Spring is coming ... Crank renovation

[MikeN]

Hi All,
terryk, I would not try and knurl the shaft, that is a bodge of the highest order in my opinion!!!
it will come loose again, if there is only a thou or two play a loctite type product will help
When the engine is assembled "properly" the crank spacer and the cush drive assembly should lock the bearing in place preventing any relative rotation between the two!!
HTH
John O R

Couldnt agree more
MN

[a10 gf]

I would not try and knurl the shaft

agree

It was only 1 thou worn, any more and I would consider spraying

Difficult to measure, but inner bearing completely loose, slides off by itself from crankshaft in vertical position.

the crank spacer and the cush drive assembly should lock the bearing in place

I'd think my cush system, tightening and spring is fine, but still the inner bearing managed to rotate.

Here's a picture of the timing side wear. Top looks fine, bottom not (no marks on crankshaft surface). Comments as to the cause welcome (maybe metal particles from worn driveside shims in oil? Had quite some residues on the magnetic sump plug)

Thanks
e

[MG]

Looks like serious fretting/seizing to me. There are no signs of wear in the region around the oil holes, so I would think it had been caused by lack of oil pressure (and/or the crankpin is out of round), resulting in mixed/solid friction in the lower part of the bearing when exposed to combustion forces. If the premature wear had been caused by abrasive particles, I would expect signs of it around the whole bearing surface, so also around the oil holes and on the top side, but as far as I could see on the pic, everything looks pretty smooth there.

I can only suggest a theory here, however I dare to say that this is not what a timing side bush looks like when exposed to normal wear after considerable mileage, this damage looks very much like lack of lubrication to me.

I think it would definitely be advisable to check the whole lubrication system, incl. the pump(s), all valves (return, pressure relief) and passage ways.

You didn't have one of those anti-wet-sumping things fitted?

Open for discussion, looking forward to hear other's opinions. I think the evaluation of damage is one of the most interesting fields in engineering, although this probably won't be any consolation for the owner....

HTH, Markus

[a10 gf]

No anti-wet-sumping 'thing', all oilways fine, good return etc.

Crankshaft itself, bigend and timingside surfaces seems fine to me. Smoooooth to the finger, no feelable damage whatsoever (photos exaggerates scratches quite a lot). No feelable up-down play in conrods.

Oil must have been ok, or else I'd see damage on the bigend bearings?

[MG]

Oil must have been ok, or else I'd see damage on the bigend bearings?

Good point, that's true. If the oil pressure was so low as to wear the timing side bush, the big end bearings would have suffered as well, but they look pretty good.

Maybe the timing side bush hadn't been bored properly so that it didn't align with the drive side bearing?
Could also be the crank pin not being ground properly (not true to axis of rotation or geometrical deviations due to grinding wheel not running true). I have seen such results on some cranks before (unfortunately not every craftsman is as trustworthy and scrupulous like the local one I use).

Somehow I still can't believe this damage had been caused by abrasive particles, I would expect these to bed into the brass and rather damage the crank pin than the bearing itself with visible traces on the crank.


Do you have a micrometer to measure the crank pin? Would be interesting to see how far the wear had gone on the crankshaft. You could also check whether it is running true in the lathe.

Cheers, Markus

[alanp]

Just a small point - behind the drive side shock absorber the spacer which clamps up the bearing needs to be the correct way around. Mine was assembled with the spacer's bore chamfer facing outwards and the sharp edge facing the bearing. The chamfer is there to fit over the radius on the crank journal and hence reach the bearing inner race. My drive side bearing inner race chewed it's way into the crank journal (and any shims behind it if fitted) which was very expensive to repair. I'm not sure if all spacers only have one chamfered end but be warned.
Alan

[a10 gf]

Markus, lots of good points to look into. Will come back with info.

Alan, thanks for the tip (no spacer on this engine, but will get one to align the primary chain, and maybe help to clamp the inner race -but, as mentioned, it's completely loose, I'd think metal spraying is the way to go). The picture should show the need for the spacer chamfer, one more detail learned.

[chaterlea25]

hi a10gf
Interesting thread going on here!!!!
How well do you tighten the cush drive nut? I know SRM recommend 65ft pounds, I have made a tool which fits the slots in the nut with a hex for a socket on the torque spanner
From your photos it looks to me as if there were foreign bits floating around in the oil???
All the other comments are relavent too!!

Before you go off and have the crank built up have you tried a new bearing race on it?
As Markus advised a micrometer check is the only real test!!!

Regards
John O R

[IanH]

Hi all,
Only started posting today, this thread is just so interesting.

Regarding those horrible thin shims.
Finding a handful of broken razor sharp shim in my sump made me swear i would never use them again.

When I rebuilt my engine I ground out an old drive side inner race, having first checked it against the new one so the bearing would easily slide on and off the crank, that way I could fuss around with the shims and get virtually neglible movement with free rotation.

Instead of fitting all those skinny shims I measured the total thickness and used my lathe to turn and part off a solid thick shim/spacer. Gues my set was worn enough for the spacer to be thick enough for this to be practical. It certainly looked like a solid job after I finished and Ive had no problems since.

[olev]

Erling,
Have a look at Goffy's A10 rebuild on his web site.
Thats the one with character (and teeth).
He has only just finished rebuilding it and had all sorts of fun.
a good read.
cheers

[A10Boy]

The spacer is there to clamp the bearing to the shims and crank, not to align the chain. There are other shims to fit between the spacer and the cush assy to align the chain. Without the spacer in place, the whole bearing-shim-crank can float around, causing the bearing to spin.

The bearing and shims can't turn if the cush nut is tight, but often the nut loosens as far as the split pin and the owner doesn?t know its loose until it all starts rattling around and the shims are in the sump.