Main Bearing Adjustment Question

Hi, recently I have been adjusting the main bearings on the E27N by removing shims.
The tractor is a three main bearing, four cylinder petrol/kero job.
My question is when I remove shims the motor is very hard to get to turn using the crank handle BUT once it gets spinning you can easily keep it turning using one hand only.
It's just the initial getting it to move which is difficult.
Do I need to add another shim, or will it 'wear in' ok?
I don't really understand why it would be so hard to budge but then freely spin once it's going?
There's plenty of oil in the mains and the crank does not appear bent as it turns round and round with even force required.
Thanks,
Chris

Hi Chris - You would be better to log onto the Fordson Tractor Pages where there is a lot of information in the archives if you dont get a direct reply. It's about 40 years since I did one of those so I am a bit rusty on it. I remember that they were fairly tight when you adjusted them but I would rely on someone who has more recent experience.Good luck with it - Best regards - Michael.

Having shims to remove was a standard practice for both mains and big end bearings but in engineering terms it is very dodgy and a way of extending the life of the cheap short life motors in an era when there was virtually no oil filtering. Taking a shim out brings the cap up but there is a single point of contact top and bottom rather than an even clearance all way round. With that type of bearing the load should be taken by a film of oil but by having a point of high pressure that film is broken and wear will be high. To learn what the situation is in your bottom end use plastigauge (put a piece in the bearing, clamp up, then remove and measure it's thickness with a micrometer. The thickness is the clearance in the bearing which you can compare with the specification limits). How deep you get into this depends on how much work the motor will be doing and whether it is rumbling or knocking now.
In answer to your question - static friction is high but dynamic friction with the same surfaces is much lower. Think of standing on ice - all well until you move and once sliding you don't stop until a over apex!