alessio

iTrader: (3)

Hi,

I'm in the middle of a full engine rebuild and there's a frustrating issue with main journal oil clearances that's frustrating the hell out of me.

With the crank basically new I went for the ACL STD size set but unfortunately the clearances were just a little on the loose side to what I was hoping to see. Based on the availability (and reputation) I've decided to go for two sets of King Racing bearings - one in STD size and one in +0.025mm with the idea to use STD on one half of the block and 0.025 on the other. The results, when measured, were quite perplexing. I then installed the full 0.025 kit and had the machine shop measure the block again and it's still weird - just look at the no.3 position (this is where the thrust bearing is in my EJ20). While the rest have generally moved to where I was expecting them to move, the oil clearance in the no.3 position with King 0.025 is actually larger than it was with ACL in STD size. I was hoping to get all the clearances in the 0.025 to 0.035 mm range as the car is a street car that gets tracked quite a lot.

Attached are our measurements and all thoughts are highly appreciated.



Thanks,
Alex

MOTORS S GT

iTrader: (2)

Either the bearings are incorrectly marked up / made incorrectly, have you checked bearing stand off ?

Has the main bearing tunnel been measured without bearings & all correctly torqued up ?.

Mixing sizes on main bearings is not something I would recommend, big ends yes.

If its a high power unit, bigger clearance will help cooling.

alessio

iTrader: (3)

Thanks for the input.

Regarding the marking/manufacturing - all I can go off are the set part numbers (MB5220XP and MB5220XP-.025) that were delivered. Also all shells in the first set are stamped with STD and all shells in the second set are stamped with .025. We haven't measured the shell thickness because the machine shop hasn't received the ordered new micrometer ball attachment yet. But yes, all M10 and M8 case bolts were torqued to spec every time.

The tunnel measurements were 64.00, 64.02, 64.02, 64.02 and 64.01 mm 1-5 respectively, so within spec even if towards the outer limit of it.

I wouldn't want to mix the sizes either ideally and it appears I'll be OK if I just go for the King 0.025 shells for all journals. Except the #3 one...

MOTORS S GT

iTrader: (2)

I would still measure the stand off, it is very influential to sizing & something a lot of bearing manufacturers have a large tolerance to.

ACL a few years ago were getting sizes mixed up in the sets, although the markings were saying otherwise, its a shame Mahle are not doing mains, as there big ends are very good, if a bit pricey.

alessio

iTrader: (3)

I'll see what I can do - perhaps I'll find the convex attachment for my cheapish micrometers.

That's what I meant by going by reputation - I've read that ACL have had issues with their tolerances and consistency and the general consensus was that King were far superior in that respect. Pricey is also relative - one good set beats having to buy three of them and still not getting the result one's after

With the factory clearances specified as 0.01-0.03 mm with the maximum of 0.04, would you assemble an engine with 0.02, 0.025, TBC, 0.033 and 0.02 oil clearances? No. 4 is a little bit on the loose side but the rest are bang in the middle - just where logic tells me I'd want them. No.3 is of course the one that has to feed two big end journals - so again logically I'd want tighter clearances there, not 0.04 that the ACL shells would give me.

MOTORS S GT

iTrader: (2)

To be honest I would not assemble a Subaru engine with hard use with less than 0.035 on the mains, 0.04 would not be an issue, in fact being a centre thrust bearing you will need more flow as its got thrust faces to lube, if an uprated clutch is used you have more loading on it.

All my big power builds on the mains will have a minimum of 0.035, big ends 0.045 is the ideal, otherwise you will not have enough oil flow to cool them, & heat is the killer.

If the King bearings have the same bearing finish as ACL they are not kind to OE Subaru cranks, causing ridging, the extra flow & clearance helps stop that.

alessio

iTrader: (3)

Wow, 0.035 minimum? Even with the nominal clearance of 0.01-0.03 with the maximum of 0.04 as specified by the factory? The engine will be fully forged with a VF34 at first and then maybe something slightly larger later but I don't expect it to ever go beyond 500 hp.

I believe these are my choices, really. I haven't measured the block with the standard size King bearings but looking at all other measurements I expect those to be looser than ACL STD. I also don't think it's an issue to use a King pair on one journal and an ACL pair on the other. So which one would you go for?



Thanks again,
Alex

MOTORS S GT

iTrader: (2)

Out of the choices you have the King bearings No1 & 5 @ 0.02 would worry me, I prefer the ACL clearances.

Don't forget the manufacturer figures are for std engines at std horsepower, & for big mileages, if your upping power @ 500 bhp your basically doubling the power, that creates a lot of heat & loadings, it needs extra flow to dissipate the heat, as soon as any of those bearings get to hot its game over.

alessio

iTrader: (3)

OK then, ACL for no. 1,3 and 5 and King for 2 and 4?

Cheers!
Alex