Projects Old school cool 248 Gmc

I don't see the line port in the pictures I have but I will have to go look at the actual block. I am just SWAGing here. If 5000 is crazy I certainly respect all the experience here.

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Can't really push the RPMs too much anyway, want to use this Dealer GMC Tach

 

I followed the link you posted on the Inliners's site I Just went through this whole thread. I have never seen a GMC block as clean as yours. I built the 270 in my pickup in 1978 I think. I've been driving the crap out of it ever since. I have regularly shifted it at 5,500 rpm and it has seen 6,000 rpm a few times. Some of the time it had no dampner on the pulley. These are tough engines and can take a lot of abuse.
You could build the engine in less time than it would take to post these pictures there.

 

Isky himself might be a good guy to talk to, if you want a vintage grind - he still has all of Mcguirk's cam masters. If nothing else, would be a fun visit! Next, would be Jerry Cantrel at Schneider Cams here in San Diego, has a lot of experience with vintage engines, and can reface your lifters too. Fir a 'hi-tech' grind, can't think of anyone better than Comp... bet you know that!

Figure out what you have for CR, before you lock-in on a cam. The KEY is where the intake valve closes to maintain or build DYNAMIC compression. 224 @ .050 sounds like a good number to start with for duration. Can you help me understand the advantage of a 108 lobe center over a 110?

LOVE your thread, mucho luck with the Jimmie build! -Tim

 

it is only clean because of the baking oven and shot blaster. One burns off the oil paint grease etc and the other blasts it away. Much better than a hot tank. Waiting on the sleeve and crank to get ground now for mock up. Driving to Daytona Beach after work (22+ hours) to the Daytona North Turn beach parade on Saturday so no more work will get done this week.

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I talked to Schneider, maybe I should revisit that email and ask more questions.

Cam overlap is a combination of how long the valves are held open by the lobes and how much the intake/exhaust lobes overlap depending on the love seperation angle they are ground on . so if you have a long duration and want better idle vac or have a power adder etc you may widen the LSA to 110-116 to improve the idle or to also help push less air/fuel out the exhaust out, and widen the power band and improve topend hp slightly. A tight lsa adds to overlap. This narrows power band improves torque because of scavaging and usually makes better overall power. These are general things and smarter men can explain how it works together better. lot of overlap also gives us the chop we love at idle. Since this will never really be fast, it should at least sound cool.

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This is what Jerry from Schneider suggested in the email I sent him on the first of the years.
"Look at the Chevy 6 cyl. page for grinds The lift won't be the same I like the 274-F or the 280-F and the lift would be .480" "

The 274-f is what I was thinking but wonder about the duration split. I assume that is for a poor exhaust port flow. Still up in the air as to if I should use the Fenton manifolds or build a header. Also worried the large 270H dual Nicson is too small, but my budget is a bit too small to keep buying parts till I get stuff together. Probably will list the Nicson Small Port with the Rochester Bs with linkage for sale early next week. I already have an Edmunds small port intake I would likely use if I ever built a 248 for something.


Not a chrome guy but I am considering "chrome" powder coating the valve cover and side cover. There is only a few chrome places here and the lead time used to be measured in birthdays to get stuff done there. The whole thought process of this engine/truck was a "day 2 build" like the muscle car guys do. If your farmer dad gave you his old truck, what would you do. It will eventually get lowered and a set of chrome reverses added. Still debating adding side racks with a label of the Allis dealership we had till the early 40s or something to tie in the family farm.

 

Man, can't wait to see how this all turns out! I think it's going to be super cool!

 

This is the 274-F specs
Grind Number: T274F
Intake Duration (gross): 264
Exhaust Duration (gross): 284
Intake Duration (.050”): 224
Exhaust Duration (.050”): 240
Intake Valve Lift*: .560"
Exhaust Valve Lift*: .560"
Lobe Separation: 110
Intake Valve Lash: .014"
Exhaust Valve Lash: .016"
RPM Range:
2500-6500
*Based on 1.75 Rocker Arm Ratio

 

I sure hope so!

 

The last time I had my 270 apart ai used Scotch Brite pads to buff the sheet metal parts. Valve cover, side cover, timing cover, and oil filler/breather. I really like the look. I painted with rattle can clear and sadly that didn't hold up. Powder coat might, A good look and cheap.

 

this is what I am talking about
https://www.eastwood.com/eastwood-extreme-chrome-bonded-powder.html

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Neb: Forgive me, I'm still hung up on the cracked cylinder. I reread everything, don't understand. It's still cracked? Sleeving it? Different block? Etc., etc.

 

The pistons in the 270 were STUCK, like not a little but like sledge hammer with a full swing. Once this piston finally broke in half the top wedged sideways and split the cylinder. It is still cracked but my machinest ordered a sleeve yesterday. It will be as strong as it was if we hadn't broke it.

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Got it. I know something about stuck pistons.

 

Ordered a Schneider cam
264 adv. 224 @ .050 intake
274 adv. 230 @ .050 Exhaust
lsa 108
.480 lift with 1.5 rockers ( I know they are less but not sure how much)

Not sure what to do about the lifters. I have a nice set from the 248 but they came off a forged steel cam and the new one is a cast iron cam. I have a rough but usable set from a cast cam but it has 4 of the lifters with holes and 8 hollow lifters. Not sure if if there is a material difference between the 2. I can get the 302 lifters ground but my ADHD is killing me with the lifters not being the same. Not sure I want to pay $250 plus for new lifters make in who knows where.

 

I ordered a set of NOS sealed power lifters from Ebay.

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That´s a great build and a lot of knowledge you are sharing!Thanks for that! I have a 55 Chevy with a 235 that I´d like to build a Jimmie for, one day when I have the chance. Looks like they are made of unobtainium over here.
I´ll shut up and be watching and learing now.

 

Look in US military 6x6 trucks. They had 270s and 302s. My last 302 came from a military truck.

 

My plaster piston mold was soaking up the alcohol so my dome measurement was off. Coated it in a thin layer of rtv after paint didn't work. They came out to 60 cc. When I get my crank ground I will be able to mock it up but it looks like 9.5-10 to one will be easily possible.

Tore apart my Mallory dual point. I sware this thing has hardly been run at all. Not sure what to do with the leather rubbing block vac advance. Planned on just using the factory style advance. Not sure what to use for dist lube.

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I have at least three or four brand new tubes of distributor block lube. I’m happy to send you a new tube if you want. No charge. Just PM me your address. Well worth the entertainment and education of this build. Regards, Randy


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Recieved my NOS Sealed Power Lifters. They all weigh in in the 90-92 grams. They are solids despite what the box indicates.

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Did a few things today.
Bored the #1 cylinder to about .408 over.
Pounded in the sleeve.
Cut the sleeve off.
Short filled the block to just above the freeze plugs.
Cc'ed the head to help figure compression again.

Special thanks to Schmidt Machine and specifically Brian.
He is helping me with my project and letting me do lots of the machining.
He has a passion for these old engines and will do work others won't anymore. There is never a time there isn't a flathead, Y block, Chevy 6, 5-20 dirt track engines, a big block or 2, Maybe a 428 Cobra jet, always something cool in addition to the regular machine jobs. If you are close to Southeast Nebraska you might look him and his Father Russ up. The last picture is a couple of cars Brian built the flatheads for just before the Daytona Beach Cruise last week.

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couple more pics

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Great pictures ,Thanks!

 

Wow, great build and pics! I love to have access to a maschine shop and a skillset like yours! Great job!

 

My skill set is mediocre at best but I have awesome friends

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Thinking next week I will take my side cover over to FPM which is a local place. They do engine turning and sell gauge panels on here and their website. I was thinking we could get a 3/8 plate of aluminum and do something with fins or engine turning. Maybe put my last name in it as a tribute to my Gramps. I don't know yet but it should be cool

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I do make a GMC aluminum valve cover and side cover...

I'll post a picture on later.

 

I would be interested in a valve cover depending on what it looks like?

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