Engine Rebuild

[silloyd]

... the crank should spin round easily in the mains...... Does any one main cap make it tight? Double check the centre main is right way round - can't go wrong with the others....

Again another major pause in progress

I've removed and re-cleaned the caps and shells (several times) but the crank still remains too tight and I'm not happy to proceed, particularly based on this post. So I've stripped the bearings again!

I've checked the main diameters (reground to -0.010) and they are all within tolerance, i.e. 1.7405"-1.741". The block seats and caps are all undamaged and therefore the only other thing I can think of is that the shells are not right somehow.

I bought the re-ground crank from eBay, and it came with Vandervell shells and marked '010', '2744', '2A 646'. They are 0.075" thick. Can anyone verify a) that they are correct and b) that their thickness seems about right? If they're

Or am I missing something else?

[bmcecosse]

If they are marked 010 then that will be for 10 thou undersize crank. At what point does it go tight? If you leave the centre main off - and just torque up the other two mains - does it spin round then?? Also -clean the caps carefully - rub away every tiny blemish on the curved section of the cap... Crocus paper and thin oil for this job! And then wipe it clean before fitting the shell. Note - the tangs must go together on the same side of the bearing - this applies to mains and big-ends.

[silloyd]

Sorry, yes -0.010", now corrected.

No one cap is tight, the crank just gets progressively tighter as each is torqued until it just won't turn easily. Doesn't matter which order I tighten them, the end result is the same, which suggests that they're all a smidge tight.

Crocus paper - 1200 grit? - if this is correct, would 1200 wet and dry suffice as an alternative? Happy to try but don't want to abrade the inner surface of the shell unnecessarily as I guess the difference between 'too tight' and too loose isn't a huge amount.

Tangs are where they should be; they'll only fit one way given the notches in the block and caps.

[bmcecosse]

Yes 1200 grit with oil. It's not the shells you will rub - it's the inner surface of the caps. DO NOT touch the shells...except to degrease them. If you are sure the crank isn't bent - then the journals will need to be polished up to get a good running fit. The centre main cap can be fitted wrong way round- hence the check that the tangs are lining up ok. To check for 'bent' - fit the crank with ONLY the centre main shells fitted and rotate it checking for any run-out at either end......

[les]

If you're sure everything is in tolerance, I'd be inclined to try some new shells. Is it possible that someone has filed the bearing caps in the past ?

[bmcecosse]

Shells are 'never' wrong....unless they have been dropped/mangled in some way. I'm inclined to suspect the crank is slightly bent... If the caps have been filed the block is effectively scrap - could be sorted with expensive machining I suppose.....

[silloyd]

Thanks both.

Will check for crank bend on the weekend. (BTW centre cap was fitted correctly)

Thanks for the clarification on using the crocus paper on the cap seats, I misread your earlier post . I assume I can use the 1200 to polish the journals as well (?)

The caps don't appear to have been filed, as they still show the machining marks rather than a smooth surface but can't be sure as I don't know the history of the block.

[bmcecosse]

I think polishing of the crank would need it to be spun in a lathe...and very great care. The idea of rubbing with 1200 and oil is simply to clean the surface and remove any tiny imperfections....it won't remove any worthwhile amount of metal.