Author Topic: 35mm fork (Read 31262 times)

kos · « **Reply #25 on:** November 11, 2009, 11:54:25 AM »

Better check that...I don't think any CB900F ever had 35's. Bring a vernier caliper with you, to double check fork OD.

KOS

IF you are roadracing....go with Yamaha RZ forks...they work well and can be revalved for dirt track or RR.

voxonda · « **Reply #26 on:** November 11, 2009, 12:15:25 PM »

The first CB900, the FZ from '79 had 35 mm tubes. Also the second, the FA had 35. From '81 with the FB the dia started to grow to 37 and later to 39 with the FD.

Rob

bwaller · « **Reply #27 on:** November 11, 2009, 04:04:39 PM »

Quote from: kos on November 11, 2009, 11:54:25 AM

Better check that...I don't think any CB900F ever had 35's. Bring a vernier caliper with you, to double check fork OD.

KOS

IF you are roadracing....go with Yamaha RZ forks...they work well and can be revalved for dirt track or RR.

Humm, just got excited for a second while I thought about that RZ catching dust in my sons garage, then back to reality, mid. prod. rules and that damn period thing. The RZ isn't period but otherwise would be a good choice.

kos · « **Reply #28 on:** November 11, 2009, 05:51:41 PM »

USA never had those models.

KOS

Retro Rocket · « **Reply #29 on:** November 11, 2009, 07:39:17 PM »

Quote from: kos on November 11, 2009, 05:51:41 PM

USA never had those models.

KOS

Didn't you get the first 3 models, i was led to believe that you did..

Mick

voxonda · « **Reply #30 on:** November 11, 2009, 11:03:32 PM »

Quote from: kos on November 11, 2009, 05:51:41 PM

USA never had those models.

KOS

Even got the aluminium lower T that came with it.

Rob

turboguzzi · « **Reply #31 on:** November 12, 2009, 12:52:16 AM »

Quote from: bwaller on November 11, 2009, 04:04:39 PM

Quote from: kos on November 11, 2009, 11:54:25 AM
Better check that...I don't think any CB900F ever had 35's. Bring a vernier caliper with you, to double check fork OD.

KOS

IF you are roadracing....go with Yamaha RZ forks...they work well and can be revalved for dirt track or RR.

Humm, just got excited for a second while I thought about that RZ catching dust in my sons garage, then back to reality, mid. prod. rules and that damn period thing. The RZ isn't period but otherwise would be a good choice.

other than the strange ribs in the bottom (could be removed....), the RZ's look pretty period to me and being 35mm they are OK with my rules (not that you'll find too many modern 35's anyway)

looking in detail the only strange thing is that they dont seem to have any real clamping for the axle and seem to depend on the axle nut pulling... Brent, can you look into that?

lordmoonpie · « **Reply #32 on:** November 12, 2009, 04:52:47 AM »

Quote from: Rod on November 08, 2009, 04:36:15 AM

or contact Maxtons in UK who do fork conversions on most Classics for racing
Rod

+1 on Rod's suggestion - Maxton take old classic forks and rework them using I think modified Yamaha R6 cartridge internals. It's a big job for them on the classic but the results are sensational...guess that's why so many top classic racers use them!

bwaller · « **Reply #33 on:** November 12, 2009, 05:23:11 AM »

First thing, I'm so locked in the past my ignorance my be showing here. When KOS mentioned 35mm & RZ I immediately thought RZ350. IF that isn't what he meant this post will self destruct.

This is a Canadian 1989 RZ350, 35mm forks, dual disc, unsure of axle size, but threaded end 12mm, 30" from axle center to top (clip-ons above triple)

Middleweight production rules will never allow these here TG, but if you can these might be a good option.

turboguzzi · « **Reply #34 on:** November 12, 2009, 07:11:19 AM »

Quote from: bwaller on November 12, 2009, 05:23:11 AM

First thing, I'm so locked in the past my ignorance my be showing here. When KOS mentioned 35mm & RZ I immediately thought RZ350. IF that isn't what he meant this post will self destruct.

This is a Canadian 1989 RZ350, 35mm forks, dual disc, unsure of axle size, but threaded end 12mm, 30" from axle center to top (clip-ons above triple)

Middleweight production rules will never allow these here TG, but if you can these might be a good option.

mmm.. Brent, you are going "production mid" with your crazy motor, CR 6-spd and this fork will not allowed?

how does the other side look like? how does it clamp on axle?

dont know which model Kos meant but this looks nice and quite period too.

TG

ColinMc · « **Reply #35 on:** November 12, 2009, 07:47:18 AM »

XS500 yamaha's had 35mm forks too I think...i'll double check when I get home. They had "optional" dual disc brakes, meaning the threaded bung is already on both fork lowers, and the front wheel has the holes for the discs on both sides too...

Not sure if they are "bushed" or not...sorry for my ignorance but how can you tell if they are?

ColinMc · « **Reply #36 on:** November 12, 2009, 07:55:34 AM »

"spring OD is 25.5mm, they are 19.75" long and a tight squeeze to compress in there and get the fork cap back on.The fork tube OD is 35mm"

That's the exact info I e-mailed to the place I buy springs from so he could make some then he informed me that's the same as the RZ350. That is for 75-78 Yamaha XS500. I wonder if the larger Yamaha XS bikes have the same size? XS750 and 850's since they are easier to find than XS500 forks.

bwaller · « **Reply #37 on:** November 12, 2009, 09:39:07 AM »

TG, Here the cut-off date for mid prod. is 76 with exception for models which remained unchanged (ie CB550 to 78). So the rules often state "must be of a style and type available during the period" meaning up to 76. Seems it's all about a time line. No restriction on gearbox, ignition and max. 5% overbore above class limit. The engine must be of period appearance, my little engine fits right in there!

Here is another couple pics. The axle passes through the legs, no clamps. I can get you an axle diametre if you need.

turboguzzi · « **Reply #38 on:** November 12, 2009, 10:41:16 AM »

Quote from: bwaller on November 12, 2009, 09:39:07 AM

TG, Here the cut-off date for mid prod. is 76 with exception for models which remained unchanged (ie CB550 to 78). So the rules often state "must be of a style and type available during the period" meaning up to 76. Seems it's all about a time line. No restriction on gearbox, ignition and max. 5% overbore above class limit. The engine must be of period appearance, my little engine fits right in there!

Here is another couple pics. The axle passes through the legs, no clamps. I can get you an axle diametre if you need.

not that I get how you tighten the axle nut without binding the fork tubes, but i guess it works somehow

will try to get one form the UK as shipping from the US would cost and arm and a leg and not many 350 yams here in italy

754 · « **Reply #39 on:** November 26, 2009, 09:49:30 AM »

I did some digging...
It appears the 750 fork from 1972 and earlier, does have double bushings on the fork tube. This means in theory that they could be made oversize, or built up by plating, however you would probably have to hone out some taper in the lower past of the leg. An obstacle here though would be that, there is the steel inner damper in the way..anyone know if it presses out?

I have an NOS lower leg here, early one like sandcast or KO uses. I mesured the bore if you need it for reference as the books only seem to list max wear limit at 1.561 or 1.562, stock inner size is 1.5566 .

So it appears you may be able to tighten these up. The lowr bushing is listed at min size of, 1.551 inch, meaning they are considered wore out at 10 thou clearance..

mystic_1 · « **Reply #40 on:** November 26, 2009, 10:16:57 AM »

Quote from: 754 on November 26, 2009, 09:49:30 AM

An obstacle here though would be that, there is the steel inner damper in the way..anyone know if it presses out?

Which part?

http://images.cmsnl.com/img/partslists/front-cushion-cb750k0-four-usa_bigma000037f08_0ccf.gif[/img]]

Note, this diagram doesn't show the damper rod, which really is just a guide in this fork design.

Been a bit since I had my forks apart but IIRC everything comes out of the lowers with the uppers upon disassembly.

mystic_1

754 · « **Reply #41 on:** November 26, 2009, 10:50:05 AM »

The NOS fork leg has a steel tube coming up the middle, up to almst the seal area, about an inch short of that..

mystic_1 · « **Reply #42 on:** November 26, 2009, 10:54:25 AM »

Should be an allen bolt recessed above the axle slot that drops that out, I think.

mystic_1

754 · « **Reply #43 on:** November 26, 2009, 10:56:40 AM »

I will look today.

mystic_1 · « **Reply #44 on:** November 26, 2009, 10:58:18 AM »

Similar to #8 in this K4 diagram?

mystic_1

turboguzzi · « **Reply #45 on:** November 26, 2009, 12:51:37 PM »

Quote from: 754 on November 26, 2009, 09:49:30 AM

I did some digging...
It appears the 750 fork from 1972 and earlier, does have double bushings on the fork tube. This means in theory that they could be made oversize, or built up by plating, however you would probably have to hone out some taper in the lower past of the leg. An obstacle here though would be that, there is the steel inner damper in the way..anyone know if it presses out?

I have an NOS lower leg here, early one like sandcast or KO uses. I mesured the bore if you need it for reference as the books only seem to list max wear limit at 1.561 or 1.562, stock inner size is 1.5566 .

So it appears you may be able to tighten these up. The lowr bushing is listed at min size of, 1.551 inch, meaning they are considered wore out at 10 thou clearance..

not sure i am following here....

I can see one top bush in that diagram, none at the bottom of the fork tube (needed to make it into a true "two bushing" fork)

then there's the question if that top busisng is low friction coated

and like mystic, not sure what you mean by the "steel damper" either

In any case, looks like finding a good condition, pre-72 750 fork here in italy would be quite difficult. I have located a Yam 350 fork in europe, am most likely going for that, looks a bit more refined and easier to service.

tnxs

Tg

mystic_1 · « **Reply #46 on:** November 26, 2009, 01:18:45 PM »

It's visible but not labeled in this diagram from a 1972 edition Clymer manual. You can also see the mounting bolt and the aluminum "foot" that's on the end of the damper rod. In this fork, the lower piston (#6 in the second pic) is both part of the damping system, and the guide for the lower portion of the fork pipe. #2 is the upper bushing, it lives just underneath the fork seal.

mystic_1

bwaller · « **Reply #47 on:** November 26, 2009, 01:30:07 PM »

Yes the upper bush has a shoulder that sits just under the seal. I have two NOS upper bushings if it helps Frank.

mystic_1 · « **Reply #48 on:** November 26, 2009, 01:30:25 PM »

Oh, and referring back to the first diagram I posted, you can see at the bottom of #5, the upper fork tube, how it's different from later forks. There is a ring of damping orifices there along with a couple of snap rings, the piston is allowed to move back and forth to cover or uncover these orifices as the fork moves, thus providing the rebound damping. Later forks provide damping with the inner rod itself, it has a series of holes that get progressively covered and uncovered by the upper fork tube itself that provides the damping action. Note also the lack of a rebound spring on the early design, the system is designed such that hydraulic action provides this action instead, if I understand the system properly.

Early forks must be used as a set, none of the parts interchange with the later design.

mystic_1

754 · « **Reply #49 on:** November 26, 2009, 07:56:16 PM »

Ok, I looked again.. yes it is held in with the bolt. looks like a part NEVER sold seperate.

Turboguzzi, with the damper rod out, if the fork were honed cylindrical (less wear at the bottom), you could fit oversaize bushings and tighten up the fork, to improve handling. I am talking a way to recondition the early forks for vintage racing or for street use. Just mentioning that it is possible.

bwaller, I probably will sell the fork leg, it is early style for KO or sandcast.

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Author Topic: 35mm fork (Read 31262 times)