Author Topic: RL250 forks - are they 35mm or 1.3/8inch ?  (Read 4902 times)

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Offline djr

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RL250 forks - are they 35mm or 1.3/8inch ?
« on: January 18, 2024, 05:51:49 AM »
Hello,
This is probably a silly question, but maybe not.
I have an RL250 Beamish with what I thought were 35mm stanchions that need replacing or refurbiing.

I also have some other 35mm forks from a few different Japanese & Spanish bikes and was hoping to be able to do some mixing of parts and use the leading axle RL sliders with some of the stanchions from one of these other fork sets.
It all looks feasible except for one problem - the RL fork stanchions measure 34.93mm, all the other stanchions measure between 35.00-35.10mm and won't fit into the sliders ( too small )

34.93mm = 1.3/8 inch ( if not exactly, at least closer to the imperial size than 35mm)

I have seen a pair of early TS250 forks advertised on eBay Germany as 1.3/8 dia

Is it possible they were actually made to an imperial size , or is it more likely to be another explanation ?

Offline PeterC

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Re: RL250 forks - are they 35mm or 1.3/8inch ?
« Reply #1 on: January 18, 2024, 04:19:18 PM »
Being Japanese and European the measurements should be true Metric. I wonder what tube size they started with, any machining and what thickness of hardchroming was used. Have you checked multiple tube location measurements?

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Offline pokey

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Re: RL250 forks - are they 35mm or 1.3/8inch ?
« Reply #2 on: January 18, 2024, 09:14:04 PM »
Supposed to be 35mm and I doubt any imperial was used on the RL. Possibly that thing they called tolerance or mass production. The actual size used on Suzuki forks is usually a tad under what is specified. My Suzuki's have NOS units and measure 29.96 and 29.97 for a 30mm specified. perhaps your other stanchions arnt suzuki.

Offline djr

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Re: RL250 forks - are they 35mm or 1.3/8inch ?
« Reply #3 on: January 19, 2024, 05:33:35 AM »
Thanks for the replies

I also 99% think they should be metric /35mm , BUT just wondered as I remembered one of my old Yamaha's that I had a parts book for , and there were a couple of imperial parts  -  small ball bearings I think ?
( And of course the wheels & tyres )

Over the years I have seen original metric /original imperial parts in  unexpected places

A new Japanese excavator with some BSP hydraulic fittings
Some Mikuni jets with imperial threads
Seat belt mounting bolts (imperial threads) on euro & Japanese cars
Whitworth bolts on a German tarmac roller
etc, etc, etc, etc,

And my favourite - a cheap set of Chinese drills that are marked in metric sizes, but when you measure them they are in imperial sizes !


Offline Dungar Pilot

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Re: RL250 forks - are they 35mm or 1.3/8inch ?
« Reply #4 on: January 19, 2024, 10:27:08 AM »
Hi Everyone,
Hello,
This is probably a silly question, but maybe not.
I have an RL250 Beamish with what I thought were 35mm stanchions that need replacing or refurbiing.
There are several RL 250s in my shed and I have not measured exactly but they are supposed to be 35mm. Yes I understand your question and I think it comes down to which Beamish you have? Is it Yellow as that is the later Beamish model and maybe 325cc?  When SUZUKI wouldn't listen to Gordon Farley,  they ended up with, shall we say less than perfect bike that did not sell well. The story goes that Beamish bought all of the remaining RL 250 and reworked them in the UK. They later models were more Beamish and less Suzuki so perhaps imperial stanchions were more readily available in England. The tripple clamps would work either way as they are close in size.

Hope this helps

Greg

Offline pokey

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Re: RL250 forks - are they 35mm or 1.3/8inch ?
« Reply #5 on: January 19, 2024, 10:42:16 PM »
I wonder what tube size they started with, any machining and what thickness of hardchroming was used.



Logic tells me they started with 35mm tube before grinding and "hoped" the chrome bought it pack to spec though an extra 5mins in the bath is worth millions after a month of production. Remember this was early/ mid 70s and Japanese marques were having a huge rush in production and parts common to many models likely received Nominal components that existed only on paper and not on the blueprints.

As for your issue perhaps throw the legs on a lathe and or install a bush or, if like me you dont have  the space for a lathe id try a few seconds with a hone as i figure thats what the factory would have done on the floor. Just ensure the the ring and seal stopper slide over  the new stanchions.

Offline djr

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Re: RL250 forks - are they 35mm or 1.3/8inch ?
« Reply #6 on: January 22, 2024, 01:34:42 AM »
Thanks for replies
Had a go at enlarging the sliders with a hone, but this was painfully slow,

plus an engineering friend didn't  recommend it as he thought that  abrasive grit from the hone may become embedded in the aluminium sliders and then wear out the stanchions ?  ( he thought it would be okay if the sliders were steel where the grit would wash off )

So, plan B , got hold of a floating reamer ( i think that's the right name ?)  set this up in my lathe with the sliders , and used this to enlarge them.
even this was a slow process and did not leave as nice a surface finish as the original suzuki machining,
but have now got some Betor 35mm stanchions that fit.
have done a trial assembly and they seem okay.

have not ridden the bike yet, but it looks like a happy ending
« Last Edit: January 22, 2024, 01:36:47 AM by djr »

Offline sleepy

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Re: RL250 forks - are they 35mm or 1.3/8inch ?
« Reply #7 on: January 22, 2024, 05:02:21 PM »
Honing is ok, example is Mower cylinders with Alloy bores. You just have to clean them properly. Boiling soapy water and a scrubbing brush just like cleaning a cylinder after re-boring. Also need a good hone with parallel stones not the crappy spring loaded things. I've done Maico forks PE Suzuki stanchions as they are meant to be 36mm but the Maico is just under and the Suzy was on size.

Offline LWC82PE

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Re: RL250 forks - are they 35mm or 1.3/8inch ?
« Reply #8 on: February 02, 2024, 11:38:41 PM »
They are metric '35mm' but they always measure a little under and not bang on 35.00. Ive got various NOS 36 and 38mm suzuki tubes and they measure slightly under when you measure with a micrometer.
Wanted - 1978 TS185 frame or frame&motor. Frame # TS1852-24007 up to TS1852-39022

Offline djr

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Re: RL250 forks - are they 35mm or 1.3/8inch ?
« Reply #9 on: February 03, 2024, 04:36:20 AM »
yeah, I agree with everyone that they must have been intended to be the metric 35.00mm, and the difference is just tolerances.
 It just intrigued me that they measured close to spot on 1.3/8 inch , and under 35mm.
Just thought it was worth asking , as i have seen imperial (and metric) turn up in some odd places.

thanks for all the comments