Main bearing shells , grooved and plain .

[hoodygoodwood 72 3 Cars]

I had to have my XU9J4 crank main bearing journals ground to 0.5 mm undersize because the engineering company cocked up the 0.3 mm grind . The standard size main bearings  that i removed had 5 grooved and 5 plain shells , the replacement 0.3 mm shells were also 5 and 5 but when i bought a set of 0.5 mm shells ( King ) there was 7 grooved and 3 plain . I spoke to the supplier and returned them then when the replacements arrived they were also 7 grooved and 3 plain . They were all sealed in plastic so were incorrect from the factory , has anybody else had this happen , i can't imagine they are supposed to be like this !

[welshpug 1,675]

Early engines were like this, 86-87.

 

 

[Pierre_b 4]

Hello,

 

I am not an expert by any means, and my engine is still not finished, but I encountered the same problem on my xu5 (one of the first génération, you would have some variation between my block and your newer xu9, but from my understanding, the logic is the same). The conclusion that I had with all the answers on my thread is that there is plenty of variation, but if the oil passages are aligned, you are good.

 

Pierre

 

[hoodygoodwood 72 3 Cars]

I have bought another set from a different supplier , the ad specifically says 5 grooved and 5 plain so hopefully they will be fine . Will keep this set for spares . Its been a right performance getting the mains sorted , will be good to get the crank fitted . 

[petert 607]

I've been having bad experiences with STD mains bearings for XU10's. Two sets from different suppliers have given 0.004" of clearance rather than the oem 0.0023". Beware and at least use plastigauge if nothing else.

[DamirGTI 345]

10 hours ago, petert said:

Two sets from different suppliers have given 0.004" of clearance rather than the oem 0.0023".

Which brands Peter ?

I'll be needing some soon , both big end and mains too ...

 

D

[SRDT 194]

On a XU10 there is no longer a standard lower plain shells, you have 4 of them and you must choose the correct ones to get your 0.038-0.069mm of clearance.

That is also true for newer XU5/7/9 with 0.025-0.062mm of clearance.

[petert 607]

18 hours ago, DamirGTI said:

Which brands Peter ?

I'll be needing some soon , both big end and mains too ...

 

D

Kolbenschmidt 77098608

ACL 5M1677 780

 

I used ACL 4B7700H for the rods. They're perfect.

 

I know that I'm not loosing it, as I fitted some 2nd hand oem mains and the clearance is exactly 0.0023" with the same crank and rods.

 

I end up solving the issue by using some -0.3mm Glycol mains I had. After giving my crankshaft grinding guru the fitted ID of the bearings, he was able to grind the mains to bang on 0.0023" of clearance.

 

I intend to give ACL a ring after I measure the shell thickness.

 

My advice is, if the mains bearing aren't scored, just scotch-brite and re-use them.

Edited March 19 by petert

[wicked 105 3 Cars]

On 3/17/2025 at 2:24 AM, hoodygoodwood said:

I had to have my XU9J4 crank main bearing journals ground to 0.5 mm undersize because the engineering company cocked up the 0.3 mm grind . The standard size main bearings  that i removed had 5 grooved and 5 plain shells , the replacement 0.3 mm shells were also 5 and 5 but when i bought a set of 0.5 mm shells ( King ) there was 7 grooved and 3 plain . I spoke to the supplier and returned them then when the replacements arrived they were also 7 grooved and 3 plain . They were all sealed in plastic so were incorrect from the factory , has anybody else had this happen , i can't imagine they are supposed to be like this !

 

My take:

The XU9J4 crank only feeds oil to the rods via journals 2 and 4 and only on those journals you could use the groove on both sides to have more continuous oil pressure on the rods. 

Later cranks have holes 4 journals, so implicit more flow to the rods. 

 

Note: this is not a proven fact, just an idea!

[DamirGTI 345]

12 hours ago, petert said:

Kolbenschmidt 77098608

ACL 5M1677 780

I see , 

Kolbenschmidt went down quality wise lately , not as near as good as it used to be , much of the parts seem "Shangai special" nowadays !

 

Most always i use King or Glyco , haven't had issues with those two yet .

 

And yes ! i used to reuse shells if they where still good , as you've said just some light polishing with scotchbrite and back in service

 

D