# 4 Smeared main bearing

Ok here it goes. I had supposedly .090+ piston to head clearance per my engine guy. I had a .052 copper gasket. kb hemi wet dry block with Bryant fuel crank 4.150, Brooks b2,s 7.100 long. I had a 2.7460 #4 journal size with .0054 to.006 main bearing clearance on all mains.
I had a problem maintaining pressure over 40 psi with 70wt brad penn. Unless I ran just a little fat to keep cool. pressure was fine above idle which is 2200. Figured block was growing so I tightened up mains by .0005 with new king bearings Part# MB5116XP 001 and I smeared #4 main slightly. And a few pistons were hitting the heads. Slight rocking. Piston to wall was .009
So why did pistons hit? and is this too tight on mains. figure I will loosen them back up.
I did notice last time out when I started the car that the pressure jumped to 120psi+ then dropped immediately to 40 psi cold motor, then right back to over 100 psi and stayed till warmed up. Upon tear down I noticed my crank had a super slight harder to turn spot when rotated. even after I easily wet sanded out smear with 3000 grit trizac foam da pad. cam and gear drive was still in it. crank being checked for run out and polished.
Curious what everyone thinks. And I really appreciate the help, still learning.

 

promodracer,

I would check your piston to head clearance again. I best way to measure your the piston to head clearance is with the head on without a gasket. Also, I warm my oil and then build oil pressure with the plugs out before starting. Cold 70wt oil is no friend to a set of bearings or the oil pump.
Hope this helps, Joe

 

How hot was the egts. Did they spike at all
Your piston to head is wrong. Rods don't grow .090
I would bet you have way more compression than you realize and your just lean. Been there done that !
Oil psi problems don't happen in the middle of block. Front and rear bearing see oil problems. In the middle is a tune up issue. Check crank for roundness.

 

Checking for roundness now.
My best guess is engine guy was wrong.
He said deck ht was .038 and no gasket .051
So he says.

 

One cheap, quick and dirty way to check is to put the assembled or parially assembled engine on an engine stand with the heads on, favorite head gaskets on, pan off, turn the engine upside down, with snug rod bolts. Rotate the engine to TDC on the cylinder you want to check, loosen the rod bolts, pull the cap (don't move the rod/piston yet). With a dial indicator on the rod face where the cap sits shove the piston/rod assembly down in the bore until the piston hits the head. Sounds Mickey Mouse but it works.

 

Ok I will try this on re assembly. Thanks randy

 

The head gasket was .052 thick. The deckheight for each piston is between .035 and .038. Just checked engine notes

 

Randy's method for checking piston to head is the way to go.
The tight spot is a worry.. have you checked the crank is not bent ?

 

Being checked now!

 

spring pressure.. check it Dave

 

480 and 490 closed on all of them. swapped intake and exhaust. cams 60 mm 875lift lsm.