LS6 Main Bearing Clearance ?
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From: Portland Oregon
LS6 Main Bearing Clearance ? What is the factory main bearing clearance on an LS6. I have some specs on a LS1 .0007-.0021. Is LS6 the same? I built my race motor with .002 and it has oil pressure problems when I run it on the track for more than 10 minutes. I'm trying to decide what clearance to shoot for next time around. Anyone else have experience with this.
Thanks
Thanks
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Originally Posted by racecar
What is the factory main bearing clearance on an LS6. I have some specs on a LS1 .0007-.0021. Is LS6 the same? I built my race motor with .002 and it has oil pressure problems when I run it on the track for more than 10 minutes. I'm trying to decide what clearance to shoot for next time around. Anyone else have experience with this.
Thanks
Thanks
.002 is good on the mains.
I've seen the oil pressure fluctuate and drop off after extended racing and that was mainly due to the sump being pumped out faster than the oil can return.
Can you explain the oil pressure issues you are having in greater detail.
Originally Posted by racecar
What is the factory main bearing clearance on an LS6. I have some specs on a LS1 .0007-.0021. Is LS6 the same? I built my race motor with .002 and it has oil pressure problems when I run it on the track for more than 10 minutes. I'm trying to decide what clearance to shoot for next time around. Anyone else have experience with this.
Thanks
Thanks
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I have problems sucking the sump dry but it happens immediately. I would say your problems come from the oil getting whipped up by the crank and getting air in it which lowers your oil pressure and the fact that the oil gets very, very hot and loses viscosity which also lowers pressure. Make sure you run synthetic so that you are getting the best lubrication possible. This is why the dry sump is going to be so cool on the new 06 for track days.
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From: Portland Oregon
On cold start up, it goes to 60, warms up and idles at 40. Runs 55-60 at WOT when I am banging gears on the country road with 10-30 synthetic oil, fram filter. That seems totally normal.
I went to the track yesterday, ran to 6500 rpm, WOT 75% of the time, and the pressure dropped to 30 in 6 laps = 8 minutes, in another 2 laps to 25, then to 20. I rolled into the pit lane, came to a stop and rev the motor to 3000. Oil comes back to 40,,, go back out on the track, 2 laps, back down to 25.
I have tried two different oil pumps and pickups, several O rings and silicone sealer.
I bought this block and crank on EBay as "Surplus GM". The crank had a quality defect with the pilot bearing hole too large. What is the defect with the block???? There may be a problem with this block that is not normal.
I went to the track yesterday, ran to 6500 rpm, WOT 75% of the time, and the pressure dropped to 30 in 6 laps = 8 minutes, in another 2 laps to 25, then to 20. I rolled into the pit lane, came to a stop and rev the motor to 3000. Oil comes back to 40,,, go back out on the track, 2 laps, back down to 25.
I have tried two different oil pumps and pickups, several O rings and silicone sealer.
I bought this block and crank on EBay as "Surplus GM". The crank had a quality defect with the pilot bearing hole too large. What is the defect with the block???? There may be a problem with this block that is not normal.
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From: Portland Oregon
I'm not dropping oil pressure in the corners, I have had that happen on other cars and it usually comes right back after you exit the corner. This motor gets warmed up and then the pressure drops, but it will come back when I slow down. I have a .145 shim in the oil pump spring, it should have monstor pressure. That's why I think there is an oil leak inside the motor, something wrong with that "surplus" block. Maybe the block is OK and it is just a classic case of too much main bearing clearance. Time for a tear down. 
I know that this is an old thread, but I'd like to know what if anything you've discovered. I think that you are having a foaming problem on the track. I wonder if it would be worth trying 4.5 or 5.0 or 5.5 quarts to lower the oil level and keep it away from the crank.
Just a thought.
Steve
Just a thought.
Steve
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I started this thread way back in August, took the motor all the way apart and checked every square inch of it. FINALLY found the problem that has been killing me for the last year. The cam bearings are worn out. The front and rear had .003 clearance, #2,3,4, had .007. My theory is that when the motor was new, I started it with the oil pump O ring not in correctly, ran without oil 3X 5 sec for 15 seconds total. That cooked the bearings. Fixed the pump with a bigger spring shim, and have had pressure problems every since. I'm pumping a lot of oil in, and it is going right back out through the cam bearings. I have cranked the motor with the starter many times with the spark plugs out to get oil pressure after a rebuild. With no plugs, there is no load on the crank or rods, but the valve springs still put the full load on the cam and the cam bearings. This can wear them out also.
Thanks for the update. The big gap (oil clearance/leak) in the cam bearings can sure do it as easily as a main bearing. In fact, the oil is first pumped up to the cam oil galleries and then down to each main bearing. The article on rebuilding the Gen III engines in Engine Rebuilder Magazine specifically mentions cam bearing clearance http://www.babcox.com/editorial/ar/eb040538.htm. There are several other excellent articles on general rebuilding of Gen III engines on this web site (Type in Gen III on their search engine).
Quote from article: "These engines have had some oil pressure problems. Some people are blueprinting the oil pump to get more pressure and flow, but there are two other areas that may be contributing to the problem: 1) Rebuilders should be very particular with the main bearing clearances with an aluminum block because it will increase when the engine gets hot, and 2) they should be sure to check the cam bearing clearance. We've seen three engines that had .005? to .006? bearing clearance on the front and back cam journals and we even ended up custom-making the cam bearings for one engine to get it within factory specs."
Steve
Quote from article: "These engines have had some oil pressure problems. Some people are blueprinting the oil pump to get more pressure and flow, but there are two other areas that may be contributing to the problem: 1) Rebuilders should be very particular with the main bearing clearances with an aluminum block because it will increase when the engine gets hot, and 2) they should be sure to check the cam bearing clearance. We've seen three engines that had .005? to .006? bearing clearance on the front and back cam journals and we even ended up custom-making the cam bearings for one engine to get it within factory specs."
Steve
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From: Portland Oregon
Excellent article Steve. I read that last month when I was searching for my third set of cam bearings and thinking that I was the only one in the world that could not find the correct size bearings when my block and cam are the right size. If you have an undersize cam or an oversize block you would be out of luck. I was ready to buy some bronze and make my own, finally got a set of Dura Bond bearings that were the right size.
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I'm going to prime it with an Accusump and fire the rebuilt motor this weekend. If that baby works, I'm going to smoke the tires off of it to break it in. This motor has been a real pain.... It is fast.
Does anyone have a part number for the #1 cam bearing? I gouged mine while removing my camshaft. It's got some pretty decent nicks in it caused by the end of the camshaft and I'm worried I'll have oil pressure problems if I don't replace it. I'm trying to find out if the #1 bearing can be replaced with the engine in the car. Any thoughts?
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Latest update: If you did not see my other thread: The oil pump pickup was too close to the bottom of the pan because the ARP main studs have 2 thick washers, way more height than the GM studs. When you bolt on the pickup bracket, it makes the pickup sit lower. Yes I checked the height with 2 squares and a straight edge, didn't read it right. Always use clay to verify your measurements.
This motor really runs now. Morel lifters, .040 head gaskets, ceramic coated piston tops and dri lube sides, Total Seal rings. I won the first road race last weekend, Started 5th, passed everyone into turn one. Thanks to all for your help, I hope that you learned as much as I did from this. Keep the revs up and the pedal down.
Racecar
This motor really runs now. Morel lifters, .040 head gaskets, ceramic coated piston tops and dri lube sides, Total Seal rings. I won the first road race last weekend, Started 5th, passed everyone into turn one. Thanks to all for your help, I hope that you learned as much as I did from this. Keep the revs up and the pedal down.
Racecar
