Replacement Crankcases

Hello all .... I have just purchased an Commando engine and frame

But ...... it has clearly thrown a rod and had a very "primative" welded repair to the hole (about an inch diameter) and extended crack (about 3 inches long).

The good news is it has been put back together with a load of new parts, pistons, rods, cam, possible crank etc.

It is a 1969 bike, engine number 20M3S/133648 (points in timing chest, tacho drive on front of engine)

So I am looking for some new crankcase

Are there any advantages on going for later crankcase which will be compatiable with the internals I have.
If so what would you recommend

I cant find any stamping on my cases that indicate they have been machined as a pair.
Did the factory stamp up paired crankcase or can I just replace the damaged half

As you might guess from my forum ID, a bit new to all this.

Thanks .... Richard

There would be no advantage to newer crankcases. I would avoid the 72 'combat' cases without the sump plug hole.

They are a matched set so should be replaced as a pair. Jim

tribonnie said:

Hello all .... I have just purchased an Commando engine and frame

But ...... it has clearly thrown a rod and had a very "primative" welded repair to the hole (about an inch diameter) and extended crack (about 3 inches long).

The good news is it has been put back together with a load of new parts, pistons, rods, cam, possible crank etc.

It is a 1969 bike, engine number 20M3S/133648 (points in timing chest, tacho drive on front of engine)

So I am looking for some new crankcase

Are there any advantages on going for later crankcase which will be compatiable with the internals I have.
If so what would you recommend

I cant find any stamping on my cases that indicate they have been machined as a pair.
Did the factory stamp up paired crankcase or can I just replace the damaged half

As you might guess from my forum ID, a bit new to all this.

Thanks .... Richard

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Hi, welcome. I looked at few for sale like that. The best part was one seller, didn't mention it at all... I've been TIG weldor for 35 years, those weld beads JUMPED right out at my eyeballs. They do come available on fleabay and other places (like our FS board here). Good luck!

tribonnie said:

I cant find any stamping on my cases that indicate they have been machined as a pair.

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Both should be stamped with the same number here, if they are:

RennieK said:

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Welcome. Do like Jim says. Later bikes have a different breather which can be a bonus. The early timed cam breather leaves some to be desired, you may want to look into that. There are various options. Your number indicates it probably started it's life as an 'S' type as the 69 Fastback started with 133668.

Dave
69S

Depends to a point on how much you're prepared to spend. Maney crankcases are racing quality and proven, and not much more than AN crankcases, which I have on my bike and benefit from a thicker casting than earlier cases and so therefore stronger.

If the ugly welded cases seal and hold crank aligned then what's the matter with just adapting a better breather location and keep em? My pre-Peel was vendors lend out demo bike that got some lasting fame long before i got it and then found cracked in mounting flanges, so 18" of weld to recover and re-enforce like old racers did - then survived tach pegging event but stayed sealed to run couple 1000 more miles till decided needed bigger engine to take on Ducci 1098's in real world here. Trixie Combat cases went through two case cracking events, comma oil piston let go then later a rod bolt let go [all under legal speed limit on low to no throttle] so just JBW resealed cracks and hole where can't be seen and worked fine for around here and out of state trips and back no problemo. My lazy buddy Wes on his '71 just let the noisey rod shells wear to road sezure 2 yr ago and rebuild insides to ride some more, so i think the worry over 750 case is mis-placed as long as not trying to stay in red zone all the time. Only real issue of Combat case is the front oil drain, not the breather pick up. Oil drain move to rear is rather easy as blocking front with a screw JBW in or just JBW like me, then grind into TS rear drain passage, no need to mess with the baffle ridge at all. On Capt Norton's site they disscuss drag racers perfering thinner 750 cases to allow more crank flex before cases resisted so much the cases crack horizontally. Then again Jim's brother cracked his Combat cases just trying to follow Jim on recent trip, so just spend spend spend or worry worry worry.

Richard I'm siding with Mr. Hobot on this one to save you some money. Simply find a competent alluminum welding person in your hometown to weld things up like before. It's been done before by many who don't have big cash for new cases and are probably not racing about town or on track. Ask the welder to file down the ugly bead part of weld so it looks presentable ? Personally I would check for any leakages before all the work of bolting it back together again just to find out the weld-work may drip oil. How to check I don't know, maybe bolt the cases back together and fill up with dyed water for a few days then observe for any leakage ? Good luck and hold onto that cash for rubber things instead ?

Ugh on welding if can't just seal with JBW as welding sure can distort cases to need horrific blacksmithing beating and pounding to mold case seams back to reasonable fit to seal again. If the dark JBW shows up too easy to your eyes can just rattle can Al paint to blend in. JBW can take days and some heat to really set up to last in this application. Next to a hair drier or torch, JBW may be my most used non wrench tool on Nortons.

Can you post a picture of the ugly weld and the crack ? JB Weld a very good product and have used it before successfully for many things. But a crack no.

You can't stop a crack from spreading using JB weld. :shock:
Bandaid anyone?
Do it right get new crankcases.
Regards,
Thomas
CNN

We have not seen the particular cases in question here so of course there's some states not even welding would work for long. Welding ain't a miracle fix either. Comstock told us about welding weakening cases and heads and not working out well in some of his attempts. Peel had case fractures, [some only DynoDave could find] and more under the surface, ground out and welded. Its a mean job as must melt beyond any fracture then fill back in. If it requires this level of repair the welding phase is the easy at pie part compared to what follows. Commandos simply complex or complexly simple.

Here's some more scope on cold welding rescues. Epoxy is not an adhesive so must have rough surface to fuse into. It black part is steel dust filled so can use magnet to draw it deep into fractures and hold it there in some non horizontal repairs.
https://www.google.com/#q=jb%20weld%20s ... 0crankcase

if its just a hole from a rod , cut it out and redo it . :lol:

later ones are webbed internally , thus tougher .

Mk III ones would work ?

IF you find a ace welder , no harm in tryiing . Marine chaps maybe familiar with alloy welding .

Got photo's?
If just a hole from a rod like my Trixie '72 then even less reason to weld as its non structural area that just needs to hold oil. In Trixie's case it didn't punch completely through so ya could stick a more that a fiber through, so beat it back even-ish then dammed and taped area on outside and magnet inside. Same with the oil passage punched though so almost 2" long crevice along its length. Can't see the repairs standing up. Here's a neat test comparison but they left out Devon epoxy.
http://www.youtube.com/watch?v=5JynysLv9R4

There are also a number of DIY al weld rods that only need a torch like soldering. Steel brushes are a bit of a no no to clear alloy before welding as may leave iron particles, SS is ok.

Thanks everyone, I have not yet split the cases to view internally.

Still undecided as re-welding bad weld repairs dosn't seem to sit right

thanks again ..... Richard

Brit bike cases are made of good alloy that weld well as my local alloy welder keeps telling me (he complains bitterly about Japanese alloy cases), so unless its really bad re-welding by a competent alloy welder should be fine.

The alloy bits on the commando weld up nicely.
I did some welding on a steel 70's Honda tank. It was steel, and that welded like crap.

We have one tale of someone just spot welding the chain guard mount back on and it distorted the whole swing arm. Besides running around on undetected slight denotation i bet most have some hidden cracks lurking too but only crack so far for such a long time its a non issue as long as don't leak oil. If fracture weld near the seam, ugh, if far away then weld away no sweat.
Very few frames short of full blown choppers have had as much welding and drilling as Ms Peel's, dozen holes and feet of bead, but so far so good as to fit and function. W/o real details can only give scope of options-opinions but not the right one for these instant cases.

Weld-o-rama ! Yes Norton cases weld up fine so don't be afraid. The 2 cases I've seen welded up where a rod went on vacation ,were not near critical areas, just on front casting round area ,that is hold in the oil purposed. If you do find new cases they must be matched because my understanding is they were line bored together to be married forever ( like swans and some humanoids). :wink:

Torontonian said:

Weld-o-rama ! Yes Norton cases weld up fine so don't be afraid. The 2 cases I've seen welded up where a rod went on vacation ,were not near critical areas, just on front casting round area ,that is hold in the oil purposed. If you do find new cases they must be matched because my understanding is they were line bored together to be married forever ( like swans and some humanoids). :wink:

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Not sure about being line bored as the main bearing housings are machined from the inside?

Certainly true that the barrel deck would have been machined with the cases bolted together though. The Workshop Manual states a new crankcase half can be provided, but must be machined to match the existing mating half.