Repairable Crank Tail? - Opinions reqd!

[Richspec]

MED crank, bought as part of a complete but dismantled race engine, to be used as basis for warmed over road engine.
Discolouration to the bearings but nothing to be felt at all, no marks, scratches etc
Tail has suffered from fretting and been repaired by the looks of it. there's some voids in the surface but its smooth enough if not pristine.

but never having had a crank thats suffered before the question is, is A) ok to use as is? and B) if not, is it fixable?

thanks,

Rich

[rich@minispares.com]

I think I would be tempted to have a go at the lumps with a fine file, use a scrap flywheel and some rough grinding paste to level it all off, then use a decent flywheel and some fine grinding paste to get it as good as it can be.

its never going to be perfect, but on a road car it could last years before the flywheel has to come off again, so its a cheap crank!


I bet you could spend a fortune getting it metal sprayed, or the taper redressed and a flywheel made to suit, but it would cost mega bucks

[mk1]

I agree with Rich, It looks like it will fettle up good enough for a quick road engine.

Patience & lots of lapping should do the trick.

[Richspec]

Thanks guys, thats what I'll be doing then, let the lapping commence

[251 ENG]

I would go with the above comments to re-use crank but you may have to shorten the end of the crank and/or machine some material out of the inside of the flywheel depending how far it goes up the taper .

[Spider]

Yeah, I'd dress it but don't use a file, use a diamond lap, you'll be far less likely to put flats in it or take it out of shape. Finish off, of course, by lapping the flywheel to it.

Gee, it really copped some serious heat from the primary gear, was the clutch slipping?

[Richspec]

Yeah, I'd dress it but don't use a file, use a diamond lap, you'll be far less likely to put flats in it or take it out of shape. Finish off, of course, by lapping the flywheel to it.

Gee, it really copped some serious heat from the primary gear, was the clutch slipping?

I'll get a pic of the backplate and flywheel....
the primary gear that came with it wont even fit on the crank, wtf??!

[Richspec]

The surface of both is like the sea on a choppy day

[minimans]

that crank has some serious heat damage! you say the primary gear wont even go on the crank? I would suggest getting it crack tested and then ground + 10 or what ever a measure up would indicate and having it re hardened. Even a road crank can go bang and leave a sour taste in the wallet!!

[Chalkie]

wouldn't it be better to have crank refinished and like a bush put inside the fly wheel? to size it down and also protect the crank?

[Richspec]

I was wondering if somehow I'd ended up with the wrong primary gear, or something, maybe got mixed up somewhere in the dismantling? who knows , other primary gears we have go on no problems. its one of the fully floating idler sets that med do as well, of course it doesn't fit my 3 sync box either!

[mini63]

The surface of both is like the sea on a choppy day

i would re-consider the use of the flywheel and backplate. the sub and surface stress cracking would set up future problems.
make sure you crack test the crank at the circlip grooves.
the spalling was caused by a mis matched taper crank to flywheel.

[Spider]

I've little doubt that the flywheel and backing plate would clean up OK, be quite suitable for further use.

When Bronze get heated (really heated), it tends to grow, as the bushes are bound on the OD by the Primary Gear itself, the ID will shink.

I also doubt that tail would need anything serious to clean it up, I'd say it would polish up quite OK.

[gr4h4m]

I wonder if the previous engine builder left the back surface coating on when it was installed? Don't med send the cranks out without them being polished off? I know my cam cam like if and I was told by the supplier mu must remove it before use?

Anyway just an idea.

[rich@minispares.com]

wouldn't it be better to have crank refinished and like a bush put inside the fly wheel? to size it down and also protect the crank?

you can do this, ive seen people make little bronze sleeves, or even bore the centre of the flywheel out and make a new steel insert (so the flywheel stays in the correct place) once the crank taper is recut, the problem of course is that either option requires specialist knowledge and machines, or costs a load of money to pay someone else to do. I don't think the slight damage on this crank would justify such investment - maybe on a £1500 race crank.....

[rich@minispares.com]

The surface of both is like the sea on a choppy day

that's not that bad, when you use either paddles or the ap comp plate they often look like that.

ive got some pictures of a flywheel that HAS got how, will dig them out

[Smiffy]

viewtopic.php?f=3&t=9850&hilit=http%3A% ... m&start=10

[ianh1968]

I would go with the above comments to re-use crank but you may have to shorten the end of the crank
and/or machine some material out of the inside of the flywheel depending how far it goes up the taper .

I had to do this myself, once - I used a hacksaw on the tail...


Another clearance to check is that the backplate does not foul up on the
transmission casing strengthening ribs when the clutch is activated.

I had one of the early MiniSpares uprated/lightened backplates that had
"Mini Spares" cast onto the rear of it, along with some sort of fancy
"cooling fins". This raised stuff on the back of the plate came into
contact with the transmission case ribs. It was easily fixed by machining
the rear of the backplate flat and this also lightened it further.

Ian

[ianh1968]

I wonder if the previous engine builder left the back surface coating on when it was installed?
Don't med send the cranks out without them being polished off? I know my cam cam like if and I was told
by the supplier mu must remove it before use?

My last cam came from Kent and it had a black coating on it.
I phoned them up to ask about this and they said to leave it on.

Maybe there are different types of "Black Stuff"...

Ian

[rich@minispares.com]

don't forget that if you 'adjust' the taper on the crank of the flywheel and have to shorten the end of the flywheel (you want at least 2mm of stand off the flywheel to be safe) you may also need to machine the inside of the flywheel where the c-ring and the saddle go, other wise the flywheel can nip them and shove them into the primary gear, which jams it all up...