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MG MGA - Cltch Release Bearing

I have just replaced the clutch release bearing and clutch plate while I had the engine out (1800 with MGB clutch cover and 5-speed box). I noticed that the old bearing is badly chipped around 80 degrees of the circumference (see image). What could have caused this?

Steve

Steve Gyles

I have lightened your picture up a little for better view.

If the rocker bushing and/or pivot bolt in the clutch release arm is worn, this can allow the release arm to wobble sideways and the release bearing to run off center. The clutch still works, but the ID of the release bearing might drag on the splined shaft and make chattering noises.

With the MGA clutch cover there are three small springs securing the release plate to the arms. When the release bearing runs off center these springs might touch the edge of the carbon ring and cause this sort of wear on one side, just as shown in your picture. With the MGB diaphragm type clutch cover this will be a non-issue.

Was this release bearing once run with an MGA clutch cover? If so, then you may need to replace the bolt and bushing for the clutch release lever.


Barney Gaylord

Barney

The clutch release lever came with the 5-speed conversion. The release bearing was also replaced during the conversion. It has, therefore, only ever run with the MGB clutch cover.

Closer inspection (see image) shows that it has been running off centre, as you suggested. I have just inspected the lever and it had considerable lateral movement about the pivot. I put a spanner to the bolt and it appeared to have loosened despite having a locking nut. A couple of turns with the spanner and all movement has disappeared. The new bearing now appears central on the gearbox drive shaft.

The pivot bracket assembly and the lever in the 5-speed bell housing is a different design to the MGA. I will take it all apart tomorrow and inspect the bushes etc. With luck I may just get away with a bit of Loctite on the nut!

Steve

Steve Gyles

Steve, I just wonder if it's possible to clobber the release bearing whilst lowering the engine into place and before the first motion shaft "finds" the spigot bearing in the crankshaft; just a thought. It looks like something that has happened once rather than repeated wear.
Lindsay Sampford

Lindsay

The thought had occurred to me. Perhaps even dropping it on the floor. I am not aware of anything untoward. There are signs of de-lamination immediately adjacent to the chipped bits. Perhaps another shoddy item from China. It might just be a combination of poor new parts and the engineering issues Barney highlighted.

Interestingly, the new bearing is new old stock Borg and Beck. It did not fit the newly manufactured (Chinese?) lever fork. I had to reduce the shoulders by at least 1/16" to get it in place.

Steve
Steve Gyles

View of the Type 9 thrust bearing and lever.

Steve

Steve Gyles

Two recommendations. First, invert the bolt such that the nut is on the bottom. That way, if the nut loosens again and falls off, the pivot bolt will remain in place due to gravity (though you'll have other problems with a nut rattling around inside your bellhousing). Second, replace the pictured hardware with a drilled bolt, and castellated nut with a cotter pin. That should prevent this from happening again, since this isn't exactly a location where you can access the bolt to inspect the nut for tightness.
Del Rawlins

Steve -
You will note in your picture a couple of posts up that the bearing has a lip developing on the ID, from running off center. The chipping is caused by the similar lip that used to be on the OD, but has been busted off by the thing thrashing about from looseness. The bolt should be shouldered, so that the nut can be dead tight; if you can tighten things up by tightening the bolt, you are bending the ears of the mount to do so, and it will fail sooner or later. The arm should be guided on the bolt shoulder by the bush, tighten the sides in is very temporary and won't do. It can also cause binding. Fit a new bush and bolt, and the bolt shoulder should be of such length as to allow total tightening in the housing, while giving 5 thou or so side clearance for the arm. I machine the bolt shoulder to match the thickness of the ears, which sometimes need to be refaced as a result of things having been loose. The shouldered bolt requires that one side of the housing have a bigger hole than the other, which means Del's reversal cannot be done. Alternatively, since it is aftermarket, there could be a distance tube inside the bush to allow tightening of a non shoulder bolts; again .005 or so side clearance should result with the bolt dead tight.

FRM
FR Millmore

FRM and Del

Many thanks for your advice. I will give it a good inspection today and report back.

The blue bearing shown in the picture is brand new. The ID lip is as machined by the manufacturer. However, I can confirm that the damaged bearing does have some flaking on the ID (see image).

Steve



Steve Gyles

FRM

The existing bolt is shouldered (see image) and unworn with a constant 0.499" diameter. However, you could drive a bus through the gap in the bush. Its internal diameter is 0.517". The bolt rocks like crazy in it.

This may be an issue for other users of the Hi-Gear 5-speed conversion to monitor. This wear has occurred in 20,000 miles of use.

By the way Del, the bolt cannot be put in the other way round as there is insufficient clearance with the bell house casing.

Steve

Steve Gyles

FRM

I am not that experienced in this type of work. I am machining a new bush out of a phosphorus bronze bush I have lying around. So far I have got a good fit with the ID and OD - quite pleased. The length I need is puzzling me. The thickness of the lever arm is 0.644". The length of the old original bush is 0.624". Should I make the new bush the same as the lever arm (0.644") or even very slightly longer to avoid the lever becoming too tight in the bracket?

Steve
Steve Gyles

Steve -
The bush should not be phosphor bronze, as that requires lubrication. It is supposed to be Oilite, ie porous oil soaked bronze, which does not require lubrication. The bush should be the same or slightly less than the arm thickness; the bush is pressed into the arm and moves with it - it's a part of the arm. The arm cannot move on the bush, so you absolutely do not want any possibility of nipping the bush in the bracket, as it would all bind up, and the arm would then move on the bush. That gives double clearance (ID & OD of bush), and more slop. Use the normal Oilite bush, which is a standard hardware store item for electric motors and such.

I was referring to the old bearing, but from the new picture it seems there is no lip. Doesn't matter, it's still what caused the OD chipping. Chipping on the ID might be from the same cause, or from contact on engine removal - and it doesn't matter operationally. Bearings are actually pressed to shape, and not uncommonly come with chips, but not like your first shows.

" I put a spanner to the bolt and it appeared to have loosened despite having a locking nut. A couple of turns with the spanner and all movement has disappeared."
>>>This means that the bolt was not tightened down against the shoulder. A new bush will certainly help, but if the bolt can move in the housing, it will do the same thing again.
Now that I have pictures, I see that my original idea that the bolt could be dead tight against the shoulder is erroneous in this case. Bad design, but you have to live with it! I would put a bit of Loctite on the bolt shank just below the head, to prevent the bolt moving in the bracket, and Loctite on the nut, Nylock notwithstanding. Being careful not to get the Loctite in the bush, although the oil in it should prevent it sticking.

The bolt large diameter should be polished; possibly a rough initial surface is what started the wear on the bush. Once they get loose, they flail about and beat things to death.

FRM
FR Millmore

Thanks FRM. You will make an engineer of me yet!

I had always thought that phosphor bronze was an oiled metal for this type of job. The bush I have adapted is a Moss item (168-008) for the MGTC distributor. I just assumed it is phosphor bronze, but may be not.

The shoulder on the bolt is about 0.06" shorter than the bracket width, hence I was able to squeeze the lever tight when I tightened the nut. Would it be worth shaving the base of the bolt head to make the shoulder flush with the bracket?

Steve

Steve Gyles

Steve -
Don't know what that bush is, but if it feels oily, it's Oilite. The usual Oilite is bronze in appearance because it is scintered bronze, but some of the Lucas distributors used a similar scintered bronze/iron/graphite, which looks silvery, will work fine, a bit more heavy duty. Under magnification you can see the pores in any grade of Oilite. Phosphor bronze hasn't any pores - it's like the old MGA/B gearbox bushes or swivel pin bushes.

You can shave the bolt head, but leave a bit to squeeze the bracket just enough that the bolt can't flop around in the bracket. If you measure side clearance, you should be able to decide how much it takes to squeeze the bracket in to where the arm has .005 -.010 clearance when the bolt is dead tight. Also not a bad idea to machine a proper flat washer with square surfaces and close fitting hole. That cheap hardware item in the picture is not what you want for such fittings, since the shoulder will be bearing on the washer. Last one I did the shoulder was too long (from wear on the bracket due to running loose) and I had to recess the back side of the washer to get the fit right.

FRM
FR Millmore

>By the way Del, the bolt cannot be put in the other way
>round as there is insufficient clearance with the bell
>house casing.

Oops. I still think it would be a real good idea to drill that bolt and use a castellated nut. I wouldn't want to trust that to a self locking nut since it is subject to rotational forces, especially considering the orientation.
Del Rawlins

This thread was discussed between 13/12/2009 and 14/12/2009

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