Is my 5.7 4-bolt main?

[Crazydavez28]

I just bought a non running 106k mile 99 4dr 4X4 Tahoe over the weekend and the motor has been messed with... the kid i bought it from said a rod bearing was blown but I get there and the plug wires are in the back seat and the distributor bolt is loose. I figure at this point I would rather not try to mess with the motor that is in the Tahoe since I have a good 2-bolt shortblock in the shop that needs freshened up and could go back in.

I did see the Goodwrench motors 12530283 for the "R" VIN code is 4-bolt main. The VIN on this Tahoe has the "R" as the 8th digit. Is it likely my Tahoe has the 4-bolt block?

 

[454cid]

I just bought a non running 106k mile 99 4dr 4X4 Tahoe over the weekend and the motor has been messed with... the kid i bought it from said a rod bearing was blown but I get there and the plug wires are in the back seat and the distributor bolt is loose. I figure at this point I would rather not try to mess with the motor...

No idea on the block question. How does the rest of the existing engine look? Would it take much to put it back together... wires, and distributor? I think I'd try to put it back together and maybe do a little trouble shooting... it could be the kid has no clue. 106K miles isn't much. My dad sold his old 96 with over 280K, and it still ran fine.

 

[Curt]

I just bought a non running 106k mile 99 4dr 4X4 Tahoe over the weekend and the motor has been messed with... the kid i bought it from said a rod bearing was blown but I get there and the plug wires are in the back seat and the distributor bolt is loose. I figure at this point I would rather not try to mess with the motor that is in the Tahoe since I have a good 2-bolt shortblock in the shop that needs freshened up and could go back in.

I did see the Goodwrench motors 12530283 for the "R" VIN code is 4-bolt main. The VIN on this Tahoe has the "R" as the 8th digit. Is it likely my Tahoe has the 4-bolt block?

If it is the stock engine that came with the truck, then no it is the 2-bolt main. The 12530283 GM Goodwrench motor is for the 3/4 and 1 ton trucks only. I wish the 1/2 ton trucks came with a 4-bolt main... The motor that is most likely in your Tahoe is "R" vin/ L31 motor GM Goodwrench 12681432 (https://www.jegs.com/i/Chevrolet-Performance/809/12681432/10002/-1).

 

[L31MaxExpress]

M

If it is the stock engine that came with the truck, then no it is the 2-bolt main. The 12530283 GM Goodwrench motor is for the 3/4 and 1 ton trucks only. I wish the 1/2 ton trucks came with a 4-bolt main... The motor that is most likely in your Tahoe is "R" vin/ L31 motor GM Goodwrench 12681432 (https://www.jegs.com/i/Chevrolet-Performance/809/12681432/10002/-1).

Just because it is a 1/2 ton does not necessarily mean 2 bolt main caps. Some where 4 bolt out of the factory.

The engine that blew up in my 1/2 ton G1500 Express van at 57K miles from bad intake gaskets, hydraulic locking cylinder #2, causing the rod to break on startup, was a 4 bolt main block.

Also had my hands on a 5.7 from a 2003 Tahoe that had a 5 spd behind it a few years ago. It was 4 bolt main from the factory as well. That truck was a bit weird. GMT800 with a 5.7 Vortec, a 5spd in a Tahoe, all the engine mount and bellhousing bolts were metric, it had dual knock sensors, a 4x reluctor, 1x distributor (cam sensor), no cats, no rear o2s, egr block off cap on the exhaust manifold and the lower intake was cast without EGR provisions and it was all being run by a Green/Blue connector 1 meg PCM that I happen to have the calibration file in HPT form for. The only emissions control on the whole truck was a vapor canister and purge/vent valve and it was not monitored by a pressure sensor.

 

[Curt]

Just because it is a 1/2 ton does not necessarily mean 2 bolt main caps. Some where 4 bolt out of the factory.

The engine that blew up in my 1/2 ton G1500 Express van at 57K miles from bad intake gaskets, hydraulic locking cylinder #2, causing the rod to break on startup, was a 4 bolt main block.

Also had my hands on a 5.7 from a 2003 Tahoe that had a 5 spd behind it a few years ago. It was 4 bolt main from the factory as well.

I'm specifically referring to this platform of trucks, GMT400. Correct me if I'm wrong, but the 1/2 ton trucks came with a 5.7L 2-bolt main (if equipped), while the 3/4 and 1 ton came with 5.7L 4-bolt mains (if equipped).

 

[L31MaxExpress]

I'm specifically referring to this platform of trucks, GMT400. Correct me if I'm wrong, but the 1/2 ton trucks came with a 5.7L 2-bolt main (if equipped), while the 3/4 and 1 ton came with 5.7L 4-bolt mains (if equipped).

In theory yes, but in actuality not so much. I pulled pans of these trucks starting back in 2004 for oil pan gaskets and the like. PLENTY of 1/2 ton trucks, SUVs, and vans were running around then on stock engines that had 4 bolt main caps. No real reason to explain it either. Kind of like GMs habit of flipping back forth between 906 and 062 heads. Two trucks, same year, same plant could have either head on it and sometimes one of each!

 

[Curt]

In theory yes, but in actuality not so much. I pulled pans of these trucks starting back in 2004 for oil pan gaskets and the like. PLENTY of 1/2 ton trucks, SUVs, and vans were running around then on stock engines that had 4 bolt main caps. No real reason to explain it either. Kind of like GMs habit of flipping back forth between 906 and 062 heads. Two trucks, same year, same plant could have either head on it and sometimes one of each!

Huh, interesting! So I guess the only real way to know what came with out trucks is to take the oil pan off and look? Did you notice any markings on the block that indicated 2-bolt v. 4-bolt?

 

[Lanny]

Huh, interesting! So I guess the only real way to know what came with out trucks is to take the oil pan off and look? Did you notice any markings on the block that indicated 2-bolt v. 4-bolt?

I believe that its in the RPO codes. Not sure which code it is but when I wen through and traced all mine I found an option for a 4 bolt main. I would assume that the 1/2 ton trucks came with 4 bolt mains.

 

[Schurkey]

GM often played fast 'n' loose with substituting 4-bolt blocks in 2-bolt applications, just as they played games with head castings and other "unofficial" variations in build. I haven't heard of them shoving a 2-bolt block into a 4-bolt application, although I suppose it could happen.

Far as I know there's no RPO code specifically for 4-bolt blocks, although there might be a code that includes a 4-bolt block as part of some other option group--heavy-duty towing package or some such.

There's no external casting marking on the block associated with 4-bolt caps,.

In most (not all) cases, 4-bolt blocks/caps aren't really needed. If the application isn't fretting the caps, more bolts aren't going to help.

 

[454cid]

GM often played fast 'n' loose with substituting 4-bolt blocks in 2-bolt applications.

It may be a case of what was on hand.