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MG MGA - MGA Center Cap Thrust Bearings

I took apart an MGA 1500 and sent off all of the parts to be machined. When it all came back the standard thrust bearings would not fit nicely and installing them causes the crank to be locked in place. Looking at the old thrust bearings it appears that someone spent some time filing them down to make them fit. It seems odd to me that the standard size bearing would be too tight. Has anyone ever run into this? I think the crank needs to go back to the shop it just seems odd that it is too big in this dimension.
Jerry Enright

Hi Jerry. I ran into the same problem when I rebuilt my 1500 engine a few years ago. I installed standard thrust washers, and they locked the crankshaft up solid. So I set a sheet of fine abrasive cloth on a flat surface, and removed about .001 inch of material from both the upper and lower thrust washer faces. On re install the crankshaft spun nicely, and my re assembled engine runs great. I think these thrust washer fit several different marques of automobiles, and are somewhat oversized for MGA engines, but spot on for others. I would not remove any metal from your crankshaft, simply modify the thrust washers a tad. At any rate, the solution is relatively quick and easy. Cheers, Glenn
Glenn

I had the same problem, and I gather that it is not unusual.

The guys in the machine shop advised that bearing materials should be scraped, not sanded, as with sanding fine particles of abrasive material get embeded in the soft bearing material and cause premature wear on the shaft, but if I was going to sand, then do the back.

I stuck the halves to a small block of wood with double sided sticky tape and rubbed them down on 600 wet and dry held down on a smooth flat piece of wood.

Takes a while - but got there in the end.

Cheers
Ian F
Ian Fraser

Hi Ian. I have heard many times that use of abrasives will cause excessive wear on mating surfaces. However,that is not my experience. I have used the abrasive sizing method on many different MG components over the years, and have never experienced excessive wear from using this method. On the contrary, on disassembly, I have found the mating parts to be in very good condition. I suspect that installing incorrectly sized parts would cause much more sever problems than installing a properly fitting part, even if it was sized using fine abrasives. Im sure however, that this opinion will stir up some controversy! Cheers! Glenn
Glenn

Jerry. Glenn has the proper solution to your problem. Ian has a point, when you sand soft metal, any pieces of abrasive which detach themselves from the sanding medium may imbed themselves in the softer metal and wear away harder metal. The abrasive, aluminum oxide, or silicon carbide, being harder than the crankshaft.

Thus, we always "sand" on the back side of such things as thrust washers to make them fit properly. That way, they are restrained in the ability to cause damage. If you sand the back sides, you should never have a problem.

What Glenn is posting of is a very basic principle in machine tools--of which automobile engines are one--work on the least expensive part.

This would be the thrust washers which are far less expensive to replace than a crankshaft.

Glenn may be correct in his assumtion that, in effect, "these are parts made to fit a number of cars". I do not think so myself. The BMC B series motor was used in a number of vehicles, sufficiently so to justify a production run of thrust washers for them. My theory would be that the current thrust washers were produced oversized. Someone, such as Moss Motors, a major retailor, will notice this, due to complaints by people such as yourself, and will ensure that, in the future, the thrust washers are made to the proper size.

Should you have the crankshaft modified, the next time it is rebuilt, you might run into a problem with the standard size thrust washers being too small. (I have never, in over 38 years of experience, seen a crankshaft that was worn sufficiently to require oversized thrust washers.)

Thus, might I commend to you Glenn's excellent advice, bearing in mind Ian's notation that the sanding should be on the BACK side of them?

I believe that would satisfy your problem with minimal impact in the future.

Les
Les Bengtson

Thank you everyone! It's good to know that I'm not the only one this has happened to as Moss told me my crank measurements had to be off. Appreciate the help!
Jerry Enright

Hi Les. In regard to your statement: Glenn may be correct in his assumtion that, in effect, "these are parts made to fit a number of cars, I do not think so myself" : Interestingly Les, the last set of "MGA" thrust washers that I purchased (through a local parts supplier), were marked on the box as being for a Nissan vehicle! They were also marked as being standard size thrust washers. At first, I thought that the parts place had screwed up my order. But when I fit the thrust washers to the MGA engine block, they were an exact fit, except that they were a tad too thick. After a minimal abrasive modification, they fit and worked perfectly! Cheers! GLenn
Glenn

Hi Glenn.

It is probable that the Nissan engine was in fact a 'B' series made under license by Nissan/Datsun.

I believe they appeared in (at least) the early 180B, and the forklift trucks.

The early Bluebirds had an 'A' series engine built under the same license system.

Cheers
Ian F



Ian Fraser

The Nissan engines you refer to are the "J" series engines. They are a close copy of the BMC "B" engines right down to the thread size in the middle of the distributor drive gear. Every other thread size was metric but the "tool" used to install the dist drive gear was 5/16 fine thread. The latest J engine I saw was a Mexico spec J-160 from 1974, looked just like the 510 here in the USA but had a carb and a point distributor and no 5 MPH bumpers.
To clarify the meaning of BACK side of the thrust brg. It is the side away from the clutch, or the side towards the front of the vehicle. If you mean back or rearward side, closest to the clutch you are wrong as that is the side the crank pushes against when you depress the clutch.
There are 4 thrust bearings on a MGA modify only the back side (the side that doesn't touch the crank) of the two bearings used on the front side of the crank. Leave the two that touch the crank on the clutch side alone.
I hope this clears up and does not muddy the waters for you.
R J Brown

This thread was discussed between 05/03/2006 and 06/03/2006

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