NorthernC5

Bought a brand new LS3 block for my build. Double checking bores on block before I do anything and find out main bores are oversize. From what service manual says - main bore is 2.750-2.751. I am getting 2.7518-2.7520. Bores are nice and round just oversize.

Called Summit who I bought it from. Guy was helpful. He called their contact at GM who said "they are all like that - ok to run it". IS this true??

Anybody out there used a new LS3 block and checked the main bores?

I am confident my measurements are accurate and have triple checked my mic's (aerospace machinist and work with millionths of an inch daily).

KCS

iTrader: (20)

I think it depends on what you're going to do with the engine.

The bore ID is really important because that interference fit with the bearing is what keeps the bearing from spinning in the bore. The bearing manufacturers list the bore size as 2.7509" - 2.7512" IIRC. In an aluminum block, I always shoot for the low (2.7509"), especially for an engine that will endure a lot of heat for extended periods of time. In an iron block, I'd let it fly if the bore is on the high (2.7512").

2.7518" is too loose for me to be comfortable with, but, I suppose it could be okay in a relatively mild street build.

NorthernC5

Yes Clevite shows the H bearings as needing 2.7509-2.7514 and the P 2.7509-2.7515.

It will be supercharged - around 650 rwhp.

Just wondering if I ship it back - will I get another with the same diameter?

1CAMWNDR

iTrader: (21)

You best bet might be to take the block to a machine shop and have it align honed and see if it needs oversized bearings.

WE TODD DID

iTrader: (2)

If the bearings fit good in the saddles, and not loose, it'll work great. It might actually be helpful to you being a little bigger because it'll give you a little more bearing clearance.

NorthernC5

I am concerned with not enough crush and the bearings walking/moving and possibly spinning the bearing...

1989GTA

What is the temperature of the crankshaft when you are measuring it?

NorthernC5

Everything stabilized at 65 deg in shop

WE TODD DID

iTrader: (2)

I've run them 2.7516" and the bearings feel plenty tight in the saddles. I would take some bearings and see how they feel. If they drop in, obviously they won't work. If they're snug, run them. I always use king bearings, so I can't speak for any others in regards to how they fit. Actually I attempted to use some federal mogul X main bearings once when I was in a pinch, but they didn't fit tight at all. I think they took the extra clearance from the back side of the bearing.

KCS

iTrader: (20)

I'm using the FM 152M bearings in my LS2. They're pretty snug, but I did set my bores to 2.7505". With the main cap installed and torqued, the bearing shells are going to push out on each other and give you the crush that you need.

WE TODD DID

iTrader: (2)

They should still have resistance when they're installed in the saddles. These just kinda dropped in. The concentricity of the bearing won't be correct if they're loose at rest, and are forced open when they're bolted down.

NorthernC5

I talked to texas speed and they factory GM blocks are all over the place - it will be fine. Just check clearances and adjust bearing sizes. Said to use Clevite H.

Thanks!

KCS

iTrader: (20)

What I'm trying to say is that if the bore is to size and round when the mains are torqued, then the eccentricity should be correct regardless of what it feels like without the caps bolted on. I'm not too concerned about how the bearings fit when the caps aren't torqued for the same reason I'm not too worried what the piston to wall clearance is without a torque plate bolted on.

WE TODD DID

iTrader: (2)

I disagree with the bearing fitment. If the bearings fit loose in saddles and don't naturally want to expand outwards, what keeps them from compressing inward toward the crank journal when you tighten the caps?

KCS

iTrader: (20)

What if they do and that's the way they're designed? I don't know about you, but I chamfer the parting line and with those tight fitting bearings, I usually have to try to squeeze the bearing together so that it doesn't shave material off of the backside when they go in.

What if it's the bore that pulls in against the bearing? I don't know how round that main saddle is without the caps bolted on, but I do know the bore will move just torquing the side bolts to 18ft-lbs.

I don't know the answer to either question above, but I do know that the main or rod bearing bore with the bolts torqued is the bore that the bearing designers had in mind. When that bore is right, the crush, eccentricity, etc will be right.

Steve - Race Eng

iTrader: (1)

Both ACL and Clevite call for 2.7509" - 2.7515" for the housing bore diameter. So you are .0003" to .0005" big on bore size.

With most cranks I have found the housing bore needs to be on the high end to get proper bearing clearance using a std. set of bearings. It is always preferable to set the housing spec at minimum to get more bearing crush regardless of the engine manufacture. If you do so on these engines, you will need two sets of bearings, one std. and one set .001" over and use half a set of each to get the clearance correct keeping the same half set in the block or caps.

What I would do in this case is carefully lap the parting lines of the caps to close up the bore to 2.7515" or a tenth less and call it a day.

Steve