Oil passages

[McBob]

One of the issues that came to light during my engine rebuild was drive side case warping due to a weld repair. The warping was so bad it couldn't be trued up, but I could assemble everything and it seemed to spin nicely. Might be worth checking

[MalcW]

The crank is on its way home from a machine shop halfway across the country. It’s been spray welded and ground back down to specs. This time I will thoroughly clean every nook and cranny of everything, especially after seeing all the metal filings and flakes in my oil. I had the case welded, rather than use a spare, (to preserve my serial number for the paperwork) and should be re-assembling soon. Thanks so much for your encouragement.

When you get your crankshaft back, make sure that the reground journals have been radiused correctly at each end, to avoid a future breakage.

Malc

[RodneyK]

McBob, I’m a bit worried about that because I had significant welding done. If everything spun freely, what didn’t true up? The two casing halves?
MalcW, only one was reground and it appears to be the same as the other. I would notice it when torquing down the big ends, wouldn’t I?

[SPRIDDLER]

McBob, I’m a bit worried about that because I had significant welding done. If everything spun freely, what didn’t true up? The two casing halves?
MalcW, only one was reground and it appears to be the same as the other. I would notice it when torquing down the big ends, wouldn’t I?

Was the engineer aware of this regrind info from the Workshop Manual..........?

http://archives.jampot.dk/book/Workshop ... CHABLE.pdf

Crank regrind dims.JPG

[Groily]

You'd only notice anything torquing down the big ends if the shoulders / radii were too wide and bound on the shells.

In some cases, shells have had to be lightly chamfered for a correct fit, even on correct journals, but I think current club stock won't need that probably. It's easy to tell if they start to bind!

If the radii have been reduced too far, the rods will feel OK if journal diameters are correct, but the crank might not be. It really is important that all the radii are present and correct: the data supplied by Spriddler are mission-critical frankly - some cranks are only good as doorstops for the want of the correct profile, which can't be regained if lost.

Ensuring a free-spinning crank on reassembly is often a function of following the protocol when fitting the carrier for the centre main - assemble the six nuts finger-tight, offer up the second half of the crank case (without camshafts etc if it's easier) and do it up tight. See how the crank turns. The carrier should settle into its correct spot - there's usually a tiny amount of wiggle - and it should spin freely. If it does, split the cases, do up the six nuts to spec, and carry on. If it doesn't, then some head scratching will be needed. With any luck the welded up case will still be 'true'. I have one drive side case that was broken into three parts by a flailing conrod, but was repaired to perfection and has done tens of thousands of miles since, so it isn't necessarily a worry.

It's also worth thinking about the option to machine a circular groove for an O ring instead of the paper washer which goes between the cases to seal the oil filter chamber. Or, with infinite patience, make a thin gasket that goes all the way round the joint. (There should be a fair bit of discussion on this on here if you do a search.)

[RodneyK]

The ground crank journal looks like the other one to a close eye inspection, complete with radii. The rods free fall but measure 0.003” clearance with plastigauge on the big end shells. Is that within tolerance? I’ll replace the main bearings and reassemble as you suggest. When dismantling the engine my manual mentions a paper gasket sealing the oil passage on the centre web. It’s not mentioned on reassembly nor in the parts books. Suggestions? I’ll use a paper gasket on the oil filter chamber as I have no easy access to a machine shop. Waiting for some parts now so will do more research.
Thanks guys.

[Groily]

The www has a good few comments and You Tubes on this topic. Bit of a minefield even so though, I reckon. Haven't been able to find anything specific to our bikes on this, although there's some stuff out there on Notruns and I bet there are comments on here too if I could find them.

One common school of thought says "1thou max per inch of shaft diameter" which would imply less than 2 thou would be good as opposed to the 3 you report. But much depends on the age of the design, the materials and the oil to be used - I doubt that today's typical clearances, using 5/30W etc oils, are definitive guides for older machinery which probably had / need a tad more.
Personally, I was raised to believe that some 'side-to-side slide' is normal and 'a bit' of sideways rock is OK as long as there is no perceptible movement at all when tugging/shoving quite firmly up and down in the line of the rod. (And that an oiled rod falls gently / slowly / smoothly from a near-vertical position when fitted to its journal.) Using those rule-of-thumb touchy-feely principles, things have worked for me, and I suspect for many others. We can assume, I suppose, that the big end eyes of your rods are known not to be oval?

viewtopic.php?t=30271 was the post I was looking for concerning the oil filter chamber sealing options. There's ingenuity on display there! The standard paper joint will usually work, but there's something counter-intuitive about introducing even a very thin gasket at one point only of mating surfaces, hence the efforts folk have made. A leak there is incredibly annoying, given the work needed to remedy it - my heart always misses a bit when I see oil in that area on my bikes until (usually, phew!) I discover it's 'just' the darn dynamo to timing side crankcase joint not doing its thing.

[shaunstaples]

I was cutting the 2 thou washers out of greaseproof paper which performed well and Rtv worked well letting it cure before final nip. The offer is still there, send me a SAE it doesn’t cost anything to cut them on laser cutter and the edges are like sealed so difficult to tear?
I am due to strip my engine and was going to have a go at drawing the full crankcase joint, or if anyone can draw it easily I can have a go at cutting them. The drawing bit is not my strongest point, mind you nothing is as sharp as it used to be these days…

Also if anyone is near to Sheffield, and has a damaged crankcase half that I can borrow to have a go at drawing it?

[RodneyK]

Grolly, I think the big ends are good now. Some side slide but no rock and no end pull. Also think I have the oil filter gallery seal figured. I still need to understand whether there is a seal (gasket) between the case and the oil port in the web. My manual mentions it only once upon dismantling.
Thanks for the photo of your M31. I like the retrofit on the chaincase for the engine shock absorber. I’ll have to do something similar.

[Groily]

Sounds good.
No gasket (as far as I know or ever have had) between centre web and crankcase at the oil feed. (Hope that's right!)

If doing a mod to get alloy chaincases on, you'd also need to reduce the depth of the 'head' on the inlet camshaft blanking plug to 'not a lot', or the inner won't go on flush. And do a bit of fettling to secure them solidly owing to differences between earlier and later drive side crankcases.
An M31 doesn't have a shock absorber of course - but those chaincases fit on a spare earlier G9 engine that I ran with while I got round to rebuilding the correct but badly damaged 650 motor. Should add that I have never tried the chaincases with a Burman box, only with an AMC, and I didn't fit the 500's c/shaft shock absorber, just locked things up that end and relied on a cush drive clutch and the pins and rubbers in the QD rear hub. There are certain advantages to the tin cases in fact, if they're the ones fitted with the detachable dome . . . at least we can get at the clutch easily. And with the better seals now available, leakage is no longer guaranteed!