Split Topic: Triple Trees

For safety sake, fit the correct ANG marked 850 clamps. That 061917 is the short lived nasty '71 750 with dodgy high speed stability.

Mick

Remember, I have an 850 frame. I can try to measure the difference at the top and the bottom, not in degrees but mm. What we should be comparing that to is an 850 MkII. (one with verifiable ANG trees)

kommando said:

Quote from NOC notes on yokes

In any case where a new frame is required I would recommend the early 850 frame . The steering is more positive at high speed with the 850 geometry but to get the greatest benefit you also need the 850 yokes but the 750 will fit and give the desired increased trail.

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I knew it was one was ok and one was not. just had id it reversed.

grandpaul said:

The clamps can't be mixed IF YOU ARE WANTING TO RETAIN ALL ORIGINAL FEATURES exactly as they were on the orignal bike.

Other than that, if you don't need the mounting provision for the idiot light panel, and if you don't need the identical steering lock setup (I NEVER use steering locks), then it matters not one whit.

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Thank you. I have been trying to tell everyone that, but some seem to think there is an extra smidgen of rake built into the trees. All 4 trees have the same offset (distance center-to-center from the steering neck to the fork tubes.) Does anyone really believe they would build a degree or two of rake into the yokes to compensate for an extra degree of frame rake when the crankcase boring bar had to be wedged with a 2x4 to keep the main bore alingment concentric with the cases? Get real.

Sounds like a Joe Walsh song, And like Nike's slogan said; Just do it. LOL LOL Your going to anyway. :roll:

I have a set of ANG trees on the bench and I also have a set of new stanchions. I'll see if I can measure any offset.

danno - how do you know that story about the 2x4 is really true? The version I heard said it was the rear iso mounting hole in the frame that they used the stick on. The guy telling me the story called it a "noggin stick" or something like that. Can't believe everything we're told! :roll: :lol:

Debby

When they moved the production facility to its final location, the old guy who bored the cases retired. Unfortuantely, the case boring bar with the worn-out arbor soldiered on. After boring a few sets of cases (badly) and discovering how screwed-up they were, they called the old guy in to tell them what was amiss. Upon seeing the old machine in it's new installation, the old dude muttered "Aye, where's me stick?" whereupon someone was dispatched to the old factory to retrieve an oily, grimy 2x4 with a half-round worn in one end. The old guy jammed it between the machine's upright and slopped-out, spinning arbor and bored a perfect set of cases. I wasn't personally present, so I wouldn't swear to it in court, but it's eminently believable. I read it in Kevin Cameron's "TDC" column in Cycle World.

Danno, "Some of us seem to think that there is an extra smidgen of rake in the 850 clamps" because that is what the factory and some other well respected sources (eg. Roy Bacon) believe and claim in their published service notes. If the factory went to the trouble to print and disseminate this information, why would we doubt them? After all most of us use and trust much of the information provided by the factory in rebuilding or maintaining our machines. We seem universally to believe that the 850 has one degree more rake, why would we not then believe that they were capable also of machining clamps to this same accuracy? The cast-in numbers are not necessarily part numbers but simply casting numbers to identify parts prior to machining - at which point they become completed parts with the correct part number attached to the part or the bag in which it comes. I can envisage two parts with the same casting numbers that are not actually the same finished part.

Taking into account production inaccuracies which may have been a couple of mm either side of a designed reference point, when they changed the reference point they were then a couple of mm either side of the new reference point.

I think this is a serious question as there are obvious safety implications involved.

UH-OH, there'll be bodies in the street soon...

Bodies in the street? Is that from running with the wrong trees or because of the discussion about them? OK, I slid a steel ruler behind the tubes on the front end of the bike and did the best I could measuring to the head stock. At the top the ruler just barely hits the tab on the headstock for the lock. At this height I got 22 mm. Then I dropped the ruler down to the bottom and measured as best I could above the stop. I got 19 or 20 mm. I didn't take the headlight off, I hadn't had a drink yet and I didnt take my glasses along with me, but that is close. It took all of about 2 minutes. Can somebody else check their bike in a similar manner? If I have to I will gladly take off the headlight and get a better measurement.


Russ

Thanks Russ, I'm not trying to be argumentative, discussion is vital in trying to further our collective knowledge and I will be happy to be proved either right or wrong.

I do however think that this is a more important issue for us all to understand than some of our other 'philosophical' discussions regarding oil brands or points versus electonic ignition.

I have looked at the fork tube angle in relation to three 750s that I currently have in my workshop and they are all parallel to the steering head, they are 1969, 1971 and 1972 models.

All you have to do is measure the distance center-to-center between the tube clamps on the bottom tree and its steering pivot and compare that to the center-to-center distance between the tapers on the top tree to the steering pivot. If the number is the same, there is no rake in the trees. If the bottom nomber is larger, rake has been increases. If the top number is larger, the rake has been decreased. My measurements indicate offsets for both 850 and 750 tree pairs are the same. Measure it yourself, if you like. And the 1 degree difference between the 850 and the 750 steering tubes is so small as to be barely noticeable in handling difference. Might have even been a production tolerance thing when they started buying frames from Verlicchi.

dave M said:

I have looked at the fork tube angle in relation to three 750s that I currently have in my workshop and they are all parallel to the steering head, they are 1969, 1971 and 1972 models.

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The difference in angle between my MkIII's forks when compared to the steering head is quite noticeable, in fact I'd say it was more than the "1.5 degrees" ludwig has mentioned.

Some while ago, member 'teeb' measured the offset of a (supposedly 850) top yoke at : 2.78" (70.5 mm).
At the time, I estimated my MkIII's top yoke offset to be approximately 1/4" greater than that, however now I have a spare MkIII top yoke amongst my spare parts collection I have been able to measure the offset a little more accurately, and although it's not quite 1/4" the offset is somewhere between 73 & 74mm, but it is certainly more than 70.5mm.

L.A.B. said:

...The difference in angle between my MkIII's forks when compared to the steering head is quite noticeable, in fact I'd say it was more than the "1.5 degrees" ludwig has mentioned.

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It could be slightly more , but likely not more than 2 deg .
When I made an alloy copy of the lower tripple tree I had a reputed machine shop precision drill the stanchion holes at 1.5 deg .
To make the fork legs fit correcly in the top tree , I had to set the 2 tripple trees about 1cm further apart , so the angle could have been a little over 1.5 deg .
so what do whe have :
850 TT defenitely are at an angle to the headstock .
rvich is adamant that his 750 TT are at an angle .
dave M checked 3 750 TT and they are parallel .
Could there be 3 different types ?
BTW , I just mesured the headstock angle of an unmolested 850 frame ( as precise as I could ..) and got 61.8 deg .
close enough the the factory 62 deg .

debby said:

danno - how do you know that story about the 2x4 is really true? The version I heard said it was the rear iso mounting hole in the frame that they used the stick on.The guy telling me the story called it a "noggin stick" or something like that. Can't believe everything we're told!

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I've heard the 'wooden plank' story. But I thought that emanated from when production was transferred from Bracebridge St. in Birmingham to the AMC works at Plumstead in London (when only four Bracebridge St. Norton employees moved to Plumstead)? However that would have been around 1962.



There was the story of "The donkeys dick"?

It was found that several Commandos fitted with the new Italian manufactured frames wouldn't steer straight.
The subequent investigation uncovered the fact that during frame alignment checking, if the acceptance gauge would not slide easily through the steering head then the members of the inspection department would hammer it through!

ludwig said:

Could there be 3 different types ?

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I thought there was also a change made to the yoke geometry for 1971?

Yes, the 1971 triple trees have unique numbers so presumably are different in some manner to the later 750 triples.

So we have at least the following variants:

pre-1971 750
1971 750
post-1971 750
pre-Mk3 850
Mk3 850

It turns out I have a set of 1971 750 triple clamps on my 850. Don't know where those came from, probably some previous owner supplied them. The bike does seem a bit "twitchy" at highway speeds compared to my 750. I was thinking that it was ok to run 750 triples on an 850 frame, but if it reduces trail that doesn't sound good. I do have a set of 850 triples that I'm planning to put on that bike. Just have to get them powder coated first.

Debby

L.A.B. said:

I've heard the 'wooden plank' story. But I thought that emanated from when production was transferred from Bracebridge St. in Birmingham to the AMC works at Plumstead in London (when only four Bracebridge St. Norton employees moved to Plumstead)? However that would have been around 1962.

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So we have at least three variations of the wooden plank story. I have the feeling it's an old wive's tale, although I suppose it could be true.

here is an e mail i received from dyno dave the other day.



This is not an exaustive survey but a small sample of antique data I have.

The late 750 front end has +.06º (kick out forward)
probably meant to be parrallel

The 850 reg and MKIII ANG front end has -1.342º (kick back)

I probably have atlas and early commando data collecting dust in the
folder too.

DAve

I'm getting a headache, Chuck. :mrgreen: