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Posted By: 68triton Timing side bearing - 04/02/14 5:46 am
Hi, Any opinions on the picture?

The picture shows the inner race on the timing side of the crank. The surface has given way to about 2/5 of the circumference of the race, rollers ok, but cage did fall apart on splitting the cases. No signs of heat. Main bearings and the rest ok.


Pearson crank
GP50 oil
Good oil pump
2k miles
10 thou end float
SKF bearing (Pearson fitted)

My friend has had the same issue with the same spec?

Many thanks


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Posted By: Per B - R.I.P. Re: Timing side bearing - 04/02/14 6:39 am
Maybe there has been a bad series of bearings, I had the same problem after say 3500 km on my Pearson engine. This bearing will make a hell of a rumbling, I heard the rumbling early and stopped way before the bearing was tottaly damaged. I just replace the bearing and had no problems after that, about 10000km has passed since I replace the bearing, My engine is from 2003.
Posted By: kommando Re: Timing side bearing - 04/02/14 7:35 am
A bad batch of steel with high inclusion levels will give you a bad batch of bearings, very hard to detect except by destructive testing. The steel makers have a test at full blast furnace quantities but if a single slab (normally 5t per slab) has a concentration then it will pass through unseen. The inclusion will sit just below the surface giving a weakened area, when the ball/rollers start to run over the inclusion breaks out and the destruction begins. All steel has these inclusions but for bearing steel the levels are supposed to be kept low, this effects both low friction bearing (ball and roller) and shell bearings (where it causes breakouts on the edge and also on the back giving bad blues.
Posted By: Ron - in California R.I.P. Re: Timing side bearing - 04/02/14 7:49 am
Rare, but have seen timing side bearings fail, do not know why. I had one fail on my BB Goldie with a lot of miles on it. The only thing I can think of, besides a "weak" bearing is the loads on it. BSA in it's infinite wisdom used a small bearing on the timing side and a much larger bearing, plus the ball bearing on the drive side. Many think BSA thought most of the load is on the drive side, but we know that is not 100% correct at all. And due to the close proximity of the cam spindles, can put in a larger bearing. Some race engines use a needle bearing on that side that have much wider and more needles than the rollers. But unless someone does proper testing, all is just a guess. BUT, the failure does not repeat, once a new bearing is installed.

Oh yes the only other known cause of timing side bearing failure is when the drive side crank nut comes loose and the crank bangs against the lip on the outer race. What does the outer race look like..?

Posted By: Ron - in California R.I.P. Re: Timing side bearing - 04/03/14 1:09 am
Not sure if a tight chain will cause that bearing failure or not.. but the slop in the adjustment of the primary is pretty bad. I went and carefully opened up the transmission holes to 1/2" and did the same to the adjuster and the lower mounting plates. The original set up is very sloppy.. Oh yes be sure to check the transmission main shaft bushing clearance as well.. those get worn out if the primary is too tight.
Posted By: kommando Re: Timing side bearing - 04/04/14 4:31 am
You need to look at your front brake, the brake lever needs moving round anti clockwise on the cam spindle so that the angle with the cable is less than 90 degrees with the brake on, look at the shoes first as they may be worn. This is an MOT failure point so if one was done recently get a new MOT tester, you pays good money and they should not miss such basic failures.
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