Projects 1954 GMC Series 1

Yes. Ill see if i cant get a pic. Its prob .030 thick at the top of the top ring groove. Has a gap, but ill be darned of i cant even use a sharp seal pic to pry it out. But it spins freely like the ring but is fitted tightly to the piston and does not expand like the ring.

 

Stock GMC pistons were 4 ring. I would be surprised the last time it was rebuilt the rebuilder rings were narrower than the original so the replacements came with a spacer. The originals were way over kill….

 

Thanks Jimmy i bet thats it. Shop Book showed me the setup and it didn’t have the spacer shim. Also only one ring is beveled to the inside and thru put it in #3 slot. Book showed all having bevels top one to the inside the next two had outside bevels.

 

Back in the day a lot of pistons with worn ring grooves where machined square but wider and the space filled with a spacer ring. There was even a manual tool to do the cut and several makers of the spacer ring.
Still available:https://ringspacers.com/ringspac.htm
Tool: https://www.ebay.com/itm/292216001473

 

As a kid in the 50s I went to work with my dad a lot in shops he ran or worked in. I saw him do a lot of things that we don't do today. A lot more parts were reused. Pistons were knurled, rig groves recut. rods resized, bearings shimmed and used parts were saved to use in other jobs. Many parts houses had full machine shops and often let guys like my dad use them. Those guys were mechanics & many like Dad were machinists. So many today are parts replacers.

 

I have one of those tools you linked to, never used it, I’d always thought it was for cleaning ring lands.

 

KenC, thats it! Awesome thanks

 

Being totally bored tonight after an all.day cuss fest at Job #1 putting a 67 Vette back together I didn't take apart, I said heck with it and tore int the 248 as well. And honestly was surprised what I found.

Low compression was due to a mostly blown head gasket. Cross blow between 2-3 and 4-5. Water jackets are a bit sludgy but should be able to flush most out.

Head is still a small port and I missed it the first time as I didn't know now that I have the 270 apart as well as I have tall valve stems, double valve springs, shims under the springs and definitely been pocket cut. Stainless valves, hardened seats.

Crank is a 248 Crank, Cam is a 302, pistons all 30 over. Mains and rods look good. Rods are tens and mains are 20s. Might toss a set of bearings at it since I have to pull the crank to replace the failed rear main.

Otner than decking the head I think I'm just gonna send it and forget about the 270 and sideline it and maybe some parts will.show up some day.

 

California Bill Fisher recommended the 248 for the street. Of course that was '54 or so and a lot has been learned since then. I put a stick 248 in my '53 pickup when I first got it while I was building the 270. It did all I asked of it. It was our work truck and hauled a lot of ranch & building supplies. I really doubt that in normal daily use you would see much difference in the two engines. The small ports on the street will be no restriction at all and might even be betters they will enhance velocity through the smaller passages. All of the heads will interchange depending on which piston style is used.
If you want a street performance engine the 248 will do that too and would be my choice for a McCuloch supercharger or turbo.

 

Got into a pretty good argument with the old man on the valves. They are the +10s I believe as the stems all have 10 on them so they definitely stick up a lot higher than the 270s stems over the keepers. Said we NEED to cut them down on a lathe to restore proper Valve Train Geometry. The valve pads on the rocker arms are dead center and not off set. The stem itself has a bit of a sharp edge nothing major. Reading another thread over on Inliners they said the longer stems is a good thing. So need more info here.

 

I’ve helped quite afew GMC guys who wanted 302’s keep the 270’s they had and used the last small port with the smallest chamber. The key is both have the 4” crank for torque (but the 248 will do also) and use an intake for the large port head. Most ended up with the Offy 4 barrel. You machine out the small port head with a taper about 3/8” in the port from the mounting edge then gently smooth or round the transition making a venturi effect.. low end to 4500 is awesome. A street “secret” to make a good runner. My dad taught me it wasn’t always a bigger port but how you used it.

 

Any wise words on the longer valves stems Jimmy on the head I pulled from the 248? Sadly I'm about to toss both in a crusher. Lol hate fighting with the old man (he's old school), and says it's not right needs to retain proper geometry so needs the stems trimmed down to match the ones in the 270. He's not a forum surfer like I am.to get info from long time builders of these engines. Lol I don't have enough hours in the day anymore to drive around and bug my machinist or down to Buffalo to ask.

The stems are exactly 10mm longer sticking out than the stock ones on the 270s head.

 

Is it that the head is together and you don't want to take it apart to deal with the valve length? Did it run this way? The rockers are adjustable and some difference can be taken up there but 10mm is a lot. Another option would be pushrod length. A shorter pushrod could maintain original geometry though put the rocker in a slightly different position. You would likely have to have them built. New shorter valves would be cheaper. Is the 10mm measurement just the stem sticking further out the top. Does the assembled spring height along with the spring pad cut in the head necessitate the extra stem length?

 

Ill get some measurements tonight. The motor did run but the valve lash was horrendous and it had low compression in 2-5 due to the now known cross blow on the gasket. Ill pull one of each and fet some measurements. I forgot to think maybe the keeper slots were just a bit deeper than a stock valve

 

Stock GMC valves had a weird keeper as I remember.
I used longer valves (+.100) because I had .600” valve lift and wanted clearance for the seals on the guides. Stock length or slightly longer had an easier time finding springs. I used the Competition Products catalog for reference when I bought. The newer valves can also use keeper where the “ledge” inside are at different heights along with 10* keepers where lash caps can help adjust the geometry.
Most rebuild shops do not or can not deal with the time all this takes let alone the hourly rate for the customer. For years all the shop would do for me was the valves and enlarging the seats. I would get the springs, retainers, keepers, seals and do the final lapping. . . My labor is free…to me. It’s all on what you want done.

 

I think the newer valves used a different retainer & keepers. That my make some difference.It is the overall height that matters. It sounds like it may have newer springs and they may seat lower on the pad. I may have an old head around with stock valves still in I could measure if needed.

 

Valves are the same length. Keepers are just 10mm lower giving it an illusion they are longer. No more late nights in my workshop when i have other major disasters going at the main shop. Lol

Put a new wiring harness in this beauty and blew the ballast resistor, voltage regulator and probably smoked the alternator. And it was a GM Certified harness. Back tonight when i can have peace and quiet. Lo

 

That sounds better.
The Vette looks nice. I hope you get that ironed out. My friend just let his brother & nephew talk him out of the '61 Vette he has had since the late 60s.

 

Got the Vette sorted. Voltage regulator contacts were welded. Dug and found another in the parts horde. Tested with it all issues solved.
Thats the hardest part i spend all day building others dream rigs leaving me with too many ideas and not enough energy to keep rolling on mine.

 

78 today, your energy won't increase with age. Do it now!

 

Well Happy BD. I hear ya. Living with an illness with no cure I agree. Why im doing what im doing. What started as a occasional help out tear a car down or help do final assembly has turned into you know what needs to be done, getter done. Looking forward to the 35 Ford. Pure Street Rod. Old school and me pulling out my A+++ game to do it.

slapping the 270 back together to jist get it back in one spot, put the 248 on the lift next, clean it up and do the bare minimum we need to get it running right.

Maybe someday parts will be remanufactured. For the 270 and i can build a rowdy build. Will see how long the 248 lasts.

Expensive lesson learned. 270 took a grand hunk out of my budget. Should of did a but more exploration of the 248 before jumping on what was a runner 270 that wasn't gonna run much longer.

 

In time you'll come across the parts you need. Especially if you set it aside for a bit. You'll find them while looking for other stuff. Actually they will find you.

 

Going to go look at a 302 that was pulled from a Bus years ago. Supposed to only have a few thousand miles on it. For the price I'm hoping it saves my project. (I won't disclose the amount publically) . He knows it's at least 20 over, but thinks it's been rebuilt twice so it could be more. It's a 54 block. Don't know what head it has. If so I'll keep all the 302 specific parts and find someone needing 228/248 parts and give someone a screaming deal on everything I don't need including the 270 block.

 

Well another bust. Ended up being a Chevy 261 with a 40 over rebuild tag. Totally not worth what he was asking, nor will any of my speed parts work. Oh well. Hopefully find the right bearings for the ones i have. Im about to pull an LS out of storage and toss it in. Least i know it runs and only has 122k on it.

 

Sad to say at this point, we are considering selling the project. Trying to keep things old school is proving to be out of my budget. Even if i went with a 292 or something my dream of building this truck on a budget has proven impossible. Borrowing shop space with limited resources (filled with her personal possessions so any mess making is out). Should of looked a lot harder to find parts for the 248 and 270 are NLA unless you pony up for Egge prices. And those locally that have old Jimmy stuff want $$$ (found a destroked 302 for $10k) or dont want to part with them. St this point i have no clue what the project is worth. Whoever would be interested would need to take everything i have accumulated. Pretty much have everything needed to make the truck complete. Body needs a fair bit of work to Un-F* some of the prior owners work. Rebuilt 9” in back, T5 would be included for the right price. Mincie 318, SM426? From the 270. Everything. If anyone local is interested please don’t hesitate to contact me.


Also both my old mans health (possible bypass this summer) and my own health including my main gig building cars time has just not been kind.

So right now thats where my project stands. Stinks but sometimes you have to realize you dont have it in you to make your dreams come true.

 

Exactly what do you need to make one of the GMCs whole? Pick one.

 

We are going to look really hard again this week. As far as we figure the 270 is a boat anchor. Needs oversized pistons, rings, 20 unders on rods and mains. Crank ground etc.

The 248 is my only canidate at this point. I need to find a way to pull the head coolant nozzles from the 270 head, have the 248 head gone thru and rebuilt. Needs valve guides. (already has the SBC valves, dual springs etc). The lower end is probably runnable for a while. Needs to put in the new rear main which I'll have to pull the crank to do, maybe dingleball the cylinders and need 30 over piston rings. Probably cam bearings. Etc.

Take all the good parts that are interchangeable and get the 248 running again. But I need to check rods and pins because I still think the noise I heard was a bit of rod knock when it did run.

Not totally giving up but definitely not as much wind in the sails this week. Thanks Six Ball.

 

We also just kicked the idea around of the S10 frame swap then we'd have a better availability of engines to swap in and not the headache of the steering box trying to stuff a V6 or 8 creates.
Heck I even looked at a VW PD TDI swap to really twist heads. Adapter to a SBC bellhousing is only $1200.

 

If you think $1200 is change then build a straight 6 Chevy.
Problem solved.
Could probably build one with the $$$ selling the gmc stuff.

 

Just kicking ideas. If I sold all the stuff for the motors I'd probably have enough to build a radical V8 motor as well. Even my last resort was fairly amazed that only Egge had the availability to make pistons. But hat was only half the fight. Finding 20 under bearings was another hard to find without $$$$ having custom cast ones made or having the crank rewelded and reground back to stock specs as both motors have 10s in it now.

I'm just trying to find something workable to keep the project alive and something not run of the mill generic. But now see why so many do subframe swaps and toss a V8 in them.

I can still go the 250/292 route keeping it a six sell the Clifford intake, 4 BBL 390 Holley and the Buffalo Nicson manifolds, and see if I can find something similar to hop it up, but then like a V8 swap build motor mounts etc. Just have to find one, still having to sell the 248/270 and all the parts so I have room.to breathe again.

I just really had my heart set on keeping a period correct motor in the thing for old school stats. Never dreamed what was a popular motor back on the day for racers, that the parts well would run dry. My fault for not digging deeper before buying it, but the 248 did run, but had a bad knock inside and surprised it ran at all as bad as the valves were set (180 out).