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MG Midget and Sprite Technical - crankshaft stiffness


Picture the scene... 1098 engine out, head off, sump off...

...can anyone tell me if when manually turning over the engine by turning the flywheel, I should expect to find some resistance when the pistons are close to the crossover point, i.e not at the top or bottom of the cylinders?

When I rotate the crankshaft is gets very hard to complete the rotation. And I have to apply a bit of force to complete a full rotation.

I have ensured the pistons are lubricated and the cylinders show no signs of wear or damage.

Any advice if this is normal or if it suggests something needing attention.

Many thanks

James Paul

When the pistons are at the top/bottom of the bores, there is very little friction from the pistons as they are barely moving. Contrast that with the situation where the pistons are halfway up the bores and they are moving at their fastest and the friction is greater.

So yes I think that you should expect the effort required to rotate the crankshaft to be greater when the pistons are mid-bore. As to by how much - I dunno - someone else on here may have a better idea
Simon Wood

Hi Simon,

Yes thanks that is what I assumed.

Hopefully someone can expand on this...
James Paul

There should be no resistance at top / bottom dead centre and quite a lot at midway - you should still be able to turn it by hand using the flywheel but not be able to turn it using the crankshaft front pulley.

If it is easy to turn at midway then it suggests worn or broken piston rings.
Chris at Octarine Services

Hi Chris,

Thanks for that, and is exactly how I find it when I rotate it. This has probably saved me a load of cash as the whole mechanism feels nice and tight.

Many thanks

James Paul

why is the engine out in the first place ? just curious given your question.
P Bentley

Hi, that's ok, in short you might like to check out my blog:

Major restoration project!!!
James Paul

This thread was discussed between 15/06/2017 and 16/06/2017

MG Midget and Sprite Technical index

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