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MG Midget and Sprite Technical - Broken crankshaft pulley

My crankshaft pulley (Frogeye 948cc) has cracked. Does anyone know if this is likely to just need replacement or is it a sign of some other sinister problem? I assume I should just try to replace the pulley first and see what happens.
It seems from the archives that I will need to remove the engine mounts to jack the front of the engine to get clearance from the cross member but will the bolt just unscrew - I would have thought that turning the bolt will just turn the engine?
Thanks
Graham M V

"""but will the bolt just unscrew - I would have thought that turning the bolt will just turn the engine?""""

Weeellllll, ....It "SHOULD" be that simple. Hahaha

2 words come to mind, .... impact wrench

Prop
Prop

1. there will/should be a tab washer round the bolt head, don't forget to knock it back first
2. you have to stop the engine turning over to undo the bolt; one method is to remove the starter motor and jam a large screwdriver or crowbar in the ring gear.
David Smith

The other is to get the starter motor to do the job for you... But unless you are SURE about what you are doing... don't try this at home....!

Mark.
M T Boldry

I bent up a bit of thick steel into an angle,shaped edge to engage with teeth and bolted it into the starter bolt hole.

There is a special tool - only seen a pic - its the teeth of a starter on a flat plate that bolts in to replace the starter - cast I think.
Angle worked O.K for me.

R.
richard boobier

Worst case you can drop the pan, and make a wooden 2x4 wedge and jam it crank and the block at the corners
Prop

Or put it in top gear and have a helper keep foot firmly planted on the brakes. Never failed yet unless the clutch needed replacing.
Paul Walbran

Thanks for the tips. From looking at the threads, assuming all models are the same, it looks like I need a 46mm size socket. Is that correct?
Graham M V

1&5/16" IIRC

And I do the same as Richard
Dave O'Neill 2

I was thinking maybe I would treat myself to an electric impact wrench. There seems to be an enormous variation in price, what sort of torque do you think I would need for this job?
Graham M V

Yeah....your the man graham !!!!

It will remove that bolt in like 12 seconds....its so fast its actually disappointing, cause you want to keep pulling the trigger loosing any and everything

Thats what I did, 1/2 inch electric impact wrench, I got mine at harbor friaght similar to your machine mart...all made in china, I got mine for under $50, I love mine, one of my top fav 5 tools....i find I use it all the time

Just 2 thoughts....1. get the most amps you can afford, 2. Buy a set of impact sockets, I didnt orginally, and im finding it does chew up the standard craftman sockets....thank goodiness for life time in store no qurstions asked warrnty.

Prop
Prop

Graham,
Don't automatically discount the simple solutions - Sometimes putting the car in first or reverse gear and having someone press hard on the brake pedal is enough to hold the crank whilst you use a long bar lever on the front pulley nut.
Guy

Just found the pic of my locking tool from the last time this cropped up...

Dave O'Neill 2

Thanks for your help. I have ordered the parts and will let you know how I get on.
Graham M V

The parts arrived, but with a note that the lock tab washer is on back order with no supply date.

Can I ask two questions please:
1. The pulley is considerably wider than my existing one (see pic). Has anyone else fitted this on a 948cc Mk1 Sprite? I realise that the original is no longer manufactured, but there is a cross member just in front of the flywheel and so it will be tight.

2. If I can take the old tab washer off without too much damage, will it be OK to re-use? I will obviously try to buy elsewhere, but I am guessing I will get the same story (all closed for the evening now).

Many thanks

Graham M V

That size should not be a problem as it looks identical to the 1275 damper pullys
Don't be tempted by the impact thingy they are the best way to broken bolts and knackered threads!

I would not reuse that lock tab if you can not find one better use locktite
Onno Könemann

Graham........

your original pulley was a single groove pressed steel pulley...right?

what you show in the picture is a dampener....a pulley integral with a crankshaft torsional dampener.

this is commonly used on 1275cc motors...BUT can be used on a small bore motor. check the following....

1) the diameter of the old pulley compared to the new pulley. (you might have to change the belt length).

2) the front shoulder of the bore of the dampner. It might require a large washer under the bolt head.

3) the grip length of the bolt. (If they supplied a new bolt, then we can assume it is the rite grip length. If you are using the OLD BOLT , make sure that it is long enough (grip length) so as to go in the hole of the crankshaft a minimum of 1 and 1/2 times of the bolt diameter.

4) the dampener groove is in the same fore and aft postion as the old pulley when it is installed.

You dont have to use the tab washer. Use 3 drops of Loctite blue on the bolt threads. Torque to about 80 ft/lbs.

You shud B able to use a 6 or 12 point socket and a breaker bar to get at the bolt head. Use some liquid Wrench or penetrant first and let it soak for a few hours.
J. Blow

Ive always re used the washer tab, just beat it flat wit a hammer and bend it back when youi re install... bbut ai did get new for the new engine

seriously go for the electric inpact wrench, the breaker bar will work ... but its not near a treat or fun as the electric impact wrench....Id think busting the head off is not likely,If it does then it would also break with a breaker bar... sorry onno, just my opinion
Prop

Yes, the original pulley was single grooved. I really appreciate the help. I have time set aside tomorrow to work on the car, so will report back after then.
Graham M V

Reporting back to base. Blasted thing wont shift! So Prop will be pleased to hear I have ordered the electric impact wrench.
Was surprised that with car in 1st gear and handbrake on, the engine turned easily with a spanner on the bolt but using Paul's advice, in 4th with the footbrake pressed, it didn't turn. Was surprised it made so much difference.
Graham M V

Graham

Where did you get the pulley from?

Have you tried a ling length of pipe to extend the power bar? (Sorry, forgot to mention before that's an essential part of the kit!)
Paul Walbran

Paul
I got the pulley from AH Spares. I think it was because their price was better.
I think my main problem is I didnt have the right kit. I was naively trying with an adjustable spanner, and a plumbers wrench. I realised that there was no point in buying a spanner (even if I can source one at 1 5/16ths inch) as the new pulley has a large inset in the damper, so a spanner wont work and I will need a socket anyway to put it back afterwards.
Graham M V

Graham I have a couple of spare 1 5/16" sockets if you need one...
David Smith

Run this dampened pulley on my 948 Frogeye. To do the job properly, and then to have to do it only once, you should replace the timing chain cover oil seal and to do that you will also need a new timing chain cover gasket.
A Anstead

David
Thanks very much for the offer. GSF car parts in Watford say they should have an impact socket in by the middle of next week, so should be OK but appreciate the offer.

AA
I certainly only want to do it once so I guess I should take your advice and replace the oil seal and gasket. Is that because the heavier pulley puts more stress on the seal? If I leave it alone, am I likely to get serious leaks or just dribbles do you think? I ask because I still have the original engine and gearbox so at some stage a major mechanical spring clean will be required, but not ready for it just yet!

Thanks
Graham M V

The oil seal may have hardened with age. It may have worn into the broken pulley. There may be machining tolerances to take into account that the old oil seal wont account for, there are numerous reasons.Last its always good practise to change oil seals when components have been taken apart.
You may have an old timing case with a felt seal rather than the later "plastic" seals in which case a later timing chain cover would be a good idea so that you can use the later type seal. Grease the lip on the seal and the boss, on the pulley that runs in it, on assembly.
A Anstead

Thought I should report back for the archives.
Took Props advice and bought the impact wrench. Mains powered so only about £65 but very powerful. Had the bolt undone within a minute!
A good purchase
And thank you to everyone's kind input on the forum
Graham M V

This thread was discussed between 07/08/2011 and 22/08/2011

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