Split Topic: Triple Trees

Debby,
How did you identify your parts as being from 1971? Also, since you have some ANG yokes on the bench, can you check yours and see if the measurements I took are even close to yours? Admittedly my method was quite crude. My frame is from early '73. I am wondering if the trees aren't from an 850 run of parts prior to ANG being stamped. If that were the case the casting numbers might be meaningless.

And to verify, you are saying that on your 850 the forks are parallel to the head?

Thanx
Russ

debby said:

1971 750
post-1971 750

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I'm not sure there's any difference between '71 and post-'71? Although there is a possibility that the last (serial 230***) 750 models made in late '73 had '850' frames, so would also have had 850 yokes?

My frame says 4/73 on the tag and has a 302xxx number. It was thru this forum that it was decided to be an 850 frame (and as near as I know now that should still be correct). The engine and gearbox are both 206xxx numbers so presumably all other 750 parts are from that same vintage. But of course it is hard to tell.

rvich said:

My frame says 4/73 on the tag and has a 302xxx number. It was thru this forum that it was decided to be an 850 frame (and as near as I know now that should still be correct). The engine and gearbox are both 206xxx numbers so presumably all other 750 parts are from that same vintage. But of course it is hard to tell.

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An additional identification of 850 frames is they have the part number stamped on the left gas tank mound at the front. '73 model year is 4140, '74 model year is 5404. Check Dave Commeau's website for detailed information on Commando frames.

L.A.B. said:

debby said:

1971 750
post-1971 750

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I'm not sure there's any difference between '71 and post-'71? Although there is a possibility that the last (serial 230***) 750 models made in late '73 had '850' frames, so would also have had 850 yokes?

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1971 yokes have different part numbers than the later 750 yokes, which have a different part number than the various 850 yokes. I do not know what the differences may be. I'll have to look the numbers up later.

Debby

I took bottom yoke from a 73 850 ANG 064083 and the bottom yoke from a 72 750 with a 06 with a hole drilled through the rest of the number. I put bottom to bottom numbers to numbers lined up pivit holes and see that the pinch holes are NOT the same. If anyone has these trees that are not on a bike or bikes could varify my findings I think we got it. Phil

Norton-Villier said:

I took bottom yoke from a 73 850 ANG 064083 and the bottom yoke from a 72 750 with a 06 with a hole drilled through the rest of the number. I put bottom to bottom numbers to numbers lined up pivit holes and see that the pinch holes are NOT the same. If anyone has these trees that are not on a bike or bikes could varify my findings I think we got it. Phil

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Would a picture show the difference. We have some "non-believers" here. :mrgreen:

debby said:

1971 yokes have different part numbers than the later 750 yokes,

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According to my copies of the parts books from '71-'73, they all appear to list the 750 "upper yoke with stem" as part 061915, and lower yoke as part 061916.

Ok, I couldn't stand the suspense so I went home at lunch and looked at the parts. Here is what I have:

061917 upper yoke on both my 750 and my 850
061916 lower yoke on both bikes

The (presumably) 850 yokes have the following numbers:

ANG 064084 upper yoke
ANG 064083 lower yoke

Looking at the bikes, the fork tubes and headstock appear parallel with the 750 yokes. I held up a carpenter's square and they still looked parallel by eye.

Next, I slid a new, straight fork stanchion into the 850 triples. It was immediately obvious that the stanchion and stem were NOT parallel, with the forks being pulled in to a steeper angle than the steering stem.

I then took some measurements of the distance from the stem centerline to the centerline of the stanchions, using the carpenter's square and a cheesy Harbor Freight plastic calipers.

Those measurements are:

061917 750 upper: 65 mm

064084 850 upper: 72 mm
064083 850 lower: 69 mm

I did not measure the 750 lower yoke offset but it appears to be the same as the 750 upper.

So what is the 061917 part and how does it differ from the 061915 part? I believe one difference is the threading on the end of the stem. When I was restoring my 750 I bought a nice new nut from OldBritts. It did not fit - wrong thread pitch. So I sent it back, asking if he could exchange it for the correct one. Fred replied that was the only one there was, he tried it on a couple of stems and it fit perfectly, and hence there would be no exchange or refund. He sent it back and I binned it and reused the old nut. I'll bet it would fit the stem on my 064084 yoke. I'll probably have to buy another one when I put those yokes on the bike.

Another little observation is that on all the parts, the numbers are cast in, not stamped.

I did not measure the distance from the stem to the steering lock on any of these parts, as that would not seem to have any relevance to steering geometry, only to whether or not the steering lock would fit properly. I don't have a steering lock fitted to either of my bikes.

So there you have it, everything I know at this point in time! :mrgreen:

Debby

debby said:

So what is the 061917 part and how does it differ from the 061915 part?

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"061917" is just the casting number for the 71-73 750 upper yoke, and not its part number, several references have already been made to that number in the previous pages of this thread.

If any number is found to be cast-in, to the part, then it's not likely to be the actual part number.

Also the upper yoke is not availabe separately, as it comeas as part of an "assembly" along with the stem, so the actual part number applies to the assembly (yoke with stem) and not to the individual parts that go together to make it.

L.A.B. said:

debby said:

So what is the 061917 part and how does it differ from the 061915 part?

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"061917" is just the casting number for the 71-73 750 upper yoke, and not its part number,

If any number is found to be cast-in, to the part, then it's not likely to be the actual part number.

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The lettering is actually raised, not recessed. "Cast in" was just a figure of speech. It would be more correct to say "cast out" I suppose.

So are you saying the 061917 yoke is used in the 061915 yoke and stem assembly, and that all later 750s used that same part?

I really want to get to the bottom of this mystery, once and for all!

Debby

debby said:

The lettering is actually raised, not recessed. "Cast in" was just a figure of speech. It would be more correct to say "cast out" I suppose.

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Yes, OK, the raised digits which are cast-into the part then! :wink:

debby said:

So are you saying the 061917 yoke is used in the 061915 yoke and stem assembly, and that all later 750s used that same part?

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From what's been said already, I think we must draw the conclusion that the 061917 casting is part of the 061915 yoke assembly, although I can offer no explanation as to why the nut from OldBritts wouldn't fit?
Perhaps we should try to identify the stem thread next time the yoke is removed?

72 replies on triple trees and counting ...:
We are digging deep on this one !
No stone is left unturned to discover the truth .
A little help for those who didn't pay attention during math class but still like to calculate their fork geometry :
http://www.easycalculation.com/trigonom ... angles.php

Hey Ludwig, Thanks for the link to those camera shots, Nice stuff. 72 replies and counting, LOL. :roll: I read back thru this whole thread and it just makes me laugh, Where do people get their information? Do they just make it up or really think they know? Have a great weekend guys.

Uh-oh...

I have been remeasuring the yokes on my bike. As stated the previous measurement were taken from the back side of the fork tubes to the front side of the head stock. There is approximately 2mm rake or taper there. However, this morning, armed with new knowledge and determination I set up a better method of measurement so that I could accuratetly measure to the center of the head stock (or at least repeat with the same error). I came up with 67 mm for both the top and bottom yoke. The only other explanation for the visible angle is that there is something else amiss. And it probably needs attention badly.

So, I would like to thank everyone involved in this exercise. Whether or not we have solved any major Norton mysteries, it certainly is going to make a big difference to me. I hope this information helps to clear up any confusion my earlier observation may have created.

Russ

Just one thing I noticed, since I purchased a set to possibly machine my own. Judging from the CNW site, the custom set done by matt do not seem to be model specific. So my guess is the difference cannot be that substantial.

I don't know what Matt is producing, but the pullback on the 850 trees is very noticeable. I suggest you obtain a set of 750 trees and a set of 850 trees and see for yourself.

Maybe Matt can join in and share his thoughts on triple tree geometry. I think everyone else has now! :lol:

Debby

Debby, I think your right. I beleave our findings yours high-tec mine low-tec should prove it. I also think L.A.B. hit it on the head when he talked obout steering geomitries and wheel-base. Phil

Vulin said:

Just one thing I noticed, since I purchased a set to possibly machine my own. Judging from the CNW site, the custom set done by matt do not seem to be model specific. So my guess is the difference cannot be that substantial.

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This is what I was saying earlier.... There are a few other aftermarket trees made by other companies also with no distinction for model also. Seems to me the oem ones if they really are significantly different are based more on material strength/cost than proper geometry?

pelican said:

This is what I was saying earlier.... There are a few other aftermarket trees made by other companies also with no distinction for model also. Seems to me the oem ones if they really are significantly different are based more on material strength/cost than proper geometry?

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Although Andover Norton still sells the '750 only' lower yoke as a spare part, they say to: "USE 06.4080 & 06.4079 as a pair" for all pre-MkIII 71-0n 750 & 850 models. Edit: Link updated: https://andover-norton.co.uk/en/shop-details/15693 The incorrect 06.4079 part number has been changed to 06.4078.
06.4080 and 06.4078 are pre-MkIII 850 yokes, I think the AN 064079 part number may be wrong, as I can't find that number using their parts search, only 064078.