Sad and very expensive day. Our 415 LS3 tore up #4 main bearing. It didn't spin, but it was close...lot of heat. The main cap pulls out with two fingers. It has has no tension at all holding it in the block.

Is there coming back from this, or is the block junk? How do you get the main cap to fit tightly again?

Only #4 was hurt. All the others were fine except for pushing trash through them. First thoughts were oil starvation/aeration...maybe a cracked or bent crank. Unfortunately it threw material up between the pistons and the bore too...

 

I would say that if it's not visually bad and it cleans up with an align-hone, run it. You do need a rebuild, though, not just a backyard dingleball hone and re-assembly.

 

The biggest concern is the loose fitting main cap. It should be held tight by the block. Not sure if this means the aluminum block has been hurt?

It’s getting pistons and going out at least .005”

Crank will be turned and checked for cracks or bends.

 

Unfortunately, I cannot answer that myself. The machinist would know.

You can fix anything, the question is if it is worth it.

 

Will need to check the main housing bores with a micrometer and dial bore gauge. There's a few specs. floating around for the range in diameters.

Check the upper saddles (upper housing bores) with a machinist straight edge.

 

I think you'll be fine. I do agree, obviously, that you need a major rebuild. Surprised the crank survived! As for the main cap, have the machinist measure the skirt to skirt distance on the block, at the known correct fitting caps. Then have him measure it where the cap is "looser." Then he can measure the cap width, and subtract the difference. If the cap width matches the rest of the caps, or the aluminum skirt to skirt distance is wider at the loose cap than at the normal fitting caps, then the aluminum has slightly widened. I'm still betting the block will be fine. After the align hone, and with the known clearance on each side, you could possibly use shim stock to set it up properly. This is too much to try explaining here, and I'm not saying it will be easy. The cap could even be doweled, like the LS7, once it is in the correct, exact position it needs to be. But I believe a qualified machinist can save the block and you'll be OK. Of course, some of this depends on how you're going to use the car. The machinist will know, just find a good one. I know, easier said than done. Wishing you the best of luck...

 

Upon more inspection, the main cap shrunk .005" from heat compared to the others. The block is ok, but need to source some main caps and choose the best fitting one before align honing. We'll take it out to 4.080" to gain a few cubes.

Turns out the crank broke which is really disappointing. Manley forged crank only lasted 250 runs down the drag strip. #4 main has .0025" runout.

It's a bracket race engine and generally lives a very easy life.

 

China metallurgy

Probably better off getting a factory ls7 crank and adding mallory to it, or just use the ls7 titanium rods also

 

I may have some take off main caps for you. TBH, that 4.080 bore scares me more than the main issue. I have a LS3 block in my garage now at 4.080 w,/ a cracked sleeve. Sleeve was even centered and it still broke on a pump gas NA motor. I would do another block, but that's just me. I gave up on doing a sleeved block for my build and I scored a deal on a new LSX block over the weekend. I want to build stuff one time and have it last somewhat. Regarding the crank, I would look at an L8T crank. You can't beat them for the $$$. The China **** will always be china ****, you can't get around it. All of the blanks are coming out of the same foundry.

 

Spanks, the blackening on the bearing face is super heated oil. Can you post a pic of the cap? Is it blue from heat? For it to shrink, it must have gotten very hot. Here’s some thoughts…
What were clearances set at?
Did you confirm this on all 5 mains?
What oil pump? Ported pump? Ported pump…even Melling…reduces cavitation.
Was crank checked for straightness? This one gets missed a lot and causes this issue often. I had this problem once and missed it. I had #4 do the same thing as you have here. ProLine Racing found the issue with the crank. It was a Callies…brand new not straight. They repaired it for me.
I hate seeing this Spanks. I’ve been here before. It’s a mess, but fixable.

​​​​….edit…pinned mains are a great idea to keep cap walk down. The caps on an LS walk a lot, even in stock applications. You’d think that with the 6 bolt skirted design that this wouldn’t be so, but it’s bad. A crank without center counterweights will whip at RPM, especially with big power builds.

 

If you have main caps we're looking for some. I think we'd only replace the one bad one..so if you have extra of #2 and #4 I'd take each of those. We found some full sets on ebay for like $60, but might check the junkyard first.

It was a 4.065 bore and is going to a 4.080 bore.

Blocks have gone crazy in price. Things are looking a bit bleak for LS stuff at the moment. I have a Callies 4" crank we'll be using after having it checked out. I've seen the L8T stuff it is definitely interesting. If we have to buy a crank I did suggest a CCW 4" piece but they're a little spendy.

It was a brand new GM ls3 block we used their bore preparation and bought Mahle 4.065" pistons, Manley crank and rods. It was meant to live forever lol.

Clearances were .0022 to .0024" for all the mains mic'ed and checked with dial bore gauge. #4 was at .0024". We also run I think the 5w20 Lucas race oil or maybe even lighter. Probably won't anymore now that Lucas stopped sponsoring everyone lol it is some expensive stuff.

The main cap did get extremely hot. Not as bad as I've seen in other pictures of actually spun bearings, but it did get hot as hell. There's maybe .050" of blackening on the main cap not quite up the side of it, but the chamfered edge just above the bearing. The biggest fear was if the block got hurt, but we should be good with just a new cap and align hone.

It was a GM oil pump that was hand ported on a bit. We had great luck with the L92 pump (high volume high pressure) in the stock bottom end L92 we had so kept the same pump for the stroker. We had initially thought oil starvation or cavitation, but now know the crank broke. Spinning the crank in the main saddles #4 is .0025" out of round. #3 and #2 were also out of round by .0012 and .0008".

Very interesting thought about the crank being bent from new. It is not anything we've ever checked, but it did turn free in the shortblock during assembly it definitely wasn't .0025" out of round when it was new. The rotating assembly was match balanced. I'd hope it would have been caught at that point if it was bent.

The crank doesn't ring like it should. It is dull when you strike it so it is definitely cracked. We have 4 crankshafts to take to the shop to be checked out so we'll have this one looked over as a sanity check see what they find.

#4 main looked ugly underneath. It walked around a ton.

We're really not being too hard on this thing and it doesn't make huge power. Decent, but pretty mild. I had a 402 in my street car that I'd bounce off a 7400 chip with a stick shift for 25000 miles and the bearings looked fine. This thing gets babied...warmed up before racing and mostly only 1/8 mile these days. 1/8 mile it never sees over 7000 lol.

 

It seems like it’s usually #2 and #4 mains that get beat up by the cranks whipping action…the crank whips like a wave through a rope when you whip it. That’s an exaggeration of course, but that’s a fair description of what these cranks see when not center counterweighted.

 

If the OP cant find a cap that can actually work correctly after an align hone, it might be best to have a machine shop make up a billet cap. If I was still in the workforce, Id make up a few of these for my own use, and send the OP one. But I'm not, so I can't. IIRC, doesnt the LS7 use billet caps made of 1010 steel?

 

LS7 has billet caps that are pinned. Not sure about the 1010 makeup. DarthV8r could answer that one.

 

Looking online I see 1141 steel alloy, which I've never heard of (which doesn't mean anything!), but the same source also says the LS7 has piston squirters, which on the OEM engines we know it does not. FWIW.......

 

That sounds more like an LS9 or LSA, because they're blown and need the pistons cooled.

 

Sounds like a 2nd or 3rd order problem

 

How did you find out (the clue it was bad or going) noise or bad oil pressure.

 

Had low oil pressure due to a plugged oil filter. The lifters were collapsed due to lack of pressure and the idle was high. Never knocked or anything like that.