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MG Midget and Sprite Technical - Another idiots engine rebuild question!

Following on from my other thread. I have now installed all four pistons into their bores. It was easy once I got the technique down!

Main caps are torqued up, big ends are done up finger tight. As I turn the crank everything seems to turn reasonably freely until no 1 piston reaches half way up (note up, not down) its bore where things get stuck and need a bit of extra force to get things moving again.

Am I going to have to pull things apart again or is this normal? (I am thinking it isn't normal... doh!)

Thanks everyone,
Malcolm

Malcolm Le Chevalier

Hi Malcolm, it will naturally get harder to turn over at approx half way because of the position the crank is in - eg flat across the block. So the stiction if you will forgive the term has maximum leverage through the crank - or putting it anotehr way for the same degree of rotation of crankshaft you are trying to move the pistons a much larger distance.

I found it very difficult to turn my rebuild over at the same stage - If the bores look un scratched and you can't detect any signs of contact anywhere I'd say thats what it is....
John Barber

Thanks John,

I thought that but was confused as it only happens when no 1 and no 4 are on the way up. Not 180 degrees after when no 2 and 3 are on the way up...

Hows the rest of the rebuild going?

Malcolm
Malcolm Le Chevalier

Did you lube up?
And I mean exesive?
Assembly lube or sticky oil (chainsaw oil)
And did you check rotation piston by piston?
So turn the crank with just one piston and the rod and mains torqued then add on that.
Be verry methodical in checking every step you do!

I would lay in the crank bolt down the mains finger tight and rotate it
Then torque up the center and rotate
Then torque up the other mains one at a time and check every step.
Continue like this and you will know what happens at every step and if something goes wrong you will be able to pinpoint it.
Onno K

Yeah I lubed up, but no I wasn't methodical! Don't be so silly Onno! I just ploughed on and put everything together in excited fashion!

Doing it right first time would be the experienced mechanics way of doing things.

Malcolm
Malcolm Le Chevalier

Only want to save you the problems I faced myself.
Once assembled the complete botom end even put the sump on and then heard a slight click when rotating....
Used 010 bearings instead of the needed 020 doh!!
Onno K

Thanks for making sure I did the right thing Onno! Found a wee speck of grit on no1 big end. Tiny scratch on the bearing but that is what bearings are for right? :-) Crank fine.

Rebuilt it all and it is stiff to turn but smooth, no sticky notchy bits.

Cheers,
Malcolm
Malcolm Le Chevalier

Glad you found it!
If you can't feel the scratch in your bearing it is fine.
Onno K

Malcolm, its a 1500 isn't it?

I've just got past that stage with my new rings... Always going to be stiff...

I would put a breaker bar (mine is 2 ft long) on the big socket on the crankshaft and turn it over a few times with that... if it is hard to turn with that leverage then there is a problem.

C L Carter

Aye Christian, its 1500. I have a slogging spanner that is a foot long at most. I can turn with that. Stiff but ok, can turn by hand, just 'stiff piston rings'

Think I am on to a winner, short of cam for rest of rebuild at weekend tho.

ON phone... Sorry about crap grammar

Malcolm
Malcolm Le Chevalier

I ran into this during my rebuild...

The 2 bolts that attach the oil filter housing are not the same size ...if you dont have the 2 bolts in there. Corrct holes... The longer one will foul the crankshaft just slightly as the #1 piston is going up
Prop and the Blackhole Midget

Opps... Sorry ... Void my above post...my engine is a 1275, not a 1500
Prop and the Blackhole Midget

Malcolm, progress has slowed. I have the rear wheel arch apart and am working out what to do to make the reapirs easy. The boot floor on the outside of the rear lever arm mounts has rusted through. Its a bu**er to get at when the car is right way up..

I will have to fashion a patch and weld it on upside down ... Then the outer wheel arch and outer wing panel need to go on as well as the rear boot deck rhs panel and offside sill, A panl bottom reapir and... think thats it for bodywork. Just brakes/suspension and steering to check out....

At this rate however I will be lucky to get it on the road this year let alone this summer.. I need some weekends free to get on with it....
John Barber

Ach, I feel your pain John, bodywork is so draining! I need to get on and do some more welding. Problem is my garage doesn't actually have electric, I have to run an extension cable over someones back wall and plug into their external socket, and I think they are on holiday so it is switched off!

Drivers side chassis rail and floor are ready to weld in though. Having both sides of the floor fully welded up will be a big milestone I think!

I wrote a list of all the welding needing doing. It was a full A4 side.

But still, the theory goes, as all the mechanicals are clean and tidy, once the body is done it won't take long at all to then have a rolling shell, then a working car!

All the best!

Cheers,
Malcolm
Malcolm Le Chevalier

This thread was discussed between 29/05/2012 and 04/06/2012

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