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Discussion Starter #1
I have a 1968 T120 that I am restoring and it could use some new gear sets (and shafts). I've been researching what I can find and it looks like Triumph made quite a few changes to the mainshaft, layshaft and gears in these three years. One of the changes was to change the gear ratio from 2nd to 3rd for 1970 models. That seems like it would be an "improvement," so I am considering putting all 1970 gear sets in. Wonder if anyone has researched this and has some suggestions as to whether this is a good idea or bad idea?
 

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Welcome to this forum...I had to change a mainshaft a few years ago on a 71 T120r 4 speed. At the time, i found many slight variations in length and found a brand new 1971 shaft which was exactly the same length as the damaged one. So, be aware, that accuracy will ensure it works well. A variation might not be compatable with a layshaft. Complete gear set from a working bike might be a good purchase. Bear in mind the inner roller bearing has a measured depth for fitting and allowing the thrust washer to work properly. These bearings are glued in place once driven in.
I would expect my 71 gear set to be the same as a 70 but never researched it. I am happy with the ratios i have.
My reason to change the shaft was a damaged tooth on the gear that is firmly attached to the shaft. I have since found that this gear will come off with heat and effort so now have a spare. I also keep a good gear set in my spares collection now. A few years ago i found some brand new single gear cogs so i am covered for any gear problem in the future.
The best idea is to find an old genuine gearset. Not seen many with any wear unless they ran without oil. The dogs usually have some rounding off with use but not much of a problem . Just be aware of those clearance measurements of the roller bearings
 

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The mainshat may need to be shimmied for proper gear engagement..I have forgotten the details but maybe someone remembers
 

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Hi mjhillsc, Yes, many changes. I don't know them. Rabers had a wall chart that showed all changes, but they're gone now. Without the chart I'm lost. Trying to get used parts for '69 Bonnie proved challenging. All the parts that were same were junk.

Just throwing this out.... Should you need to get too much money in this trans, new 5 speed kits are available. 5 speed is in my mind a very nice upgrade. You know when you're riding your bike 2nd is revving too fast & 3rd motor tends to bog, like on steep twisty canyon roads? 5 speed cures that with ratio of 3rd gear. 1st is lower on 5 speed so gives brisker take off & easier with 2 up.

Back to 4 speed I feel the later ratios are a little better. I don't know if much though.

I hope Mick chimes in. He would know way better than me on the gears, shafts.
Don
 

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Late 4 speed ratios are very good. 3rd gear is an ideal overtake gear up to 70 mph. 4th gear is still pulling very hard at 80 mph. I find that 1st and 2nd gear are rarely used once on the move. Not found any hills around here that i cannot go up in 3rd gear. Many of the hills are 1 in 10 but there are the short areas where it can be 1 in 5 or lower .The 1 in 3 hills in North Devon do require 2nd gear and you cannot stop and try pulling away again. Porlock hill is what i am saying here. One of the steepest and longest hills in the UK. The T120 engine seems to have much more low down pull than a T140 with most pull coming at around 3000 rpm.
I dislike the modern idea of many gears. My Thunderbird LT has 6 on a 1700 twin. Rocket 111 has 5 but needs just 3 when out on the road.
 

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Don - I'm curious about that wall chart - was it something they put together at Rabers? Or was it a Triumph publication?

Anyone else aware of such a chart? This kind of information will probably be increasingly useful as time wears on and definitely something that would be worth running down and preserving.

Cheers!
 

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When searching for a replacement mainshaft, i found some information that there maybe 8 variations so i looked specifically for an old stock 1971 type and came across one labelled 1971 at a jumble. The seller had a few different ones there so i did notice the slight difference in length.
 

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Discussion Starter #9
Don - I'm curious about that wall chart - was it something they put together at Rabers? Or was it a Triumph publication?

Anyone else aware of such a chart? This kind of information will probably be increasingly useful as time wears on and definitely something that would be worth running down and preserving.

Cheers!
If we can get a bit more clarity on the chart I’d be happy to try to track down the Rabers. Might be difficult to put hands on as I know they were putting a lot of things in storage.
 

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Hi All, Looked like a factory wall chart. But was it?? Raber's penciled in further changes & newer part #s. Was large like 2X3' as I recall. I tried to photo it, but lost the photos in phone change... Called Michael & left voice mail. Maybe I only have shop cell # & it's not longer being monitored?
Chart was on right wall. Entering shop, turn right & go to counter. Was on wall to right behind counter as I recall.
Don
 

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Hi All, Looked like a factory wall chart. But was it?? Raber's penciled in further changes & newer part #s. Was large like 2X3' as I recall. I tried to photo it, but lost the photos in phone change... Called Michael & left voice mail. Maybe I only have shop cell # & it's not longer being monitored?
Chart was on right wall. Entering shop, turn right & go to counter. Was on wall to right behind counter as I recall.
Don
I'm a bit late in the thread (sorry Don), but here goes. First, I have to say that most of my experience has been in converting 4 speed pre-unit boxes to 5 speed, and although that does have it's challenges, there were few changes of any importance in the early 4 speeders, in fact precious little even on the unit boxes until 1969. First, don't worry about the mainshaft lengths, it was all about the change to UNF threads, and the associated nuts, the length between the gears and the taper on the shaft remains the same. The fun comes in '69, where the 3rd gear pair were changed, the good news is the part numbers were listed in a service bulletin, TIB329, and the numbers will be stamped on the gears. The number on the layshaft 3rd will be one digit different, as the stamping is the gear only, the given part number is the assembly with bush. The generally published parts book on line for 1969 is probably wrong, it lists all of the other gears as same as 1968, with a change in number for the 3rd gear pair only, but different again from the sevice bulletin. I think what happened was they made a decision to go to the "shaved" finish gears after the parts book was written, the part numbers going to T3000 series as shown in the 1970 manual in real life. Again, the numbers should be stamped on. The shaved finish gears apparently have a better surface finish to the teeth, and SHOULD be functionally the same as the earlier gears, but it is always good practice the fit gears as pairs - if one is visibly damaged, there will be some damage to the mating gear. 1970 and onwards are basically the same, except that the leaf spring camplate detent came in, with a different camplate to boot. It is possible to use the late cluster with an earlier camplate and plunger detent, a common "fix" for the dubious leaf spring did just that.
All of the above has been gleaned from the likes of J R Nelson's book (ex Triumph service manager), Roy Bacon's book, the Triumph service bulletins with a bit from my experience.
So - if you are staying 4 speed, then 70 onwards with the earlier camplate is probably the way to go, but a late 5 speed conversion can be wonderful. John Healey's writeup on this is excellent, and one quiet day I may update it with stuff I have found on pre-units. I'm not sure abut copyright on that, but it is around on the web - I guess I'll have to contact JH before plagiarising his work, as well as Phil Pick, who also has some good information written. If you can find someone locally who knows the conversion, so much the better.
More info, ask away.
Mick.
 

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Discussion Starter #12
So - if you are staying 4 speed, then 70 onwards with the earlier camplate is probably the way to go
Hey, Mick--thank you for your post. I am thinking going 70 gear sets is the way to go. I was also planning on going with the 70 camplate. Assuming you meant the 70 camplate in your comment above??? You mentioned "earlier camplate" and that has me wondering if you meant the old style.
 

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The 70 cam plate is for the leaf spring detent, so you want the 69 or earlier one. If it’s ok, the one you have would be fine.
Cheers,
Mick.
 

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Discussion Starter #14
The 70 cam plate is for the leaf spring detent, so you want the 69 or earlier one. If it’s ok, the one you have would be fine.
Cheers,
Mick.
My understanding is that the 1970 camplate (57-4055) was introduced sometime during the 1969 model year builds and was used on all 1970 models (plunger & leaf spring). Source is Gaylin and Nelson and my bikes. I have three 1970s and all have the new 57-4055 camplate (2 of the three were original parts when I got them). The later UK production model I have came with the leaf spring. I had that case machined to accept the plunger. Am I wrong about this camplate? (I know 3-1970s and 1-1968 sound like a lot of bikes, but I barely ever have more than two running at the same time; excuse sorta works with my wife.)
 

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Discussion Starter #15
Hi All, Looked like a factory wall chart. But was it?? Raber's penciled in further changes & newer part #s. Was large like 2X3' as I recall. I tried to photo it, but lost the photos in phone change... Called Michael & left voice mail. Maybe I only have shop cell # & it's not longer being monitored?
Chart was on right wall. Entering shop, turn right & go to counter. Was on wall to right behind counter as I recall.
Don
I did some sleuthing around and it seems like this was a factory gear chart. If I can get a copy of it, I will share it. If anyone else can track one down, I would be happy to photograph it (it's what we do) and circulate it back. It could be really valuable to have.
 

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My understanding is that the 1970 camplate (57-4055) was introduced sometime during the 1969 model year builds and was used on all 1970 models (plunger & leaf spring). Source is Gaylin and Nelson and my bikes. I have three 1970s and all have the new 57-4055 camplate (2 of the three were original parts when I got them). The later UK production model I have came with the leaf spring. I had that case machined to accept the plunger. Am I wrong about this camplate? (I know 3-1970s and 1-1968 sound like a lot of bikes, but I barely ever have more than two running at the same time; excuse sorta works with my wife.)
I just had a dig back, and you're right, the 57-4055 was introduced at DU88630 probably mid '69 model year and continued 'til the end of the 4 speeders. The leaf spring came in at ED52844, so May 1970. That tells me that the '70 camplate should be fine with the plunger detent, as per your experience on your own bikes. Nelson also mentions other dimensional changes during the '69 model year, so you'd definitely want to steer clear of a '69 cluster if you weren't sure that it was all good and original. The gears had their numbers stamped on, but AFAIK there is no such identification on shafts, so even if a copy of the factory chart can be found, it may not help in some cases, That said, such a chart would be ever so useful!
 

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Hi Mick,


In August or September 1968; the DU number range was only used up to 90282 then Meriden switched to the new format from NC00100 in October 1968.

Hth.

Regards,
Hello Stuart,
I was going from the Roy Bacon dating, which is a little confusing! Of course if 90282 is October '68, it's a '69 model year, (starting 85904?). Funnily enough, I'd spotted this once before, and thought no more about it. I was just prompted there to check the numbers on my own '69 Bonneville, something I'd never checked, and that really makes no sense, they are matching and are T120 11439, no DU, no month and year code! I have the original green log book with date of first sale and those numbers, and rough as it was when I got it some 40 odd years ago, the spec is '69 with all it's lovely mix of fasteners etc.
I think it's time for a drink.
Cheers,
Mick.
 

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Discussion Starter #20
Following up on the
Rabers had a wall chart that showed all changes, but they're gone now. Without the chart I'm lost.
Just to follow up this thread about the chart. There was a chart at Raber's. And, the chart is available through John Healy's Coventry Spares and also through JRC Engineering. It is a reproduction of the factory chart and good quality. Although a strong pair of reading glasses should come with it. Attached is a snapshot of what it looks like. Also, the essential data is also available in a pdf for free from the JRC site: TRIUMPH 650 4 SPEED GEAR INTERCHANGE | JRC Engineering, Inc.

Appreciate all of the comments and suggestions. Very helpful!
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