Re-assembling Crankcases on a 850

AZScott · May 28, 2015

I am in the process of putting the two halves of the crankcase together on a '74 850. Had the crank dynamically balanced and have new main bearings.
Watched the Mick Hemmings DVD last night on engine restoration. There were lots of good tips in the DVD, but no mention of end float of the crank when fitted in the crankcases. He never even paused to look or measue it. The workshop manual does not cover this as well, but does show a "Permissible end Float of 0.005- 0.015 in." A question for others that have done this, is this somthing I should be concerned with ? The parts book does show a Main bearing shim (NMT2196A). Thanks.

Anonymous · May 28, 2015

Hi AZscott.
I just put my 750 cases back together and am happy at 0.007" - did not change mains.
Ta.

toppy · May 28, 2015

I changed mains on my 74 850 last year and had 8 thou of end float on crank which had been reground by Mick Hemmings. I also had 20 thou of end float on the cam after talking with Mick he reassured me these amounts were fine an that as a rule 850 motors with original match crank case halves normally required no attention to the end float unlike earlier motors which could be more of an issue.

pete.v · May 28, 2015

toppy said:
I changed mains on my 74 850 last year and had 8 thou of end float on crank which had been reground by Mick Hemmings. I also had 20 thou of end float on the cam after talking with Mick he reassured me these amounts were fine an that as a rule 850 motors with original match crank case halves normally required no attention to the end float unlike earlier motors which could be more of an issue.

.020" end float on the cam is ok as long as you don't use a power arc ignition.

cjandme · May 29, 2015

pete.v said:
...........020" end float on the cam is ok as long as you don't use a power arc ignition.

Hi Pete, can you elaborate on this a little bit since I have a power arc in my bike, what am I missing or forgetting? thx Cj

pete.v · May 29, 2015

cjandme said:
pete.v said:

...........020" end float on the cam is ok as long as you don't use a power arc ignition.

Click to expand...

Hi Pete, can you elaborate on this a little bit since I have a power arc in my bike, what am I missing or forgetting? thx Cj

The encoder wheel and the optical sensor have, for a lack of better word, a delicate relation ship. In and out movement can cause rough running as it will loose focus of the starting point. It seems I also recall reading something about it in the instruction or on Old Britts web site.

I do know that I had to remove the timing gear to shim the cam to around .'007 to improve functionality. I remember my cam was out more than .020 though.

cjandme · May 29, 2015

pete.v said:
........I do know that I had to remove the timing gear to shim the cam to around .'007 to improve functionality. I remember my cam was out more than .020 though.

All right then, thanks for that info, I must be living right, mine seems to be okay in that regard. What type of ignition system are you running with AZScott ?

norton73 · May 29, 2015

Are you guys measuring cam end float with the sprocket installed? I just pulled the top end on my 73 850 and also removed the timing chain and sprockets. The cam can probably move more like a 1/4inch. The bottom end has never been apart, bike has about 50k miles.

pete.v · May 29, 2015

norton73 said:
Are you guys measuring cam end float with the sprocket installed? I just pulled the top end on my 73 850 and also removed the timing chain and sprockets. The cam can probably move more like a 1/4inch. The bottom end has never been apart, bike has about 50k miles.

I'm sure you should check it with the sprocket in place. You should be able to slip the sprocket on to bottom the shoulder of the cam and get a good idea on what you have left for play.

AZScott · May 30, 2015

My plan is to install a Pazon PA2 (on a MkII 1974 850). In the past I have always installed Boyer systems on Triumphs with good luck. This is my first Norton, and I was told by an experienced Norton mechanic that the Pazon is a much better system. A little more expensive but thought I would take his advice.

grandpaul · May 30, 2015

It's a matter of dry fitting the crank, after ensuring the main bearings are FULLY HOME in their case halves. Then, nip up the cases with all the bolts, then measure both sides (long feelers help).

My guess is you won't need shims, especially if your crank is original to your cases.

AZScott · May 30, 2015

Grandpaul,
My drive side crankcase, trany, and frame have matching numbers, however I found the cases to have different markings.

On Triumphs it means the cases didn't leave the factory together. Not sure if this is the case on a '74 Commando that came out of the factory 9/73.
I have found no other indication these were a non matching set.

L.A.B. · May 30, 2015

AZScott said:
however I found the cases to have different markings.

On Triumphs it means the cases didn't leave the factory together. Not sure if this is the case on a '74 Commando that came out of the factory 9/73.

Yes, the stamps should match.

Re-assembling Crankcases on a 850

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