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MG MGB Technical - conrod colliding with block

Hello,

I am in desperate need of some assistance. I have had my engine refurbished by a recommended company. They said the block had got damaged during dismantling and that a new unit was required. Therefore I supplied them with a different block (both believed to be 18GG engines). However when I have come to reassemble it all was going well till i connnected the conrods to the crankshaft, and now when I turn the crank the conrod bolts (holding the big end cap to the conrod) collide with the block (please see photo). I have placed the pistons in the right way round (the supplier already attached them to the conrods) so all i had to do was make sure 'front' was facing the front of the engine one each piston.

Please can some one check from the photos what if anything I have done wrong?

The second photo shows the orientation of the conrod in respect to the engine (looking at the front of the engine) - I was wondering if the conrod had been put on the piston wrong?

Many thanks


Alex Davies

I've had a look in the Leyland manual and it says that the big end caps must be on the camshaft side of the engine, so yes it looks as though the pistons have been mounted on the rods the wrong way round.
Mike Howlett

Thanks Mike,

As part of the work done on the engine, he rebalanced my crankshaft (with all the ancillary parts on - flywheel, clutch cover, pistons etc). Is it likely that if i rotate the conrods round this will throw it out of balance?

Regards,
Alex Davies

I don't think that it will make a difference as the rotating parts are still located in the same place relative to each other. Bad luck with the backwards mounting of the pistons. With the earlier design, all you would have to do is remove a circlip from the piston, push out the wrist pin and reverse the rod. RAY
rjm RAY

Alex. The balancing of pistons requires weighting them and lightening the others in the set to the weight of the lightest one. The balancing of rods means that each end is weighed. The one with the lightest small end becomes the standard and the others are lightened to that weight. Same thing with the big ends. As Ray notes, none of this will have an effect on the overall balance of the rotating portions of the system.

Les
Les Bengtson

Apologies for my naivety, I was under the impression the company would have spun the crankshaft with all the aforementioned items attached and removed weight where necessary to balance the whole system. Is this incorrect?

Regards,
Alex Davies

Alex, that is incorrect! The crank is spun with no loose bits on it, and the rods and pistons are equalized the way Les says. The crank should first be balanced on its own, then with the flywheel, then with the clutch. If you do it once all together you might end up with a flywheel that you cannot transfer to another engine or rotate to another position.
Art Pearse

I'm trying to imagine the mayhem caused by spinning the crankshaft with the pistons and rods attached. Stand well back please ladies and gentlemen! Sorry, Alex, I'm not poking fun at you, we all had to learn how things are done. It's a pity your supplier's mechanic didn't think about what he was doing.

The dynamic balancing is an interesting business. I recently had my V8 done and I was given the computer print-outs, before, during and after - quite fascinating. Les and Art have told you what is done. The only bit Art missed out is the front pulley which is also part of the balancing procedure.
Mike Howlett

This thread was discussed between 06/04/2010 and 07/04/2010

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