Found a possible cause for some lower oil pressure LS1s (~25-30 psi at idle)
08-10-2004, 07:40 AM
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Found a possible cause for some lower oil pressure LS1s (~25-30 psi at idle) The motor I built several years ago had been somewhat lacking in oil pressure...not bad...but not great... about 30-32 psi hot (at 1000 rpm, under 30 @ 800 rpm) with 10W30.
I tried all the remedies (shimmed my Katech ported oil pump), new "blue" o-ring, etc with no real marked improvement
Since I was freshening up the motor...I wanted to investigate.
Back when I built the motor I used FM 152M STD main bearings...my dumbass didn't think to really check the clearances since I was using a STD crank
This time, I put in a new set of 152Ms and all my clearances spec'ed to .0030 which is a bit on the loose end of the spec. Jason99TA said he prefers to go ~.0020 on the mains and that .0030 can cause a noticeable drop in oilpressure
I guess that was the culprit 
So I pulled out my brand new 152Ms and replaced them with 152M-1s (.001 undersize) now my mains all spec at 0.0020
All the rod bearings spec'ed at ~.0025 (best I could estimate using plastigage all were greater than .0020 and all were less than .0030)
Never take anything for granted
I tried all the remedies (shimmed my Katech ported oil pump), new "blue" o-ring, etc with no real marked improvement
Since I was freshening up the motor...I wanted to investigate.
Back when I built the motor I used FM 152M STD main bearings...my dumbass didn't think to really check the clearances since I was using a STD crank
This time, I put in a new set of 152Ms and all my clearances spec'ed to .0030 which is a bit on the loose end of the spec. Jason99TA said he prefers to go ~.0020 on the mains and that .0030 can cause a noticeable drop in oilpressure
I guess that was the culprit So I pulled out my brand new 152Ms and replaced them with 152M-1s (.001 undersize) now my mains all spec at 0.0020
All the rod bearings spec'ed at ~.0025 (best I could estimate using plastigage all were greater than .0020 and all were less than .0030)
Never take anything for granted
Last edited by Fireball; 08-10-2004 at 07:46 AM.
08-10-2004, 08:28 AM
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This is the exact reason why 99% of the people on this forum complain about low OP! I have been saying this for two years! These motors need to be run tight. I run the mains at .0015-.0018" and NEVER have issues with low OP or problems with the motors living. I believe that the aluminum block expands so much that an oil clearance that tight ,ends up being closer to .002-.0025" or even .003" when hot.
I learned this the hard way on a few motors I did a couple of years ago where I made the clearances to the "old school" spec. The motors all had unusually low OP at idle and at 4500 rpm.
I always keep extra sets of std and .001" over bearings so we can fine tune the oil clearances.
Run em; tighter and use lighter oil!
I learned this the hard way on a few motors I did a couple of years ago where I made the clearances to the "old school" spec. The motors all had unusually low OP at idle and at 4500 rpm.
I always keep extra sets of std and .001" over bearings so we can fine tune the oil clearances.
Run em; tighter and use lighter oil!
08-10-2004, 04:02 PM
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Fireball,
Remember the very newly built LS6 you and J pulled out of my car to put my 6.0L in...old school bearing clearances equal 20 psig at idle!
And the machine shop's answer was stick straight 40W in it!! When I finally pulled that engine apart, I found that the mains were down to copper from starting in cold weather with 40W
BTW - the SMC Performance 6.0L that went in is awesome (thanks Shaun)!! 42 psig at hot idle with Amsoil 10W30 in it! And it is quieter than any stock LS1 I have ever heard - no piston slap what-so-ever (coated pistons are worth the extra cost)!!
Hope to see you at the EFA shootout in Sept - looking to put the smack-down on a few Stangs
Remember the very newly built LS6 you and J pulled out of my car to put my 6.0L in...old school bearing clearances equal 20 psig at idle!
And the machine shop's answer was stick straight 40W in it!! When I finally pulled that engine apart, I found that the mains were down to copper from starting in cold weather with 40W
BTW - the SMC Performance 6.0L that went in is awesome (thanks Shaun)!! 42 psig at hot idle with Amsoil 10W30 in it! And it is quieter than any stock LS1 I have ever heard - no piston slap what-so-ever (coated pistons are worth the extra cost)!!
Hope to see you at the EFA shootout in Sept - looking to put the smack-down on a few Stangs
08-11-2004, 12:29 AM
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9D9LS is exactly correct. You definitely need to set the motors up a little tighter than "normal", especially the mains. An Iron block 6.0l can take a slightly looser clearance during assembly as the steel has 1/2 the expansion rate of aluminum. You really need to take this into account while setting bearing clearances prior to assembly.
Another thing to keep in mind is the housing bore on the mains. Nearly 90% of all the LS1 motors I have done required a line bore to get the housing bores back round and into spec. With a loose housing bore, you loose your bearing "crush" and your bearing clearances do open up quite a bit. Federal Mogul's housing bore spec is a little tighter than GM's spec (2.7509-2.7514" vs. 2.7508-2.7515"). This is one reason why the FM 152M bearings do show up as being a little looser than the GM specs, especially if the housing bore is out in left field.
Jason
Another thing to keep in mind is the housing bore on the mains. Nearly 90% of all the LS1 motors I have done required a line bore to get the housing bores back round and into spec. With a loose housing bore, you loose your bearing "crush" and your bearing clearances do open up quite a bit. Federal Mogul's housing bore spec is a little tighter than GM's spec (2.7509-2.7514" vs. 2.7508-2.7515"). This is one reason why the FM 152M bearings do show up as being a little looser than the GM specs, especially if the housing bore is out in left field.
Jason
Last edited by Jason99T/A; 08-11-2004 at 12:35 AM.
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08-11-2004, 07:19 AM
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It seems as if quite a few guys who assemble there own motors, experience this problem. Mostly probably do to lack of measuring equipment or lack of the knowledge. It is a very critical step of properly assemblying this particular series of motor.
Another thing to do when you yank the motor , to replace the bearings, is to replace the plastic plug that closes off the oil passageway in the back of the block. GM has an updated plug that will not back out and cause internal oil leaks within the motor. The current design has about an .125" of clearance between it and the back cover. Under high oil pressure loads it can be moved.
Tighten up the clearances and run 5W-30 and you should be in good shape!
Another thing to do when you yank the motor , to replace the bearings, is to replace the plastic plug that closes off the oil passageway in the back of the block. GM has an updated plug that will not back out and cause internal oil leaks within the motor. The current design has about an .125" of clearance between it and the back cover. Under high oil pressure loads it can be moved.
Tighten up the clearances and run 5W-30 and you should be in good shape!
Last edited by 9D9LS; 08-11-2004 at 07:26 AM.
