Author Topic: A65T Fork Slider Length  (Read 317 times)

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DODGE

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A65T Fork Slider Length
« on: 30 October, 2017, 12:39:53 »
Hi,
I'm just returning to British bikes via a 1970 A65T (Pre-OIF) project. Previously I've restored a Bantam and B31. I'm a new member of the BSAOC.
On rebuilding the forks, I cannot correctly align the front wheel. It appears that all components on both sides are identical except for the sliders and axle/spindle caps. The RHS (Brake plate) slider seems to be ~ 1/8 inch shorter (from top of slider to top of spindle groove) than the LHS, with end caps also showing ~ 1/8 inch difference.
- Have I got sliders from different models?
- Which one is correct?
- Can I just file down the spindle groove on the LHS slider?
Any advice would be appreciated.
Cheers
Andrew

JulianS

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Re: A65T Fork Slider Length
« Reply #1 on: 30 October, 2017, 13:05:41 »

DODGE

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Re: A65T Fork Slider Length
« Reply #2 on: 31 October, 2017, 15:14:01 »
Thanks Julian,
so it seems I have different model sliders. Any idea which one is correct, or what the correct part numbers should be?
Cheers
Andrew

Bess

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Re: A65T Fork Slider Length
« Reply #3 on: 31 October, 2017, 17:12:04 »
Hi,
    The correct sliders have counter bores along with the clamps at the bottom. Pt nos 97-3641 LH, 97-3645 rh. Julian's post has all the info on the BSA service sheet.

I have tried to buy new, not sure there are many out there, I only found one which was badly pitted inside. There is also a great mix up by sellers offering the wrong used items without the counter-bore.

Can you provide images of the bottom section of both?

Best wishes...
« Last Edit: 31 October, 2017, 17:15:44 by Bess »

DODGE

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Re: A65T Fork Slider Length
« Reply #4 on: 03 November, 2017, 09:19:44 »
Hi Bess,
here are the images. It seems both have the 'counter bores' if they are the small dimples behind the drain holes.
Rather than file a deeper axle groove in the longer leg, I might just shim the oil seal holder 1/8 inch to make the total length from spring seat to axle the same. What do you think?
Cheers
Andrew

JulianS

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Re: A65T Fork Slider Length
« Reply #5 on: 03 November, 2017, 10:14:28 »
Cannot see the flat side of the end caps but presume they are also marked with the counterbores? The fork bottoms certainly look like the description of A65 items.

Th earlier post with service bulletin 254 shows that the A65 forks are different to the other models in the range.

I have attached a page from Pitmans "The Second Book of the BSA Twins" and a snip from the 1969 A65 owners maintenence handbook, they both mention the difference in the end caps and the need for proper assembly.

If your end caps are also as described it would appear that the lower part of your forks are as the designer intended.

Bess

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Re: A65T Fork Slider Length
« Reply #6 on: 03 November, 2017, 10:17:00 »
Hi,
     I'm not convinced they are an A65 sliders, possibly for a Triumph?  Seems a bit of a mismatch.

See the mudguard bracket on the attachment is not the same as yours and the lug which fits into the brake plate is longer on yours.

Best wishes...
« Last Edit: 03 November, 2017, 10:28:30 by Bess »

JulianS

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Re: A65T Fork Slider Length
« Reply #7 on: 03 November, 2017, 12:12:39 »
BSA were constantly changing part specification which must have been a nightmare for the big dealers who kept a large stock!

They revised the fork bottom and mudguard fixing arrangement in parts Service Bulletin G60 from December 1969. The previous arrangement was changed to use a captive nut. See first photo.

The parts book illustration was not changed for the A65 but you can see it in the B44 and A75 books. Second photo below is from the 1970 B44 book. You wiill see the different bracket and the captive nut marked 61. The key shows it as 97 3926.

I am happy that the part you have are A65, but the modified parts not illustrated in the A65 book.


Bess

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Re: A65T Fork Slider Length
« Reply #8 on: 03 November, 2017, 20:05:17 »

Cool, just goes to show you never stop learning, another fact my library.

Thanks Julian.....

Charles R

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Re: A65T Fork Slider Length
« Reply #9 on: 03 November, 2017, 21:58:33 »
Dodge

I've got a 1970 BSA A65L (pre oil-in-frame) that has a similar problem:

The right fork outer member (Pt No. 97-3934) is 268mm long (10.54") - this is the one with the brake lug.
The left fork outer member (Pt No. 97-3933) is 272mm long (10.71"), ie 4mm longer.
(Dimensions measured with a steel rule and don't include the end caps.)

The part numbers come from the BSA parts list (00-5707 Aug 1969) but I have no way of telling if that's what I've actually got!

The 4mm difference would try to put the wheel spindle out of alignment.  In practice it would be pulled into alignment when the fork end caps are bolted on.  This would then put slightly different compressions on the fork springs.  This just doesn't sound right.  Id like to know if the discrepancy is acceptable or whether I have a problem (incorrect part from a previous repair?).

Before I dismantled the forks I hadn't noticed anything untoward, though I got the bike as a semi basket case so never saw it in a running state and it could have had all sorts of hidden issues.

The photos shows the offending items, though I could have done a better job on the photos to show more detail!

Is it a coincidence that these outer members have a remarkably similar difference to yours?

Is it anything to do with compensating for the brake forces being taken up by only one of the outer members?

Cheers, Charles
« Last Edit: 03 November, 2017, 22:07:11 by Charles R »

Bess

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Re: A65T Fork Slider Length
« Reply #10 on: 05 November, 2017, 16:47:20 »
Hi,
    Just looked at my bikes, I have the 1969 sliders  97-3641 and 97-3645.

The image shows a set without the counter bore (not for 650 twins), everything about them is the same as the counter-bore type except for the spindle clamp dimension.

The clamp material is solid not hollow and is 5/8" long, the counter bore sliders clamp material is 3/4" long.

The counter-bore and the ones shown are 10 1/2" long.

Best wishes...

DODGE

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Re: A65T Fork Slider Length
« Reply #11 on: 06 November, 2017, 10:26:16 »
Wow - thanks for all of the information.
I checked on the weekend and my spindle caps also have the counterbore - so it seems that everything is correct. The bike is original in every other way and shows less than 10k miles so I can't imagine why one of the slider legs would have been changed.
The different leg lengths might also explain why the manual says to tighten the thicker RHS cap first. This leads to the question - why? Maybe it does have something to do with the brake forces as suggested by Charles - who knows. Unfortunately after nearly 50 years, tightening the caps (even with some preload (my wife) on the forks), does not fully align the spindle by compressing the longer LHS leg, but rather cock's the wheel off centre - the reason I first started this investigation. The only way I can get the wheel vertical is to shim the bottom of the RHS fork leg a few mm, hence my original thought of simply filing down the longer LHS leg.
I've now played around with the various seals and spacers and think that I can 'extend' the operating length of the RHS leg by placing an additional washer above and below the oil seal. I might even skim a mm off the LHS upper bush flange too. Less drastic and permanent than attacking the leg itself. I have some parts on order and will let you know how it goes.
If anyone can see an obvious flaw in my logic, please let me know.
Cheers
Andrew

Charles R

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Re: A65T Fork Slider Length
« Reply #12 on: 07 November, 2017, 12:24:44 »
Dodge

Before I dismantled the forks I didn't notice any wheel misalignment.  My A65L had done 18,000 miles, but I have no history as to why it was off the road for a number of years before I got it (who knows, it could have been pranged) and reassembled with whatever was to hand.

Unfortunately the dismantling process involved destroying the stanchions as they were so badly corroded!  This means I don't have the stanchions to quickly reassemble the forks to check whether the wheel spindle really does clamp up properly (at right angles to the forks).

Please forgive me asking the obvious, but have you checked the spindle is true?  Is there distortion or looseness in the clamps?  Are the clamping nuts really pulling down fully onto the clamps?  Could a very thin metal shim be placed around the spindle ends to create a better clamp?  The thought of modifying other parts would worry me.

It looks as if a job I've scheduled for later may need to be brought forward - I'm going to have to buy a pair of stanchions and do a "dry" assembly to see what happens to my front end!

Cheers, Charles

Bess

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Re: A65T Fork Slider Length
« Reply #13 on: 17 November, 2017, 18:56:27 »
Hi,
    To put your mind at rest the spindle hole in the sliders is not bored at 90 degrees. See attached images, the angle I have been told is 89 degrees (thank-you, John Phelan).

I was going to buy a set with a shallow counter-bore but was told the normal fork sliders were also used on some "A" group twins before the change (97-3641 & 97-3645, 1969 and before shown in the attached images and 97-3933 & 97-3934, 1969 and after, shown in your images). So I won't be changing mine, saving some cash for other projects.

This angle will bring the sliders inline when the wheel is fitted. No need to add shims or alter the arrangement, it is as BSA intended. It also tilts the fork slider brake lug into the brake plate.

The poor chap in the photos actually machind his sliders to 90 degrees and fitted caps of equal length.

Best wishes...