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MG MGA - Clutch throwout bearings

Looking through the MGA parts on Ebay, I keep seeing an updated roller type clutch release bearing for sale. I was just wondering what the group opinion is on these. The body appears to be made of plastic, and I am kind of suspicious when plastic gets substituted for parts that were originally made of metal.
Del Rawlins

My roller bearing is all metal and works great.
jeff becker

Original carbon release bearing is cheap, and it lasts about as long as the clutch disc (and gearbox layshaft and 2nd gear syncronyzer ring), maybe 80,000 miles depending on your driving habits. The plastic shell roller release bearing will almost certainly fail in less time, sometimes in as little as a few weeks (or days if you drive a lot). The all metal roller release bearing should fare better, but could also fail prematurely if left to run continuously in contact with the pressure plate.

To have any expectation of long life from a roller release bearing in an MG you need to install a return spring and adjustable lever stop on the release arm. Then you get to make occasional adjustments to the lever stop as the clutch disc wears. To me this means increased installation expense, added maintenance procedure, and maybe still no benefit for increased life as the clutch disc will still wear out on the same schedule.
Barney Gaylord

Thanks, I think I will stick with the original type carbon release bearing.
Del Rawlins

One thing I notice with my Roadster (carbon bearing)is that the engine RPM drop about 300 when I depress the clutch (rubbing action) which does not happen with my Coupe(roller bearing). I will install a roller bearing in the roadster next time. Have a good day!

John
John Progess

The rev drop can be a symptom of excess crankshaft end float.
Malcolm Asquith

Malcolm,
When I rebuilt the engine I did check the crank end float and it was in spec but you may be right. I did not think of that. Oh well nothing I can do about that now, I will just live with it. Have a good day!

John
John Progess

I wouldn't live with that. A 300 rpm drop when releasing the clutch is a sign that something is binding up or dragging severely. It might be benign, but I wouldn't want to bet on it.
Del Rawlins

John. I agree with Malcolm and Del. A significant drop in engine speed, and I consider 300 rpm to be significant, indicates that as the throwout bearing is depressing the pressure plate release it is also pushing forwards on the crankshaft sufficiently to cause some form of binding to take place. How significant this is can only be determined by installing a dial indicator on the nose of the crankshaft and measuring how much play has developed. A roller bearing will not correct such a problem, nor would a new carbon bearing.

Les
Les Bengtson

The carbon bearing is original, but not always the best.

The roller bearing, if the fork has excessive play can be out of centre and wear rapidly being as though this system was not made for it.

Barney, most of my other vehicles do NOT have a return spring. Just like brakes, your clutch slave cylinder rubber pulls the roller or carbon bear back a few thousandths out of what would otherwise be normal wears path.

Malcolm, even with motors we have completely rebuilt and even some with a light layer of various wheel bearing grease, I have noted significant RPM drop when depressing the clutch. Disconnect the ignition coil some time and crank the motor over for 10 seconds, the first 5 with the clutch in, the second 5 with the clutch released. With a standard Carbon bearing, you will note a significant RPM difference, especially with the stock starter!

Most of the experience MG guys will probably be able to tell you to NOT depress the clutch whilst starting a cold motor on a brisk fall morning, say 35 degrees F. If you do, the motor will drop in cranking speeds and become more difficult to start.

Now say your starting a modern car or an MG with a roller bearing at 10 Below 0 F. You will note that by depressing the clutch, you will not have the friction of the carbon surface AND because you are depressing the clutch, the input shaft is not turning and not trying to move that gearlube that is thicker then honey. Most 'modern' cars motors spin over FASTER with the clutch in when starting. <<That is to say as long as they dont have a safety release switch!!!>>

Back to the MG at 10 below F---- its a toss up- will it start better with the carbon face friction or the friction of the gearlube on the input shaft at these speeds....

Going one step further- if i was going to start an MG in Minnesota or cooler weather winters, I would want a gear reduction starter, roller bearing and a ignition system in tip top shape, but this is outside the original question!

Temperature, motor speed (cranking, idle or 2000RPM), motor condition and input shaft can be reasons for motor speed to alter. 300 RPM is about right for the 10 second test at idle, but excessive at 2,000+ RPM. at 2,000 RPM, I am guessing 300 RPM is the limit that should happen if your testing by using the choke (NOT your foot!) to hold throttle but the further the motors RPM increases, the more power and the less this could be noticed.

Finally (Yup, I'm to the end!) I have seen lots of modern motors with warn clutches and CRANKSHAFT THRUST surfaces inside the motors because people are not letting their foot off at the light for three minutes at a time. Since the carbon bearing has been replaced by a good bearing that can take the abuse, I see crankshafts wear out with these thrust bearings. Moral of the story- Even if you replace a part (carbon bush with a roller bearing), expect other weak (and far more expensive) links (such as the crankshaft!!) to break or wear out.
(For every positive there is a negative)

-BMC.
BMC Brian McCullough

I think one of the missed issues is that some of these roller bearings, as Barney mentioned, have plastic shells. I ordered a clutch for a Japanese friend and he paid extra for the roller bearing, which happened to have the plastic shell. Needless to say you know what happened almost as soon as it went back on the road--and he is very, very gently on his A.

I'm not as hard on my A as Barney is on his, but in my younger days I did beat my MGB about as hard as you could. I mean I drove that car without mercy (still well maintained, though)--and this was after a beautiful full restoration. It did about 70,000 miles before the bearing face wore completely off.

I like the idea of a roller bearing, but from my expererience it falls into the '46mm Weber on an otherwise stock motor' category.
Tommy

If this is the one your talking about:


http://cgi.ebay.com/ebaymotors/MGTC-TD-TF-MGA-Hillman-Minx-Husky-Roller-Release-Brg_W0QQitemZ140042849798QQihZ004QQcategoryZ34208QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


I believe Moss sells the same kind. It has a coating over steel, probably cast. I used one on the last MGA we restored. The vehicle has only seen about 2,000 miles now but no problems reported since restored. I have used theses elsewhere too and they seem fine... At least the units from Moss, but there were some posts on this board (midget section?) a few years ago about some misalignment problems..

That said, were there also recent complaints about a certain carbon bearing problem on one of the various models within the last year as well???

-BMC.
BMC Brian McCullough

The carbon thrust bearing is perfect for the job if you know how a clutch should be used.

Roller bearings are for people with very, very strong left feet who love to hold the car in gear until the traffic eventually moves again. We all know people who do this, I have never discovered why; this is obviously why the modern car has them.

When used briefly, putting the car in gear and changing between gears, the carbon bearing is a fantastic, longlasting bit of economical kit. Hold the pedal down and the poor thing overheats and rips itself up.

Our satisfaction comes from just understanding what's going on down there doesn't it.

Pete
Pete Tipping

This thread was discussed between 15/10/2006 and 19/10/2006

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