Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Bevel orientation: '69 T120R clutch thrust washer

I ordered a 57-3931 clutch center thrust washer for my '69 T120R. The 57-3931 is the 1970 upgraded part with steel on one side and copper/bronze on the other side.

The part I received looks more like 57-1735: the part listed for my '69 which is solid copper/bronze.

Ok, so I will go ahead and use the part I received, but unlike the two old 57-1735's and one old 57-3931 I'm looking at, the new part has a bevel on one side of the inside diameter.

Does anyone know which side the bevel should face? Or if it matters a whit?

Hi Hermit, I just ran into that when I replaced my thrust washer recently.

My dealer says he has trouble sourcing the steel backed washer & all he sells is the solid bronze. This really sucks as the chamfer is too large for best fit. Too bad they didn't replicate the original exactly.

I'm not saying if I'm right or wrong, just what I did & why.

So, normally a chamfer would go against the sharp corner of the small hub.... You can see that on the original washer.

However with new washer the chamfer is so wide I felt it didn't allow the washer to center well on the hub so I faced chamfer towards clutch basket.

Close examine showed the washer would seat good onto hub & center well with the square side against hub. There was a slight chamfer on the square side which allowed a good fit.

So I put the square side against hub. It has worked good for 600 miles so far.

I don't know if the solid will last better or not. I found the originals did not last well long term. This was a quick wearing item. In my experience the steel side would wear more than the bronze side.
Don

Hi Don - I read you post and then went over to the bike shed and re-examined the parts I have.

I'm thinking that when you say original you mean the bi-metal part for your '73 750 that was introduced after the solid bronze part that came stock on my 1969 650. In which case I agree, the bi-metal part showed more wear than either of the solid bronze parts that were previously installed in my bike. And like you said, it was the steel side, which runs up against the clutch hub, that showed the most wear - mine had multiple grooves worn into it.

So now I'm thinking maybe it's a good thing, going back to the solid bronze part. I'm taking notes now and it should be interesting to see how things look the next time I tear it down.

As to the orientation, I looked everwhere for that except right under my own nose - the "answer" was right in my own parts database:

57-1735 / T1735
Washer, thrust
Thickness .052/.054 in.
Ref# 3 Fig. 10 Page 31 #7 (Qty:1)
Clutch center
Orient: 57-3931 copper to clutch basket / 57-1735 bevel to hub

So the bevel does normally go to the hub. However, I think I'm going to follow suit and put the square side to the hub as you did, because a) neither of the first two thrust washers that were in my machine had any sort of bevel on them, b) there's nothing about the hub that will impinge upon the square edge, c) the shoulder on the hub is very slight and the chamfer may, as you say, fail to always center on the hub - especially after it's worn down some.

So even though I might have thought that I had the answer, I'm glad I posted the question. Thanks Don.

The original design was to have the "copper" face against the chainwheel, the steel face against the hub flange.

I doubt that it is catastrophic to get it wrong.

One thing I noticed when using a new hub, was how poorly finished the holes in the flange were.

The internal diameter of the washer runs on those holes. I think it is worth smoothing the edges of the holes so they don't act as a lathe.

Once that starts happening, the eccentricity develops rapidly.

I'm going to have a closer look (and feel) of the holes in the clutch hub flange - if they're rough that would explain all the gouging on the steel side of my last 57-3931 thrust washer.

Also did a little more research and it turns out that Triumph tried quite a few variations on these parts. They are available in solid bronze, copper-coated steel, and bi-metal steel on one side and copper/bronze on the other. Like the original washer in my -69 650, early types had tabs to keep them centered.

If anyone's interested there's a pretty good discussion of these thrust washers here:
http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=112550&page=2

In that discussion Mr. Healy suggests that the copper-coated steel washers may be the best, while the bronze parts may have the shortest life. I'm going to put a micrometer on all my old ones and I may end up using one of the copper-coated steel ones instead of the new bronze part if one of them is still in spec for thickness.

Let's clear up a few things.

Triumph never used anything other than the bi-metal washer. It came in two iterations: a. The first 57-1735 which had a smaller inside diameter and two tabs that engaged holes in the hub. b. The second 57-3931 had a larger inside diameter and no tabs.

This led to the two iterations of the hub: a. 57-1734 with two holes for the tabs and machined to fit the smaller i.d. 57-1735 washer. b. the last iteration of the hub 57-3929 with no holes for the tabs and a larger machined area for the washer.

At first people thought that they could use the later 59-3931 washer on the earlier hub, but this didn't work out. In a reasonably short time the hub would wear the i.d. of the washer to an oval. Often it would wear it to the point where the i.d. would wear to the point it would create a gap in the washer.

We get a lot of complaints about the bronze replacement washers that do the same thing. They would wear oval to the point the i.d. would break through the outer edge. This was also a complaint about the earlier washer where the tabs would break off and the i.d. become oval and fail. This is why the change was made in the first place.

If the bike is going to be used it is my opinion that the earlier hub should be replaced with the newer one and the latest bi-metal washer installed (57-3931 washer and 57-3929 hub)

I believe you ride a 1973. The 1973 used a 57-3931 even though the parts book lists it as a 59-3921. The 57-3931 is readily available from multiple sources! This is an item that we have never been out of stock on!!!!!!

The only problems we see with the 57-3931 is when they are used with the earlier 57-1734 hub where they float around and are not held in place. In this case the i.d. will wear oval.

Hi John, Thanks for the info. Yes my bike is '73 Tiger 750. It indeed came with 57-3931. My hub has 4 holes in it from new.

Interesting about the solid bronze thrust washer. I felt uncomfortable with the way it fit as the large chamfer does indeed give less area to center on hub.

I was able to find a good used steel/bronze one when I was there buying new washer. I may take apart soon anyway for other issues with clutch.

Speaking of clutch my basket & cush hub was grooved. I filed them smooth. This widened slots. Installed new Hyde 7 plate. Steel plate tangs were still good & not very worn. Of course filing by hand cannot assure the slots are all same size or parallel. Top of slots on basket & inner edge of basket has very minor grooving.

Replaced cush rubbers at same time. I got rubbers from Rabers & they look & feel like rubbers I installed 9k miles ago. Those from Rabers also.

Adjusted spring nuts flush with dome.

Now clutch tends to be grabby on take off. Not awful, but not smooth like it was.

In your experience does filing slots cause this? Does the remaining grooving cause this?

I don't want to buy new hub & basket & not fix it...

Thanks!!
Don

Yes, thanks to Mr. Healy for those clarifications!

After reading that post I went over to the shop and took some photos. I have my bike's original clutch center (57-1734) as well as the updated part (57-3929) from MAPCycle. In each photo there are two thrust washers for both hubs - one new and one used. The two photos show the two sides of all the thrust washers.

The updated 57-3929 center has 11,000 miles on it. Both it and the 57-3931 bi-metal thrust washer show a good deal of wear.

The original 57-1734 center and original 57-1735 bi-metalic thrust washer have 65,000 miles on them. Note that the original thrust washer is the tab type.

Given how apparently prone the inside diameters of these thrust washers are to wear, I don't understand why they would be made with a bevel there. Undoubtedly there is some explanation beyond the ken of an amateur such as myself.

Anyway, looking at the relative wear of the original and updated parts, and since I have a brand new copper-plated 57-1735 thrust washer on hand, I think I'm going to revert to the original 57-1734 center if it is compatible with everything else.

My solid bronze thrust washer disintegrated and turned the oil into interesting extremely metallic liquid. Mine was the one with the tabs that are pressed out so may be weaker.

Dave

Hi Dave, I wonder if the poor track record of bronze thrust washers could have anything to do with primary chain case oils that are not yellow metal safe? Do you recall what lubricant you were using?

I'm guessing that copper is not affected by the same oil additives and formulations that 'eat' bronze, so as long as the thrust washers were copper/steel, the primary oil formulation wasn't so important aside from being light in weight and non-detergent. But once these parts were produced in bronze, choice of lubricant became an issue.

I'm not sure, but sulpher seems to play a part in this.

I use 30 weight api sf oil. I think only gear oils have the bronze eating additives? Anyway I think mine broke into two big chunks first at the points where the tabs are stamped out and then got minced by the chain. I put a steel backed one in and this has survived for a long time. I think I actually used the plain big diameter one because there was a big gap between the inner diameter and the step in the hub. I recommend people get the correct one. For next time I found a steel backed one with tabs.

Dave