problems fitting crank
Turbo Mini Forums

right, here goes;

I started building up the short motor today. As a bit of background info, the crank was reground approx 5 years ago but never fitted.

I tried dropping in the crank with standard thrusts and it just would not drop in. Took the thrusts out and laid the crank in on the new shells and tried to slide the thrusts in but still tight. After a bit of measuring, we were happy these were standard so took a couple of thou off the backs to see if that would help - crank now sat in the block.

Next step, tried to fit the centre cap but had the same problem - decided to fit the 2 other mains caps and centre cap would then go on without too much trouble. Torqued everything down and the crank seized up;

next stage, decided to take the thrusts out - the crank now moved with a socket on the pulley bolt but there was an obvious bind point; took the centre cap off and noted a polished area on the bearing surface at approx 2o'clock and some further wear at 8 o'clock.

Took the centre shells out and put a dial gauge on the centre journal which shows just under 1 thou variation. What I cant get my head round, bearing in mind that only 2 points of the bearing surface have been polished, is if the crank could be bent or the machine shop have ovaled the journal? my other though was that it could have been re-ground off centre?

Any thoughts guys?

cheers

Rob

Rob, put a dial on the tail as i was telling you about, see if theres any run out that could correspond to the run out on the centre main,

highly unlikely the centre is ground off centre,

could be a line bore problem,

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

cheers Carl, I'll give it a try

seems to me the certre maain is mis alighned,

check the centre maiin is on thre right way rount, if it is try it the rong way, it may have been line bord with it on wrong.

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

Carl, Rob and I tried the centre cap the wrong way just in case and it wouldn't even look at it. It's amazing how many times you can remove and re-fit a crank in 3 hours!

Something is obviously wrong, but unfortunatley what is wrong isn't.

It appeared at first to be a problem with the thrusts being too tight, althought they were standard. We measured the size between the thrust faces of the crank and also the centre cap/block + the two thrusts and should have given us .002" end float. However, with everything fitted there is no movement. As Rob has said thinning down the thrust allowed the crank to rotate more easily, but it still wasn't right.

With the crank located on the two end caps (torqued down) and the centre cap and bearings removed the centre main is running out by .0008". this measurement is the same on both sides of the journal.

Rob, the dial gauge is sitting out on my bench if you get back up before me.

Keith

14.914 sec 1/4 mile @ 91.38mph, NA 1293cc on 1.1/2" SU's (all steel and glass shell)

less than a thou shouldn't give problems,

maybre you could have ago at straighening the crank to better than it is,see if it eases things,

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

Have you got another crank you could try?

Take everything off and fit the cap to the block and tighten it down. Then feel with your finger where the cap and block meet on the inside. The locating rings can crush and make the cap over hang.

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

Double post

Edited by MikeRace on 1st Mar, 2009.

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

Rob

I'll try and get up the workshop one afternoon this week. I'll do as Carl suggest and measure the run out on the tail. Once I've noted this I'll strip the crank out my short motor and we can try this (as Vegard suggests). We know my crank is OK so this will prove if it's the block or crank that is at fault.

Cheers for the help guys.

Keith

14.914 sec 1/4 mile @ 91.38mph, NA 1293cc on 1.1/2" SU's (all steel and glass shell)

its never easy - i'm going to head back up today and look like an idiot for another 3 hours

I've had cranks lock up under torqing, trust me check locating lugs. Then build up the engine one cap at a time. Fit the cap torque it up and rotate the crank then move onto the next.

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

Obviously you've double checked the size of bearings?

I don't think the crank would even go in tbh

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

one thing we didn't do - assumed, as the others were fine and they all came from the same sealed packet they would be ok.

will head down the workshop this afternoon and will double check everything

I had this same problem, the centre main cap had sprung when machined for a centre main strap and went tight when torqued down. I had the block fitted with steel caps and line bored, a cheaper solution would be find another block.

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

thought I'd give you all an update;

went back down the workshop last night and tried a number of things;

Carl, dial gauge on the mounting surface for the primary gear shows no movement although there is some on the tail just above the taper (I can't recall how much)

The crank spins freely with the outer caps on. When I fit the centre main on without the thrusts, it will spin when torqued up to 35lb/ft but any more than that binds it up.

I've checked the bearings and they are all the same thickness (i couldn't get an accurate internal diameter). The centre cap is on correctly and no signs of distortion when bolted up without the crank in place.

Our final try will be to swap the crank over; Keith is going back down this afternoon to strip the crank out of his engine and try that; hopefully this should lead us in the right direction

Cheers for all the help so far

Rob

have you tried fitting the centre main on its own first?

OK, Keith went down the workshop this afternoon and has just phoned to say his crank is fine in my block.

prior to removing mine, we noted 5 thou on the dial gauge just beyond the step in the tail for the primary gear. Basically, my crank is the problem.

Now back on the market for a good crank

cheers for all your thoughts

Rob