Finding a V6

[Hantke]

On the west coast (Oregon / Washington), how hard is it to find a good running 351 or a 305 V6? And which is easier to find all the parts for a rebuild for? I haven't spent a lot of time until just recently looking into the 351.

Thank you!


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[bigblockv6]

The 351C V6 seems to be the most common out here in the west coast, I know Ed Snyder has come across quite a few in the past and he's in the southern end of Oregon. The 351C has smaller port heads compared to the 351E & M engines but it's still a significant upgrade over a 305 V6.

[bigblockv6]

The 351C V6 seems to be the most common out here in the west coast, I know Ed Snyder has come across quite a few in the past and he's in the southern end of Oregon. The 351C has smaller port heads compared to the 351E & M engines but it's still a significant upgrade over a 305 V6.

As far as parts everything's basically the same between the 305 and 351C other than pistons, head gaskets and different intake and exhaust valve sizes. lately NOS oversize pistons for the 351 have been showing up on ebay.

[Hantke]

Awesome, thanks! I know the M is more sought after, and would like to drop a 351 E into a '63. It's not a done deal on the truck yet, but I wanted to see what would be a good option for me.
My understanding is that both the 305 and 351 have identical mounting bolts and same assembly for the transmission. Is the wiring harness the same? I might be looking at jumping in over my head, but we will see


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[bigblockv6]

There is no wire harness on an engine assembly, generally you will have wires that hook up to the distributor, starter motor and sending units.

[Hantke]

I was thinking about it over complicated I think, that's like what, five things? Distributor, starter, at tachometer, heat, oil pressure, does the odometer in these trucks hook up to the engine?
I haven't spent much time on any older electronics, more so with the newer stuff unfortunately


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[bigblockv6]

There's not much to it as there are no electronics on 50 year old vehicles. If you're running a Tachometer it would have to be hooked up to the coil, all the wiring to the starter motor, distributor & coil, oil sending and water temp unit will all interchange from 305 to 351. That's really all there is for wiring.

[Hantke]

That's cool, the truck has an inline 6 now so I will figure that part out as the time comes, thanks for the info!


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[bigblockv6]

That's cool, the truck has an inline 6 now so I will figure that part out as the time comes, thanks for the info!


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Since the truck is an inline six it will involve shortening some wires and lengthening others.

[George Bongert]

Greetings Hantke!

Its been awhile since I've posted anything here, Guess I haven't found anything to reply to that hasn't been covered one way or another. Regarding your swap from an inline 6 to the V-6 will also require that you change the frame mounts (pedestals) for the engine since they are different from inline 6 to V-6. You will probably have to scrounge a bone yard to find those (if there are any old GMC's still floating around in a bone yard), or if someone in the club has a parts truck sitting around, and you will also need to use the bell housing from the V-6, since it also is different from the inline 6 bell housing. I know about all of this because I did the same kind of engine swap on a 1963 Chevy truck back in 1984.

[Hantke]

Okay, i had thought about having my friend fabricate some, he works on a CNC mill and is allowed to use it on his breaks and after work. Other than the bell housing, the rest should just boot right up, shouldn't it?


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[bigblockv6]

Looks like everything's been mentioned for the conversion except the flywheel, you'll need a flywheel from a 305 or 351 that's from a light or medium duty application, I'll post the correct part number a little later.

[bigblockv6]

Here's the part number for the 305E and 351E flywheel:2369959.

[Hantke]

Is that a universal part number that I could take to like NAPA or somewhere?


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[bigblockv6]

Not at all, this is a GMC part number. The purpose for posting the number is so when you come across a flywheel you'll know if it's the right one. Without a doubt this flywheel was discontinued around 20 years ago so you just can't go to a dealer or parts store and expect to buy a new one.

[Hantke]

Okay, thanks! I'm sure I can find one somewhere, I almost wonder if it would be something I could snag off of a diesel forklift or something. I remember someone mentioning the valves off of a CAT diesel. Thank you again for the help!


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[bigblockv6]

The way everything is setup with spacing, mounting, bellhousing clearance and clutch assembly the flywheel can only be specific for the GMC V6 light and medium duty applications. Yes possibly a Hyster Forklift equipped with a 305 or 351 V6 may have a correct flywheel. I had a custom flywheel built for my 478 to fit the light duty bellhousing and you would be surprised all the little details that had to be correct in order to make it fit. The flywheel manufacturer didn't machine a relief area on the flywheel to clear the four inner mounting holes from the front of the bellhousing to the engine block, luckily I was able to grind down half the surface face of each bolt to get clearance. As far as the Caterpillar valves go those are an alternative to replace the large hollow stem sodium filled exhaust valves used on Magnum engines. The stock valves can easily snap from over revving and that's why governors where installed in big truck applications. At one time I had a list of Cat valve part numbers but they're gone.

[Donny]

You know what Engine those valves came out of that you used big block
To narrow it down maybe a tractor engine or a truck engine
I'm getting ready to take my motor to the rebuilder first I got to change some flywheels be around , you were right the three bolt starter has a bigger gear
So I have to see if one of the flywheels gears off my 401 Will fit

[bigblockv6]

I can't say for sure but for starters the Cat 3306, 3406 or 3116 may be the engines that have the correct valves, I do remember one had the correct intake valves and another had the exhaust valves. The exhaust valve stems will have a much smaller diameter so new guides will have to be installed in the Magnum heads.

[Hantke]

I know the 3406B has a fairly different valve setup than a lot of other diesels as I've rebuilt a few. I haven't had the opportunity to tear into a 305 or a 351 myself yet. I've been thinking I might be better off getting a cheaper Chevy and modifying it for now until I can afford the gmc with the big block that I actually want. Plus I won't feel bad swapping a turbo diesel into a Chevy.


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