MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - A little guidance before I pull the engine...

Hi, posted in the correct section now, please ignore the post in General.

I used my car to go to work today and on the way home I felt a vibration through the clutch pedal when pressing it down.

If I drove in gear for a while I would get a couple of gear changes vibration free.

Once home the car would cut out on tick over if the pedal was pressed. If the car was revved and the pedal pressed the revs would drop approx 500rpm.

There was also a slight scraping sound before cutting out.

Does this sound like the release bearing?

The clutch, bearing and cover were all replaced less than 1000 miles along with a gearbox rebuild.

Could you offer some advice which may save me having to pull the engine?

Many thanks
Mark
Mark Whitmore

Mark I hope it isn't but it does sound suspiciously "worn out carbon thrust syndrome" to me.

Can you get a mirror to look inside the bellhousing access hole at the carbon thrust.

A small digital camera and a torch can often "see" inside there when we cannot get our eyes lined up properly.
Bill1

if your camera/phone has a flash close to the lens then just taking literally shots in the dark might work - I done this (not on midget tho') only the other night, took about 6 and all the photos turned out pretty well with Sod's Law the first one being the best
Nigel Atkins

Thanks both, will get some snaps and report back.

Mark
Mark Whitmore

If it had been a 1500 engine, which I realise it is not, another favourite cause of these symptoms is the crank thrust washers becoming displaced and allowing the crank to move too far along its axis when the clutch is pressed, which can cause fouling in the crancase.
Not good news, but I am not sure if the A series is susceptible to the same malady.

It can be checked by seeing if you can move the crank pulley forward and back by levering with a long screwdriver. A small amount is acceptable.
JB Anderson

Hey JB,

Sadly for mark... the 1275 thrust bearings are almost bullet proof...but I did mention the same on the general side of the forum

But I have heard of it happening, on 1275s so its not out of the realm

Prop
Prop and the Blackhole Midget

Thrust bearings, I agree. I think you guys are on the right track. I would still get a look at the clutch components too but whats the difference if your that deep into the motor? You will be doing a lot of R&R
that will need doing to make it dependable one more.


Goodluck!
Steven Devine

If it is crank thrust bearings you can check for movement at the crank fully. Use a lever between fully and chassis cross rail to push it back. Then feel and look for forward movement as your attractive assistant presses on the clutch.
Guy W

Many thanks, I found the thrust bearing test whilst trawling through the archives (sleepless night) so will check that one out.

Is it worth the extra cost to purchase a roller release bearing such as Peter Mays. The archive has both good and bad points but mainly good?

Thanks
Mark

PS sorry for the double take on the thread as I mistakenly posted his in General (mind must have been side tracked with the thought of pulling the engine once more!!)
Mark Whitmore

Of course if it is just the crank thrust bearings, you can do those in situ by just removing the sump rather than removing the whole engine. Makes for a much easier repair. ;-)
Guy W


Mark & all.

This is exactly the same symptons I have with my Midget 3.

It's not a worn carbon release on mine - I took pictures to prove it to myself & those in the know.

Guy - are you able to explain to a 'hack' in more detail your method to check the crank thrust bearing please?

Ain't this a great site!

Gavin.
Gavin Rowles

Hi Gavin,

When the crank thrust bearings (shims) are worn, the crank itself is able to move back and forth within the cranckase. No a lot, but a bit! The fault as has been mentioned, is much more prevalent on the 1500s though, but can still happen with the A series engines.

You start by making sure that the crank is as far back as it will go. Do this by levering on the crank pulley at the front, using something like a flat iron bar, crowbar or large tyre lever. Lever against the pulley using the front chassis cross rail as a fulcrum, maybe with a block of wood in there to lever against. It doesn't need a great deal of force, just enough to check that it is snugly back where it should be. It may well not appear to move at all.

Then you get your Attractive Assistant to sit in the car and press the clutch fully down, with a single firm stroke of the pedal. But wait until you are ready! You need to observe that crank pulley closely. You are looking for movement, but even if worn it will be quite small so watch closely and maybe rest a finger on the gap at the back of the pulley between crankcase and the pulley. You won't pinch your finger because if it does move, the gap will get bigger, not smaller.

I should have started off by saying that this is all done with the engine switched off of course!

On a good engine there will be no discernible movement. A - series crank end float is 0.002 to 0.003 (two to three thou)which you might just feel with a bit of added imagination. If the crank visibly moves then there is summat wrong. Redo the procedure to be sure.

The good news is that if this is the fault (or a fault) then it can usually be fixed with the engine still in situ. I say usually as I once had a car (not a BMC one) where the shims had worn and dropped out and the crank moved so much that it had chewed into the crankcase centre web. Surprisingly, the car still ran and wasn't making any unusual noises - until the clutch was used!
Guy W

"""I should have started off by saying that this is all done with the engine switched off of course!"""

ROFLMAO....hahahaha, the image that your comment created has me rolling....thats just classic

I lost 3 fingers, are you sure im doing it right. LOL.

Prop
Prop and the Blackhole Midget

If it is thust ( what are they really called ...washers, shims, or bearings )

They are maybe 1/8 inch thick and "C" shaped, I want to say you remove the center main bearing cap then the thrust bearings /shims just slide up between the crankshaft and the block portion that holds the center main, put the main center cap back on retorqeto spec replace pan and oil and your ready to go

Btw...."""I should have started off by saying that this is all done with the engine switched off of course!"""

Hahaha

Prop
Prop and the Blackhole Midget

Posted a reply in this topic in general!
Daniel Stapleton

Hi all, had a look tonight and darn, it looks like the release bearing.

The odd thing was that the metal carrier was in contact with the clutch plate.

A look to the slave cylinder showed that the rod was fully pushed out as though the clutch pedal was being pressed. I pushed it back in manually and it slid back out.

I presume this means that the seals have failed in either the slave or master cylinders?

The first pick is as found. I would imaging that the fine coating of dust is the remains of the carbon ring!


Mark Whitmore

The second pic is with me pushing the slave rod in.

Is there any way that these 2 events are related as I had no trouble with getting drive or gears with the exception of the vibration through the pedal.

The pedal was good last night once I'd parked up. It seems odd that the pedal would flop and the slave pressurise overnight, any ideas?

Looks like I will have to start stripping things down to haul the lump out.

Oh well needed a winter project!!!!

I will also check the crank end float if I get a clutch pedal back and my attractive assistant becomes available

Thanks
Mark


Mark Whitmore

Jesus " mark " and mary,

Id say you found your problem but for the life of me I cant figure out how that happened in only a 1000 miles

Damn grimlins....

Well that roundish hexagon thing on the pressure plate is about twice as thick as it is now, and there ""USED TO BE"" a carbon ring on that other piece and the 2 sections rubbed agianst each outher....I say "USED TO BE""... cause its not there now, im thinking ""dust in the wind, all it ever was, is dust in the wind....la laaaa la lUULLYYY, DUST in the wind"" ,,,, hahaha

What would cause that... grimlins driving your car at night ridding the clutch non stop.

A fly wheel heavly over resurfaced maybe...the rubber boots for the fork and the slave completely shot, I just dont know...im looking forward to what others come up with, for 1000 miles, thats just nasty...if it were 185,000 miles I could understand that

If its any constellation, you will have this fixed and running before I ever have the 3rd cly stud installed on my car....hahaha

Hang in there buddy... youll make it, its inly cash and time plus your personal sanity

Prop

Good luck
Prop and the Blackhole Midget

Mark,
just shows how useful a small camera can be for "looking" at places that you cannot see directly! Very smart!

The checking of the crank thrust that I described in some detail is clearly a red herring. Or a wild goose, or some other mythical beast; maybe a unicorn? But had it been the problem then it might have saved you having to remove the engine. At least you now know hat time spent removing the engine won't be wasted.
Guy W

Mark,

Looks like you have one of the rubbish quality carbon bearings that has broken up.

It will likely have knackered the pressure plate also.

As noted above the faulty ones have pins locating the carbon.

Tough luck - poor quality parts again - where did it come from ?

R.
richard boobier

Thanks for the comments,

I came across an old post regarding clutch bearings where the locating pin was mentioned, funnily enough I had replied to this by saying "It doesn't look like mine has the pin but will report any issues once the car is back on the road!" I'll confirm this once it's removed.

This was in 2011 but I haven't used the car that much due to work commitments (slap wrists!)

The clutch was replaced completely with a Powertune branded kit sold by David Manners.

Richard, is the pressure plate likely to be knackered due to the excess carbon dust or vibration caused by the carbon breaking up?

I suppose it would be worth swapping it all to save having to pull it out again. I think I will go for a roller release bearing, once bitten.....

Thanks again
Mark
Mark Whitmore

I'm glad the camera trick worked.

Pity your carbon thrust didn't. :-(

I think this is even more hard thinking for the usual suppliers to worry over, carbon users will all be stockpiling old ones now. The ones replaced 'cos they are out of in-between instead of bec'os worn down.

I think I may have one hanging round someplace, I'll have to look, later when my other jobs are done.

That looks to have been a really bad one, I hope you can get some recompense from whoever sold it to you.

Date of sale plus MOT mileages should help you get something back for it.
Bill1

Mark,

My comment about the pressure plate is based on the fact that without the carbon, the release bearing - iron/cast steel ? will have been in direct contact with the bearing surface of the pressure plate.

I have both good and bad carbons here somewhere ?
Will try to sort and post pics.

Not so sure about roller bearings - some are heavy and can cause other problems.
I'am using original carbon types that have been used sucessfully for generations !

R.
richard boobier

On my datsun 5 speed

It uses the ball bearing release bearing, but...

We have to cut off the round hexagon part that hooks into the fingers for better clearance

If thats also the case with the ribby case and the ball bearing release bearing...then your pressure plate maybe okay to re-use if you have to cut off the round hexigon block

Prop
Prop and the Blackhole Midget

Hi
i wonder whether there may be something we're missing here.
While it is true that the carbon on the bearing could have just failed due to a manufacturing issue it could also be linked to something else that Mark mentioned.

"A look to the slave cylinder showed that the rod was fully pushed out as though the clutch pedal was being pressed. I pushed it back in manually and it slid back out."

could this mean that for some unknown reason for the last 1000 miles the slave has been exerting pressure on the throw out arm pushing the bearing against the clutch?
This would have the same effect as riding the clutch pedal and would probably wear out the bearing pretty quickly.

What does everybody think? I don't think the clutch salve is supposed to work this way (but am happy to be corrected). Question would then be, why is it misbehaving? One thought would be that the clutch hydraulic pipe is partially collapsed acting like a one way valve preventing the slave from returning when the pedal is released..

Cheers
tim
T Dafforn

The slave cylinder is behaving normally. There is a light spring in it for the express purpose of keeping the release bearing in close proximity to (= in light contact with) the release ring on the pressure plate. If this did not happen then most/all of the clutch movement would be taken up getting the bearing up to the pressureplate, with precious little left to actually operate the clutch. This system is self adjusting - as the position of the ring moves in response to wear on the plate, then the release bearing is kept in the right place automatically.
The MGB has the same system. It's not a feature which causes rapid wear of the release bearing.

What does occur to me is that the reported symptom of a vibration through the pedal can be caused by the release ring on the pressure plate being at an angle rather than normal to the clutch axis. This can cause rapid wear of the release bearing. When the ring is out of true it also knocks the release bearing out of contact, to the extent that a couple of pumps might be needed to get the clutch to release. The cause of this situation with the release ring is a faulty diaphragm spring, usually weak on one side, sometimes caused by over-stroking of the clutch arm (for example if the clave cylinder is too small the pushord will move further).

While the clutch is apart check the ring with a straight edge in a couple of directions to make sure it's parallel to the flywheel.
Paul Walbran

The piston only retreats into the slave cylinder when you take your foot off the pedal because the clutch diaphragm, acting via the lever and pushrod, pushes it back up the bore. This is why the thrust remains in light contact, just kissing the pressure plate ring. As Paul says, usually (but not always) there is also a light spring inside the cylinder to maintain this light contact.

If the contact with the clutch diaphragm ring is uneven then the release bearing gets kicked back too far as Paul describes. As well as being caused by damage, if the lever arm pivot is worn it allows the lever arm to droop so that the thrust bearing is not central or square to the diaphragm ring and then it will also increase wear.

I am taken with Tim's comment about an internally failed flexible hose. This would act, as with brake hoses, like a one-way valve, maintaining too much pressure in the slave cylinder and therefore on the release bearing contact with the clutch.

Prop is right; the roller release bearings, or at least those with a rounded profile, operate direct on the diaphragm fingers so the attached diaphragm ring is removed.
Guy W

Guy wrote


"""Prop is right; the roller release bearings, or at least those with a rounded profile, operate direct on the diaphragm fingers so the attached diaphragm ring is removed.""


Omg.... please!! Dont tell Onno, he will pop for sure.

hahaha

Prop
Prop and the Blackhole Midget

for those that haven't seen this on the other thread it might be of interest, stay with it until the very end -

- http://www.youtube.com/watch?v=d173K60GSU8&feature=c4-overview&list=UU40j4KqUJPMVv4FQ29ro-xQ
Nigel Atkins

Hi, will check the ring with a straight edge whilst apart.

When the engine was last out I changed the pivot bush, bolt, nut and washers etc, but will check them again (I'd hate to put it all back in and find that the bush needs replacing again!!)

As far as I know my slave and master cylinders are standard and the clutch hose is braided.

Thanks
Mark
Mark Whitmore

This thread was discussed between 24/09/2013 and 26/09/2013

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.