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MG MGB Technical - Crankshaft thrust washers

It's a long time since I did an overhaul, my memory is a bit dim. When the book says that 5 thou over size thrusts are available is that a total of 5 thou or 5 thou each giving 10 thou difference.

Tony
Tony Oliver

Aren't these split washers? So both have to be the same size? They sit end to end, so both at +5 (if that's what they are) still ends up as +5 overall.
Paul Hunt

Thanks Paul. I may have worded the question a bit vaguely. There are 2 washers (which should be called Bearings) on either side if the centre journal so if they are 5 thou each then it would be a 10 thou difference. I would just like to make sure before I order the bits, especially after my rod bearing catastrophe.

Tony
Tony Oliver

Tony. Please go away. You are asking too many intelligent questions, requiring thinking.

On the other hand, a splendid question and one that I have never bothered to investigate. All of the crankshafts I have had turned over the years never required the use of the oversized thrust washers. I have always had the machine shop turn the journals the minimum amount necessary to true them up. This, sometimes, results in the situation you noted where the main journals, which do not wear as much as the rod journals, will be a different size than the rod journals. And, it is the amount that the main journals must be turned which is most likely to have an effect on whether the oversized thrust washers will be needed. (The transition from the straight portion of the center, main journal to the upright portion of the crankshaft needs to be radiused sufficiently that there is not a stress point at the transition between the two. As the diameter of the journal is reduced, the radius needs to be increased to ensure that the stress point does not develop, resulting in a broken crankshaft. This is something which the competent machine shop has to make a decision on, not the owner of the parts.)

If you need oversized thrust washers, your machine shop should make that decision, should tell you that the oversized thrust washers will be needed before doing the work, and should be able to obtain for you the proper washers to go with the work they have done.

Your job is to install the parts correctly and measure the end shake (back and forth movement of the crankshaft) when assembling the components to make sure that the proper specifications are met.

Thus, it would be quite interesting if someone had both the standard and the oversized thrust washers available to them and would bother to post the thicknesses of each. But, only on an intellectual basis. The machine shop is expected to be able to perform the machining operations in a competent manner, be able to determine if they need to grind the crankshaft such that it will require oversized thrust washers, and do the machining in a manner that will be consistent with "good machining practice". If not, they should expect to buy you a new crankshaft.

Les
Les Bengtson

When you buy new thrust washers the thickness of each half washer should be checked. On a set I purchased several years ago there was .010" between the thickest and thinnest washers. I used the old washers to make up a matching set. The next set I ordered was closer but still not matched. On the few MGB engines I have worked on the old thrust washers had little or no apparent wear.

Clifton
Clifton Gordon

This isn't directly connected but some time ago I had a B engine line-bored and the shop machined enough off the center cap that I had to file the ends of the thrust washers before they would fit in the circle.
Leland Bradley

This thread was discussed between 09/10/2008 and 11/10/2008

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