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MG Midget and Sprite Technical - Clutch confusion

The clutch release bearing has suddenly failed and I am now wondering if I have the best set-up. It is:

948 engine and flywheel
3/4" master
7/8" slave
1098 gearbox
1098 release fork
1098 release bearing
1275 clutch
Thin backplate

Having failed to get 9-spring clutches to work properly I had the flywheel drilled for the 1275, which was a massive improvement. When assembled I ensured that there was correct clearance for the release bearing. I checked the travel of the slave and ensured it wasn't pushing the clutch too far. The failure of the bearing was sudden which suggests breakup not wear.

To get this to work I have a slave pushrod which is just over 2" from hole to end. I have just been reading the Gerard's Garage site (http://gerardsgarage.com/Garage/Tech/TO_Bearings/tobearings.htm) and he says that a 1098 box should not be used with a thin backplate as the input shaft is longer and it can bottom out in the spigot bearing. I am now wondering whether I should use the 2" slave and the thick backplate (I have one in stock). What do you think? The box bolted up to the thin backplate perfectly well with no apparent binding.

BTW as the engine has about 70 bhp I never wanted to rely on the standard clutch. I would rather not change the backplate as I have a rear main bearing lip seal and it's a swine to refit that.

And also BTW, why can't I view old posts here? I only seem to be able to see one page.
L B Rose

Hi

The 1098 box and fork is the same as the 1275 one dimensionally so effectively you have a 1098/1275 set up.

The 1275 clutch cover is shallower than the 1098 or 948 one and uses a different release bearing. I would set yours up as a 1275. As you already have the smaller bore master, use the 1275 slave which has a larger bore, the standard 7/8" means further travel and the risk of overthrow on the clutch leading to premature wear and a stiffer pedal. You will need an adapter on the end of the clutch bundy pipe as the thread in the 1275 slave is bigger.
Change the backplate to the thicker one. Its better anyway than the thin one and is more rigid.
I would also use the 1275 pushrod.
I got the slave and adapter from Powertrack who were very helpful when I overhauled the 1275 clutch in my Frogeye
Bob Beaumont

Thanks Bob

What do you think about a roller release bearing? The carbon ones are getting a very bad press.
L B Rose

I've a Peter May roller bearing in mine as it was becoming a pain hauling the engine/gearbox out to replace yet another duff carbon thrust bearing. It works well although I've added an adjustable pushrod as the supplied one wasn't long enough.
Jeremy Tickle

Not had any experience of the roller ones personally but Peter May's equipment is usually very good. Not cheap though. I still have the carbon thrust as I found a couple of NOS items. You are right in that the repro stuff is of variable quality.
Bob Beaumont

LB.
Go into the technical archives, and read this thread. "Chris Buvkhenham 1275 Clutch carbon release" I started it because mine failed. I made my own roller release as a replacement.



Lawrence Slater

Cheaper and easily as effective as any I've seen for sale. Mines been in for quite a while now and works a treat. However, Alan's version is slimmer and better looking than mine.

Lawrence Slater

Yesterday I pulled out the engine and gearbox and found that yes, the carbon release bearing has broken up. Some of the bits had fallen into the release fork gaiter and jammed the fork, so when I hit the pedal it didn't move and fluid was forced out of the slave. There is no evidence that the input shaft has bottomed out in the spigot bearing, or that the clutch has been overthrown. This seems to be simply a failure. I have thought about a roller release bearing but remain a bit doubtful, as it won't run concentrically. The carbon can accommodate that. Peter May Engineering sells a concentric roller bearing system but it only fits a Formula Junior engine. The 1275 clutch doesn't move as far as the coil spring one so the eccentricity should not be as severe.

I'll have a look at the archives re the home-made roller bearing system. Worth a thought if I get another failure.

To be on the safe side I have fitted the thick backplate and have ordered a 1275 slave. I will weld up the pushrod to suit. So I will have a 100% 1275 system and if the bearing fails again it will definitely be a quality issue. The new one I am putting in is not the scroll pin type.
L B Rose

" -- I have thought about a roller release bearing but remain a bit doubtful, as it won't run concentrically. -- "

Not so LB. As long as you make the roller sit on the pressure plate, and there isn't too much throw, it will run just as concentrically as the carbon does.

This is a picture of my home made roller in situ, in my 1275 midget.

IMO, the Peter May version is too long, and therefore too front heavy, because it involves removing the pressure pad on the cover plate to run on the fingers. I retain the pressure pad on the cover plate. Mine is lower profile, and thus has less tendancy to fall under it's own weight and run off centre.

The proof of the pudding, is that it is working very well. Over a couple of hours in stop start traffic on the M25 is a good test, that might have goosed the carbons on sale today. My diy roller coped with that without a murmer, and is still working perfectly.

Lawrence Slater

This thread was discussed between 07/11/2015 and 09/11/2015

MG Midget and Sprite Technical index

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