Crankcases

Can you post a photo of the of the timing side?

The 3 digit numbers on all my cases are on the inside, half-way between the main bearing and the cylinder base. I also bought some non-matching halves and the cylinder base gasket surface will have to be machined to level. One side is 4 - 5 thou higher. Have you checked how yours fit together?

Previously Jonathan Soons wrote:

Can you post a photo of the of the timing side?

The 3 digit numbers on all my cases are on the inside, half-way between the main bearing and the cylinder base. I also bought some non-matching halves and the cylinder base gasket surface will have to be machined to level. One side is 4 - 5 thou higher. Have you checked how yours fit together?

Hi Jonathon,

Regarding you c/cases that need machining, you really need to check that the bearing housings are in line on the vertical and horizontal plane.

Regards, Ian.

Previously ian_hay wrote:

Regarding you c/cases that need machining, you really need to check that the bearing housings are in line on the vertical and horizontal plane.

Regards, Ian.

Right, that is much more difficult and and might even be a deal breaker.

This pic may help (last one) http://atlanticgreen.com/engcases.htm

What is obvious is that the Mk3 has a timing plug seen in the above pic. If you have that there's no doubt, just alignment to consider. I have 850 cases on my 750 and the ID nos don't match but they are aligned in respect of the cylinder base. I have no idea on the bearing bore though.

The important ones are the crank and camshaft, if they fit and spin freely the rest is relatively easy, if they are not it means taking the locating dowels out, finding the correct position for spinning free and then relocating the dowels so they stay spinning freely.

Previously john_holmes wrote:

The important ones are the crank and camshaft, if they fit and spin freely the rest is relatively easy, if they are not it means taking the locating dowels out, finding the correct position for spinning free and then relocating the dowels so they stay spinning freely.

Not really the ideal way to do it but it might work.

Ideally the crankcase needs setting up on a boring machine and for the bearing and camshaft housings to be line bored and faced, this is the only way to get the housings truly in line, it wouldn't be cheap and you would need to know the capabilities of the engineers doing the job before you handed it over.

When I did this to a square four crankcase I had a toolroom to hand and was able to do it after work hours so all it cost me was my time.

Oh how I miss all that machinery.

Regards, Ian.

Pete Lovell (Tel. 0121 558 2110) is your man, he is a Commando specialist and has all the necessary jigs and equiment to hand to do the job, he's a great guy too, very knowledgeable.

Previously ian_hay wrote:

Previously john_holmes wrote:

The important ones are the crank and camshaft, if they fit and spin freely the rest is relatively easy, if they are not it means taking the locating dowels out, finding the correct position for spinning free and then relocating the dowels so they stay spinning freely.

Not really the ideal way to do it but it might work.

Ideally the crankcase needs setting up on a boring machine and for the bearing and camshaft housings to be line bored and faced, this is the only way to get the housings truly in line, it wouldn't be cheap and you would need to know the capabilities of the engineers doing the job before you handed it over.

When I did this to a square four crankcase I had a toolroom to hand and was able to do it after work hours so all it cost me was my time.

Oh how I miss all that machinery.

Regards, Ian.

Ian, are you talking about enlarging the bearing recesses or moving them? Will the main bearings still fit after that?

After you have bored the housings in line at least one will be oversize, you then either copper plate the bearing OD if its a small enough difference or bore it out even more for installation of a sleeve. You could right from the start plan on using sleeves and line bore to suit which may end up being the best option.

Previously john_holmes wrote:

After you have bored the housings in line at least one will be oversize, you then either copper plate the bearing OD if its a small enough difference or bore it out even more for installation of a sleeve. You could right from the start plan on using sleeves and line bore to suit which may end up being the best option.

Relocating the dowels is so easy by comparison and I have the technology to do that. Then level the cylinder base (if necessary) and Bob's your uncle.

I would just put a crank and cam in, bolt the two halves together and check that they spin freely. Then skim over the crankcase mouth if there is any discrepancy there. You don't need to get too technical and rebore the main bearing bores unless you are looking for a lot of expense. (Thats my opinion of course) I think you'll be surprised at how good a match the two non matched halves are.

Previously david_evans wrote:

I would just put a crank and cam in, bolt the two halves together and check that they spin freely. Then skim over the crankcase mouth if there is any discrepancy there. You don't need to get too technical and rebore the main bearing bores unless you are looking for a lot of expense. (Thats my opinion of course) I think you'll be surprised at how good a match the two non matched halves are.

I think we would all wish for that dream scenario where we don't have to do anything drastic. Probably everyone does exactly what you outline above, then finds out the good or bad news.

Actually, Nortons don't seem to be too bad in this regard. Even back in the days of the singles, they used to recommend line-reaming the crankcases, as well as the timing cover which included cam bushes but in practice, NOS parts often fit together.

Although good practice suggests that it shouldn't be done, it often seems to be possible with Commando engines too....We're not talking Triumphs here !

Previously Jonathan Soons wrote:

Previously ian_hay wrote:

Previously john_holmes wrote:

The important ones are the crank and camshaft, if they fit and spin freely the rest is relatively easy, if they are not it means taking the locating dowels out, finding the correct position for spinning free and then relocating the dowels so they stay spinning freely.

Not really the ideal way to do it but it might work.

Ideally the crankcase needs setting up on a boring machine and for the bearing and camshaft housings to be line bored and faced, this is the only way to get the housings truly in line, it wouldn't be cheap and you would need to know the capabilities of the engineers doing the job before you handed it over.

When I did this to a square four crankcase I had a toolroom to hand and was able to do it after work hours so all it cost me was my time.

Oh how I miss all that machinery.

Regards, Ian.

Ian, are you talking about enlarging the bearing recesses or moving them? Will the main bearings still fit after that?

Hello Jonathon,

If the main bearing housings are misaligned either horizontally or vertically the ammount of metal required to be removed would be such that plating would be out of the question.

It would be necessary to bore and shrink sleeves into the housing, this is only practical where there is sufficient metal in the area occupied by the original housing.

Because of the labour involved it would be costly, as Iv'e said previously at the time I was working and the machinery was freely available to me.

Ian.