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Fork stem thread

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

Fork stem thread

Postby gp200ts1 » Sun May 22, 2022 9:48 pm

Can anyone please tell me what size and pitch the thread is on a series 3/gp lambretta fork stem?
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Re: Fork stem thread

Postby gaz_powell » Mon May 23, 2022 9:09 pm

M10x1.5 (x35mm long bolt) if memory serves me
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Re: Fork stem thread

Postby Warkton Tornado No.1 » Mon May 23, 2022 9:24 pm

If you mean the large thread - which seems likely - a commercially available bearing lock nut (SKF KM series) KM6 has the correct (identical) thread which is M30 x 1.5.

I have used them in the past with the matching lock-washers, but care must be taken in avoiding anything snagging on the castellated tags. For making a thread dressing tool, they would be ideal... ;)
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Re: Fork stem thread

Postby gp200ts1 » Mon May 23, 2022 10:11 pm

Warkton Tornado No.1 wrote:If you mean the large thread - which seems likely - a commercially available bearing lock nut (SKF KM series) KM6 has the correct (identical) thread which is M30 x 1.5.

I have used them in the past with the matching lock-washers, but care must be taken in avoiding anything snagging on the castellated tags. For making a thread dressing tool, they would be ideal... ;)

That’s great, thanks very much. Looking to fit taper bearings to the top race and looking at options for locking it in place. Already sussed out the locking washer but was unsure on the lock ring. Have measured everything else and just waiting on the steel to arrive before machining.
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Re: Fork stem thread

Postby gaz_powell » Mon May 23, 2022 10:41 pm

gaz_powell wrote:M10x1.5 (x35mm long bolt) if memory serves me


Opps thought you ment the clamp....
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Re: Fork stem thread

Postby AL BARKER » Wed May 25, 2022 9:32 am

Following the top tapered bearings use, been looking myself but can't find tapered bearing small enough.. assuming you will have to machine top cup to hold bearing and possibly a shim to fit between stem and race??
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Re: Fork stem thread

Postby gp200ts1 » Wed May 25, 2022 3:00 pm

AL BARKER wrote:Following the top tapered bearings use, been looking myself but can't find tapered bearing small enough.. assuming you will have to machine top cup to hold bearing and possibly a shim to fit between stem and race??

It’s done using drawings that Ian from Taffspeed gave me years ago. Only thing I had difficulty sourcing was the top bearing dust shield but that’s used on lots of Chinese bikes and scooters so a source has been found.
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Re: Fork stem thread

Postby hullygully » Wed May 25, 2022 6:08 pm

do you want them CADing up so that everyone else can make use of the drgs/sketches? 8-)
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