Reassembly of crancase and crankshaft after regrind

[David1977]

Hello. I have crankshaft regrind for -020 . I ordered new conrod bearing +20 and centre bearing +020 from the club . Yestrday I start with reassembling but I find out that the crankshaft doesnt turn freely in crancase. I did not tight fully the 6 nuts on centre web straigh away but the crank just doesnt turn freely. So I dismatle the centre web and I found out that the new centre bearing is badly worn . So I was wondering Why this happened ? I reassemble all in the same position as was before.

[Groily]

Well . . . that's clearly not right.
Not the first time a crank hasn't wanted to spin nicely - but there's quite a lot of scuffing there unfortunately.

The scuffing pattern would suggest to me that the journal was very slightly on the 'tilt' - misaligned - when the timing side case went on, as the shells would suffer less in the centre where the misalignment had least effect.
But, that said . . .

. . . I assume that if you assemble JUST the centre bearing on the crank, on the bench, and tighten it up, the crank turns freely? And also with the crank and centre bearing attached to the drive side crankcase? So it only goes stiff when the timing side case is fitted?

If the centre main is always a bit stiff, though, could it possibly be that the chamfers on the sides of the shells are somehow fouling the radii on the journal when things are tightened up? That is something I have had once before, with big ends - solved by increasing the chamfers very slightly.
I'm sure the journal finished size is good across the width of the journal and I doubt if there's a problem with the bore size of the centre web (without shells fitted) when torqued up - but maybe worth double-checking both?

So far in my life, I've found centre webs can be inter-changed without problems, and that they'll go into any pair of cases. But I suppose it's possible that something needs relieving on the registers round the bearing web to provide a fraction more movement as you test fit the parts. I don't suppose any of the centre web studs are 'off' from vertical in the drive side case by any mischance? That could cause a problem. Similarly, we can assume there's nothing peculiar about the roller main bearing fit in either crank case?

It has to be something reasonably simple, but very hard to measure of course. What you don't want to do is go through loads of bearing shells in the trials though, so I'd use the scuffed ones for test fitting until it spins freely by hand, before putting another set in if you have a spare (in the picture it looks as if you might?)

There are a lot of people on here who know much more than me about this particular issue, so maybe someone will chip in with some more useful hints?

.

[David1977]

Hello Bill. Thank you for your replay. I appreciate it . If i assemble the crankshaft and centre web to the drive side of the crankcase than the crankshaft turns freely but If I put timing side on than it is beacome stiff .I need to investige what is wrong.Now I do not know. I am almost sure that I ruined the new centre bearing shells and I would probably need to get new ones. That is ok but need to safe crankshaft ! I think that big ends journals are ok. The conrods after assembly fall down by it's own weight so I was happy about that but the centre web makes me wory. I should have sent the crankshaft to T-L engineering in Bedford when I was in Stafford last weekend and collect it n September on my way to Manx Grand prix. I will make another mechanic check If the regrinding was made properly and than I will know more.

[g80csp11]

can you measure the centre web diameter, it should be 1.60675 / 1.60625 for 0.020 bearings , this is not the same at con-rod at 0.020 which is 1.60575 / 1.60525 as the running clearances are different ( info from pg 24 ) of the workshop manual
http://archives.jampot.dk/book/Workshop ... models.pdf

if everything is free to turn when torqued up before fitting to the crankcase then its not the bearings or journal

[Groily]

As g80csp11 says, if it all turns fine until the timing side is fitted, it's not the journal or centre web dimensions that are the trouble, it's the 'fit' of the cases and the centre web.
One thing you could do is clean (again?) all the holes in the centre web to be sure they are all good, get the outside 'rim' of the centre web and the register in the drive side crankcase squeaky clean and free of any burrs (again!), and then maybe even experiment with some of the studs for the centre web removed (or swap their positions). If you find it then settles into a 'good' place with the crank turning freely, you know you are on the right track.
We're only talking a tiny error here. I seem to remember similar difficulties with one of mine in the past and it took quite a few attempts doing some or all of the above to get it right.

[g80csp11]

just a thought , have the centre web fixing studs been helicoiled , perhaps some are sitting proud and pulling the web off true
Its unusual for a regrind to be wrong , sometimes teh radius might be too small and require the edge of the shell to be scraped to ensure clearance
good luck tracking down the problem and be sure to share

[Groily]

just a thought , have the centre web fixing studs been helicoiled , perhaps some are sitting proud and pulling the web off true
Its unusual for a regrind to be wrong , sometimes teh radius might be too small and require the edge of the shell to be scraped to ensure clearance
good luck tracking down the problem and be sure to share

Yes, I thought maybe that radius thing Peter, because I've had it with big end shells before as I said, and had to modify a couple of sets in fact. T&L have a nifty twirly cutter thing that does the job by hand in a nano-second - but I made a jig using the sawn-off b/end eye of a damaged con rod as the fixture to go in the lathe. But not had the same issue with a centre main (so far!).
Could be the radii though, who knows when you're into a 2nd grind. I also wondered about the thrust washers - but dismissed the thought as fast as I could! (Are those new ones in yet, dare one ask )
The more I think about it, though, and the more it becomes clear that it's a 'when the timing side goes on' thing, the more I reckon David's problem is alignment. A proud helicoil would certainly do it! I do seem to recall distantly having to ease a hole or two in a centre web one time, to get the tiniest bit more 'wiggle' for things to self-align on the trial run.

[g80csp11]

The new thrust washers , are on the ship so must be nearly here by now and will also be available in an oversize
There was a oversize available in the day , but ive never seen one !

over tightened studs can pull the thread especially in aluminium proud and not be notice , and with only a 6lb-ft torque on the 6 nylocs . It may have been over tightened by a previous owner

[David1977]

Hello . I checked studs on centre web and they looks all original no helicoil I have also noticed that there is a little play between studs and centre web but this is probably right . I ordered micrometr today to check diameter of the centre journal. I am wondering If the crank has been reigrinded corectly . Thank you for your commets and help so far. I will keep you informed how is it going .

[David1977]

Hello , I noticed that clubs offers new centre bearing shells +20 but they looks differents than original.