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Big end bearings...

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I have a 2.25p 90, which developed a nasty clonking noise from the engine last week. :o I stopped pretty much straight away and the landy was towed back for examination.

The noise seemed to be coming from the rear of the engine at the head and first thoughts that unleaded fuel in a leaded head combined with continuous high revs (i do lots of motorway miles) had killed the top end.

However on inspection there was nothing found in the head that would account for the noise, so we dropped the sump and had a look. The big end on number 4 had some play. This was examined and we found no unusual wear, BUT when i undid it it seemed a little on the loose side :o . It was decided to reassemble it and torque it up properly and see if this made a difference and it has. No more play. :D

The others were checked for tightness and although they were all slighty under the book figure none was as loose as this one.

Has anyone seen this before where parts have come loose? The workshop manual does not mention loctite or any other method of preventing parts coming undone... <_<

Finally, can i replace the shells on this cylinder without getting any machining done, and if so would it be a good idea as a precaution? I have not checked for ovality but considering the state of wear on the bearings i dont believe that i would find it out of tolerance.



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A set of big-end shells are quite cheap - less than £20 I think and they can be changed by just dropping the sump pan as you know. You might have caught it in time and no damage has been done to the big end itself or the crank pin.

Listen for a knock when the engine is under load - this is a sure sign of big end failure.


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If the bearing cap was loose then you do need to check that the shell bearings are still correctly fitted and not rotated round blocking the oilway. I would be tempted to change the bearings while everything is apart as it would be better then finding there is wear that you didn't notice. However, if you can, do check for wear with a micrometer so, if nothing else, you ahve a record of what things are like now for comparison later if things go wrong again.

Also there should be tab washers or equivenlent fitted to prevent the bolts working loose in the first place.

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How long have you had the vehicle?

Who last had the mains apart?

Never heard of them coming loose...

Well that is not quite true. Thirty years ago I stripped my Bonnie engine which had broken a con-rod. When taking the remains of the old con-rod off the crank one of the bolts was very loose and this was due to the con-rod having cracked through at the shoulder. Whether this happened before the broken rod or after I don't know. This was an alloy rod though...

I guess that if a rod cracks in this manner it would present in the manner that you say - and tightening would then take up the little gap that is usually left on one side of the big ends when you tighten them, but it wouldn't last for long in that condition once subjected to the stresses of a running engine.

IMHO you should:

1. Remove the caps and check the condition of the con-rods (as far as you can), caps and all threads.

2, Check/inspect/replace the shells while you have it apart. You can check for wear on the old shells and clearance on the new with Plastigauge (see eBay item 190187276981).

Also (IMHO) you should consider replacing the bolts - they are designed to take a certain amount of stretch under tightening and on most engines it is recommended that they should not be used twice...

All of the above is assuming that the engine is worth the effort, if it's a bag-0-nails like mine then just bolt it up to the torque of uuumph and hope for the best :lol:


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I've had the vehicle 9 months. Have no idea who last had it apart.

The shells look fine, the crank looks ok- no scores or anything sinister.

The engine is nice- the bores look like new, with no scoring and no lip at the top- it looks like it was rebored only comparitively recently (i.e last 5 years). And although the 2.25 does lack a little power for hills, it generally keeps me bumbling about quite nicely.

Thanks for the replies, will let you know what happens when it all goes back together. :)

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Yes I had a No 4 bearing cap loosen up on a lightweight I owned nearly 30 years ago. I've had it happen on a couple of ancient (ie pre war) cars too, I got away with just new bearings (white metal cast direct on the rods & caps on one but it knocked the journal out on the other so rebuilt the whole lump).

If I were you I would replace the bearings and bolts / nuts as a matter of course but would also get a micrometer on the suspect and other journals.

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