Crank Binding when torquing mains
Turbo Mini Forums

Hey,

Firstly should prob give the info that this is a freshly ground crank for my build and torque setting for mains i have been using is 68ftlbs - 92nm as per minifilms 1380 mini builder dvd, is this correct ?

So laid the crank in the block today and fitted and torqued the centre main (strapped) and all spins freely with 3 thou end float - all good :)

But when installing either of the outer two mains the crank nips up and is very difficult to turn. The timing end cap causes it to be tight but turnable by hand but the flywheel end cap causes it to require a lever to get it moving then is only just turnable by hand !

What i have found...

When removing the flywheel end cap after forcing a few rotations, i found a band of about 1mm thick around the inner edge of the bearing (closest to the crank) that is highly polished.

The timing end cap has this same polished section on the inner edge but just not as severe.

Possibly a tapered journal ? Hope not on a fresh grind !??

Things i have tried...

Swapped the bearings in the two end mains to see if the fault followed the bearings but it didnt, its still the flyweel end thats very tight.


All this is only after torquing to 68ftlbs, I tried 50Ftlbs just to check and its turnable but with a hint of this problem appearing.

Anyone had any problems like this when instaling a crank ?

Thanks guys :)

Will my project ever be finished !!? hopefully you guys can help !
Its only been like 10 years in the making and I'm only just assembling my engine!

Get it out and measure. Check you have the right shells - all the same

I seriously doubt it!

Have you tried each of the end journals on their own and together without the centre one in place?

If Carling made Mini engines
it would probably be like this one!

ok,

get a dti on the centre main journel with the crank just laying in the block with only the flywheel and timing end mains in, spin it over and see what the run out is (ie is the crank bent) unlikly to be an issue but worth checking non the less....

Also check the main bearing surfaces on the block for any crap/ burrs, it wouldnt hurt to give them a go over with a bit of 200 wet and dry to polish them up a bit,

run a needle file across the edges of the block and caps to break the sharp edges, and also do the bearings at the ends near where the bolts go.

How do the caps'block fit onto the dowels? are they snug? of not they can move and the bearing bore goes to cock, if the dowels are passed their best Siftune do some really nice extra thick billet ones for about 15 quid a set

Are you sure that the centre main bearing cap is still round after machining for the strap?

In the 13's at last!.. Just

as above and more than likley

but dont overlook if someone has droped an odd oversize shell bearinging in there i have had this befor many years ago

Steve, if they were oversize shells the crank would flat about like a cock in a coat sleave and would most certainly not be tight,
but i know what you are trying to say,lol
carl

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

yes carl its many years ago some buffoon droped just one in a std set a 0.010" shell in there to my amazement straight out of the box wrapped

arge measure the journal sizes to eliminate them there all the same..............stranger things have happend
check also you havent replaced any oval, or goosed dowels in the block for the main caps

Might be worth using some plastiguage to see if the main bearing housings are not tapered

Plastigauge it, this will eliminate any guesswork.