Crankcase compatibility

Does a '73-'74 850 timing side engine crankcase fit to a '72 drive side crankcase? Opening up options to resurrect my original number crankcase.

Will they fit together -yes.

Will the bearing bores and gasket surfaces line up -probably not. Jim

you will also have to fix an oil pickup in the 72 case half IF as jim points out everything else lines up.

In the not too recent past it was not uncommon for special DS race case to be fit to factory TS case then snot run out of em. How would one determine non destructively if the 2 bores were too mis aligned? Hell being Norton just as likely to get a better fit than the factory matched set. Can one really get valid data to make a cost effective decision ahead of time concerning a Commando? It stops being a frugal thinking man's hobby if following the academic alerts of best advice no brain'r path - all new parts especially if not Norton numbered parts.

This topic does raise a good question. I have read here to never use mismatched cases because bearing bores for the crank and cam might not line up. This makes a lot of sense. Of course I don't know how accurately they were ever bored to begin with. I suspect that the reason some engines lasted longer than others from new had as much to do with alignment and tolerances as treatment from the rider/mechanic. So what all really is involved in using mismatched cases and is it worth the effort and expense? Is it feasible for a semi-skilled Commando owner to assess a set of cases for fit and alignment before deciding whether or not to bring the machine shop into the picture? This last question could pertain to matched case halves as well.

Russ

I think the process is called line boring and one issue I can think of is keeping bores tight is as much an issue as aligned so would line boring leave at lease one bore loose that allows race to spin at full heated throttle up operation. Crank shaft racers says up to .002" run out is survivable for scale of concern, don't know if applies to bore or not.

rvich said:

This topic does raise a good question. I have read here to never use mismatched cases because bearing bores for the crank and cam might not line up. This makes a lot of sense. Of course I don't know how accurately they were ever bored to begin with. I suspect that the reason some engines lasted longer than others from new had as much to do with alignment and tolerances as treatment from the rider/mechanic. So what all really is involved in using mismatched cases and is it worth the effort and expense? Is it feasible for a semi-skilled Commando owner to assess a set of cases for fit and alignment before deciding whether or not to bring the machine shop into the picture? This last question could pertain to matched case halves as well.
Russ

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Gidday Russ. well said. well here we go. I expect to be shot down in flames but would love to hear opposite reasoned argument.

The male and female spigots machined in joint faces control the alignment of the main bearing bores. In everything from british singles and twins to Shovel heads.
The dowels regulate the alignment of the barrel base surfaces as well as main bearing alignment..

Norton did not rough machine the cases, then line bore to finish off. If the fit of the spigots is held to size for size or VERY slight interference, good alignment results. I reckon there would be very little tolerance regarding parallelism and maximum 1/2 thou tolerance on offset. if the spigots are good, I cannot see why different cases cannot be used, the main misalignment is the barrel mounting surfaces.

However this can be corrected easily. Remember these are Production engines. any extra operations will have been culled. I have just repaired 2 HD cases, one a 82 Shovel and a Model U flathead. the shovel needed repair where the driveside cast in bearing housing came loose. by making and using a set up plate, the bearing was repaired.
having the drive side set in lathe and bolting on timing side, the clock read 4 tenths runout.

the flat head timing side was cracked and welded around the main and some of the bushing holes. the owner had the original drive side and a replacement timing side. again, the main bearing alignment was 1 thou and gasket surfaces were very good. 1 thou was fine for this application as not much hard riding or high RPM's on a sidevalve getting intermittent use.. this is amazing as these U's are very old engines.certainly used again .

the main trouble will be in the gasket surfaces, not the Main bearings. BWolfie, your missus is at the factory. would not take much of a squiz to see if they line bore or not.

But I say again. in principle there is no reason why different cases are Verboten!
Just check before use. the problem area is the gasket surfaces which are more easily remedied than main bearing bores.
The main trouble also comes from old case being distorted, but when bolted up there is a good chance of being main tunnels being OK. The issue of economics to repair is a very personal one. depends on individual circumstances, and how many good machine tools your mates have.

Russ, as for your self checking of your cases. U need a lathe big enough to swing the cases. Mount the drive side to a faceplate or hold by suitable means. Then get the spigot face and diameter running true on the drive side. the faces may show some distortion. this is where a setting plate comes in useful. bolt the plate to the spigot and set the plate. use a tenths clock. u need to set to 3 tenths or so. and have the drive side monted rigidly. then carefully bolt on the timing side. dont disturb the previous setting. rotate by hand and record the clock reading. anything over about 3/4 thou will require attention. 1/2 thou is quite acceptable. bearing books quote acceptable angular misalignment.

if repairs are required, that is another story

Remember Nortons in the 70's were not made on toolroom grade machine tools. they are not a Swiss watch. street engines anyway. the above alignments may not apply to racing. I have no experience with racing engines. I am about to check a set of mismatched cases for a M20. i am expecting no unfixable problems.
Russ, I hope this helps. I am bracing myself for the expected coming storm.. be very interesting. Aussie bradley

B.Rad said:

Norton did not rough machine the cases, then line bore to finish off.

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How do you know that? It would have been rather uncommon not to do so (especially considering rather imprecise equipment as machining paired stuff would at least mean the error is identical on both halfs of the assembly .... ) And if they were not matched during production why would the factory have bothered with giving them matching nos? Just to mimic common industrial practise? Sounds rather strange to me ...


Tim

I dunno know but suspect even if two halves were finished together they may not of stayed together in Norton's turmoils. I've never found a serial number on TS cases for any mate matching certainty. How can we find out how they were made to judge how much sense there is to even think about one half economy recovery. What is wrong with orignal case as it might be repaired easiest.

Depends if it was the same machine operator using the correct plank................

Tintin said:

B.Rad said:

Norton did not rough machine the cases, then line bore to finish off.

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How do you know that? It would have been rather uncommon not to do so (especially considering rather imprecise equipment as machining paired stuff would at least mean the error is identical on both halfs of the assembly .... ) And if they were not matched during production why would the factory have bothered with giving them matching nos? Just to mimic common industrial practise? Sounds rather strange to me ...


Tim

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it certainly dont sound strange to me at all. Respectfully mate, were you production machining in the 60's and 70's pre CNC.

I do not know for certain the production process. However based on production practices of the time, (preCNC), it would have added considerably to the cost to employ another unnecessary process especially having to use a specialised machine. if they were line bored it probably be done on a double ended line borer but this would still present considerable difficulties compared to doing them seperatly. Blind holes are the difficulty here.

bearing in mind line boring is Mostly used for through holes. due to complexity in line boring a left and right blind holes, needing a left and right hand tools set on the same bar, the practical difficulty of mounting the assembled casing, then inserting the bar, and then the removal process, it makes it highly unlikely they were rough bored, then put on another machine to be finished. So I will still say line boring would have been uncommon for this operation

Tim, please explain your meaning of imprecise machines. read the specs supplied in the manual. plenty of tight tolerance there.just because machines were pre CNC does not mean that high accuracy and close tolerances were not achievable. if the dowels were done on a completed case half, in a jig borer, the accuracy would still be in tenths.

the crankcases were probably bored on turret lathes. as the bore, spigot and face were done on each half in the one setting, there is no appreciable error in each half. if design tolerances were adhered then no appreciable error will result on assembly of the 2 halves and the job would still be in spec..

so here is what I reckon happened.

the case halves were put on a turret, spigot done, main bearing bored, face done. then either into a jig borer, or a fixture made on a jig borer, dowels and holes drilled and reamed where necessary. cam bores were probably done now as well. a pair of cases were then stamped with same number.

then these cylinder base surfaces were machined as a pair. they were then separated for any further operations and cleaning.

remember there were a lot of cases. they had to be dismantled for at least cleaning. the easiest way to keep track of a loose pair would be to stamp them with the same numbers. especially going through automated cleaning baths.

As for why would anyone do seperate halves. as I said, the bearing sleeve in the Shovel drive side came loose in the casting. these were a matching set but were repaired success fully without line boring. still need good accuracy. with the flathead, the timing side case was severly cracked around the main bore, and cracked wher the timing gear bushes run.These were not a matched pair but aligned good enough to use. The M20 had been butchered by a previous owner and was far too much work to repair one half..

I am not a business, and I do this stuff for my mates. i dont charge much, if anything at all. so for me it is economical. I never have argued economics, just engineering and I say it can be done. not a common job but certainly do able.


Would someone please describe the process using line boring. my explanation is credible. to claim line boring was used a credible process must be described using a single bar machine or a double ended borer. I cannot claim my process is "Gospel" but it is practical and credible.

back to the question, can different cases be matched and then used. Yes.

did Norton line bore the assembled cases. highly unlikely. this is based on the good ol business principle"time is money".

anyone from any british motorcycle factory out there care to chime in. there must be a lot. Mr Damp perhaps. If the evidence proves me wrong, I can readily accept that. and publicly say i was wrong.

but there must be good evidence to refute my claim.
waiting to hear from someone who was there please. Aussie bradley

Edit. I will stick me neck out here. I doubt even the cases made today for Andover are line bored assembled as a pair. cylinder base surfaces , yes. there is a difference.Someone from Andover correct me please.

Only one way to find out for sure. Try it. You will have to mod. the oil pick up as pointed out by Bill. I do know one thing for certain , & that is the cranks were ground as a pair & then separated for cleaning, never to go back as a pair unless by pure chance (Wolverhampton made engines). I read this in an article by a factory tester who carefully assembled an engine for his own bike. Interestingly enough this featured a head with full hemispherical chambers, which he said gave better performance & more MPG. (Bob Rowley I think)
I think Bradley is correct in that Capstan / Turret lathes were used for crankcases, gearbox cases, brake hubs & even crankshafts as well as a host of other items. This was certainly the case at AMC who in the mid to late fifties spent around £1000,000 with Alfred Herbert Machine Tools re equipping their machine shops. The Matchless cases were held in a fixture & faced, spigot turned, the bearing bore rough bored to depth, then finish bored using a micrometer boring head. All this was done from the turret & front & rear tool posts. The camshaft bores were done in a separate set up.

B.Rad said:

did Norton line bore the assembled cases. highly unlikely. this is based on the good ol business principle"time is money".

waiting to hear from someone who was there please. Aussie bradley

Edit. I will stick me neck out here. I doubt even the cases made today for Andover are line bored assembled as a pair. cylinder base surfaces , yes. there is a difference.Someone from Andover correct me please.

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yes it would be good to hear from someone who was there at the time....

OK...main bearings are one thing...line boring....camshaft bushes are another... I have always assumed that the camm bushes are pressed in undersize and are then reamed in situ, first build and repair work, so if you were using unmatcheds cases....

Try to estabish if the main bearing alignment is sufficiently close to proceed, check if adequate end float clearance can be achieved with the crank you propose to use, check if face alignment is sufficiently good to seal, if not machine and go back and recheck end float clearance. Sort oil pick up, check barrel face alignment on joined cases, machine flat...install new cam bushes and ream to ensure clearance and parallel with crank axis?

Are we done?

And if we are paying for these operations at commercial rate how far did we get before it was more economical to buy a set of use matched cases or a new AN matched set at £895 plus shipping (and taxes), or Maney cases at £995 plus, but also plus some additional work for the non-standard build etc..

You seem to want to do this to have a bike with matched numbers, may be percieved to affect value! Only you can decide if this is a wise investment on your part.

It seams you may have already changed the cases after the TS failure' which would be the less commonn failure so surely there are '72 TS case halves out there as well?

In my own view, you are entitled to stamp new unstamped cases with any number you want....including the number stamped on your original DS case!....I also thinkk it is better they are stamped with some number rather than none....

B.Rad said:

Blind holes are the difficulty here.

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That's true, to be precise it would be back-boring for one of the bearing seats.

bearing in mind line boring is Mostly used for through holes. due to complexity in line boring a left and right blind holes, needing a left and right hand tools set on the same bar, the practical difficulty of mounting the assembled casing, then inserting the bar, and then the removal process, it makes it highly unlikely they were rough bored, then put on another machine to be finished. So I will still say line boring would have been uncommon for this operation

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I remember vaguely that the design of most British twins reflects the fact that lathes were more common than mills so mostly these engines were designed with lathes in mind.

If you mount the timing side of the assembled crankcase to the lathe chuck - using a dedicated fixture which positions the assembly via the two dowels - a bore rod (with two cutting edges so that the turning motion could be performend in two consecutive operations) could have an effective diameter of something in the region of 45mm which can be easily inserted. The turning diameter is 72mm. To me this sound feasible but I'd really be interested how it was really done.

Off course this represents more effort than relying on the repeatability of al leats two different machines but it's not something a skilled engineer or tool builder wouldn't master.

Tim, please explain your meaning of imprecise machines.

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I'm used to machinery operating with repeatability in the region of some µm - and we still line bore our crankcases (although blind holes are a no-go, granted). :wink:


Tim

Gidday All.
Matchless, thanks for your post. Indeed herbet7B and Ward 10's and 7's were the foundation of lots of british engineering. Your claim that Matchless cases were finished individually is strong evidence that any for British single or twin the cases were finished individually and not line bored.

Tin Tin. thanks for your reply. Mate, you seem to understand the difficulty in line boring blind holes. I am merely claiming that the cases being bored in line would have presented difficulties and extra costs and in doing this makes it unlikely that they were line bored. especially in a production environment. I refer to Mr matchless. It is highly unlikly that the case were assembled and then line bored on an turret lathe. refer Matchless. this was a production environment.What sort of cases do you line bore now. they dont seem to be blind holes. Are they Norton. A photograph please if not too much trouble. also I agree those old turret machines would not have repeatability of a couple of microns. to get that repeatability on size u probably have CNC.

this is why turrets used david Brown floating reamers and microbore boring bars. these tools are probably not used today. but in doing them individually, repeatability is not an issue if the spigot and bearing bores were done in the same setting and drawing tolerances adhered to..

Steve A. thanks for your reply. U seem anxious to end this discussion. this is a norton forum and the thread is relevant to Nortons.or maybe I misread the post. I do try to be very civil.

mate, u r right about cam bushes being reamed after fitting in some cases.. however the holes taking the bushes must still be in very good alignment. u dont want the finished bush axis to be off from the locating bores. that is a no no. so the holes must still be in line. And all that other stuff is what I do when evaluating mismatched cases.
and for me economics is not relevant. to some it may be.

if some people think I am being pedantic I do apologise. But I do love my Norton and this forum.

I really like to contibute something of substance from time to time. I am not a engine guru,, a motor tuning wizard, carburettor guru, mathematical genius, or other specialist things.

I am just an old retired turner who only knows engineering. but I dont like to see half truths or plain wrong stuff being promoted as fact. I dont post unless I am pretty sure my posts are factual. I will admit publicly if I am dead wrong. engineering is the only subject I can post on. peace and good wishes to All Aussie bradley

B.Rad said:

What sort of cases do you line bore now. they dont seem to be blind holes. Are they Norton.

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No, they are rather at the other side of the spectrum:This picture is a couple of years old but you might get the idea... :mrgreen:


Tim

gidday Tim. thank you very much for posting photo. i get the idea allright. I am a bit gobsmacked. really awsome. the skills on this forum are really amazing. I never even been close to doing that sort of stuff. a class above what I do. I am just what we call in Aussie a jobbing machinist. however I did spend sometime in a machine shop doing F1-11 jet engine stuff, that was different. temperature controlled shop, mainly repairing bearing housings and journals that were reclaimed by nickel plating. everything was bladey and flimsy. all held in fixtures.tolerances to a couple of tenths only.

makes old Nortons really agricultural.

Tim. do you machine from the raw castings. U must have one hell of a machine shop. do you sell the finished engines or race them yourself.
Thanks very much. much appreciated. Aussie bradley

B.Rad said:

back to the question, can different cases be matched and then used.

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Drive and timing side crankcases for Nortons were also listed separately until 1970, although parts books up to the early sixties contain a note about the need to return the sound crankcase half to the factory for "matching".

I've read here on prior question of fitting 850 crank in 750 cases to be alerted the 850 crank is a bit longer so keep that little factor in mind. The world wide major B.I. parts vendors are my source of mix/match wisdoms if not getting definite answers from the few hobbists online.

B.Rad said:

Steve A. thanks for your reply. U seem anxious to end this discussion. this is a norton forum and the thread is relevant to Nortons.or maybe I misread the post. I do try to be very civil.

mate, u r right about cam bushes being reamed after fitting in some cases.. however the holes taking the bushes must still be in very good alignment. u dont want the finished bush axis to be off from the locating bores. that is a no no. so the holes must still be in line. And all that other stuff is what I do when evaluating mismatched cases.
and for me economics is not relevant. to some it may be.

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Not at all Bradley, engineering is interesting......and we all thirst for knowledge, surely.

But in my world someone has to pay, if it involves Nortons, normally me, so the economics have to be addressed as well..... 'make or buy' is also always part of my business life systems engineering decision making, so it is natural for me to consider that. I imagine it is also a consideration for the original poster, who, if he had some of the knowledge already posted here probably would not have needed to post his question! So I am guessing he would have to pay for the machine work too.

The fact that you are in a position to help others without worrying about recovering the cost is great.

Keep it coming.

Steve