11 replies to this topic

[andy120nz]

Hi
We have overhauled our clubman thou and had it apart again to try to work out why the crank is damn near solid as soon as we torque up 3 big ends. We can just turn it with a spanner with all 4 done up, but there is no way the starter will turn it.

Any help greatly appreciated.

Andy

[Guess-Works.com]

Have you got the right shells ? have you mixed up the caps and rods ? have you checked the crank journals for size and ovality ?

[corrado vr6]

Have you put one together and torqued one up individually and turned that one before starting to build up the next one so to know if its all 3 or just 1 of them that is binding?
Did you oil the shells whilst building up? I know that's obvious but you never know

[ace01]

You might also want to check that the caps are not the wrong way round.

[Cooperman]

It does sound like either two caps aer on the wrong rods or one or more caps are on the wrong way around.
In terms of cap/rod alignment the little tangs on the bearing shells are both along the same edge of the rod/cap.

[andy120nz]

We are checking the rods are in the correct bores. Shells are correct. Oddly they freed up a bit when the clutch was removed.
Andy

[tiger99]

It does not matter which bore the rod is in. What does matter, totally, is that each cap is on its own rod, and the right way round. During manufacture they are bored as an assembled pair, with bolts torqued up, and if they are either the wrong way round or on the wrong rods, or both, the half shells will not align with each other, and it is guaranteed to be tight. Likewise the main bearing caps, but only the middle one will go on the wrong way round.

If any caps have been on the wrong way round, look very closely for damage to the shells, which is likely.

[andy120nz]

Ok, we have all the piston/rods out. Only 1 of our 7 piston/rods has a number. Of the 7 piston/rods the parts numbers of the rods we have every con part number is different. The crank rotates freely with nothing attached.
Andy

[jd24-7]

If the crank turns ok with main bearings torqued down, then at least you have narrowed it down to the big ends (or piston bore problem) .
Have the rods and caps been used before, or are they from a pile of bits? If they are just mixed up then put them together, not on the crank, and feel for the best alignment where the edges touch and get a bore gauge and micrometer and measure diameter. Failing that, take one rod and assemble to crank with bearing (not in a bore) and try all four caps . You Will need some trial and error, and remember, you could have a rod cap combination that is loose.
If the rods and caps came from a bag of bits, you Will need to find a good machine shop that Will skim the cap faces, and then re machine the bore in the rod/cap while assembled and torqued.
Not sure what the sizes and tollerences are tho.

Good luck
Jd

[tiger99]

I think that the ONLY way is trying the bits to get correct fit. 7 rods/caps and two ways of fitting each cap is "only" 10080 possible combinations for the first one, then it gets better!

Machining will not work, unless you fit shells that are oversize on the OD. If you just skim the mating faces, and then rebore, it does not correct for sideways misalignment, so although the diameter would be correct in one direction, the two semicircles would not align with each other at the mating faces.

I would start by trying caps on rods, and feeling very carefully at the join for a discontinuity. If you have fingertips in good condition, it is possible to feel less than a thou. That will reduce the number of possibilites somewhat, and when you have selected those that will fit that way, you can then try then carefully on the crankshaft, nipping up slowly, one at a time. Then check for play in the other direction. If there is any looseness, pick another pair that align and try again. It will take a lot of time and patience.

[Cooperman]

If there is any possibility that the rods & caps are not as-manufactured matched items, the only real solution is a new set of rods.

[andy120nz]

Thanks all.
We have all sorted. One cap did not belong to any rods we had. We acquired another matched con rod to bake a set.
Thanks again
Andy