The Stovebolt Site Forums The Shop Area Engine Shop 302 GMC Rebuild

Hey guys,

I acquired a 1959 302 GMC and it was running a few years before I bought it. Needs a knew intake and exhaust, oddly enough it has no serial number just stamped 302, has anyone seen that before? I am just going to go the route of rebuilding it. As I have only ever attempted to rebuild an engine once and it was a S/B chevy, this is going to be an adventure. If you guys can help along the way it would be greatly appreciated, I want this to be a driver. What im thinking is this,

- Intake and headers from Clifford's
- Also Clifford's said they can grind the cam for a driver engine.
- Full flow oil mod with spin, (ill have the machine shop do the modification, but i wl need help with the plumbing after that.
- head done for modern fuel and any suggestions here would help.
- bore the cylinders just to clean them up, this engine has one rebuild on it so we will see how much it's been bored. Then I would like to go aluminum pistons but I'm at a loss on where to source that.
- if I can keep stock rods and bearings I would like to but suggestions here also

Thats to start with, let me know what you guys think and can help with.

Egge would be a good source for piston also Ebay for stock oversized pistons.

Yes, I have had two 302’s come in the door with just 302 stamped on the boss - that is not unusual for a replacement engine. (Assume you have a civilian block 302?).

straightforward rebuild. Fun project. Acquire a manual. I have a military rebuild and assembly manual for these but the standard manual is the same...for these and other inline 270, 248, 228’s.

Post pics!

It's very obvious you've never been inside a GMC engine. It's already got full pressure oiling, a huge oil pump that flows far more oil than a stovebolt Chevy, full flow oil filter, and aluminum pistons- - - -they were all built that way. Is there some reason to believe the cylinders are worn enough to require another rebore job? Unless the cylinders are scored or have bad taper wear, there's no reason to whittle away more cylinder material- - - - -just do a slight scuff with a glaze breaker or a button hone to create the cross-hatch pattern needed to seat the new rings. If one or more cylinders are rust pitted or scored, install a sleeve and reuse the same pistons. Custom made GMC pistons are horrendously expensive, just because the people who make them are greedy and the people who purchase them are gullible enough to pay. I have a problem with Clifford's- - - - -their promises of major power gains with simple bolt-on items are blatantly false, and they refuse to publish any documentation of their claims. I have a problem trusting people who tell tall tales. The last GMC rebuild I was involved in was on a 256 cubic inch- - - -an oddball Canadian military engine that was a hybrid of a 248 and a 270, a 270 bore and a 248 stroke, IIRC. The biggest problem was finding the correct intake valves. I also straightened a twisted connecting rod and put a knurl on the piston skirts to get the clearance right after honing the cylinders. The rebuild turned out very well with using the original major parts such as pistons and connecting rods, and the crankshaft only needed polishing, not regrinding. GMC's are pretty tough engines, and they were made to be rebuilt multiple times. Good luck!
Jerry

What makes you think it neds rebuilding?

Yes it is a civilian block, I pulled it from a 1959 schools bus that had been turned into a schoolie. I will throw up some pics soon and as I go as I know I will only create more questions as I go.

Yes Jerry this is the first gmc engine I have been in, I have only rebuilt a sbc before and really only been around more modern engines and drivertrains. I just had a passion for the history this engine has so im embarking on this and it will go into a 1954 gmc. So it doesn't need the full flow mod that is talked about a lot? I will see once I open it. Then I can just swap the canister oil filter for a modern spin on and it should be good? That would be a lot easier as I could just follow the plumping it has now. I knew the numbers were off for the Clifford's stuff but chalked that up to advertising, but is the quality not great? I'll see if I can track down some Fenton and nicson stuff. I don't know if it needs to be bored but I always plan for the worst and if I don't need to even better. I do think I will shave the head a little to get the compression up.

I'm not sure if it does need a full rebuild but parts are rusted out and pitted plus
It leaked oil from everywhere and I just want to fully rebuild it before I set it into the truck, piece of mind I guess 😅

Delta cam in the Seattle area has a good reputation.

Ed

Why would you want to swap a very efficient canister oil filter with several times the area of the media available for filtering, for a terribly inefficient spin-on filter? The GMC original equipment filter is at least twice as tall, and almost twice as big in diameter than any conventional spin-on filter I'm aware of, with the possible exception of one for a Diesel road tractor. "Old" isn't necessarily "bad" where oil filters are concerned- - - - -the only reason I can imagine for swapping to a spin-on filter from a canister type might be laziness? The best method of filtering oil is to have two filters- - - -one full flow to strain out the big chunks that can damage bearings, and a much tighter media filter set up in a bypass configuration to catch particles down to a few microns in diameter that can pass through a full flow filter like it's not even there. There are several industrial hydraulic fluid filters that are capable of filtering out particles in the 1-2 micron range, while a full flow filter usually has media that traps 15-20 micron stuff.
Jerry

Well based on your comments Jerry its clear I should be doing research on my own instead of reaching out to ppl on here. Thanks to all replied to my query.

Woah. Slow your roll, cowboy. Jerry has a gruff manner sometimes, but he knows what he's talking about. The internet is not the ideal place to seek advice if you're going to take offense to something that's written in a way you don't like. Humans communicate with facial movements, tonal changes, and eye and lip movements, none of which can be conveyed with bland words on a page. If you want good advice, stick around.

http://www.inliners.org/tech/full_flo_GMC.html

This is all I was referencing and trying to have a simple conversation about. I did state that my knowledge was limited on this topic

I have to echo Paul's comments, Comediann. Jerry lives and breaths the "If it ain't broke, don't fix it" philosophy and he's apt to administer his very good advice with a ruler across the knuckles delivery to the hot rod guys (like me). It's not personal, I assure you. Hang around. No site on the Intarweb except the one devoted to old Jimmy trucks has more information about your engine than this one.

And we're having that conversation. But it's been sidetracked (ever so slightly) because you took offense to Jerry's choice of words. HIs advice is rock solid. What he's saying to you is that sometimes, modifications tend to make things worse, not better. Some pretty intelligent people designed the engines that we deal with, and it's always wise to consider that they might have known what they were doing, even back in those olden days.

My 235 has been modified to use a spin-on filter, but that's because it had no filter at all when it came from the factory. Some filtering is clearly better than none. But, as Jerry points out, you already have a very good filtering system on your engine. Modifying it for a spin-on filter would make it less effective. That's what Jerry's trying to tell you.

Don't take offense. Take it under advisement. That article you referenced is one man's opinion, and it's quite dated. Now you can balance it against Jerry's, and he has a wealth of experience.

Thx

The article in the link refers to converting an older engine set up for bypass oil filtration to full flow, which has already been done by the factory on later model GMC engines such as the 270's and 302's made from the mid-1950's and later. I have a complete GMC full flow filter system stashed away somewhere, and it has a huge filter canister and lines about 5/8" in diameter. If I choose to use it as a primary filter on an engine build at sometime in the future, I will still add a bypass filter with extremely fine weave media as a backup. One such filter is the "Frantz" design which uses a roll of industrial-strength toilet paper as a filter ("John Wayne" paper- - - -rough and tough, and won't take "stuff" off of anyone!) It does a great job of filtering oil, but it can't flow enough volume to keep an engine supplied. Hence, the need for a full flow filter to catch the rocks, marbles, and bowling balls!

30+ years of teaching high school auto mechanics to a bunch of ghetto gangbangers who knew a lot about stealing cars, and virtually nothing about fixing them has a tendency to make me speak very directly when myths about mechanical stuff get repeated. Some of those hardcore misfits are making a good, honest living using the skills I was able to pass on to them. Others are graduates of the River Bend school of advanced thuggery. River Bend is the Tennessee State Prison facility near Nashville. Keeping in touch with members of both groups can have advantages at times.
Jerry

I don't mind directness as long as it comes with all the information this post does, I really just want to learn from everyone here. I'm a big research guy and like facts before I dive into things. Its good to know I don't have to modify this, I want to keep it looking as original as I can while improving anywhere I can. Now this came out of a bus so just need to find the appropriate replacement filter. Also after your post I did research and learned the true inefficiency that model spin on have, something i never took into consideration as thats only things I have really had to deal with in my more modern engine experiences.

I had a long post written, and hit a wrong key and erased it. When I owned a Diesel repair shop and road service in central California back in the late 1970's, I was a distributor for the Frantz oil filter system sized to fit a LuberFiner 750 oil filter canister. The tissue paper filter element for that one was about 8" in diameter and over a foot tall, and the canister held about 2 gallons of oil. The Cummins and Detroit engines it was designed for usually held 10-15 gallons of oil, depending on the engine application. We would change filter elements every 10,000 miles and simply add enough oil to replace the volume lost during a filter change. Some of those engines had over 100K miles on the oil, and laboratory analysis of samples taken during filter changes indicated no loss of lubrication capability or other deterioration of the oil. Saving 8-10 gallons of oil per change was a major advantage of running the very efficient bypass filter. The engines were also equipped with a regular full flow filter, but it was only changed about once a year because there were virtually no large contaminants to filter out. The oil got black, like all diesel engine oils do since the sooty carbon is almost impossible to remove due to its extremely fine particle size, but the filter media kept the oil performing like new under operating conditions a gasoline engine virtually never sees. Good luck on your project!
Jerry

"It's very obvious you've never been inside a GMC engine. It's already got full pressure oiling, a huge oil pump that flows far more oil than a stovebolt Chevy, full flow oil filter, and aluminum pistons- - - -they were all built that way."

Jerry, I do have a comment about your previous post.


I have never seen a GMC engine of that era that came with full flow oil filter filtration, only bypass from the Factory.

Install the spin on filter and keep the bypass filter. The best of both.
Thats what I did on the 270 installed in my 40 Gmc

Tearing into the motor and I noticed even though this came from a 1959 bus the engine is older, based on block casting numbers 52-54. Also, the head casting number, 2188477, doesn't match any of the casting numbers on the oldgmctrucks forum. Seems this engine has a story to tell.

The late 12 Port Charlie Baker was a pretty good mechanic and craftsman. He was in a wheelchair most of his life but managed to become a lifelong devotee of old iron and speed equipment. He made patterns for casting aluminum side plates, valve covers, timing covers, 12 port GMC heads, all kinds of things. His business was called vintage design and development and he was one of the founders of inliners international. He was a pretty good machinist. In fact, Charlie machined up the 302 rods I run in one of my 261 chevy motors and I have one of the few offy knock off side covers he made for the 235/261 chevys. So he was not just some crack pot expressing an unfounded opinion.

I am not terribly versed on gmc motors. But this same conversion can be done to a 235/261 bypass motors. That being said, I don’t know which GMC blocks or year motors were full flow filters or bypass filters. His tech tip was designed to take a bypass filter motor, which bleeds off a little oil from the main galley, ran it through some relatively small lines to a canister filter, filtered this dribble of oil, and then the clean oil was dumped directly to the pan where it was instantly diluted with dirty oil, and change it to a full flow system where all of the oil was pulled from the galley, filtered through a full flow, easily obtained, spin on oil filter, which then redirected that clean filtered oil directly back into the galley, as opposed to the pan, supplying nice clean oil to the bearings and the rest of the motor.

While there are opinions on both side as to the propriety of this modification, it is still a viable method to convert a motor from a bypass filter motor to a full flow filter. And frankly, there is a third option. Don’t convert and don’t run a filter. My 235/261 motors are all heavily modified and I don’t run a filter at all. I just change the oil frequently primarily because I don’t get a lot of miles on my vintage vehicles in the course of a year. And make no mistake, I am hard on my motors. Is one option better then any other, I don’t know, but like I said lots of opinions.

Roll your sleeves up and dig in. That 302 motor is one really great motor and truth be told, it responds to all manner of hot rodding. You still see some of them being run at Bonneville. If you don’t want a stock 302 motor, then don’t build one. Build what you want. Register for the inliners international bulletin board and ask your questions. There a still quite a few very knowledgeable 302 guys there if you need or want a second opinion.