8.1 vortec into 1979 k30

[Lu Blunt]

@hoagster the gmt800 trucks pull air from the passenger fender. Squarebody trucks pull air from a hole in the radiator support that’s between the passenger headlight and radiator. If you box in the air filter make sure it has a source of fresh air

 

[Lu Blunt]

Damn coolant plug broke on me. Took a few days but finally got the threads clean enough to install the squarebody coolant sensor

 

[Lu Blunt]

I got the exhaust fixed today. Had about a 30 mile drive back to my house. Maybe 10 miles from home and the engine starting making a knocking sound. I had double checked everything before driving and nothing seemed wrong. Never got hot and had good oil pressure. I drained the oil when I got home and it doesn’t look good.

 

[Lu Blunt]

There’s lots of metal in the oil and oil filter. Mostly copper colored non magnetic flakes of metal. The engine was supposed to be rebuilt with low miles. I think my only option is to pull everything apart and have the 8.1 rebuilt correctly. Sucks but that’s the way she goes

 

[AuroraGirl]

There’s lots of metal in the oil and oil filter. Mostly copper colored non magnetic flakes of metal. The engine was supposed to be rebuilt with low miles. I think my only option is to pull everything apart and have the 8.1 rebuilt correctly. Sucks but that’s the way she goes

if its mostly or only non magnetic that suggests the engines bearings which means crankshaft and rod bearings to me, if you still have good oil pressure (camshaft)

I dont know what pressure you did have.

but maybe someone without actually doing anywork slapped bearings on the crank, including not checking clearances or wear evidence etc... and then sold it as "rebuilt"

 

[Lu Blunt]

The guy I bought the 8.1 from owned a local auto repair shop and seemed honest. He said “Pistons and rings, bearings, heads resurfaced and valves lapped in, complete gasket set, camshaft and lifters, and timing components.” Everything looked to be in good condition and very little rust. Back in 2022 I paid $1500 for the 8.1 and it came with the harness, the ecm and Alison tcm. Not sure why the 8.1 ate itself up but I’ll get it taken apart and see what I find. Only thing cooler than a big block is a cammed big block lol

 

[AuroraGirl]

The guy I bought the 8.1 from owned a local auto repair shop and seemed honest. He said “Pistons and rings, bearings, heads resurfaced and valves lapped in, complete gasket set, camshaft and lifters, and timing components.” Everything looked to be in good condition and very little rust. Back in 2022 I paid $1500 for the 8.1 and it came with the harness, the ecm and Alison tcm. Not sure why the 8.1 ate itself up but I’ll get it taken apart and see what I find. Only thing cooler than a big block is a cammed big block lol

definitely keep us informed because there should be evidence of said work done if it was or tolerances somewhere it wasnt

 

[Bextreme04]

The guy I bought the 8.1 from owned a local auto repair shop and seemed honest. He said “Pistons and rings, bearings, heads resurfaced and valves lapped in, complete gasket set, camshaft and lifters, and timing components.” Everything looked to be in good condition and very little rust. Back in 2022 I paid $1500 for the 8.1 and it came with the harness, the ecm and Alison tcm. Not sure why the 8.1 ate itself up but I’ll get it taken apart and see what I find. Only thing cooler than a big block is a cammed big block lol

Bearing kits are sold as "all BBC", but that is not actually the case. The GEN VI and GEN VII BBC have different #1 and #5 bearings, and the only correc t ones I could find are chevrolet performance ones. I rebuilt my 1997 Gen VI a few years ago and found that out when I had a general BBC set of cleavite bearings and when I measured everything to set the clearances, those two were WAY out of spec. I ended up ordering a few different sets and all of them were wrong in the same way. Ordered a set of chevrolet performance Gen VI bearings and just swapped out those two and everything was back to dead on factory specs.

So if the guy just rebuilt it using standard Cleavite BBC bearings and assumed it would be fine, that's probably why it ate itself. The #5 was fine for bearing clearance, but the thrust clearance was way out. #1 was super tight.

 

[DoubleDingo]

Bearing kits are sold as "all BBC", but that is not actually the case. The GEN VI and GEN VII BBC have different #1 and #5 bearings, and the only correc t ones I could find are chevrolet performance ones. I rebuilt my 1997 Gen VI a few years ago and found that out when I had a general BBC set of cleavite bearings and when I measured everything to set the clearances, those two were WAY out of spec. I ended up ordering a few different sets and all of them were wrong in the same way. Ordered a set of chevrolet performance Gen VI bearings and just swapped out those two and everything was back to dead on factory specs.

So if the guy just rebuilt it using standard Cleavite BBC bearings and assumed it would be fine, that's probably why it ate itself. The #5 was fine for bearing clearance, but the thrust clearance was way out. #1 was super tight.

The builder/seller probably just slapped in some bearings not checking. That's what it sounds like, anyhow

 

[Hunter79764]

That's tough to hear for your sake, but good to know. I've got 2 8.1's now, including one that hasn't run since being refreshed by the previous owner and is getting ready to go into my 87... (The other is all stock in my motorhome). What are the chances I can figure out if I've got the wrong bearings in it by just pulling the pan? Or any other method?

 

[Bextreme04]

That's tough to hear for your sake, but good to know. I've got 2 8.1's now, including one that hasn't run since being refreshed by the previous owner and is getting ready to go into my 87... (The other is all stock in my motorhome). What are the chances I can figure out if I've got the wrong bearings in it by just pulling the pan? Or any other method?

If they actually measured the clearance like you are supposed to when assembling an engine, they would find out real fast there is an issue. If they machined the crank to standard BBC specs or honed the block to standard specs it will take standard bearings as well.

 

[Hunter79764]

If they actually measured the clearance like you are supposed to when assembling an engine, they would find out real fast there is an issue. If they machined the crank to standard BBC specs or honed the block to standard specs it will take standard bearings as well.

I don't believe he did any machine work, mainly just a rering/reseal/freshen up before going into his truck before plans changed and he sold it to me. So to verify, I need to pull the pan, remove #1 and 5 caps and plastigauge? I'm assuming it will either be fine or WAAAAY off?

 

[Bextreme04]

I don't believe he did any machine work, mainly just a rering/reseal/freshen up before going into his truck before plans changed and he sold it to me. So to verify, I need to pull the pan, remove #1 and 5 caps and plastigauge? I'm assuming it will either be fine or WAAAAY off?

Yep, that's what I did initially. Used standard BBC bearings and plastigauged just to make sure nothing was too far off. The #1 bearing was VERY tight and the plastigauge showed that. The #5 was close on clearance, but the thrust was WAY too tight and would have required a bunch of sanding to bring in spec. I can probably find the set of chevrolet performance bearings I ordered that ended up fitting just right if you need the PN. I got them from summit and they were about 4x the price of the cleavite ones, but still only ~$120 I think.

 

[Camar068]

Damn coolant plug broke on me. Took a few days but finally got the threads clean enough to install the squarebody coolant sensor

not knowing an 8.1, but you couldn't use a 3 wire camaro sensor for the gauge and the ECM signal? They might be threaded differently than a 5.3....dunno.

...and you may have answered this already previously, sorry if you did.

 

[Lu Blunt]

I’m not familiar with the 3 wire camaro sensor. Sounds like its similar to the oem 8.1 sensor. The 8.1 uses a three wire temperature sensor located on the passenger side head. Two of the wires go to the ECM. The third is not used from the factory but supports a temperature gauge and you can use that third wire for the square body gauge. Around 79-81 the resistance values that the temperature gauge uses changed from one value to another. The later model gauge is the one that uses the correct value for the factory 8.1 third wire from the temperature sensor.

I thought it would be cool to use the squarebodys temp sensor but if I’d known the plug would be such a problem to remove I would have tried the using the 3rd wire from 8.1 sensor.

Weather was nice the last couple days and I was able to make some progress on the dually. Drained fluids, removed driveshafts and t-case. Front end taken apart. Next step is remove trans and pull the 8.1