1978 GMC K25

by Iggy Tue Apr 14, 2020 8:51 pm

This is a truck I picked up last fall to take to my place in the Upper Peninsula

by Iggy Tue Apr 14, 2020 9:08 pm

I put those there to see how pictures were posting. I bought the truck almost three hour drive from where I live and drove it home when I bought it. It ran fine, even on the expressway! However, something was nagging at me so I decided to tear the engine down to go through it. I found the engine was a 1972 400 SBC from a full size car, it had a 1972 400 head on the drivers side, a 1973 350 head on the passenger side! My gut feeling was trying to tell me something.

Pulled the heads, at least the 350 head had steam hole put in it, the 400 head was cracked from the exhaust port to the spark plug on two cylinders. Those two cylinders were clean enough to see that it still had original pistons

by Iggy Tue Apr 14, 2020 9:13 pm

At this point I knew I needed to tear down the engine to see how badly the block was cracked! Much to my surprise the block was the only thing I could salvage from the engine. It turned out to be crack free and had no ridge! The crankshaft was a completely different story - it came out of a 1974 engine and looks like it was part of a spectacular failure! It was ground .020 on the rods and .010 on the mains. I refused to reuse it and bought a Scat 400 crank.

by Iggy Tue Apr 14, 2020 9:17 pm

I decided to have the block machined - it cleaned up at .020 over, was align honed with main studs and decked .010

Here it is mocked up so we could make sure everything cleared. New Scat crank, Scat 5.7 rods and KB dish pistons. After that it was disassembled and taken to be balanced.

by Iggy Tue Apr 14, 2020 9:24 pm

Because the heads were cracked, I took a set of Vortec heads in to have steam holes added - they were already rebuilt with new guides and valves and are getting new springs on them now.

At this point I am waiting to get things back so it can be assembled and run on a break-in stand. Nothing fancy here, mainly parts I had laying around as far as the cam and internals - cam is a Summit 1103 that never got installed, Vortec heads were something I traded a set of Dart TBI heads for - I had to buy crank, rods and pistons!

by Iggy Tue Apr 14, 2020 9:31 pm

Because of the current slow down in everything and basic shutdown in Michigan - the truck sits until I can get some help!

I have a TH400 and NP241C that I was going to put in a K5 Blazer, but I got an offer I could not refuse on the rolling chassis, so the freshly rebuilt TH400/NP241 will get put in this along with a fresh 400 small block. The truck came with a set of Doug's Tri-"Y" headers in great shape so I will use those and a dual exhaust system. Will also use a Quadrajet I have that was rebuilt by Cliff Ruggles for a project like this!

by bigredlaguna Tue Apr 14, 2020 9:48 pm

That engine should be a stump puller when you are done. Don't you just love dealing with somebody else's train wreck?

by thatfnthing Tue Apr 14, 2020 10:41 pm

X2 on that.

And I love my Doug Tri-Y's. You will too. Smile

by Iggy Wed Apr 15, 2020 9:34 am

The truck is from Arizona, fenders were rusted just behind the front tires and along the top of the wheel opening. Cab is solid, but the bottom of the doors are rusted. I had a 1977 K20 from California a couple of years ago that were rusted in the same areas - looks like dirt accumulated there and held moisture when there was some. My shop floor looks like the Arizona desert as it falls of the bottom of the truck! I have new fenders, inner fenders and a set of good used doors that I need to get to my body guy when he is ready.

Since I have a new fuel take for the Blazer I sold, I am considering pulling the side saddle tanks and putting a single 30 gallon tank behind the rear axle under the bed.

by Iggy Wed Apr 15, 2020 11:34 am

bigredlaguna wrote:That engine should be a stump puller when you are done. Don't you just love dealing with somebody else's train wreck?

I am counting on it being a stump puller! At least when I made an offer far below what the guy was asking I assumed the driveline including the engine was toast! I already had laying around the shop a fresh 1974 350, the TH400 and NP241 so I knew I had a complete driveline, but really wanted something bigger than a 350. My options were rebuild the 400 if it was fine or put together a 454 which I have several blocks and cranks ready to go. I am glad the 400 block checked out as I wanted to stay with a small block since I did not have the HD front springs or any extra BBC headers for the truck (I do for the Laguna).

by Iggy Thu Oct 15, 2020 12:05 pm

Been a long summer with little getting done. I brought my Dana 60 to guy who rebuilds them (along with trans and t-cases), when he opened it up it was full of water - we were able so salvage the housing/tubes, knuckles and spindles! Since I needed a new carrier I went with a Trac-Lok and replaced the 3.73 gears to match the rear 14-bolt. All new axle shafts, bearings, races, hubs,.....

by Iggy Thu Oct 15, 2020 12:39 pm

Also had someone assemble my engine, I needed time this summer to help out family. Between COVID 19 and my father having a series of mini-strokes (TIA's) I have not had time to work on things. I hope this winter give me more time - have heated shop and can get things done!

The lower end is complete on the 400 SBC, Keith Black pistons with Speed Pro Moly Rings, Scat 5.7 capscrew rods and Scat crank - all balanced. Heads are ready to bolt on, with any luck will put on a break-in stand in then next two weeks for the initial break-in! Once that is done, I will have the engine, transmission and transfer case ready to set on the frame. Hope my body guy has some time this winter!

by REVINKEVIN / Mr. 600+HP Thu Oct 15, 2020 7:26 pm

You are doing a great job on your truck. I have a 400 abc in my 1986 Silverado. Stout performer for sure. I am also thinking about ditching the dual tanks and going with the single tank in the rear. I have taken apart my share of other peoples projects. There is no telling what you will find. This is the main reason that I am re-wiring my entire Laguna project. Good luck brother.

by Iggy Sun Oct 18, 2020 5:20 pm

I happen to have a brand new Spectra 31 gal tank for a 1973-1981 K5 Blazer - considering using that installed behind the rear axle. Found a factory in-box spare tire carrier at one of the local pick-n-pulls, cost me a whole $5 bill (I paid, quietly got in my care and drove off before they changed their minds!), I did not hesitate.

Have not gotten into the wiring yet, but figure if it is anything like the mechanicals, it we be rewired.

by Iggy Sat Feb 04, 2023 10:00 pm

Reviving the old project - finally have time to work on the truck and get it together! My heart attack set me back a bit and I almost put it up for sale. Good friend of mine was out of work and looking for a project so I am having him do the body work, which overall is in very good shape, few little dings. I ended up selling the 400 SBC off the break-in stand, but kept everything else I had set aside, the Dana 60, TH400 and NP241 are still all fresh! I have a 327 that needs to be assembled (1969 327 block and crank with Dart heads) and I will use that to get the truck back on the road. Trying to find my one 5.7 roller cam block and will use that to eventually put a 383 with Vortec heads in the truck down the road, or possibly the LG4 6.0 LS sitting in the corner, or maybe even the 8100 Vortec I am pulling from a 2003 2500HD! Will start with the 327 to motivate it and decide later.

What I really need to do is get this guys brother to make some room in his shop for my Laguna! He has worked at body shops in the past, and restores cars you would think were not restorable - his Buick GS had trees growing through it when he bought it! He wants my 1975 GMC C35 Dooley Camper Special and I want body work on my Laguna and he is willing to trade! Just waiting for him to make room. In the meantime, will at least get my old truck back on the road.

by g3chevy / Mr Pontiac Sun Feb 05, 2023 12:18 pm

The Vortec 8100 would be a perfect choice for that truck. It's a literal stump puller as a buddy of mine used his flat bed truck with that engine to pull out 4 stumps from my front yard without even trying.

Horse trading to get your Laguna done sounds like an awesome plan.

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