350 GTR clutch dilemma?

[Sye]

When I took the clutch basket out the banding around the top edge had broken in a number of places. I have ordered some 10mm x 1mm thick steel band that I intend to get welded up by someone with the skills to do it and then I got to thinking.

The original clutch basket didn't have this band welded around the edge. As I understand it, the band was added to stop the plates from fracturing? It is clear that this modification didn't work well and that the plates still break up. In addition it seems that the banding breaks too causing bits of metal to be deposited in the clutch basket.

I have a new set of remanufactured plates from Richard that should be better than the originals, so, do I leave it without the banding or do I get one added. It seems almost pointless if it doesn't work?

[BRT-GTR]

I seem to remember a Service Letter mentioning the addition of the metal strap around the clutch basket to "stop the basket spreading under svere load". Presumably that means trying to beat 750s away from the trafiic light stop.

I found the same with my 350 - a couple of the strap sections were missing, and the clutch worked OK for several years with no problems. On the basis that the strapping was put there for a reason, though, I didbraze in a couple of short sections to replace the missing bits when I had the motor down for rebuild.

Graham

Hi Sye ,       See above quote from Graham Weeks on a recent similar post.  Bridgestone got most things right, unfortunately, the clutch wasn't one of them as you are now aware. Missing banding is common but replace it, maybe try a 1.5mm X 10 or 12mm band for additional strength. GTRs were advertised and sold as very high performance bikes, inviting abuse by unsympathetic/young owners. In their day they were at the forefront of two stroke technology. Also,they didn't benefit from years of production development. Used sensibly the clutch will be fine.
  Brian.

[Colin]

Hi Sye,
I agree with everything Brian said there, it doesn't seem necessary to fit the banding however if you did choose to fit such a band I'm sure the metal banding used for packing cases tacked on with tig would do a more than ample job. I had slight notching on my basket and got rid of most of it with a little bit of filing, however this gives a little bit of slap on the plates and if I was a boy racer and continually dumped the clutch away from the lights it might just break the plates like you mentioned, but if your a sensible adult and I suspect you are then I see no reason to alter your clutch in any way.
Colin.

[Gerrit]

I'm not sure why the GTR clutch would need a reinforcing band. Assuming a redline of 8,000 rpm the clutch spins at no more than 2,585 rpm. The Kawasaki H1 with a redline of 8,500 spins the clutch at 3,531 rpm- yet the fingers of the drum spreading simply isn't an issue, and it doesn't have a reinforcing band. Even running at 9,000 rpm means the GTR clutch is doing no more than 2,907 rpm, well below the H1 clutch rpm. I don't have a GTR clutch drum yet, but without seeing one is forced to conclude that perhaps the fingers are too thin. 

[slawsonb]

Gerrit, I have several uninstalled clutch baskets, so will do some measuring tomorrow. If you can measure the H1 basket we can compare data.
...bert

[Gerrit]

Bert, I don't have an H1 or H2 clutch gear at home at the moment, but I do have a couple of sets of friction plates, plus a set of GTR plates which I recently purchased, so I can take some measurements.
The H1 and H2 friction plates have 12 tangs, GTR 10. OD of the H2 plates is 132.25 mm, so the ID of the drum wil be slightly larger. GTR plate OD is slightly larger, 137.00 mm so ID of drum will be slightly larger.
The OD of the H2 plates over the tangs is 143.8 mm, with the exception of one plate, which is 138.9 mm. This is because the H2 clutch has a steel reinforcing band and has to fit over this plate, the fingers of the clutch drum are thinned at the outer edges to enable this band to be fitted. It is retained by the tangs of the last friction plate plate to be installed (the 7th), the plate with the lower tangs is the 6th. The fingers of the drum are therefore approximately 3.3 mm at this point, but thicker  further inwards. I don't have a band which I can measure, but it is at most 4.8 mm wide, being the thickness of one friction and one steel plate (2.8 + 2 mm). The H2 clutch spins much faster than the H1 clutch (4,000 rpm at the 7,500 rpm redline) so KHI probably thought the reinforcement would be necessary. However, tuned H1s running at 10,000 rpm send the clutch to over 4,100 rpm without any sign of distress, though to be fair the H1 clutch plate pack is slightly thinner at 29.2 mm vs 31.8 mm for the H2 due to the H2's thicker steel plates, hence shorter fingers.
Later H1 and all H2 clutch drum fingers have a “V” cut out of their outer edges, probably in an effort to reduce inertia effects, but as far as I know this was never an issue on early H1s.

[Gerrit]

A possibility just occurred to me. I have not seen an original GTR friction plate, but if it has a fibre core then there's your answer to the problem of breaking plates. Early Kawasaki H2s, S1s and S2s (1971-73) had fibre-core friction plates and these broke/break regularly. Curiously, the early H1 friction plate has a steel core, as does the A7 plate. For the 1974-75 H2s Kawasaki switched to friction plates with an aluminium core, these were also used on the H1 in later years and were/are troublefree.
I purchased a 1973 S2-A engine last year; when I took it apart there were three broken fibre-cored plates in the clutch. I had a similar experience in 1985 when I bought a 1973 H2-A: six of the seven friction plates were broken. No wonder the clutch didn't work!

[BRT-GTR]

Hi All,
         Ok, we all know that the clutch plates break (if abused?).    If you look at the clutch Service Letters available on the forum and the net, BS and Rockford make no reference whatsoever to  plate breakage being an issue (obviously, not in their interest), Yet, in a very short space of time from production start,  they made at least three modifications to the clutch assembly. Let's look at the sequence :-

        Production started June 67.
        August 67 at Vin1022,  field modification 1 issued with a special outer plate, fitted at the back of the clutch. No reason given for mod.
        Also shown at Vin1022, Field modification 2, issued with redesigned Clutch hub and pressure plate. (Guess these took longer to produce and issue)
        August 67 at Vin2633,   Inner right crankcase cover(Clutch) and right carb cover redesigned to ''prevent right crankcase cover from touching the clutch housing''.
                                         Basically, clearance around the clutch was increased. This was maybe when they added the band to the drum.
        October 67 at Vin4022,  Another redesign of the clutch hub and the special outer plate. Reason -With 1500 machines delivered to ''completely satisfied customers'' dealers         identified ''occasional report of objectionable clutch noise''

 All these modifications were made within a span of 4-5 months, what problem were they really trying to solve? ..............You decide. Seems a lot of effort to quieten the clutch!! Surprisingly, the friction plates and the clutch drum were never changed, as far as I know.
 In answer to one of Gerrit's questions the GTR drum fingers are 3.2mm thick. Gerrit, I assume you calculated the max clutch rpm to compare the centrifugal force affecting the fingers on the machines you know about. It occurs to me there is another effect. The torque that the clutch is required to transmit is multiplied by the primary drive reduction. In the case of the GTR, the torque at the clutch is at least 3 times that produced at the crank. For engines with a similar max rpm and HP, the lower the primary drive reduction the lower the torque transmitted at the clutch, although the clutch will spin faster. This in turn can adversely  affect gears changes!! So it's all a matter of compromise. Hope this makes sense.
   Brian.

        

[slawsonb]

Brian, thanks for providing some dimensions here. I had promised Gerrit I would measure, but simply have not gotten around to it, my apologies. Are other measurements needed?
...bert

[srpackrat49]

Well   I was one to get to it..... Raceing..... There was one guy on a 650 Bonnivile that was not happy... Took 20 bucks off of him.....  but my bike was hot.....  In the winter of 67/68   my highshool shop teacher asked for my bikes motor   Y  ?  Well he told me the brigs in Rockford was going to teach motorcycles repair in shop class for 1968..... WE got the motor out and he took it to brigs for there schooling class.... They were so dam happy to have one to work on..... They did EVERYTHING they could to hop it up.... for FREE.... got the motor back and we put it back in the bike.... he said that i mite need expansion chambers ?? I went over to Rockford BS and asked around..... One guy asked me if that was my motor?? YUP.... they gave me the stuff i needed for FREE..... Now i,m a 18 year old kid with a hot bike..... And yes it would do the ton.... alot........ Then just like that... i got my draft notice in june of 68 @#$%$#@&*^%$# Went into the service and mom sold my bike... I allways think about hoo got it......

[Sye]

Just a quick update.

I found a local engineering firm with a spot welder where the MD has a collection of over 30 restored classic British bikes. One of the lads has done the job for me and what an excellent job it was for a tenner! To say I'm pleased is an understatement.

It's in the bath at the moment getting nickel plated. Picture tomorrow, then I can fit it all back and get nearer to the 1st start up (for me anyway).

Edit: Another question please. I am aware that the marks on the clutch basket and hub need to be matched to one another but do they need to be aligned to anything else such as the gear timing marks? Or is it just those two and the rest don't matter?

TIA

Oh, and here's the basket ready to go in.

[disc_valve]

Sye,

The only mark I can think of on the 350 clutch is the one on the periphery of the clutch centre, and it needs to line up with the small hole on the clutch pressure plate. If they are not matched up, the pressure plate will splines will not enter the clutch centre splines as you tighten the spring fitting bolts. Result, a clutch that looks fine when assembled but provides no drive.

I hope that answers your question - if I've missed something, let me  know.

Graham

[Sye]

Thanks for the advice, the clutch is back together and woorks fine. I'm now looking for the two lock washers that hold the clutch hub not and crank nut for bike number two. Part numbers are:

09047-104
09047-106

Where can I get these from please?

[Mike Anderson]

Have you tried Richard the site owner for these parts? He may have them.
Later Mike

[Gerrit]

Brian, I've looked at the drawings of the clutch in the service letters as well and I don't see the mods making much difference to clutch noise. Face it, a dry clutch will make more noise than a wet clutch; one only has to listen to, say, a Yamaha RD350 and a TZ350 clutch to hear the difference. And if the mods were attempts to cure breaking clutch friction plates I don't see them making any difference either. The proper solution to that problem would be a stronger core for the friction plates- steel, for instance, or high-grade aluminium.
If one wanted to reduce noise then the answer would be to have as few loose parts as possible, i.e. only the seven friction and six steel plates, and/or make the clutch/carb cover and the shrouding round the clutch on the primary drive cover thicker.

[BRT-GTR]

Gerrit,
         I have to agree with everything you say, the saga of the 350 clutch mods as put forward by BS via the service letters, does just not ring true or make real sense.
Over the winter I have read a lot about two stroke history and general engine development. I now believe  BS did exactly the same before designing the GTR engine. This together with the inherited knowledge brought in by their recruitment of designers, led to them incorporating many of the most advanced features then available in the 175/350 engines, E.G. Twin rotary valves, chromed cylinders, 3 transfer ports, 6 gears etc. They wanted machines that would flatten the Suzuki/Yamaha/Kawasaki competition on the US market and they did for a while up to 1967 when sales dropped off but that's a different story. I think this is what attracts us to them.

  One of those features was a dry clutch. There seem to be 3 issues, noisy, plate breakage and rubbing on the outer cases. Sales were dropping off during 67/68 (-30%) when the majority of 350s were built, so they went for easy, low cost fixes. Regarding noise, as you point out, they did get rid of the six loose, steel, clutch spring thimbles by redesigning the pressure plate to incorporate them. Also added a rubber grommet to seal breather slot in the outer cover.  
      I don't believe BS really new why the other two issues were occurring, so they added the steel band suspecting the fingers were spreading and catching the case and increased the case clearance. The clutch drum sits on the end of a 3'' overhang from the main case bearing of the input shaft, did it flex?, never broke though. It also relied heavily on the 40mm ring nut being tight for stability and they would come loose.
     They introduced at least two 'special outer plates' to try and reduce breakage but not always successful.
    Yes, stronger plates would have been an answer, maybe more tangs might have done the trick. How accurate was the plate tang/ drum finger manufacture ? If only a few of the tangs took up the drive, that would concentrate the loading. Who knows??

    For all their faults they are still wonderful examples of advanced 60s engineering, you don't need a shedfull of special equipment to work on them and they do look good.
   Brian the Brit.

[slawsonb]

When I first acquired my '67 build GTR in '74, the first thing my riding buddy asked me when we met up was, "Is something loose in there?" He had a Norton Atlas that shook parts off, but the GTR's clutch sound was a brand new experience.
...bert

[bert Lilley]

Gerrit, i have just now Modified a Yamaha clutch basket ti fit into the 350 Housing ( in fact they are very close in size) so i can now use Yamaha TD2 TD3 & TR3 factory Roadrace Dry clutch plates .
its not that the BS350 ones did not work but after a race i would find 1 or 2 cracked plates. So i'll see this year 2015 how it works for me but truly the Yamaha plates have stood the test of Roadracing time and time again.
Bert

[Colin]

Hi Bert,
That sounds very interesting how about posting some more details and if possible photos for the ones on here (me) that like to look at things.
Regards Colin.

[slawsonb]

I second the motion too see the modified basket. Sounds like a great play for clutch supply longeviety. While Richard and Ray have temporarily kept the wolf from the door. GTR clutches plates will return to rarity before we know it. I understand the goal was to make Bert's roadracer more reliable, but this may be a double bonus.
...bert