Engine Rebuild

I'll be pulling the engine out of my 1971 850 Commando in the next few weeks for a rebuild, I'm sending the head to Comnoz to get a fin repaired and the exhaust threads sorted out.

I'd like to ask the collective wisdom of Access Norton for tips and recommendations, this is my first time rebuilding a motorcycle engine, but I do have a little experience with temperamental British car engines.

So far I'm looking into the following:

- Bottom end rebuild kit
- Head rebuild kit
- New pistons/rings
- Sending the barrels away for reconditioning
- Swapping the chain primary for a belt
- A kit to replace all seals and gaskets
- A new wiring loom (main and headlight)

The bike already has a Tri-Spark digital ignition, Mikuni carburettor, and modern coil which I will be keeping as is. That's all I can think of at the moment but I'm sure I'm missing something!

Have Jim do the whole top-end for you while he has the head there.He does beautiful work and will not sell you something you do not need

YING said:

Have Jim do the whole top-end for you while he has the head there.He does beautiful work and will not sell you something you do not need

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Funny you should say that, I've just messaged him about doing that plus a few other things.

You might consider having it balanced. Even if you just have someone balance the new pistons, rods, etc. Remember to pull the crank apart and clean it out.
Pull the oil tank, clean it out along with the lines. No point in going through all the work and leave crud in the tank.
While it is out, go through the isolastics. Replace the main seal in the gearbox while it is easy to get to.
Replace the timing chain...cheap insurance.

That I know of, there are no "top end kits" or "bottom end kits" other than gasket sets (and those typically do not include oil seals).

I've also not heard of packaged oil seal kits, although I still cannot figure out why not...

Don't forget to check the camshaft bushes.

Dave

grandpaul said:

That I know of, there are no "top end kits" or "bottom end kits" other than gasket sets (and those typically do not include oil seals).

I've also not heard of packaged oil seal kits, although I still cannot figure out why not...

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All Andover Norton 'full gasket' sets (http://www.andover-norton.co.uk/SI%20Gaskets.htm) include oil seals :!:

cash said:

Don't forget to check the camshaft bushes.

Dave

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+1 and you might want to consider one of Jim's cam chain tensioner kits, comes with an iwis chain too IIRC. ..........not sure what your budget for the rebuild its, so it's easy for us to spend your money , but since you're already shelling out for new pistons, have you given any thought to the jsmotorsports light weight pistons and longer rods? You might be able to save some coin by not switching to a belt drive just yet......just replace the chain with one of andychain (a forum member here) it's an iwis chain too, then later when the CnW electric start kit becomes available you could get it , as it comes with it's own belt drive. Just a thought

and one of Jim's breathers? You could either buy the screw on sump plug breather or have the cases drilled to fit the rear mounted breather.
See many threads here for the benefit; wish I knew about the bolt on one when I had mine rebuilt (screw on sump plug will not fit my 1970).

Just a couple of more thoughts about belt drive conversions:
I fitted a Norvil kit and am happy with it. They come in a range of drive ratios which provide the opportunity to speed up the gearbox.
This enables you to raise the overall gear ratio of the bike without increasing the stress on the gearbox mainshaft.
Alternatively, if you want to keep the overall ratio as it is, you can go to a smaller gearbox sprocket, thereby reducing stress on the mainshaft.
Either way, you get the added benefit of making kickstarting a little bit easier by virtue of the changed primary ratio. Maybe an electric start would not then be necessary.
Ratios aside, by running the clutch dry you can reduce clutch spring pressure and also clutch lever effort by increasing the clutch stack. Funny how diaphragm springs work eh. My clutch is now a 2 finger one.
Oh and don't forget to install one of Dyno Dave's clutch rod seals to make sure no gearbox oil finds its way into the clutch.
Rebuilding can be a lot of fun, especially with great advice from this forum.

Thank you all so much for the advice here, I hope I don't wear out my welcome asking questions over the next few months!

nortonspeed said:

All Andover Norton 'full gasket' sets (http://www.andover-norton.co.uk/SI%20Gaskets.htm) include oil seals

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...but you cannot simply buy a "seal kit"

I've been very pleased with the JCC pistons and the rings that came with them.
About 7,000 miles on them and I can't even measure the oil consumption, great compression.

Funny how no one has bothered to mention the stress raiser Norton / AMC / NVT left within many drive side crank halves, directly beneath the big ends outer 90 thou stress reducing radius one so carefully has put in when regrinding the crank so as to reduce the stresses at this point of high stress concentration. As one friend said to me several years ago when i phoned to tell him all about the stress raiser I thought I had discovered...'Oh didn't you know about that problem...i have been removing it from many of my customers road and race cranks for years...they break if you dont'.
When the 'clever souls' machined the cranks they shoved a drill up the inside of the D.S. half to clean it out. The drawing shows the drill to leave the sharp corner / edge to finish well into the web where it does no harm but it clearly required the person doing the job to drill further which took more time which cost money especially when being paid piece work rates so they left the sharp stress raiser directly beneath the big ends outer stress reducing radius and guess where the cranks break!!! A friend and I checked all our 'spare Dommy etc cranks and those with the stress raiser in the wrong place went to a certain aircraft company for checking and two of the D.s. halves were thrown into the scrap bin as they were already starting to fail. of course in my young days our motors spent much of their time anywhere between 5,000 - 7,000 rpm which could well of been one reason we had cranks fail!! Well they called the lumps Sports Specials etc didnt they and we used them as such as we defied death not that some managed to defy it..........guess why they named part of the old A20 a few miles from Brands Hatch Death Hill all those years ago!!!! !!!
I wont go into the subject of the camshaft oil bath Mr Hopwood so very carefully designed into hios Dominator engine design way back in the late 1940s so that the cam would be CORRECTLY lubricated especially during the initial engine start period ............a design feature the idiots slowly designed out a bit at a time with every new crankcase pattern made. Tis an interesting exercise in crap Engineering to lay out the various editrions of crank cases starting with some original 77 ones and ending up with Mk3 Commando ones........To quote Mr Hopwoods letter to me on that (and other) subjects ..'The camshaft tunnel of the Dominator Engine was designed to retain as much oil as possible......'

J. M. Leadbeater said:

When the 'clever souls' machined the cranks they shoved a drill up the inside of the D.S. half to clean it out. The drawing shows the drill to leave the sharp corner / edge to finish well into the web where it does no harm but it clearly required the person doing the job to drill further which took more time which cost money especially when being paid piece work rates so they left the sharp stress raiser directly beneath the big ends outer stress reducing radius and guess where the cranks break!!!

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Interesting fact, however for race use the smaller diameter Dominator (500/600) cranks are prone to break anyway. Personally I would never have raced with the standard 3-piece crankshaft.

nortonspeed said:

J. M. Leadbeater said:

When the 'clever souls' machined the cranks they shoved a drill up the inside of the D.S. half to clean it out. The drawing shows the drill to leave the sharp corner / edge to finish well into the web where it does no harm but it clearly required the person doing the job to drill further which took more time which cost money especially when being paid piece work rates so they left the sharp stress raiser directly beneath the big ends outer stress reducing radius and guess where the cranks break!!!

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So what's the best way to remove the aforementioned step? Ball nosed endmill? Die grinder? It's a bit of a pain to get at!

cheers,Brian

[/quote]

So what's the best way to remove the aforementioned step? Ball nosed endmill? Die grinder? It's a bit of a pain to get at!

cheers,Brian[/quote]

OK, I'll answer my own question .... Dremel!
Takes a while, but not as tough as I thought.

Has anyone got a picture or diagram showing this stress concentrator? I'd love to see one.
Jaydee

jaydee75 said:

Has anyone got a picture or diagram showing this stress concentrator? I'd love to see one.
Jaydee

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Not sure if this helps but I typed in commando crankshaft porn in the "search this topiic" and found a pretty good shot of a radiused and polished PTO shaft on the second page.

If memory is correct 500SS cranks had a smaller hole up the centre to strengthen them up. Clearly someone realised that in calling the lumps SPORTS SPECIALS people would tend to rev the proverbial nuts off of them!!! Well we did when young defying death and they were not even SPORTS SPECIALS!!.........of course some failed to defy death and even worse serious life changing injury.......Guess why for example part of the A20 near to Brands Hatch was named and signed DEATH HILL !!!
As for breather systems we found the best was to fit a BMW motor cycle reed valve to the top of the oil tank and take all engine breathers back to it. Apparently BMW spent a lot of time and money looking into motor cycle engine breathing at one time. Start the motor and it can be heard clicking away but it quickly stops as all pressure is exhausted except for the occasional click which I suspect was pressure build up due to blow bye on the rings . The section on crankcase breathing in the book ' Tuning BLs A-Series Engine' (David Vizard ...ISBN 0-85429-732-4. Page 397) is an interesting worthwhile read......well I found it so a great many years ago but I have always needed to get a life!!
As for timing chains I cannot for the life of me understand why some enterprising soul has not come up with a proper chain system......the forces that poor old singlex timing chain has to survive are ridiculous and timing the cam correctly with any degree of accuracy is difficult. it must be 40 years ago that I grafted a couple of Tiger Cub 17t sprockets on to the existing idler and cam sprockets giving a duplex chain system allowing cam timing increments of 0.4 degrees. With a tad of modification to a Commando timing cover it even fitted but I never found the time to fit and test it.Of course Renold never manufactured a duplex half link that the system required but a Renold Morgan owning Ipswich office Engineer borrowed a few for me from a German chain manufacturer and I still have one in a tray somewhere and in my loft some of new 17t Tiger Cub sprockets along with the modified ones.....more lumps in store I will never get around to using......