Hi Folks. The A65 rebuild grinds on slowly. I've had far too much work lately so have not been able to get on with it!
I was about to fit the barrels which have been bored out to +.020 and noticed one cylinder is off kilter, see photo. The difference between the cylinder wall thickness is about .13" between the thickest and the thinnest area. The thinnest area is about .089" and the thickest .22"
I had this done by a Reputable engine builder and I will of course be contacting him (not always easy!) But I thought I'd ask your opinions too. As it was only rebored to +.020 I guess it must have been skew wiff before but the engine came to me in very many pieces and I didn't notice the offset. I can see no problem at the top but there are no easy reference points to measure from.
Just wondered what you guys thought.
Many thanks Glenn
only way you will find out if its been done right is to mount it on an angle plate , the head face clamped and run a dial indicator up and down to see if its been done square.
of course, its easier in an engineering company. I would put it up on our CMM (computerised measuring machine ) and check it that way.
if you know someone with a milling machine or big lathe, its possible to check on that.
If all is ok, then probably done in the factory and been like it for 60 years!!
only problem is , out to +0.040" is another ten thou a side, but at max +0.060" look at a re line.
It definitely does not look too good. I would measure the distance at the top of the cylinders from the outside lip of one bore to the outside lip of the other and then compare with the corresponding distance at the bottom of the cylinders. The RH cylinder looks to be coaxial with the 'liner' but the distance measurement will confirm whether the LH cylinder has been bored at a significant angle out of line. That certainly looks to be the case from the photo.
Hi,
They are all like that, for assurance, check the gasket is sitting correctly on the top surface.
Best wishes...
Hi Spaceman, good idea, why did I not think of that ::) Using the best method I can think of though by no means scientific, the difference from top the top width and the bottom bottom is about .2 - .1mm, nothing like the the 2.5 mm the difference in cylinder wall would suggest. So I think Chaz might be right that the factory may be to blame. Yes it doesn't give a lot of room for further rebores but I doubt I'll live long enough to see that necessity.
However .2mm is still up too nearly 8 thou according to mr Google. Is that OK?
Just seen your response Bess. Thank you, very reassuring. Probably all ok then.
Many thanks for your help
Glenn
Hi Glenn,
Its okay, all the popping and banging happens at the upper end. Here's an image of one on my bench, I have another in for rebore exactly the same.
Best wishes...
Quote from: GlennA65 on 10 Sep, 2022, 16:08
Hi Spaceman, good idea, why did I not think of that ::) Using the best method I can think of though by no means scientific, the difference from top the top width and the bottom bottom is about .2 - .1mm, nothing like the the 2.5 mm the difference in cylinder wall would suggest. So I think Chaz might be right that the factory may be to blame. Yes it doesn't give a lot of room for further rebores but I doubt I'll live long enough to see that necessity.
However .2mm is still up too nearly 8 thou according to mr Google. Is that OK?
Just seen your response Bess. Thank you, very reassuring. Probably all ok then.
Many thanks for your help
Glenn
0.2 mm difference is nothing to worry about - it certainly points to the accuracy of the casting of the bottom of the RH bore being a bit poor. As said, the forces on the bottom of the shirt are not that great and the remaining wall thickness should be more than adequate.
Fabulous, thanks guys. I'll crack on regardless!
Many thanks
Glenn
Ive seen barrels still being used with lumps out of the bottom.
you can work out the actual swept length and trim off the bottoms to make look better.
As long as the skirt of the piston does not drop too low and the piston go too far down, it shouldnt be a problem.
:) :) :) :)
That looks just like the one I have on the bench, and strangely we were very recently discussing the vaguries of unit A series twin castings/borings. Cant speak about pre unit---too long ago
With regard to lumps out of the bottom, My A50 barrells were dropped and knocked a bit out. No problem, runs fine. Not really surprising when you consider that the M20 and the M21 used the same barrel, with a couple of lumps ground out on the M21 to allow for the conrod to miss the skirt. .
So I woulnt lose too much sleep over it. The barrells I'm about to use have a couple of cracks in the skirt that have been drill stopped. Just hope the "lump" between the two cracks doesn't break off. Not that I would know unless it dropped somewhere serious. Be a bit of a doer if it jams between the big end and the crank web Might just slow the motor a lot.
Mike 8) 8) 8)
Mike 8) 8) 8) 8)
Quote from: chaz on 10 Sep, 2022, 18:19
Ive seen barrels still being used with lumps out of the bottom.
you can work out the actual swept length and trim off the bottoms to make look better.
As long as the skirt of the piston does not drop too low and the piston go too far down, it shouldnt be a problem.
Well, less weight, more speed! If I didn't have a million other jobs to do on the bike I might consider that ;D
Also, thanks Mike. I shall sleep sound now.
Cheers Glenn