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...is this going to be?

A little back story; about 2010, not long after I joined this forum, (and promptly forgot about it) my 750 Commando engine deceased itself for reasons unknown.
It was stripped down, bent conrod, broken piston, cracked crank found. Couldn't find replacement parts at the time, and it sat in boxes while I rode harleys (yes I know... we all make mistakes.) Barrel was +80 according to the inspecting mechanic and needed replacing.

12 years later, I have obtained another barrel (not new) and another crankshaft and rods (not new.)

I am about to begin ordering the various parts, rebuild kits, rings, gaskets etc, and begin the rebuild.

So.. I guess my questions are;

1) if I have mix 'n' match engine components, what are some of the idiosyncrasies that I need to be aware of?
2) If I am changing the cam type or compression, which parts will work best with which? I am in favour of a standard cam and lower compression.
3) are there any things that you have all learned from engine rebuilds to improve longevity or reliability that I will not find in a haynes manual?
4) which non-OEM parts should I avoid?
5) Which retailers should I avoid? I am buying from RGM

I am sure this is pandoras box type post, and there will no doubt be such well meaning advice as 'take your time and follow the manual... do your research... did you search the forum first... eat healthy and be good to your mum... etc etc' Yeah I know, not my first time on the internet, I'm under 50.

Thanks in advance chaps

-Ben


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Originally Posted by -BW-
1) if I have mix 'n' match engine components, what are some of the idiosyncrasies that I need to be aware of?
2) If I am changing the cam type or compression, which parts will work best with which? I am in favour of a standard cam and lower compression.

Edit:
I just noticed the"72" Commando in your signature so is this a Combat model? Assuming it has the original cylinder head, does it have a "C" (Combat) stamp on the top? AMAL 32mm (932/19 and 932/20) carbs?



Originally Posted by -BW-
5) Which retailers should I avoid? I am buying from RGM

RGM and Andover Norton are good or Norvil Motorcycles if you can't get the parts you need from the first two.

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What is "internet"?


1970 T120R - 'Anton'
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Originally Posted by L.A.B.
Originally Posted by -BW-
1) if I have mix 'n' match engine components, what are some of the idiosyncrasies that I need to be aware of?
2) If I am changing the cam type or compression, which parts will work best with which? I am in favour of a standard cam and lower compression.

Edit:
I just noticed the"72" Commando in your signature so is this a Combat model? Assuming it has the original cylinder head, does it have a "C" (Combat) stamp on the top? AMAL 32mm (932/19 and 932/20) carbs?



Originally Posted by -BW-
5) Which retailers should I avoid? I am buying from RGM

RGM and Andover Norton are good or Norvil Motorcycles if you can't get the parts you need from the first two.

The crankcases are identified as being Combat. (When the engine was disassembled the mechanic pointed out to me the internal differences between the combat case and a standard Commando case). However I don't think the engine originally belonged in the frame. I also can't find a 'C' on the head... only an 'O'...
It has a 930 AMAL on a single carb manifold.
Its registered as a 72, which should be based on the frame number and not the engine, but it has a murky history.


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Originally Posted by -BW-
The crankcases are identified as being Combat. (When the engine was disassembled the mechanic pointed out to me the internal differences between the combat case and a standard commando case).

There were no specific Combat cases only the "063334 Crankcase Halves Assembled" for all '1972'.
http://www.tioc.org/partsbooksnorton/pb-nort-750%201972%2006-3402.pdf

I think only the camshaft bushes would be different between standard and Combat cases.
Note that the rear case breather does not conclusively identify cases as Combat because the standard 750 models produced during and after the Combat series ended had the same lower case breather.



If, however, the engine number (assuming it has one) falls within the 200976 - 211110 range then the cases are likely to be Combat. If not, then it's unlikely they are actual Combat cases.


Originally Posted by -BW-
However I don't think the engine originally belonged in the frame. I also can't find a 'C' on the head... only an 'O'...
It has a 930 AMAL on a single carb manifold.
Its registered as a 72, which should be based on the frame number and not the engine, but it has a murky history.

Ok, many 750 engine parts are interchangeable but without knowing exactly which cases and other parts you have makes it a little more difficult.

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Hi L.A.B.
That's interesting, the mechanic pointed out part of the casting at the bottom of the cases, something to do with the oil, and insisted that this was different in the combat, and that this identified them as combat cases for sure. Aside from the case numbers also being with the combat range, 202 022, He went on to explain that this design difference was a poor one, and that a modification could be done to this area of the crankcase to improve the oil feed, and make it more like the standard model.
Just to check that I hadn't misunderstood what he explained, I perused the internet and found this :



at 2:05 he mentions a modification to the 'windage tray', this ties in with what I remember.


Anyway, a digression,.. It probably doesn't matter, aside from the camshaft bushes you mention. Should I measure these before replacement to ensure I have correct bushes? I'm assuming I can use a standard cam?

Last edited by -BW-; 09/23/22 10:35 pm.

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All i will say is please don’t butcher your cases like in the video. Dyno dave has a much better way to address the oil pickup issue. Yes to keeping the breather in the stock location.


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Originally Posted by -BW-
That's interesting, the mechanic pointed out part of the casting at the bottom of the cases, something to do with the oil, and insisted that this was different in the combat, and that this identified them as combat cases for sure.

Yes, there was a change made to the oil scavenge from the beginning of the 200000 series cases where the gauze sump strainer plug was deleted (reinstated on 850 cases), and the scavenge pickup moved further forward, however, your mechanic isn't quite right as that applies to all* 200000+ 750 cases, both standard and Combat and continued on into '1973' so well after the Combat series ended.
http://www.classicbike.biz/Norton/Parts/1970s/Commando_Parts_73-74.pdf

*(Except for a few late '235' correction '230' series 750s that were built with '850' cases)


Originally Posted by -BW-
Aside from the case numbers also being with the combat range, 202 022, He went on to explain that this design difference was a poor one, and that a modification could be done to this area of the crankcase to improve the oil feed, and make it more like the standard model.

That's basically correct as doing the scavenge modification can be worthwhile but it doesn't reinstate the pre-'2' series gauze strainer plug.


Originally Posted by -BW-
Anyway, a digression,.. It probably doesn't matter, aside from the camshaft bushes you mention. Should I measure these before replacement to ensure I have correct bushes? I'm assuming I can use a standard cam?

If they are the Combat cam bushes then it would be wise to replace them with the earlier or later type if you intend to fit a standard camshaft so you can eliminate the troublesome 06.2601 thrust washer(s) in the link below, that the tangs break off and often get drawn into the scavenge pump and wreck it (due to the lack of the gauze strainer).
https://andover-norton.co.uk/en/shop-details/15903/thrust-washer

Last edited by L.A.B.; 09/23/22 11:51 pm.
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Originally Posted by -BW-
the mechanic pointed out part of the casting at the bottom of the cases, something to do with the oil, and insisted that this was different in the combat, and that this identified them as combat cases for sure.


LAB is somewhat muted in his reply here. !?

This subject has been somewhat thrashed to death. !!
There is no difference in the combat and non-combat cases for 1972.
(other than those tangs on the cam bushes - and they can be changed.).

You CANNOT look at the cases and definitively say if they are combat or non-combat.
Period ?

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Thanks LAB, I think you cleared up the point about combat cases for me. Either way, its not particularly important at this point, (unless I decide to do the modifications) and I don't want to create a contentious digression about identifying combat motors... just looking for rebuild advice.

I cannot find a mark underneath the shell bearings to indicate what size they are, only a 5 digit number. Does this indicate standard size?

With regard to the camshaft bushes, RGM are out of stock of some choices, so would it be plausible to use a pre 200,000 bush on one end of the cam, and a post 307,311 bush on the other end, if they all fit the same?

Cheers


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Originally Posted by Rohan
Originally Posted by -BW-
the mechanic pointed out part of the casting at the bottom of the cases, something to do with the oil, and insisted that this was different in the combat, and that this identified them as combat cases for sure.


LAB is somewhat muted in his reply here. !?

This subject has been somewhat thrashed to death. !!
There is no difference in the combat and non-combat cases for 1972.
(other than those tangs on the cam bushes - and they can be changed.).

You CANNOT look at the cases and definitively say if they are combat or non-combat.
Period ?

Cheers Rohan, duly noted. I only made mention of identifying the crankcases as I was unsure if it effected the choice of components in the rebuild. It appears it makes no difference if I am choosing to rebuild it as a standard motor. I don't particularly care what it was, only what it will be.


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Originally Posted by -BW-
I cannot find a mark underneath the shell bearings to indicate what size they are, only a 5 digit number. Does this indicate standard size?

Knowing the number might help.

Originally Posted by -BW-
With regard to the camshaft bushes, RGM are out of stock of some choices, so would it be plausible to use a pre 200,000 bush on one end of the cam, and a post 307,311 bush on the other end, if they all fit the same?s

The RGM bushes should be 063020 T/S and 065425 D/S (the Combat type were internally scrolled 062600 x2).

https://www.rgmnorton.co.uk/buy/cam...plain-bore-with-flange-righthand_276.htm
https://www.rgmnorton.co.uk/buy/camshaft-bush-eng-no-200000-on-l-h-plain-bore-no-flange_275.htm

The same for Andover Norton:
https://andover-norton.co.uk/en/sho...ases-crankcase-breather-tachometer-drive
Items 4A and 4B.

Whichever T/S bush you use the tapered thrust washer 061086 must be fitted.
https://andover-norton.co.uk/en/shop-details/15521/thrust-washer-camshaft

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This is what I did on my recently rebuilt 72/73 Combat Commando:-
- crank was reground to -30, this requires that the crank is disassembled, sludge trap cleaned and new bolts used for reassembly, red loctite used to keep nuts secure
- new big end nuts and bolts together with new shell bearings
- new roller main bearings
- timing side cam bearing converted to use bush with flange instead of tabbed washer and nonflanged bush, drive side bush kept as original.
- new 2s camshaft and followers refaced both from Newman cams
- new IWIS cam chain and rubber-faced tensioner
- new Andover Norton oil pump and pressure relief valve
- new MK3 timing side cover, which has an ani drain valve that actually works
- new Hepolite Pistons and rebore to +20

I didn't bother with the breather mods to the crankcases, instead, I opted for a one-way valve in the breather hose, RGM sells one, and also Holland Norton works. By using a one-way breather crankcase pressure is reduced, which helps to stop oil from blowing out of the breather.

All of this work seems to have paid off, I now have a really nice running engine that pulls well throughout the rev range and the oil pressure is excellent.

Some of the key takeaways are to use a flanged timing side bush as the original setup with a tabbed washer had a tendency for the tab to break off and block the oil return in the sump. The other one is to use new nuts and studs when reassembling the crank and conrods, these are considered one-time use only since they stretch when torqued up. Use assembly paste on all moving components, especially the cam and followers.

Last edited by gunner; 09/26/22 5:15 pm.

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Please don't "uncombat" a combat. It accomplishes nothing. They work just fine as-is.
Russ

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Apologies for the slow updates on progress. I finally recieved the first batch of parts from RGM, it takes over a month for UK>NZ shipping, and I am waiting on lot number 2 from Andover before I start any work.
I have pictures of things, but I don't have a picture Hosting thing.

Anyway, further questions :
1. Before I disassemble the crankshaft for cleaning and replacing of bolts, I noticed the studs are not all aligned centrally and some of the nuts are different sizes. Is for reasons of balance? Or should these all be symmetrical?


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Lots here use postimage.org to upload your pics, and show the links here.
You don't have to join, or anything like that.
And, touch wood, it seems to be free and permanent.

We probably need to see some pics of these bolts/studs to comment.
Andovers set would suggest they should all be the same. And symmetrical.
Perhaps some previous work has altered something ??

[Linked Image from andover-norton.co.uk]

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[Linked Image from live.staticflickr.com]

Is this the 'flanged bush' that's been referred to?


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[Linked Image from live.staticflickr.com]
[Linked Image from live.staticflickr.com]

Sorry I should elaborate, hardware appears to be installed asymmetrical, with differing nut sizes and a combination of studs and bolts.
Of course I am replacing the studs & nuts set with a new one from Andover, exactly in the picture above, but I am wondering why my crank bolts are fitted the way they are.

Last edited by -BW-; 10/28/22 4:11 am.

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Maybe thats what the PO had to hand.
Maybe thats what the factory had to hand !
I'll leave it to someone who has seen more of them.

I'd comment that I ordered a set - for a dommie - locally,
and it came with a mix of UNF and Cycle Thread nuts.
Even though all the studs were cycle thread !

Don't always assume a PO had any logic or reason for anything you find inside !?

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Haha yep, it doesn't surprise me that there is was no real reason for it!


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Originally Posted by -BW-
Sorry I should elaborate, hardware appears to be installed asymmetrical, with differing nut sizes and a combination of studs and bolts.
Of course I am replacing the studs & nuts set with a new one from Andover, exactly in the picture above, but I am wondering why my crank bolts are fitted the way they are.


Early models (including '1972' according to the parts book) had a combination of (BSC) studs, bolts and nuts so what you have there is normal with the extended nuts in their correct positions.

https://andover-norton.co.uk/en/sho...t-kit-500-600-650-750-up-to-end-of-1971-

Later models and what is shown in the AN picture had all (UNF) studs and nuts so there will be four extended nuts.

Factory manual, section C27, Fig. C33.
[Linked Image from i.postimg.cc]


Originally Posted by -BW-
Is this the 'flanged bush' that's been referred to?

Yes.

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Interesting. does this mean that the random crankshaft I bought off ebay is by coincidence a combat one?
So does this mean I can replace the bolts with a standard set like in the AN picture?


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Originally Posted by -BW-
Interesting. does this mean that the random crankshaft I bought off ebay is by coincidence a combat one?

As it has bolts and studs then it could be any Commando crankshaft up to approximately '1972' production assuming the combination of bolts and studs are the originals.


Originally Posted by -BW-
So does this mean I can replace the bolts with a standard set like in the AN picture?

Yes.

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And
Originally Posted by L.A.B.
Early models (including '1972' according to the parts book) had a combination of (BSC) studs, bolts and nuts .

And that combination of studs and bolts extends as far back as early 500cc dommies - 1950 ish

[Linked Image from i.postimg.cc]

I've not seen any explanation of the rationale of why a mix of bolts and studs ?

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Ok that clears up that mystery. Thanks for the info.
The next question relates to bearings.
When I received my order from RGM, a gentleman by the name of Paul left a note in the box. He said 'bearings changed to C3 clearance instead of standard. standard not suitable for combat or 850.' or words to that effect,
I have since emailed RGM, over a week ago, to ask what this means, but had no reply. I tried the two email addresses listed on their website but I don't think they are active.
Can anyone else elaborate on this? (or have a recent contact email for RGM) ?

Last edited by -BW-; 10/29/22 12:28 am.

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