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MG Midget and Sprite Technical - 1500 shells tight

Big end shells in but too tight to turn on crankshaft pulley when tightened up (not even torqued). Is this normal?
Dave Squire (1500)

Doesn't sound normal at all.

Were you meticulously clean? When I built mine a tiny speck of dirt on one of the shells caused it to bind half way round its revolution. Had to pull everything apart again, fortunately didn't score the crank or anything.

Dirt on the back of the shells can force them to sit proud too, causing things to be tight.

I would loosen them off one by one and see if it is one of them specifically causing issue.

Malcolm
Malcolm Le Chevalier

Caps on the right way round (tabs same side) and on the right rods?
Chris at Octarine Services

Definitely Chris, some were on wrong and I have turned them to be right as you say but did each one separately so know they are the matching ones to the rods.

Its the conclusion I have come to Malcolm, will try each one in turn and see. Checked the part number and its definitely correct type and I have the correct shells - standard.

Thanks fellers, back under the velocipede in a mo.

And just thought, I bet the bottom of the rods touched the main shaft journals while I was sorting out the shells. That may have done it.


Dave Squire (1500)

Erm "some were on wrong" ?

if some were fitted the wrong way and the crank was free then it sounds like there is a problem with the fit - are there any numbers or marks on the caps / rods?

A PO may have juggled the caps and rods...
Chris at Octarine Services

Some of them were on with the tangs on opposite sides (number 4 was for instance) so I swapped it to the same side. This is in line with some 1500 rebuild instructions I have as well as your advice so went with it. Had to give my shoulders a rest so still not back together it will have more attention tomorrow.
Dave Squire (1500)

Look carefully at the caps & rods for numbers or a series of dots - these should match and be adjacent on each rod/cap.
Chris at Octarine Services

Thanks Chris, serious sleeping probably happening soon. Mondays are long days at workies here and together with the undoing knackered cap nuts yesterday exertions say no more.

Pressure off as I have the modern for the next few days to get by to the weekend.

Thanks for the advice re numbers and stuff that's really helpful. Will be having them out, laying them out, and putting them back one at a time to check each one is correct and rotates OK before the next one and so on till all OK. That's the plan anyway.
Dave Squire (1500)

Dave, this is a bit obvious but when inserting the shells do make sure that the tangs are accurately located into the notch on the corresponding cap. Especially as you seem to have found them wrongly assembled by a PO.
If they get put together with the tang not properly located as it is tightened it will deform the shell and clamp it tightly onto the journal, giving the symptoms that you describe. Slacken the caps again one at a time, checking after loosening each one to find out which one(s) were the culprit. Then remove and inspect that one closely. If the PO was a "bodger" as may be the case, then it is possible that they decided to grind the contact surfaces of one of the caps in an attempt to compensate for big end wear. It is a criminal solution that doesn't actually work, but has been known!

When trying to turn by hand remember that the pistons will create quite a lot of drag, making it hard to turn. Especially if the crank is starting from a positiond at tdc. Also, if you still have the head on, then removing the spark plugs so that you are not fighting the compression does make it easier to get a proper "feel" for how it is turning.

Have you decided that the mains can be left, or haven't you checked them yet? It is usual to replace them first. As I think Chris advised earlier - with the big ends disconnected you can then check that the crank does in fact spin freely as it should. Once the big ends are done then the piston friction prevents you from checking this.
Guy W

This thread was discussed between 11/08/2013 and 12/08/2013

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