850 Bottom end rebuild - Tips please

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I need to rip down my MK II 850 bottom end - what do I need to look out for and what mods or things do I need to change, improve. I have rebuilt a few BSAs this is my first Norton!
PS timing side big end has excessive play hence the rebuild. I have done the head, barrels have been re-bored to +60.

Any tips or advice extremely welcome

Regards
 
I think most here would suggest you start by getting the shop manual and also the motor rebuild video
 
+1 to the above. Be patient and don't break anything! If you get the crank ground make sure it is somebody who will actually use the proper radius. Apparently the crank radius is not common and most shops will not dedicate a stone to it. Make sure you use C3 superblend bearings. Shim as needed. Consider whether you want a breather installed while you have it apart. Now would be the time to decide if you want to do something like lightweight pistons and rods!

Russ
 
Nigeldtr said:
I need to rip down my MK II 850 bottom end - what do I need to look out for and what mods or things do I need to change, improve. I have rebuilt a few BSAs this is my first Norton!
PS timing side big end has excessive play hence the rebuild. I have done the head, barrels have been re-bored to +60.

Any tips or advice extremely welcome

Regards

I'm in the middle of a similar project. Do you have vertical play on the crankshaft? What is the mileage on the motor?
 
May just need routine new rod shells for the loose rod. Get all new rod cap fasteners from respected source. Equalize masses R/L and get the crank dyno balanced. Might consider cyro tempering steel/iron items before assembly. Be alert to the bearing bore condition to keep a grip on races. Dremal a bit more oil drain funnel in case wall openings to supple cam bushes. Decide how to measure crank studs by torque guessing or direct stretch measure. 850's tend to bust the front lower cradle holes so double check or double plate for next fella.
 
1up3down said:
I think most here would suggest you start by getting the shop manual and also the motor rebuild video

Thanks -I have the manual, just seeing if I can get hold of the DVDs.
 
Nigeldtr said:
I need to rip down my MK II 850 bottom end - what do I need to look out for and what mods or things do I need to change, improve. I have rebuilt a few BSAs this is my first Norton!
PS timing side big end has excessive play hence the rebuild. I have done the head, barrels have been re-bored to +60.

Any tips or advice extremely welcome

Regards

Hi Russ, breather seems to be working fine, direct into the oil tank which I think is standard.
 
fatmatt said:
Nigeldtr said:
I need to rip down my MK II 850 bottom end - what do I need to look out for and what mods or things do I need to change, improve. I have rebuilt a few BSAs this is my first Norton!
PS timing side big end has excessive play hence the rebuild. I have done the head, barrels have been re-bored to +60.

Any tips or advice extremely welcome

Regards

I'm in the middle of a similar project. Do you have vertical play on the crankshaft? What is the mileage on the motor?


I think its high mileage as the bores were +40 and very worn but in good condition - lips top and bottom of stroke.
 
hobot said:
May just need routine new rod shells for the loose rod. Get all new rod cap fasteners from respected source. Equalize masses R/L and get the crank dyno balanced. Might consider cyro tempering steel/iron items before assembly. Be alert to the bearing bore condition to keep a grip on races. Dremal a bit more oil drain funnel in case wall openings to supple cam bushes. Decide how to measure crank studs by torque guessing or direct stretch measure. 850's tend to bust the front lower cradle holes so double check or double plate for next fella.

Hi,

Thanks for the info, just a couple of questions

1. Balancing - sorry to be asking but I thought this is not so critical on the commando?
2. Any more info on where to use the Dremal - pictures?
3. Why the "cyro tempering" - is this like de-stressing?
4. I assume I need to replace all the crankshaft and big end bolts?
5. "Lower cradle holes busting" Is this where the isolastic mounting bolts onto the engine

I have also noticed one of the small ends is a little over size (not bad but not perfect) - can these be bushed?
 
The crankcase breather topic has been discussed in great detail. Do a search on it and a little research. There are a number of ways to improve upon the stock breather.

Russ
 
1. Balancing - sorry to be asking but I thought this is not so critical on the commando?
Naw if did ok as it then this is just extra expense for bit extra isolation and engine refinement. Mostly just get the pistons and rods withing a gram or less is the standard approach.


2. Any more info on where to use the Dremal - pictures?
On my 750's there are a tiny hole in case wall that leads wall splash oil into the cam bushes. I just funneled them a bit more and made a slight groove in wall to help aim some oil into the holes. Just something to do to feel like a caring rebuilder.

3. Why the "cyro tempering" - is this like de-stressing?
Its both a temper toughening and a de-stressing as cycles through the slow freeze then a slow heating and cooling phase. I'm pensive of cast iron flywheels and fasteners backing off torque so just extra peace of mind while apart as shipping costs more than the freezing. I did not do this to my bone stocker Combat but don't run it like it was meant too either.

4. I assume I need to replace all the crankshaft and big end bolts?
Its standard practice as hi stressed fasteners can enlongate or get grain fractures that let corrosion creep across till Powie.
Minimal wisdoms say at least replace nuts each time.


5. "Lower cradle holes busting" Is this where the isolastic mounting bolts onto the engine?
Nope its where the cradle attaches to rear of crank cases, where the cradle holes not much meat around them. The fix if busted in weld thicker plate over area and fit longer bolts.

6. I have also noticed one of the small ends is a little over size (not bad but not perfect) - can these be bushed?
Seems I've read it done but now over my head to advise on what to use/do thermal expansion wise or rod weakening effect.
 
Before you open the crankcase,fit the barrel with no pistons.Measure how central the conrods are in their cylinders.Then measure crank end-float.
When it all goes back together,you want minimum end-float and central conrods.If you do enough measurements on the old and new parts,you can get it right first time.Anything less than central and minimum is wasting a lot of power to friction,and causing unnecessary wear.I will get dis-agreement over this,but any off-centre forces cause bending.If it's possible to bend a 6-cylinder Chevy block 0.030" with hand pressure (and it is),it doesn't take a lot of off-centre force to flex a conrod (or any other column).

1./ It's easy enough to balance pistons an rods (big-ends and small-ends) within 0.1 grams.Put 2 rods on one gudgeon pin and face them 180 degrees apart.Use a drop of Loctite,so they don't move on the pin.Put the pin on level straight edges (reasonably level vice-jaws will do),and the heavy big end-will fall.If your vice jaws aren't dead level,you can double-check by reversing the whole assembly so the rod at the left now goes to the right.
If the rods and pistons are balanced within nothing,your 1/2-way there to being dynamically balanced.There may or may not be any difference in crank counter-weights.If one counter-weight is more than the other,you still get a rocking couple but the piston and rod weights aren't adding to it.

3./ I'm not into deep-freeze heat -treatment,but tuftriding the crank (nitro-carburising) can almost double its fatigue strength and extend the cycles-to-failure by about 10 times for a given load.Cheap insurance (better than money spent on balancing),and the rod journals become harder and more wear-resistant.

4./ Any rod bolts you buy these days are likely to be junk,and weaker than what you already have.Measure the elastic bolt extension when you tighten the rod bolts.Use a torque wrench too.If you get bolt extension without a corresponding proportional increase in torque,the bolts are junk.If all looks OK,they'll last forever because the bolt tension exceeds any cyclic loading they will experience.
 
Rod bush replacement piss easy . Though Id press out , inspect , the install new .

Yr going to need a micrometer or vernieer , and a D T I would be usefull . Investment .

The notorious Freddie Dixon spent most of his time ensureing component revolved or operated FREELY , with no binding , grabbing , or drag .

ANY excess clearances , beyond working limits ( this is where the ' tuners ' have learnt the prefered operateing ' clearances ' , start to get
' free movement ' . as in rattleing . clatter . Shock Loadings . Understandably this last are more invasive than regular opperation .
In fact they can be cumulative & explosive .

Outside that , the Oil Pump wants to be beyond question , and cam drive ( chain - sprockets ) very carefully inspected .

Often cowboys will lap cases ( studs removed ) on glass plate , to ensure mateing / sealing . Seeing EVERYTHINGS SURGICALLY CLEAN is priority
Neumero Uno .

This lot isnt a total load of garbage : ron-wood-norton-flat-track-tuneing-t11637.html
 
Thanks for all the replies and tips. I will take the bottom half out of the frames in a couple of weeks (A65 currently on the ramp) and start going through it. Sadly bike its a bit of a bag of sh** the PO lied trough his teeth and was probably the words was mechanic - I am having to fix nearly everything :( I will definitely need more help!

PS concerning nuts and bolts, I had an engine blow on me once because the slots in the "NEW" big end nuts were machined too deep (where the lips are bent down to lock it) and they fell apart after about 20 miles, was a real mess completely screwed the bottom end and barrels. So I don't trust any suppliers anymore seems to be pot luck. Also now use loctite everyvhere

Thanks

Nigel
 
Now would be the time to decide if you want to do something like lightweight pistons and rods!

yes!

this is a great time to install JSMotorsport's pistons and rods, and maybe get a new cam with followers

seriously, the cost is worth it for the much less reciprocating weight on the vitals for many years ahead

I don't know if Jim Schmidt of JSmotorsport is offering 60thou oversized, I would give him a call

time to consider a nice quiet and blessedly dry belt primary set up, Trispark, and new carbs?

consider al these costs much cheaper than either a cocaine habit or psychiatric treatment!
 
Nigeldtr said:
Thanks for all the replies and tips. I will take the bottom half out of the frames in a couple of weeks (A65 currently on the ramp) and start going through it. Sadly bike its a bit of a bag of sh** the PO lied trough his teeth and was probably the words was mechanic - I am having to fix nearly everything :( I will definitely need more help!

You will be hard pressed to find a better source of parts than those from Andover Norton.
Some of the tools (pullers etc) for other Brit bikes will work on the Norton but I think you need to be careful ? as far as the timing side on reassembly with the intermediate shaft and torquing the nuts with it unsupported.?
I ended up getting the support tool off Norvil.

I wouldn't get to disheartened,I have two Norton's like that,you just shake your head in bewilderment,put your hand in your pocket again and carry on fixing what has been inflicted on the bike.
You have to laugh I guess,the first TR5T I brought was described as a good runner yet it had 0.019" wear in the bore,valves with no margin left and so on with 4800 miles on the clock.
Sometimes I feel like a rescue shelter for neglected motorcycles. :lol:
 
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