Topic: Main bearing clearance. 0.0015” go up a size?

[HondaMan]

Well i did check them dry, and it seems pretty dam similar to me. Im going to run with what i have.

The first picture looks like dead-on 0.0015".
That second picture looks like 0.0016" to me(?).

[PeWe]

About grease to make the plastigage to sit.
I used a little WD40.

A test with case sealer is bubbling in my mind.
More to clean, but I'll know how much that will add to clearance.

[MRieck]

About grease to make the plastigage to sit.
I used a little WD40.

A test with case sealer is bubbling in my mind.
More to clean, but I'll know how much that will add to clearance.

I wouldn't spend a lot of time thinking about it Per......there is a lot of "imprecision" in these "precision" units. People worrying about 2 lb loss of oil pressure can't even accurately or reliably measure it. Everything in engines is so fluid and dynamic it's just impossible to control. Literally controlled chaos. I've experimented with bearings in 600cc race bike s up to the point of mismatched main bearing trying to get squish tighter. Now I ask myself was it worth it?
 I've built a number of R6 engines now and cringe when I think about those engines revving at 16,000 RPM.

[HondaMan]

I'm still fascinated by the old Subaru engines with their 3-main-bearing crankshaft. After you'd Plastigage all 3 bearings to see what size shells to use on a rebuild, you had to go 0.0004"-0.0008 tighter than 'zero clearance' on the center bearing in order to make it run quietly. If you didn't, they had a loud knock in them from that day forward. Something weird about how those cases bolt together...

[Tracksnblades1]

I'm still fascinated by the old Subaru engines with their 3-main-bearing crankshaft. After you'd Plastigage all 3 bearings to see what size shells to use on a rebuild, you had to go 0.0004"-0.0008 tighter than 'zero clearance' on the center bearing in order to make it run quietly. If you didn't, they had a loud knock in them from that day forward. Something weird about how those cases bolt together...

Am I reading this correctly..?

0.0004 - 0.0008” tighter than “Zero Clearance” or the same as 0.0004 - 0.0008” “press fit”… ?

[Don R]

 What amazes me is how the case sealer seems to disappear where the cases meet. One 750 that I recently took apart has black permatex on the edges below and above the meeting surfaces but barely anything shows on the actual sealing surfaces. 

[HondaMan]

I'm still fascinated by the old Subaru engines with their 3-main-bearing crankshaft. After you'd Plastigage all 3 bearings to see what size shells to use on a rebuild, you had to go 0.0004"-0.0008 tighter than 'zero clearance' on the center bearing in order to make it run quietly. If you didn't, they had a loud knock in them from that day forward. Something weird about how those cases bolt together...

Am I reading this correctly..?

0.0004 - 0.0008” tighter than “Zero Clearance” or the same as 0.0004 - 0.0008” “press fit”… ?

Yep, that's right, an interference fit! I've not figured it out, either, but had 2 Subaru mechanics tell me the same thing (my Subaru's engine had developed that 'knock' in it. I had it 14 miserable months, hated that thing...). One was an ex-Subaru mechanic, working as a machinist in the automation company where I worked in the 1990s, and he confirmed what the Subaru mechanic had told me the week before. He also said that despite the legend of the long-lasting Subaru flat fours, they could be destroyed by poor oils, especially if that center bearing was too loose. It would make the crank "chatter" (whatever that meant?) and then the rod bearings would get rounded and the oil PSI would fall off quickly.