55.2-59 59 GMC 270-336 swap.

[72 k15]

I am debating on swapping in a 336 GMC v8 into my 270 truck, the 270 blew up and spun all rod bearings and I am having trouble finding parts I was thinking it might be easier to just find a running 336 and swap it in? Has anyone done this and what would need to be changed over? Truck currently has a 3 on the tree and a 235 chevy in it.

[mr48chev]

Unless you are absolutely bent on keeping the truck all "GMC" why would you waste time and money sticking an old Pontiac engine in the truck?

Your money your call but I would put a later small block Chevy in it and be done with it.

Any 336 engine that isn't documented as a fresh engine with low miles has to be considered to only be a core engine that needs a total and rather expensive rebuild. Plus you have to deal with how you are going to bolt it to the transmission. Meaning that you need a different flywheel and bellhousing. It's isn't just a case of "I'm going to buy this used engine and stick it in and go" 99% of the time when dealing with a 60 year old engine.

I'd have to say what is more important, being able to drive and enjoy the truck or being able to open the hood and show folks at a show that it has a GMC /Pontiac V8 in it.

[_Ogre]

if a gmc swap is anything like a chevy swap, the only thing you get to keep is the trans. motor, mounts, flywheel and clutch and bell housing all get changed. i sort of agree with mr48 on this, unless you wear that gmc badge proudly

[daveshilling]

Originally Posted by mr48chev

why would you waste time and money sticking an old Pontiac engine in the truck?

Coming from a guy who chopped his truck, which adds only time and money and zero functional benefit whatsoever, I'd think you would wholeheartedly support going the extra mile to do something you think is cool!

To throw my 2c in, the Pontiac 336 is the same exterior size as a Pontiac 389 or a Pontiac 400. Only an eagle-eyed observer will know the difference, they otherwise look identical.

If you're going to keep it Poncho, which is COOL, then I vote you skip the 336 and find a 389 or 400 to build there instead. More torque, and more likely you'll find one in good shape as the 336 is a rare engine.

If you go chevy instead, maybe carburete an LS? They are durable engines, and carburetion lets you skip the PCM, the high pressure fuel line, etc.

[daveshilling]

Originally Posted by _Ogre

if a gmc swap is anything like a chevy swap, the only thing you get to keep is the trans. motor, mounts, flywheel and clutch and bell housing all get changed. i sort of agree with mr48 on this, unless you wear that gmc badge proudly

GMC's are awesome. Sometimes it stings a bit more to look cooler than the common Chevy, but you do what you gotta do.

[geezer#99]

Swap in a 396 or 427 and claim it came out of a Canadian Pontiac!

[mr48chev]

[QUOTE=daveshilling;8995707]Coming from a guy who chopped his truck, which adds only time and money and zero functional benefit whatsoever, I'd think you would wholeheartedly support going the extra mile to do something you think is cool!

To throw my 2c in, the Pontiac 336 is the same exterior size as a Pontiac 389 or a Pontiac 400. Only an eagle-eyed observer will know the difference, they otherwise look identical.

If you're going to keep it Poncho, which is COOL, then I vote you skip the 336 and find a 389 or 400 to build there instead. More torque, and more likely you'll find one in good shape as the 336 is a rare engine.

If you go chevy instead, maybe carburete an LS? They are durable engines, and carburetion lets you skip the PCM, the high pressure fuel line, etc.[/QUOTE


My chopped truck has been driven 300 thousand miles serving as my daily driver and a couple times as the family vehicle. The chop has nothing to do with it's mechanical systems. Simply meaning that over the past100 and something K with the 250 in it I could walk into any Autozone or O'Reilly's in the country and buy any engine related part over the counter then and there and buy any critical electric part then and there.

The hardest to get part on the truck are the stock AD truck front wheel bearings and the only mechanical parts on the truck that I have ever had to wait extra days for the parts house to get.

I even built a new driveshaft to get away from the expensive and hard at times to find combination U joint at the pinion end of the drive shaft.

The truck got driven on a 4000+ mile road trip when it was pretty well worn out engine wise. From Grandview Wa to Bonneville for speed week, then to Pleasanton for good guys and back up 5 and 97 Home. The only problems the whole time were a bad battery that got replaced in La Grande Oregon a 7:30 in the morning at the Les Schwab and a broken wire to the connector to the alternator in Wendover that caused me to have to carry the battery across town on the shuttle bus to have it charged after I figured out the broken wire. Oh there was the bent tie rod in California from hitting a huge pot hole in the toll road south of Oakland.

All stock GMC show trucks that never get driven anywhere are fine, most of the time they probably get trailered rather than driven.
I don't know what 72 K15's budget for rebuilding his truck is but doubt he plans to spend 4K rebuilding a stock 336 engine and is thinking he will find a runner for three or four hundred and stick it in and go. Unless he buys a running driving donor truck with everything on it, some parts are going to be hard to find and seriously expensive.

There is no GMC 336 V8 stick bellhousing on Ebay to even get a price from. Then you have to find the 336 flywheel if it didn't come with the engine.

Don't get me wrong, I usually take at least one photo of all stock GM trucks at shows but seldom spend any real time looking at them because they are boring and all the same. At times the only reason I stop to take a photo of one is to post it here unless the workmanship is outstanding and the attention to detail is top notch. Unless you are at a national Chevy truck show where there is a points judging system the quality of "totally restored" trucks usually is no where near the quality of work on custom trucks.

Now why do "restorers" always think they have to bad mouth guys who modify their trucks? I've put up with that nonsense ever since 1973 when I first drove my 48 to the Street Rod Nationals in Tulsa, I have seldom had a hotrodder or custom car guy say anything bad about it but restorers seem to want to badmouth anything that they see that is modified. The OH you ruined it by chopping it, Oh you ruined it because you took the original engine out, Oh you ruined it by lowering it. Then the nonsense of "oh it would have been worth more money if you had kept it all original. We all know that is total nonsense on anything except maybe a few Corvettes and tri-5 Chevy Nomads and Convertibles.

[dsraven]

here's my 2 cents.
daily driver, long haul driver, driven by/with wife or family or often driven truck-swap in an injected LS engine with the proper exhaust system (catalytic converter). they start easy, don't get finicky when it's cold, don't stink up the atmosphere around the truck no choke to pull or need to pump the gas, smooth power and easily upgraded for more power without having to spend a lot of money and time to do so. others will find the truck more interesting because they don't feel they need a shower and launder the clothes after standing close. I know, we are truck guys and that may not bother us. others-not so much. even older folks that have driven fuel injection for the last 20 years have basically forgotten how to start a carbed engine.

driven only periodically to the car shows or the good guys coffee shop outings-try to go with something that is original or at least looks more period correct. personally I would stay away from the big blocks simply due to fuel costs and everyone's mindset on ecological viewpoints and global warming these days. it will be a hard sell when the time comes.

small block chevy is common, easy to find parts and upgrades for etc but look anywhere and you will find the LS engines are the new small block. if you decide to change to something that isn't stock then why not go with a modern power plant. like said on other threads, why go with upgrading/replacing something that is obsolete to something that is new to you but already "old" in the big scheme of things. check out the car shows and what guys are doing on the tv car programs. mostly LS engines. guys are taking small blocks out and replacing them with LS engines. soon they will be taking the LS out and installing an electric power plant.
ok, that was 5 cents. haha

[_Ogre]

oh crimeny, guy, play nice

[dsraven]

I'm (and I'm sure others are) just trying to give options and make sense of getting the truck driveable. the old engine and driveline(?) can be removed carefully using wrenches instead of cutting it out somehow, then oiled up and stored for a future buyer if wanted. meanwhile a new modern powerplant will make the old truck more desirable to drive, it will keep up with traffic on the freeway and parts are easy to source on a weekend in small towns. if done correctly with this in mind the old could be removed and a stock system placed back inside where it was originally. I'm not saying chop it and cut it I'm saying repower it but do it wisely and save money for something else. there are even bolt in IFS available if wanted that could be removed later and swapped out with the original stuff that was palletized when removed. it depends on what the intended use for the truck is and what the budget will be. no use trying to rebuild something that you can't get parts for. a modern donor truck wreck with the engine and trans wanted may be the way to go.

K15, thoughts? intentions? dreams? knowledge/skill level? tool and shop space availability? pics? anything else needed on the truck? wanna keep all stock and matching?
lets not get all bent outta shape with each other just because we don't have the same views. lets see what the original poster has in mind and give ideas when he comes up with a plan/budget
ok, now I'm up to a dime's worth.

[mr48chev]

You can bolt a SBC into that truck without doing any cutting or hacking. That was my reason for suggesting it over a quite expensive task of putting in a "stock 336" Meaning that later the SBC could be replaced just as a 235 can be replaced with what ever engine 71 K15 feels appropriate at the time. Painted the correct GMC engine color for the year 99.999 % of the people who look under the hood won't know the difference anyhow but the truck will be drivable and enjoyable/

The other way is to just drive it with the 235 and collect parts to put a 336 in it and have everything there and ready to do a swap in short order with little down time.

[1project2many]

If you get "everything" then it's probably a good deal. Plan to spend a bit if you're going to refresh the engine. I'd look at GMC school buses through mid '60s as some used Pontiac engines (Some used Olds engines, also). Do you have manual transmission? Old buses were usually spec'ed with manual transmissions although a large truck trans will usually have a different bellhousing than a light duty pickup.

How about a GMC V6 from a later truck? That's an "all GMC" engine and there are plenty of folks still building them so you might be able to find parts. There must be an old grain truck around with a 351 or 379 or even a 60's light duty truck with a 305?

Factory built V8 truck generally differ from 6 cylinder trucks in throttle linkage, fuel lines, exhaust, front and rear engine mounts, possible front crossmember modification or bracket change, radiator size, fittings, and location, bell housing change, wiring changes, starter rod elimination or change. If you're going to go with V8 I'd say spend a bunch of time locating original pictures and service manual pages to ID differences before jumping in.

[dsraven]

the assembly manual should show you how the small block was installed and what linkage looks like etc.
https://www.trifive.com/d1/55-59Assy.pdf
you will need a new bellhousing, flywheel, clutch etc to fit the small block but the bellhousing will sit on the cross member like the old one and likely could use the same mounts there if the old rubber is still good. find a 55-59 v8 truck or 55-57 car bellhousing.
you will need a starter that bolts to the bellhousing from same era v8 and then you will need to install a starter button to replace the "step on the starter" pedal, if thats what you had before
depending on what year of engine you buy, you may need to drill and thread the front motor mount holes in the block. some had them and some didn't
the front engine mount may interfere with the fuel pump spigot but if you get the right pump the spigot can be indexed to a different angle so it fits fine. if you have power steering the motor mounts may interfere with the pump mount
you will need some ram horn exhaust manifolds and then some simple exhaust hookups
if you decide to go with a more modern rear transmission mount instead of the crossmember behind the engine, but want to use the stock front mount engine mounts then think about bracing the engine somehow with a torque limiting device (chain usually) so the engine torque doesn't allow the engine to twist up and bind linkages etc.
if you do a search on this site you will likely find a thread on the small block swap and what parts you need

engine mounts
https://www.classicindustries.com/pr...ts/556038.html

trans mount rubbers
https://www.classicindustries.com/pr...rts/14501.html

exhaust manifolds
https://www.classicindustries.com/pr.../a7700104.html

[1project2many]

I think USA built GMC frame is not Chevrolet frame. GMC engine has single mount in front, two in back. Chevy has two mounts up front. GMC crossmember is different as well. GMC core support bolts to crossmember while Chevrolet core support bolts to frame rails. Pictures:

http://67-72chevytrucks.com/vboard/s...5&postcount=10

SBC does not "bolt in."

[daveshilling]

Originally Posted by mr48chev

My chopped truck has been driven 300 thousand miles serving as my daily driver and a couple times as the family vehicle. The chop has nothing to do with it's mechanical systems. Simply meaning that over the past100 and something K with the 250 in it I could walk into any Autozone or O'Reilly's in the country and buy any engine related part over the counter then and there and buy any critical electric part then and there.

I just don't want our truck brothers feeling like they're foolish for wanting what they want, just because its not what WE would do. People like what they like.

[72 k15]

Thanks for all the responses everyone! The truck is more of a weekend driver when it’s not 100*f outside or 30*f I already have a good daily with a LS. The main reason I want to keep the truck GMC is it just seems like everyone puts a 350 in it and calls it a day and I feel you loose some of the “GMC” aspect when you do that. Side note, I live in North Dakota, the amount of old 58-59 GMC grain trucks sitting in fields is astounding I’m thinking I could get a running 336 out of one of those or might even be able to find a 270 or 302.

[mr48chev]

As I said earlier, your money and your call. Plus it has to be what you want and not what many of us see as more practical or less expensive in the long run.

I'd say that the majority of those old grain trucks that are sitting are sitting because those engines gave out and the owners don't see them as being worth rebuilding that engine and don't get shocked if a large percentage of them already have small block or big block Chevys in them when you open the hoods. There may be a number of them that got retired when they got away from using bobtail trucks to haul grain though. It used to be all 2-1/2 ton trucks hauling wheat to the silos or hauling corn to the local Del Monte Cannery here in town but now it is almost all done with semi tractors and 40 ft beds often as not with belt trailers. Even the silage hauling is almost all done with truck and trailers now rather than the trucks with sileage beds on the back.

[1project2many]

Originally Posted by 72 k15

Thanks for all the responses everyone! The truck is more of a weekend driver when it’s not 100*f outside or 30*f I already have a good daily with a LS. The main reason I want to keep the truck GMC is it just seems like everyone puts a 350 in it and calls it a day and I feel you loose some of the “GMC” aspect when you do that. Side note, I live in North Dakota, the amount of old 58-59 GMC grain trucks sitting in fields is astounding I’m thinking I could get a running 336 out of one of those or might even be able to find a 270 or 302.

You could even "upgrade" to a 60 degree V6. A 305 or 351 would twist the tires right off that outfit.

[72 k15]

Originally Posted by 1project2many

You could even "upgrade" to a 60 degree V6. A 305 or 351 would twist the tires right off that outfit.

I know our farm has a grain truck that is sitting with a running GMC v6 so that is a option.

[_Ogre]

Originally Posted by 72 k15

I live in North Dakota, the amount of old 58-59 GMC grain trucks sitting in fields is astounding I’m thinking I could get a running 336 out of one of those or might even be able to find a 270 or 302.

i'm more than a little jelly of this. i doubt there's any old trucks left in fields anywhere in se michigan

Originally Posted by 1project2many

You could even "upgrade" to a 60 degree V6. A 305 or 351 would twist the tires right off that outfit.

i don't know a lot about gmc v6 motors, so i googled it. wikipedia taught me this:

The 477.7-cubic-inch (7.8 L) 478 was one of the largest V6 engines ever built. Gross output was 254 hp (189 kW) at 3700 rpm and 442 lb⋅ft (599 N⋅m) at 1400 rpm. Bore and stroke was 5.125 in × 3.86 in (130.2 mm × 98.0 mm). It was introduced in 1962 for the 6500 series trucks.

great googly moogly 478ci, 254hp w/442ftlb of torque in a v6
that's stump pulling torque plus, my ramjet 350 only has 400ftlb of torque

start looking for the 702 v-twin if you want a unique gmc setup

[dsraven]

Holy doodle, can you imagine if mick53 got ahold of one of those? A blower, polished trinkets everywhere and a wheel standing grain truck, lol

[1project2many]

great googly moogly 478ci, 254hp w/442ftlb of torque in a v6
that's stump pulling torque plus, my ramjet 350 only has 400ftlb of torque

Grampa had a 478 in one of his egg delivery truck years ago. No matter how heavy the truck was loaded it would still do 65. On flats, on hills, even on vertical surfaces. My dad swore that it actually collapsed one of the fuel tanks it used fuel so fast. '70s gas crisis sent it to the crusher on the back of a tow truck.

Holy doodle, can you imagine if mick53 got ahold of one of those? A blower, polished trinkets everywhere and a wheel standing grain truck, lol

That would be awesome. Those engines just don't get enough love.

I once met a gent outside Cody, WY who was building a V6 Jimmie for performance. He was using modified Buick 455 pistons and a set of cylinder heads that stopped being "stock" a thousand hours ago with a homemade sheet metal tunnel ram intake. In the days before internet this guy was a bona-fide V6 guru. I'd pulled into the driveway on a whim and asked to look at some of the old trucks there, ended up spending a few hours listening to stories and tech articles. Yes, he had a 702 locked away in a shed, which he let me see, and another with the heads and intakes removed for 'spearmentation. Yes, he was going to surprise all them young-uns with their 350's and 454's. Way cool.

[_Ogre]

way cool! hard to believe a motor with 5.125" pistons would rev over 1000 rpm, much less 3700 rpm

[72 k15]

Update: I have tracked down a 336 GMC that’s runs good with everything needed to swap over and tranny for $2000. Turns out my 270 block might not be Savable but I also tracked down another 270 block pistons and crank for 1000$ I can’t make a decision keeping the 270 would make the truck original but loose some driveability while putting the 336 with and being able to swap in a nv4500 later easier, would give me a lot more driveability while still being “correct” for a 59 GMC. What do you guys think between the two? I believe in the long run the 336 would be easier to find parts for as it’s a debored 389 Pontiac. I plan on driving the truck 2-3 times a week in the summer and the occasional road drip for fun thats a day adventure at about 60 MPH.

[1project2many]

I don't think you'll lose points with truck guys no matter what route you go. One thing I do know from experience is that people tend to ask "If you're going through the work to swap an engine, why wouldn't you use the biggest engine that fits?" So switching to a 336 is likely to earn criticism for that. But if you don't care than it won't matter.

I can tell you my truck does plenty OK with original brakes and steering and the "little" 302 Chevy I've put in it. I would not be interested in going to a smaller engine unless it produced similar power and torque numbers.

I think the issues for me would be more financial and how long will it take to get the truck running? It seems like a bunch to pay for an engine and trans that may require more $$ and work. Is it manual transmission or auto? Will you be comfortable using this transmission without a rebuild or at least a re-seal? Will you be comfortable using the engine without going through it? What is the plan if you take it apart and it needs unobtanium parts? Just putting it out there...