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What the fork? #688457
03/17/17 11:43 pm
03/17/17 11:43 pm
Joined: Dec 2014
Posts: 82
Perth, Western Australia
H
Howley Online content OP
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Howley  Online Content OP
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Perth, Western Australia
Hi guys,

As part of my '49 m21 rebuild, I've been refurbishing the forks. So for I've replaced:
- Stanchions
- bushings
- seals and holders
- springs (with srm progressive)
- oil

I've also honed the inside of the lowers so the bushings fit smoothly.

Despite all this they still don't operate smoothly. There seems to be heaps of stiction. Once I pump them they seem *OK*, but not great. I'm not expecting them to feel like sportsbike forks, but I thought they'd be a little better.

It's unclear to me how the top bushing is oiled, am I missing something there? I didn't pre-oil the bushings or anything.
I put (from memory) about 150ml of 15w fork oil in them.

Any tips or feedback on what to expect from these things?

Thanks,

Luke

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Re: What the fork? [Re: Howley] #688494
03/18/17 8:32 am
03/18/17 8:32 am
Joined: Aug 2001
Posts: 7,025
scotland
triton thrasher Online content
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Do you feel the stiction on the bench, or is it with the weight of a motorbike on the forks?


Amateur Loctite enthusiast.
Re: What the fork? [Re: Howley] #688496
03/18/17 10:16 am
03/18/17 10:16 am
Joined: Dec 2014
Posts: 82
Perth, Western Australia
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Howley Online content OP
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Howley  Online Content OP
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Perth, Western Australia
They feel OK 'on the bench' (mounted with no front wheel on). They feel significantly worse with the weight of the bike on them.

Re: What the fork? [Re: Howley] #688498
03/18/17 10:34 am
03/18/17 10:34 am
Joined: May 2004
Posts: 3,569
Sydney Australia
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BSA_WM20 Online content
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Sydney Australia
If they are goon on the bench and bad on the bike the first thought is a twisted upper or lower clamp.
Dod you check them for truth before assembly ?


Bike Beesa
Trevor
Re: What the fork? [Re: BSA_WM20] #688501
03/18/17 10:58 am
03/18/17 10:58 am
Joined: Dec 2014
Posts: 82
Perth, Western Australia
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Howley Online content OP
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Howley  Online Content OP
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Perth, Western Australia
The lower clamp is twisted a little. I have been attempting to straighten it, but it's bloody hard work!

Re: What the fork? [Re: Howley] #688609
03/19/17 8:16 am
03/19/17 8:16 am
Joined: Dec 2014
Posts: 82
Perth, Western Australia
H
Howley Online content OP
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Howley  Online Content OP
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Perth, Western Australia
How do the bushings get oiled? It seems like it'd be OK if the entire lower was filled with oil but 150ml is bugger all.

Re: What the fork? [Re: Howley] #688732
03/20/17 9:07 am
03/20/17 9:07 am
Joined: May 2004
Posts: 3,569
Sydney Australia
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Originally Posted by Howley
The lower clamp is twisted a little. I have been attempting to straighten it, but it's bloody hard work!


Clamp the steering stem tight then clamp around 6' of pipe in the leg hole.
Heat to a dull red and apply a lot of the WA beef to the pipe.
The clamp is forged so heating it will not make much of a difference to it strength wise but best avoiding bringing up to forging temps


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Trevor
Re: What the fork? [Re: Howley] #721896
01/13/18 8:54 am
01/13/18 8:54 am
Joined: Dec 2014
Posts: 82
Perth, Western Australia
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Howley Online content OP
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Howley  Online Content OP
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Perth, Western Australia
Well, I've finally had a chance to look at this again...
These forks are doing my head in. I assembled them all sans spring and they operate smoothly through the whole range. They were difficult to extend, but only because of the vacuum. They were also spot on for alignment.
After pumping them a bit it seemed the oil was well distributed around the insides and they felt good.
I out them back on the bike, pumped them a few times then bolted everything up while they were compressed. Alignment is ok, not great, and they operated better than ever but still not great. This was in the morning.
By the afternoon, they were dry, sticky and horrible again. I can barely compress them, and when I do I need to pull on the bars to extend them again. I'd like to pump them but I don't think I could.

What the fork am I missing here?

My only thought is that the fit of the bushes in the lowers is too tight, but if I adjust that theres no going back. Apart from that I don't know what these bloody things want from me.

Help!

Re: What the fork? [Re: Howley] #721901
01/13/18 10:34 am
01/13/18 10:34 am
Joined: Dec 2004
Posts: 9,051
Scotland
kommando Online content
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When you say they work on the bench without springs is the wheel and axle in place ?

Re: What the fork? [Re: Howley] #721907
01/13/18 11:35 am
01/13/18 11:35 am
Joined: May 2013
Posts: 4,664
Rotherham - S. Yorkshire
Allan Gill Online happy
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Remove the progressive springs and put the old ones back in. I just fitted a pair to my A65 and found them tighter wound than the originals and the set I had fitted previously. They only just went past the wider section of the stanchion. My forks are stiffer but do operate. On the A65 there is a big fibre washer and disk that sits against the top coil of the spring ( fibre washer against the bottom clamp) I assume it is to stop the spring digging away at the bottom yoke or act as a water seal maybe, but it could also allow the spring to twist/uncoil slightly when under compression to stop it binding (as a guess) I also greased my springs when I fitted them.


beerchug
Re: What the fork? [Re: Howley] #721957
01/14/18 12:02 am
01/14/18 12:02 am
Joined: Dec 2014
Posts: 82
Perth, Western Australia
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Howley Online content OP
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Howley  Online Content OP
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Perth, Western Australia
On the bench the axle is fitted, and the top triple is on enough to align the steerer tube.
When installed the springs were lightly greased. Unfortunately putting the stock springs in isn't an option. They are ruined, and they don't fit properly inside the seal holders. The srm springs are loose around the stanchions.

Re: What the fork? [Re: Howley] #721974
01/14/18 6:41 am
01/14/18 6:41 am
Joined: May 2009
Posts: 77
Australia
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MattL Offline
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Do the forks free up when you slacken off the lower yoke?

Re: What the fork? [Re: Howley] #721975
01/14/18 6:59 am
01/14/18 6:59 am
Joined: Dec 2014
Posts: 82
Perth, Western Australia
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Howley Online content OP
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Matt, no they don't really.
They feel like they're dry, how the heck do the bushes get oiled? Could the oil drain out of the top bush?

Re: What the fork? [Re: Howley] #722009
01/14/18 3:56 pm
01/14/18 3:56 pm
Joined: Aug 2015
Posts: 1,009
Bolton Lancs UK
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Andy Higham Offline
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Bolton Lancs UK
It sounds like something is out of alignment.
Are the correct spacers in the front wheel?
Are the yokes straight?
Are the yokes both off the same model?


1955 BSA B31 400cc "Stargazer"
1962 Greeves 200cc "Blue Meanie"
1962/67 Greeves 350cc
1967 Greeves 360cc Challenger
1984 Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc grasstrack
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Re: What the fork? [Re: Howley] #722077
Yesterday at 01:10 AM
Yesterday at 01:10 AM
Joined: Dec 2014
Posts: 82
Perth, Western Australia
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Howley Online content OP
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Perth, Western Australia
Andy, yes to all. If I clamp the stanchions in the bottom triple alone, the alignment is good. I worked on the alignment at the triples yesterday and got it spot on too. Maybe I'll crack the axle bolt again and let that align a bit better...

Does anyone else have issues with the bushings feeling a bit dry after a break? Do they need time to oil up?

Re: What the fork? [Re: Howley] #722147
Yesterday at 06:34 PM
Yesterday at 06:34 PM
Joined: Aug 2001
Posts: 3,506
argyll. scotland, uk
gavin eisler Online content
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A good test for truth, fit fork legs no springs into bottom yoke, fit front wheel. offer up top yoke, if the fork legs enter the tapers and the centre nut fits easily then the yokes are straight. if not probably the bottom yoke is bent.
Fit top yoke and tighten fork cap nuts, now test stroke full travel, if there is binding and the stanchions / yokes are true then you have a problem with the slider bushes, steel sliders can be bent or bruised preventing clean travel.
Fork bushes have pretty generous clearances even new if they are correct, you should get easy full length movement even dry..

Bottom yokes will straighten cold using an old stanchion as a lever, they are quite malleable and act as soft links for the front end in a shunt. Yokes and tubes bend easier than wheel rims, DAMHIK.

yokes = triple trees for you colonial types.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: What the fork? [Re: Howley] #722161
Yesterday at 08:35 PM
Yesterday at 08:35 PM
Joined: Feb 2014
Posts: 382
Cork Ireland
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chaterlea25 Online content
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Hi Howley,
Are the new stanchions you fitted the later type with two oil holes drilled near the bottom?
If so I believe they need more oil, 1/3pint (I think)

Some BSA stanchions that were supplied to me were CRAP!!!!!
The sliding part was not Concentric with the parallel part that the bottom yoke (tree) clamps to
This fault will cause problems like yours

John

Re: What the fork? [Re: Howley] #722221
10 hours ago
10 hours ago
Joined: Dec 2014
Posts: 82
Perth, Western Australia
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Howley Online content OP
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Perth, Western Australia
John, to be honest I can't remember if they have one hole or two. My old ones had two, and had smooth transitions between the diameters. These ones have a step at the lower triple clamp area. They are NOS bsa items so I'm assuming they are ok.. I've got 1/3 pint in each.

The more I feel these things the more I think I need to hone out the lowers more. The lowers were dented meaning the forks would jam up at the dents. In addition the new bottom bushings were oversized and were extremely tight in the lowers, so honed the lowers to fit better. I went to a completely arbitrary diameter based entirely on feel, so it seems entirely possible they are still too tight.

That brings me to my next question. I would hate to go too far with the honing. How loose is too loose between the lowers and the bottom bushing? Is it a thou' between too tight and too loose or do I have 10 thou' to play with?
My problem is that I've never felt what these are supposed to be like so...

Any insight appreciated.

Re: What the fork? [Re: Howley] #722224
8 hours ago
8 hours ago
Joined: Aug 2001
Posts: 3,506
argyll. scotland, uk
gavin eisler Online content
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argyll. scotland, uk
About 3 thou min clearance for the slider top bush, might be better to remove them and machine a thou or so off the OD of the bush if they were very tight to fit, re dents in sliders, thats your problem, better to massage the dents out as far as you can, honing dents will thin the tube out. The bushes need generous clearances because the fork do not remain dead straight in action.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: What the fork? [Re: Howley] #722225
8 hours ago
8 hours ago
Joined: Dec 2014
Posts: 82
Perth, Western Australia
H
Howley Online content OP
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Howley  Online Content OP
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Thanks Gavin. From memory the clearance in the top bush is ok. I think machining the od of the bushings is a good idea. I'm pretty confident my small clearances are causing problems.

What would you say is the upper limit?

Re: What the fork? [Re: Howley] #722282
19 minutes ago
19 minutes ago
Joined: Aug 2001
Posts: 3,506
argyll. scotland, uk
gavin eisler Online content
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argyll. scotland, uk
Just to be clear I mean the OD of the top bush, for clearances, pulling numbers out of thin air ( looked in the manuals , NADA), i would be happy with 3 thou min , 5 thou max for Bush ID to stanchion OD. If you have dented sliders they will be pinching the bottom stanchion bush, you may be able to drive the dents back out with a suitably sized mandrel ( ie sized at the bottom stanchion bush OD, with the top bush removed for access)), put a lead in taper to the business end of the mandrel and heat the fork slider to red as the mandrel is driven into the dent area ( you will need to repaint after), If the mandrel is drilled through or tapped for some threaded rod it should extract OK. There may be better less brutal methods , but this would help. You need some method of mandrel extraction, it may knock back out from the lower centre hole if it has one( not sure about early forks , later certainly have this.) Alternatively some sort of pipe expander tool may be useful if you can get in place and operate it.
if you have access to a lathe the mandrel should be easy to knock up.
Ive seen dents taken out of exhaust pipes by welding a screwed rod to the centre of the dent then heat and slide hammer till dent be gone, cut off and grind to finish.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod

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