Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Forkin' Around with 68 & 69 Differences

I posted a question earlier about the transition to a wider fork that occurred mid-model year 1968 to the T120s. I got lots a good suggestions and help. Thanks!

But, I thought it would be worthwhile to dive into this issue and document it. So, below is a link to a Google Drive PDF that is a short reference document I created to understand the changes that occurred when the fork stanchions where widened in 1968 and then how to figure out which axle is which. Feel free to distribute this to anyone who would benefit.

https://drive.google.com/file/d/1WvIZ6UUlqvO7IE7-Z-fNMHI6ngeonGL4/view?usp=sharing

thats excellent.

you illustrate the 68 and 69 lower yokes with castng numbers 97-2278 and 97-2288, respectively.

ive got two that appear to be numbered 97-2289. where do they fit in? i was told they are 69/70.

triumph lower yoke https://imgur.com/gallery/N9s5UHs

Excellent information and super cool .pdf write up.

However, those changes, although occurring in 1968, were for the 1969 model year. That is important as it gives the impression that it affected the 1968 model year bikes.

I can see how what I said in my post would be potentially misleading. The change that is certain in 1968 was to migrate the fork lowers to unified threads after DU68363. However, my bike is a DU718XX and it has both the Mark II cases and the 69 spec'd fork. Now the fork could have been changed at some point, so this is not proof that the factory made a rolling change to the 69 forks.

I think the important thing with a 68 is to determine whether it has British or unified threaded lowers. Then if the center-to-center distance happens to be the wider 6-3/4" then to ensure the proper lower sliders and axle are used.

I appreciate you making this point. My writeup is not intended to break new ground and it does not say that the 68 T120s had 69 forks. I should have been more careful in my post.

So, this is another vexing problem. Casting numbers are not always part numbers. There are situations where they changed the part number, but not the casting number (cams come to mind). According to a good source, a casting number of 97-2289 is part number H2288 (97-2288). 97-2288 was the triple tree for a 1969 T120. The triple tree for a 1970 T120 changed to 97-3659. This makes sense as the axle from 1969 to 1970 model years changed as well.

ah

thanks for that

Hey, Kevin--
I went back and compared UK/General Export and US Catalogues and found that your H2288 is good for US models in 1969 and 1970. Here is a JPG of the chart I made to try to figure out what triple tree went where.
Mike

what exactly is going on with H3659?


what makez it different?

Hi, Kevin--
That question was fortunately answered on this Forum back on 12/30/2011 (otherwise I wouldn't know) when @Bruce Martin explained that H3659 had more casting at the fork stop abutment to keep TR6R and T120 (UK) larger tanks from being hit. That makes sense. So, why run two different parts? Seems possible it had to do with the crate of H2288s they ordered and needed to use. Just a guess there. It's these little things that are gotchas. I'm going to update my sheet to reflect this info. Thanks for asking the question!

I've updated my Pdf to reflect the different triple tree numbers.

https://drive.google.com/file/d/1WvIZ6UUlqvO7IE7-Z-fNMHI6ngeonGL4/view?usp=sharing

I updated my document to include an explanation for why the fork lower members (sliders) part numbers were superseded in 1970.

https://drive.google.com/file/d/1WvIZ6UUlqvO7IE7-Z-fNMHI6ngeonGL4/view?usp=sharing

I have updated my document (once again) to outline which triple tree is used with which tank. The fork stop abutment is different. The link to the revised document on my Google Drive is:

https://drive.google.com/file/d/1WvIZ6UUlqvO7IE7-Z-fNMHI6ngeonGL4/view?usp=sharing

Thank you for this very useful information.

I never understood why my front forks could contact the fuel tank on my 1968 general export T120 with large tank. I'll check triple tree numbers and seek out the correct one to prevent this. The original forks had been replaced by the time I got the bike in the early '90s.

Cheers
Ray

Great to hear that the document helped!

If your front end was replaced and the wrong triple tree used, it might also make sense to check your center to center fork tube measurement to know whether you have the narrow or wide configuration (68 or 69). Also, check to determine which lowers they used. You don't want to run 68 lower legs with a wider 69 triple tree because the brake plate abutment would be too short and potentially dangerous. This was so subtle a change back then, if someone didn't understand the tank stop differences, then they might not have known (or cared) about the change in width from 68 to 69.

As is seen in Mike's photos, the only difference in the bottom yokes is the "stops" are machined off the ones used on TR6C and Bonnevilles with the narrow "slimline" 2-1/2 gallon tanks.

There is another solution for those with the big "Home Market U.K." 4-gallon tank, to have two special longer nuts machined and threaded to secure
the fork stanchion pinch bolts. These would contact the frame to limit the swing of the forks and thus would prevent fork contact with the fuel tank.

I have seen this done once: It was on a bike with the TR6R 3-1/2 gallon tank whose owner was having the same problem.

well, here's an application.

i have a 65 TR6 frame with some forks on it:



these forks use the 97-2289 casting, which we have decided earlier here is the 2288 part number, for 1969-1970. and when i measure the forks, they are indeed the wide ones, 6-3/4 inches center to center, not 6-1/2 inches:



i have two TLS wheels. here is one installed in these forks:




the nubbin on the fork leg does not fully fill the notch in the brake plate. but i don't know whether the wheel is 1968 or 1969-1970, because i have nothing to compare it with. the engagement of the nubbin with the brake plate is greater than 1/8-inch, but does not appear as large as 1/4-inch. hard to measure because i can't get anything back in there.

the axles appear to fit the forks just fine, and lead me to believe that this is the correct wheel for these forks:

right fork leg:



left fork leg:



when i unscrew the fork cap bolts, i can see that the bolts are correctly centered in the groove in the axle:

left side:



right side:



since the 1969-1970 axles are not interchangeable with 1968, i am concluding that i have a 1969-1970 wheel and axle installed in a 1969-1970 set of forks, and that the nubbin to brake plate engagement that i see is correct. alternatively, i have 1968 fork legs installed with 1969-1970 triple trees and wheel. this set of forks was built from loose parts, so that is very possible, and if so, i am in the market for fork legs..

can anybody with a 1969-1970 TLS brake compare what i have photographed with their own so i can know for sure?

Hi, Kevin--
What you have determined is that you have the 1969 triple tree (wide 6-3/4"). (Restating your fact.)

The next question is which fork lowers do you have. There are only two choices from your pictures. Either 68 or 69. The 70 brake plate abutment on the right lower leg is quite different.

I think the easiest way to determine whether you have 68 or 69 lower legs is to figure out whether your axle cap bolts are BSC (1968) or UNF (1969). If they are BSC then you have the wrong lowers for the triple tree and your brake plate abutment would be a bit too short. The brake plate abutment has a tube center to edge measurement, but that is pretty impossible to measure with the wheel on the bike. So, I think the threads of you legs will answer your question.

A picture from another bike is probably not the best as angle of the camera and lens focal length will play trick on the gap, probably.

The good new is that it looks like you have the right axle for the 69 triple tree. If you pull the caps, you should be able to measure the points that are in my PDF and determine which year the axle is. I suspect it is the 69.

Not such a direct way of answering your question but if you think that the TLS brake was wedded to the forks at the factory then there is a difference between the 68 and 69 TLS brake plates.
On the 68 the cable came into the brake plate on a long sweep and was about horizontal as it fixed to the brake.
On the 69 the cable came down parallel to the fork leg.
HTH

I believe from Kevin's pictures that he has a 69/70 brake plate. I see in a couple of the pictures that the cable attaches to the brake plate next to fork lower making it a 69/70 plate.

cool, here we go


yes, based on casting number and center to center width.


i forgot to mention that. the bolts that secure the axle caps to the fork legs are 5/16-24, NF, not BSC, standard late SAE sizes. definitely not a 1970 as well.


that appears to be correct-- the bolts in the axle caps line up precisely in the center of the machined grooves in the axle as they should. i can't measure the length of the axle without removing it from the wheel.

the anchor plate is a bit loose on the axle. could be just the securing nut is loose. i didn't tighten it because this is just a mockup, but i wondered whether there might have been a missing spacer behind th ebrake plate. i can't see one in the 1969 parts book:

my forks were assembled from various boxes of bits, so the one thing for sure is that it is full of parts from everywhere. but the backing plate has the vertical run for the cable, rather than the earlier horizontal one. so the backing plate is a 69 for sure.

did they change the 1970 backing plate to accommodate the changes to the 1970 fork leg?

i also have a 1969 Tbolt with the same brake, so i went over and looked at it. it appears to have the same size nubbin on the right fork leg as the one in question above. it extends a smidgeon farther into the slot on the anchor plate, but not very different from what i have. it is tight on the axle. that one is a bit of a bitsa as well, though, so i wasn't sure.

i'll take the wheel apart and make sure nothing is missing behind the backing plate, but it appears that all my parts are the later ones.

[quote=kevin]

the anchor plate is a bit loose on the axle. could be just the securing nut is loose. i didn't tighten it because this is just a mockup, but i wondered whether there might have been a missing spacer behind th ebrake plate. i can't see one in the 1969 parts book:

There is no spacer. When the nut is tight the plate should be firm to the hub. If it isn't, then it might be warped. That would seem unlikely as it is a pretty solid cast piece. I suspect your nut is loose. Which, of course, is better than one having a screw loose.

Sounds like your fork assembly is 69 through and through.

Looks like you are working on a cool project.

the forks were something of a challenge, as both upper and lower trees were bent. the bottom one was a bit too far gone for me to feel comfortable, but one came up on eBay. the upper one responded well to a nudge with a three-foot crowbar.

we'll see where the machine goes. it's a track bike that i'm assembling from stuff in boxes and piles in the shop. when it's done i'll see whether i have enough reflexes left in my system to take it out on a road race course.

the only issue left with these forks is trying to get the clip ons to tighten up on the tapered stanchions. on the later OIF forks the legs are constant diameter all the way up through the top triple tree. can get some sheet lead to wrap around the legs at two different thicknesses top and bottom, and that should finish that part of the bike.

your PDF is excellent, by the way. a single source information sheet for stuff like this is very valuable.

Mike

Thanks for the tip. I do need to check this out. The bike had disc forks on it when I got it. I bought a complete set (69 or 70) and fitted that when I first got the bike.

The bike had a close encounter with a car a few years ago and I replaced the front end with a 6 1/2' setup (I supplied the parts) when the insurance claim fixed that. I supplied the correct 6 1/2 axle but they fitted it all up with the original 6 3/4" !!!

I haven't checked casting #'s or the fork slider (which was replaced).

Cheers
Ray

No spacer, but I found one of mine had a very thin washer fitted under the nut. This solves the problem and pushes the backing plate up against the wheel bearing. I think, in general, the axle runs out of thread just short of the nut pushing the backing plate up to the wheel bearing. This stops that annoying brake plate rattle without the need for shims at the post on the slider.

I cant get dimensions for that washer until I get home. But will supply that if anyone needs it.

Cheers
Ray