical, and does turn out to be 1/4-20 LH, look for a 1/4-20 LH UNC screw. It might fit well enough.

 

[puffernutter]

Give us a clue as to what you mean by “all the usual sources”.

I've had a look on line at all the suppliers of parts for old engines and searched for Lucas SR1 and SR2. SR2s are available, but at a price!

I have both the workshop manual and maintenance manual for the SR2, they have a parts list but finding this screw is difficult. I have approached a number of repairers, but they cannot help. I know that Tracey Tools have the taps and dies, but I would really like to be certain that it is a 1/4 BSW, all I am going on is that the internal thread is around 4.7 to 5.0mm and that could be BSF as well!

I intend to call Clerkenwell screws tomorrow as I know they have a huge selection.

I do have a lathe, but I'll need to check I have the right tooling for it to cut the thread.

Cheers

Peter

 

[puffernutter]

Would it not be prudent, instead of just thinking it is 1/4 BSW LH, to confirm it is so?

Whittle a piece of dowel down to exactly 6.35mm diameter and insert it into the hole, turning in an anticlockwise manner as you do so.

Withdraw by turning clockwise and measure the distance between the oily grooves on the dowel. If ten grooves span 1/72 of a yard, your thinking is correct.

Excellent idea, I hadn't thought of that - that's a job for the weekend!

Cheers

Peter

 

[frank horton]

Never known Tracy tools to send the wrong part....n I've had a few weird'ns...

 

[armalites]

Why not helicoil it to a more easily availble size?

 

[zeppelin builder]

I'm fixing up a Stuart Turner P55 marine engine and it has been missing the magneto until now. I have just sourced a Lucas SR2, but it has a damaged cover (I'm hoping I can repair that) but the impulse body (that takes the drive from the engine) is held on with a key and a rh threaded nut. Through the centre of that nut, into the magneto drive shaft is a threaded hole which I think may be a 1/4 BSW but LH thread.

its only there to stop the nut undoing
a splodge of loctite retainer on the thread will be ok
lots of armatures going about with the broken bit in them as they have undone the nut and broke the screw
its more like 1/8 diam

 

[puffernutter]

Never known Tracy tools to send the wrong part....n I've had a few weird'ns...

I haven't got that far yet! I don't want to order the wrong die and waste money. When I lived in Ivybridge, I'd visit their shop when they were in Dartmouth.

Peter

 

[zeppelin builder]

i think its 3ba lh
570 to head
660 total
head diam 310

thou that is

 

[puffernutter]

Wonderful,

Thank you

Peter

 

[Agroshield]

Maybe:

3 BA DIE - NO MAKERS NAME - LH - 13/16TH OD - ENGINEERING | eBay

Find many great new & used options and get the best deals for 3 BA DIE - NO MAKERS NAME - LH - 13/16TH OD - ENGINEERING at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

 

[mikegolding]

i think its 3ba lh
570 to head
660 total
head diam 310

thou that is

View attachment 429223 View attachment 429224 View attachment 429225

are you sure you don't mean 2BA or possibly 3/16" BSF

 

[zeppelin builder]

had a closer look under a magnifier
and its 32 tpi so 3/16 bsf
id go for

 

[zeppelin builder]

GRRRR