DIY Roller Throw Out Bearing

[RAC68]

Recently I came across this article (https://www.mgexperience.net/article/diy-roller-throwout-bearing.html) directed at MGBs and was wondering if anyone tried this for a Healey?

RAC68(64BJ8P1)

 

[Bob_Spidell]

Seems like it would work as long as the pivot-to-bearing face distance was close to that of the carbon bearing. My concern would be that there would still be some rubbing between the bearing face and the contact plate on the clutch diaphragm.

Moss Motors has been doing quite a bit to provide modern upgrades to some components; maybe we could talk then into engineering an out-of the-box part.

 

[57_BN4]

There is an article I read which I can't seem to find again that shows why this is a bad idea. The very hard steel bearing is being pressed up against a soft cast iron plate and the plate quickly wears down. As Bob says there is still a fair amount of sliding going on due to the arc that the lever makes and the carbon block partially compensates for this by sliding. The bearing will attempt to compensate by sliding which will quickly turn to grinding.

Another lesser issue in that some release bearings, particularly cable-clutch ones sit away from the rotating clutch when not in use whereas the Healey bearing constantly sits lightly against the clutch. This may shorten the bearing life and also will wear a groove in the cast iron plate.

I am also toying with the idea of uprating the clutch release as I have a project coming up in a few years which involves a lot of driving. Perhaps the best solution involves using a release bearing from a hydraulic-clutch vehicle which stays in contact with the clutch when not in use and attach a large hardened/ground steel washer to the face of the thrust plate. This would address the two known weaknesses people are reporting from roller bearing retrofits.

Andy.

 

[Bob_Spidell]

Sounds then like you'd need a big graphite disc between the bearing and the plate on the clutch. Oh, wait ...

In the meantime, I make a point of putting the gearbox in neutral and releasing the clutch any time I'm going to be stopped for more than a second or two.

 

[57_BN4]

Yeah true... I'm wondering if a teflon/plastic plate might be better than hardened steel. It'd need a release bearing with a flat surface rather than arounded ring like most modern ones. The rounded shape is to provide a pivot point for the diaphragm fingers of a modern clutch.

Its interesting to see the design history here, my Ford uses USA derived technology as opposed to the UK derived Austin designs. The Ford has a snout on the gearbox which the release bearing slides along and the arc of the lever is compensated by the end of the lever sliding on the back of the release carrier. It uses a similar clutch except the roller bearing presses directly on the three release arms rather than a carrier plate. It also has a return spring on the slave cylinder and an adjustable pushrod to compensate for wear. The Zephyr release bearing can last the entire life of the vehicle if necessary/lucky.

 

[RAC68]

Bob, good idea to ask Moss if they have any interest in developing a roller throw out for the Healey.

Andy, the points you’ve made throw a wet blanket on the idea…for now. I wonder if the unit installed in the MGB has experienced the problems you’ve identified. I’ll see if I can get an e-mail address and response regarding any experiential information developed since his installation.

Thanks for your responses and all the best,
Ray (64BJ8P1)

 

[Duane_Rhynard]

Try Austin-Healey Spares:

https://www.ahspares.co.uk/austin-healey/performance-parts/Clutch/RELEASE-BEARING-BALL-RACE.aspx

 

[DerekJ]

Dennis Welch sells them.

 

[John_Progess]

One of the MGA guys came up with a simple device that mounts between the slave cylinder and transmission. It is a thin plate in conjunction with a spring and arm that pulls the throw out bearing pivit arm back 1/16" to keep the carbon bearing and the pressure plate from rubbing when not in use. Seems to work fine.

 

[RAC68]

Duane and Derek, thanks for the information. I would rather install a unit presumably tested for fit and reliability as I would not like to uninstall the transmission any more than once.

Andy, I read the write-up of the unit from British Spares and noticed that stated something was also required, however, I didn't really understand what they were talking about. Can you clarify? Also, do you think these units would cause the issues you previously mentioned?

To further this discussion, Keoke mentioned installing a roller pilot bearing on a much earlier thread. Has anyone installed a roller pilot bearing or could identify where to acquire or make one?

If I am decide to install a roller throw-out bearing, it would be good to also install a roller pilot as well.

Thanks all,
Ray (64BJ8P1)

 

[57_BN4]

A properly prepared carbon bearing should last the life of the clutch plate. Many, if not all failures reported are due to either junk repro carbon bearings, race/heavy clutch springs or sloppy installation- approximately in that order as a guess. What is the reason you are looking to fit a roller bearing?

I can't find any installation instructions online but I did see some references to removing the thrust plate so the roller release bears against the clutch levers. This will move the wear point from the plate to the levers and doesn't really address the geometry problem. For a race car I'd definitely go with a roller bearing setup because the carbon block won't handle the stronger clutch spring and the wear on the fingers over the relatively short mileage of a race car won't be an issue. On a bog standard road car I'd be very hesitant to fit a roller bearing unless the known weaknesses were addressed.

This thread discusses most of the issue points https://www.mgexperience.net/archive/Heavy_duty_throwout_bearing/1218233 The image shown of the roller bearing kit looks like a good solution as it has a flat face with some sort of coating to allow sliding against the thrust plate.

This thread also has some good info on a different type of roller https://www.mgexperience.net/archive/Pics_of_the_Roller_Throwout_Bearing_From_BPNW/1342432 This highlights one of the probable reasons for carbon block failure- not replacing the fulcrum bushings and pin. If the lever is tipped on even a slight angle due to bushing wear then one side of the bearing or block becomes more loaded plus that side will drag constantly when not in use.

On the roller pilot bearing issue- you'd need to bore the crankshaft out to take the bearing- not a trivial exercise and for virtually no improvement.

Andy.

 

[RAC68]

Thanks Andy,

I knew I could count on your expertise to present a balanced view. I think I will stick with the carbon throw-out and original type pilot bush as the benefits in the area I would like to be using my Healey and hope not to be caught in heavy (Jersey Shore) traffic.

My interest was triggered by my eventual intention to rebuild both engine and clutch. After seeing so many modern cars using roller throw-outs and pilots, I was hoping this would increase the longevity of the throw-out as well as pilot and be the last time, ever, to address this area of operation. However, without the confidence that these replacements will perform as desired and not having an anticipated high or demanding use (other than possibly being caught in the heavy NJ Shore traffic), I will stick to the technologies that have served me for the past 25 years since my last replacement. If they last that long, I will be 95 years and not give a dam.

Thanks again,
Ray (64BJ8P1)

 

[57_BN4]

Thanks Ray, I'm tending to think the same way now. In the absence of a roller bearing design that really works I'm not keen to experiment with something that is such a pita to find out the hard way it didn't work.

The thing that bugged me initially was how the revs drop down a little when the pedal is pressed. Is this a normal feature or will my bearing bed in eventually and I won't notice any change in rpm? So far my Healey driving experience is limited to about 100 yards up the drive and onto a trailer although this will change on Saturday as it is finally coming back from the panel shop.

Andy.

 

[Bob_Spidell]

..

The thing that bugged me initially was how the revs drop down a little when the pedal is pressed. Is this a normal feature or will my bearing bed in eventually and I won't notice any change in rpm?...
Andy.

Normal behavior on both my Healeys (BJ8 and BN2). The throwout bearing is pressing the crank against the thrust washers. The only thing that changes when your bearing beds in is the clutch won't disengage completely and you'll crunch the gears even more than normal.

 

[57_BN4]

Thanks Bob, that is pretty much what I was thinking re the revs drop.