Inliners International Forums Thread Like Summary - 54 GMC 270 Rebuild Help

Hello, new on board here. Got the advice to join from a great local resource, Buffalo when i picked up one of his last remaining Nicson Exhaust Manifolds.

Been working and building cars and bikes pretty much all my life with my old man. Even already did a 235 Full Pressure in a 51 Chevy Coupe we built. I got the itch to finally get my own build in and the old man has a soft spot for 5 window Pickups. A good friend had a great start on a 54 GMC 100 5 Window. Tons of parrs, pretty much everything we needed to get most of it built.

Upon getting it home things started going no so good. He opted to drop the torque tube, who can blame him, and put in a 55T rear end with a Muncie 318. Well neither one was in really good condition so out with that and now has a bullet proof 9� and found and fixed up a low mile T5 to run behind the 248. During winterizing the motor being in a unheated barn, motor ran but had some rod knock, and upon examining the inside found lots of carbon, and some serious wear on the cylinder walls.

So I knew of a 270 locally, and knew it was a low mile rebuild, and i helped personally pull it out of the 2 ton wrecker the shop i help at do a V8 swap. So i made an offer and brought home the 270.

All it really needed was a few gaskets as they probably used 3-4 tubes of RTV squeezed out between layers. So i ordered a Best Gasket Kit off the interwebz and started tearing into it. Pull the valve cover off and the oil pan, and it looked super clean. A bit of oil sludge at the bottom of the pan but i half expected that. Pulled the timing gear cover off and the fiber gear looks brand new, again super happy.

But sadly thats where the good ended. I figured since i had the kit, id pull the cam out and sure enough no gasket or shim under the retainer. Pull the cam out and it looks brand new except for some scratches on the last bearing surface on the cam, then look at the bearing itself and appears ot was beat in with a screwdriver. And i am not talking about to stake it. Deep scratches and divots on the bearing.

So i started pulling rods and main caps. And one after another im finding trash and fod in under the bearings and scratches on the journals. My heart is sinking at this point.

Pull all the pistons out and not a joke pretty much all the ring gaps are dead in line, and the piston skirts are all knurled. And i have a tiny bit of rod slop but not terrible.

All the bores have a pretty good ridge at the top and some fresh honing marks telling me they probably just dingle balled the cylinders tossed some rings (3 out of six had rings out of order to the manual)

Crank has been turned for 10 unders and all bearings are 10 unders

Block is a D Block so it left the factory as a standard rods and mains with a .005 overbore.

The head is a different story. I have some sunk and some protruding valves. And i think it was not touched during rebuild. When i checked vakve lash i found they had set the lash with the motor 180 out. With it 180 out the #1 valves were in rocking position and #6 was tight. With it at TDC Compression #1 was tight. I am surprised how well this motor ran before we pulled it.

So hopefully I can drop the short block off with my local old school machinist. And he gives me good news.

I have a complete 248 for parts as well as another cam, crank and head. All 3 heads are small port. And to my understanding the 248 crank and 270 are the same?

Second part is finding 20 under rods and mains and prob 20 over piston and rings. All mine are flat top and not domed like Egge sells but even then it looked like all they had were standards.

So im stumped and a bit disheartened tonight. And apologies for no pics. Not letting me upload jpeg photos but can supply my Drive album privately if someone wants to see the pics.

Do not want to V8 swap this thing. I know personally what a nightmare it is. Lol. But i look to be heading down a deep rabbit hole getting this thing proper and running strong.

-Dan

Thanks in Advance

Verify on that large of a bore by sonic checking, but many of the GMC 302's have been bored .125" over and are still thick enough to race with high compression....Many Flathead Ford's can withstand 3/16" of an overbore, or .187".
Thankfully, most of the engines of that era are blessed with extremely thick cylinder walls and decks.

The 228, 236, & 248 are all 3.8125" stroke
The 256, 270, @ 302 are all 4.000" stroke

I have a '57 270in a '53 Chevy pickup (5 window) I originally built it in 1978 I think. So I have the same block & head as you. It seems that the older style (domed) pistons are easier to find now. They sometimes show up on eBay. That would require you to use and earlier domed chamber head.

There were only 4 different heads used for all the GMCs 228-302. #1 had dome chambers and small ports, #2 (H-head) had dome chambers and big ports. #3 was the later 302 with a D shaped chamber and big ports. #4 the ones we have for later 270s with a sorta D chamber and small ports. For a street engine small ports are fine. Bill Fisher recommended small ports for the street.

The rods for all of these engines were the same length and had the same bottom end bore. There was a difference in the size of the notch that held the main bearing insert. There were two piston pin sizes.

The 302 crank should be OK. I'm not sure how many flywheel bolts it has. Early cranks had 4 and racers sometimes drilled 4 more. Later cranks had 6 bolts. This obviously effects flywheel choice. This can be an issue because 6v & 12V starters use a different number teeth in the ring gear. You can run a 6v starter on 12v.

Don't give up! These are good engines and fun to drive. I just got mine back in the road today. I had a fuel pump issue and just stuck an electric pump on it. It has a T5 & Dana 44 limited slip with 3.55 gears. Fenton headers a 4bbl carb and custom ground cam. It will cruse 75 mph all day and get 17+mpg.

Yes, my pistons are flat top too. I can not remember how much the head was shaved and I can not find the cam specs. I have all of the paper work around here somewhere. I think I stuck with stock valve size but not sure.

Have the head done. Small block Chevy valves will work. Some use a 0.100 + stem length. 1.87-1.92 intake & 1.60 exhaust. You may have to enlarge the spring seat. The stock stamped steel rockers are plenty strong for the street. LINK

Picture from when I last had mine opened up in 2008. It doesn't look that nice now.

Attached Images

When I pulled my 270 from it's original home a '57 GMC 1/2 ton pickup it was orange. A little yellower than Chevy I think. A friend in high school put a junk yard 270 in his '54 Chevy sedan. We raced before he got the hood on it. I was running what I thought was a hot flathead in a '38 Ford coupe. I beat him twice but that long orange valve cover was never out of sight.

Yes Clifford intake but mine in not marked. They were doing some changes when I ordered it. I'm running a 500 Edelbrock sidewise. My cam is Clifford too. I originally had Clifford Viper tube headers and the engine turned higher rpm with them. I use a cable throttle and after having to drive from Reno about 30 miles home over the mountains through Virginia City using the hand throttle late at night I cary a spare cable under the seat.

All if the GMCs are good street engines. Bill Fisher really liked the 248 for street builds. I had a 248 in my pickup while I was building the 270 because at the time I could not find a 302. For a driver you would hardly notice the difference. The shorter stroke has some advantages. Someone with an honest sense of how their engine will be used might be interested in your 248 stuff especially if they like turbos or superchargers.

There are iron & steel cams that call for different distributer gears. I have a couple of NOS cams. I don't know how to measure them other than lift. I can not remember the details but all the info you need is out there. There is a ton of information in old posts on this site if you can learn to use the search feature here. A lot of it posted here by some of our long gone members who helped develop the performance side of these engines.

Sadly this site is not as active as it once was and not many here are still into the engines Inliners International was built around. There are far more people into these on the H.A.M.B. "LINK" You may find more help there as well as sell or trade your parts if that is what you decide to do. Their search feature is easier to use also. We have a Swap Meet page here if you decide to sell. You can likely sell your 270 stuff of enough to buy 250-292 stuff. Don't overlook the 250 it can be built to at least equal the 270 for less money.

I have gathered the parts for a 292 to replace a worn out 350 in a '68 C20 flatbed. Parts are still available over the counter. Manifolds, headers, cams......are easy to find. I had Crower grind a cam. 12 Bolt Tom can fix you up with all you need. In truth a 292 doesn't need a lot of work to be impressive.

I'm Six Ball there. I'll check your build.

Sounds good. I couldn't find a 302 when I built my 270. I have 2 in the pile now. If you have fun a good running one that is a real cool factor for your build.

Two other guys here that have 250-292 stuff are Twisted 6 & CNC DUDE.

One advantage the GMC's engines have is that they can take a huge overbore because their cylinders are so thick. So that opens up many more options to switch and swap parts from other brands and makes....