Xu9 Bearing Selection

[mhyphenl 10 1 Cars]

I'm just trying to sort out new main bearing shells but the info in the Haynes manual seems to contradict itself.

 

Haynes quote a Crank main Journal diameter of between 59.981mm and 60.000mm. I've measured my main journals in 3 places at 3 different angles to check for roundness and all my mains come out at 59.94 to 59.95. Nice even wear but below what Haynes say.

 

However if I measure the bearing casings and calculate the clearances I get the following, aiming for a clearance of between 0.025 - 0.062mm example :

 

Casing measurement without bearing installed - 63.70mm

Main bearing journal measurement - 59.94mm

Top Bearing (Groved) - 1.856mm

 

You then get a choice of 4 plain bearings to make up the clearance, between 1.836 - 1.870mm. If I choose the 1.870mm I get the following:

 

63.70 -59.94 = 3.76 - 1.836 (fixed bearing) - 1.870 (thickest plain) = 0.054mm clearance.

 

To my eyes this should work even though the main journals are slightly below the 59.981 minimum. What do you guys think? I measured the internal diameter of the bearing casings several times, all done with digital vernier calipers at room temp.

 

Also Haynes quote a tolerance of 49.68 - 50.00mm for the big end journals but a clearance of just 0.025 - 0.050 with only one size of bearing available how can that add up??

 

[Tom Fenton 1,526]

Firstly forget trying to measure it with a caliper. Micrometer needed for accurate enough measurement.

Secondly to be honest don't mess about, take the crank to an engine machine shop, have them check it and either polish if ok or grind to next undersize, then ask them to supply new bearings to suit.