Racer Buzz

iTrader: (1)

LS1 Tech Team Members,

Can I get some feedback from those in the know on the suggested clearances for both the main bearings and the rod bearings in an LS (aluminum) series race engine running an Aviaid dry sump oiling system?

NEW:
Oil is / was 20W50 Joe Gibbs Driven racing oil #XP6. Oil temperatures were running at 250 to 270 degrees at the Homestead NASA 2 hr race. I then added a second oil cooler for the Sebring PBOC race and that lowered it to a 230 to 250 degree range at a 6000 RPM shift point. Oil pressure cold at start up was 65# and it would slowly drop into the 40's then to 30 #'s during a 2 hour race at Homestead. After letting the car sit and cool for 30 minutes the oil pressure would go back to 65#'s which is still really low for a dry sump pump with the adjusting screw set for max pressure. Not sure what brand of main & rod bearings.


Anybody have a connection with a LS series real race engine shop where they might share their suggestions that you could then pass along?

The GM factory specs says:

Crankshaft Main Bearing Clearance - Production
0.0008-0.0021 in

Crankshaft Main Bearing Clearance - Service
0.0008-0.0025 in

but that seams like a pretty big spread.

My engine guy says my motor is running .0022 to .0025 and I have now lost the #4 main bearing twice. Once in a wet sump 383 CID motor and now again in a dry sump 405 CID setup.

Strange that the main would go before a rod bearing as the mains are fed first! And if the oil feeds from the rear of the engine also strange that the second to the rear main brg would go before the front main or front rod brgs.

This is actually a continuation of my earlier thread on my race setup oiling system problems.

I've received a lot of helpful input and suggestions from the members on several new ideas to incorporate but I'm now struggling with what clearance to run in the rebuilding of my 405 CID motor.

I certainly appreciate any input.

Buzz Fyhrie
"Racer Buzz"
rcrbuzz@bellsouth.net
www.buzzfyhrieracing.com
www.totaldollarflorida.com
Pres, PMA Marine Insurance
Radio Spotter 4 Corvette Factory Team '01, SCCA Regs, Nats & 5th in "A" Prod in '76 Runoffs, SCCA T/A w/best of 6th, twice IMSA's Rolex Daytona 24-Hr, Finished 2nd in '00 Viper-Vette Shootout @ Moroso.

'98 C5 Coupe PBOC R1 Class with a best lap time @ Sebring = 2:18.00 in 2006

'06 CTS-V Caddy Infra Red

'07 Four-Winds Thor "Fun Mover"

ChucksZ06

iTrader: (9)

I would be looking at some other cause if it is the same bearing both times...like misalignment. You do not say if block is aluminum or iron. What wt of oil and what was pressure like? There are so many variables other than oiling that could be causing your problems. Aluminum will expand and needs to be tighter than iron block on the mains to keep your pressure up...you do not say what your pressure was.

HTMtrSprt

What type of bearings are you running? Also, what oil, weight, and temps are you running at?

racecar

I run a LS6 with the mains .0015- .0018 and the rods .002. It holds good pressure at 240degrees oil temp. If you take the middle of those GM crankshaft tolerances, you get 0016That's a good goal. My calculations are that the mains will open up .001 when the motor warms up to race temperature. Anything with mains over .002 cold, will be over .003 when it is hot. That's where your pressure is going. Also check your cam bearing clearance. I had to try three sets to get one under .003.

Racer Buzz

iTrader: (1)

Thanks Racecar. That the first really good piece of solid information I have received so far on my ongoing oil pressure problem.

From what I learned building engines years ago and also what I have discovered just recently from various conversations I think you are right on the money with the clearances!

Thanks again.

Racer Buzz

iTrader: (1)

By lost it I mean the oil pressure finally went to zero during the race after slowly fading down from 65# and the bearing turned in its journal. I did not see the problem #4 main bearing just the signs of it turning in the block. Pictures available. But I cannot post pics. The motor was align honed and the bearings measured and fit. As a side note my engine builder says he has only recently discovered that Chevy CAM bearings have considerably tighter clearance than the after market CAM bearings and he feels that was a contributing part of the pressure loss problem.

What are your thoughts on the main bearing clearances growing more in an aluminum block over an iron block and if so by how much? If the aluminum block expands more / faster than the steel crank does what happens to the clearances if they start at .0022? Does it grow by a thousandth to .0032 or more? If Chevrolet says .0008 is OK on the tight side what does that tell us we should be doing to keep the oil pressure high as the bearing clearances grow while the oil temp hits 240 to 260 degrees and up. 240 is probably more than what a typical street engine sees and consequently there is more clearance in a hot race engine and then more oil loss occurs and then I end up with lower oil pressure.

Am I going anywhere with that thought process? I'm thinking the mains should be on the tight side say .0015 to .002 in an aluminum block race motor that also sees higher oil temps like you find in road racing.

KCS

iTrader: (20)

The general rule of thumb many professinal engine builders follow is .001" for every 1" of journal diameter, plus .0005" to be safe. Main journal diameter is (off the top of my head) about 2.5589" or so and rods are 2.0899". Going by that, you can shoot for .0025"-.003" on the mains, and .0021"-.0026" for the rods. Those are typical clearances of many LSx race engines out there running with no problems. If that runs fine, then you can trim down the clearances from there, if you want, till you start to see problems again.

As for bearings spinning, the main force keeping the bearings from spinning is the crush when the caps are torqued to spec. The O.D. of the bearing is larger than the I.D. of the rod/main bore. The more crush, the better grip the bearing has in the bore and the better heat is transferred as well. But this is to a point, as too much crush can cause distortion. Clevite's bearing catalog lists the "low" (tightest) and the "high" (loosest) recommended bore diameters. Have your machinist align hone to Clevite's "low" and set the clearances as already mentioned, and you should have no problems. As long as there is no oiling problem.

Also, another common solution to spinning bearings is honing rods/mains out of round. There is at least 1 NHRA Pro Stock shop that I know of that practices this method routinely. Basically, honing the bores (rod/mains) in such a way that the diameter at the parting lines is larger than at 12 and 6 o'clock position, ensure that the bore is round under higher loads. Especially if the rods or mains are made of a weaker or more flexible material.

Hope this helps out, and good luck.

427

iTrader: (3)

In an aluminum LS road race engine we have always run the mains under .002, and are really happy if we can get .0012 on 1,2,4 and 5 with number 3 at .0015. If you are not using a drysump oiling system, we would add a accusump to help with oiling.

Kurt

Racer Buzz

iTrader: (1)

Thanks Kurt 427 for the good bearing clearance info, I appreciate it.

My oil system setup:
I have a Aviaid 4 stage Dry Sump system with a mix of -10 and -12 lines from the pump pressure out to the cooler, to the 2nd cooler, to a Canton 6" paper oil filter, to the engine oil inlet in the ARE pan. I have two oil coolers, one in each headlight bucket feeding air in from the parking lights, a 5 gal Patterson oil tank in the passenger side knee area attached to the door bars of the roll cage, -16 oil line from the pump out to the top of the tank via a Johnson aircraft micro screen filter and a -16 line from the tank outlet to the pressure inlet side of the pump.

I'm now changing the pressure pump section from 1.25" to 1.50" width, going to use Mobil 1 10W30 this go around having just tried Joe Gibbs Driven and before that R.P. & Red Line. Will also tighten up the mains as you suggest and the rods and use GM part cam bearing as they have a tighter clearance fit.

As a side note I had a pisser of a oil leak problem with your high dollar, high vacuum, steel housing, rear main oil seal. Turned out it was a loose fit in the rear cover and was not detected by the deaf, dumb & blind engine assembly guy. It would only leak after I shut the motor off. While running the crankcase vacuum created by the DS pump kept the oil in. It took forever to figure out what was wrong and where the damn oil leak was coming from until we finally pulled all the drive train out. I then was able to pop the seal out of the rear cover by hand!!!! What's up with that? Have you seen that before?

HTMtrSprt

First off, do not use a production style main bearing.... we've had them flake apart under the load of a racing engine. I would recommend a speed-pro 3/4 groove race bearing p/n 152M. Also 8-7100CH competition rod bearings. Stock GM cam bearings should work well for your application as well. You could have the rods and mains coated for a little additional protection.
As for clearance, the main cap is still sintered iron (if it's stock) or steel (aftermarket) and doesn't grow that much. You should have a minimum of .0022" main clearance and .0025" rod clearance. These blocks are lightweight aluminum (meaning weak) and they move around alot under load... if you don't give them enough clearance, to bend and twist, you will lose bearings. Low pressure in these motors is often caused by too much clearance in the lifter bores.... with a stock aluminum bore, you should only have .001" clearance. If you put bronze bushings in them, you drill small oil feed holes in the bushing (.025-.040") and run them at .002". Another thing to consider is about 1.5" of hard block in the water jackets to firm up the block and keep the mains in line (as well as helping ring seal). I have a 408" motor built from an LS2 block with the ARE 2 stage dry sump in a ZO6 that road races all the time and it NEVER gets hot or has a big loss of oil pressure so I know it works. Oil temp runs 220 and water runs 185. Oil pressure comes down a little bit as it comes up to temp but it always has at least 50 PSI WOT and that is more than enough to run it at 8000 RPM.
I would not recommend Mobil 1 oil however, I would stay with a good synthetic race oil like the Red Line.

Brian
HiTech Motorsport

427

iTrader: (3)

I have never ran into the TKO seal fitting loose in the cover, but I always use a light coat of silicone because of the metal to metal install. If you have problems, measure the inside diameter of your cover and call me with the dimension.

Kurt

blackz93

iTrader: (2)

So, how much are these clearances growing when at operating temperature?

Louis

iTrader: (7)

A lot. More than you think, and the problem is exacerbated with higher/climbing oil temps.

We have made them live, and honestly Im not too keen on releasing how. Buzz, go off of what Kurt said, and Hitech motorsports have to say, they are on the right track.

blackz93

iTrader: (2)

Yeah, I know... I was just wondering how much.

Jon@WAR

Typical clearances on a drysump application are .0016"-.0018" on the mains, and .0022"-.0024" on the rods, assuming a 2.100" rod journal. The LS engines are pretty efficient oiling engines, not alot of gpm needed. I would suggest re-checking your clearances, and using a lighter weight oil.

Redline-Motorsports

iTrader: (3)

That's exactly where we run them. Expect a big drop in oil pressure if the mains are approaching .0020-.0025" with an aluminum block. The rods are a bit more forgiving. I just went through three sets of bearings to final get yesterdays LS7 TT motor to those specs.

Racer Buzz

iTrader: (1)

Anybody else out there have some main and rod bearing clearance, oil make & weight, DS pump, AQ lines, oil filter, etc input before I meet with my engine builder tomorrow to discuss the rebuild plans?

Right now I'm going with:

Main clearance at .0018 to .0020

Rod clearance at .0020 to .0022

MAIN & ROD BEARING BRANDS: Any favorites as far as brands?

Lifter bores, to sleeve or not to sleeve, that is the question? And a very expensive operation to machine and complete.

Cam bearings: Will use stock GM brgs

AQ LINES: What about the size of the AQ lines running from the DS pump to the coolers to the filter to the engine oil inlet? >>>>> Use -10 AQ or go to larger -12 or is bigger a bad idea. Maybe -12 would give too much line / hose expansion leading to pressure fluxuation and pressure loss and it's just more bulk oil weight to push through all the lines & fittings?

DRY SUMP PUMP: How about I go to a wider (from a 1.25" to a 1.50" width) and switch from an aluminum to a cast iron housing on just the pressure pump section. The cast iron would expand less and hold tighter clearances between the impellers and the housing for less pressure loss when it get real HOT?

OIL FILTER: Any feedback on using a 6" Canton aluminum housing & paper element oil filter placed in-line just before the oil goes back into the engine?

OIL: Use a 10W30 weight oil (Mobile 1 or Valvoline or Royal Purple or Red Line) and stay away from using any thicker 20W50 viscosity oil as it could hurt the motor more on cold temp start ups than any gains you might get from the oil being a tiny bit thicker when it gets really hot.

My thanks to everyone for all the valuable input supplied to date. I hope this thread and the discussion has been helpful to others with oil flow and pressure issues.

Racer Buzz

iTrader: (1)

Any further input from anybody?

racecar

Buzz, Back to post #4, I said mains .0015-.0018. I would aim closer to the .0015 as a nominal. If you go .002, that is too much IMO. Check post #8 from Kurt .0012-.0015, yea that's the ticket. They will grow .001 when the motor is at race temp. Have you ever run the mains in a steel block at .003, probably not. More like .0025, that is what you will have with LS6 mains at .0015 cold.
It may not sound like much, but it takes a tight motor to make good oil pressure.

AQ- I ran #12 on my Trans Am cars, but they were 8000 rpm. A 10 should work if you are under 7000 rpm. Dry Sump pump - I ran all aluminum on T/A, never had a pressure problem. Your alum pump should work fine. Valvoline 10-30 for me.

If you have a leaking main seal, or any other vents in the motor, your dry sump may be sucking air and foaming the oil.

blackz93

iTrader: (2)

Nothing wrong with .003" on a iron block, but .0025 is good too.