Engine swap on 65 GMC 2500 305 V6
 

We have a customer truck here that has a 305E engine. It has two dead cylinders with piston and cylinder wall damage. I purchased an engine from a wrecking yard that was listed as a 305. When it arrived, I checked the numbers on the right side of the block and it is a 351. I realize that the timing cover, possibly the oil pan and intake may have to be swapped. It appears those gaskets are the same on both engines. Is there anything else on this swap that will cause a problem? Will the flywheel, clutch etc all bolt on?

Thanks

Re: Engine swap on 65 GMC 2500 305 V6
 

Pursellauto:
Which 351 is it? Could be a 351c or 351e. In either case, flywheel and clutch will be okay. Reason I ask is that 351c is small port engine vs 351e is a large port magnum engine. 351c can use 305 manifolds. 351e manifolds are different.

Hope that helps.
Regards
Steve
New Orleans

Re: Engine swap on 65 GMC 2500 305 V6
 

The stamping numbers on the right front of the block say 351 only, no letter after that. The used engine came with intake and exhaust manifolds attached. The carb on the 351 appears to have a governor mounted under the carb. I am making another assumption that we can use that carb minus the governor to fuel the 351.

Re: Engine swap on 65 GMC 2500 305 V6
 

Couple of pictures of the motor would help. Magnum has trapezoid carburetor base, for instance. Non magnum carburetor base is symmetrical.
Regards
Steve

Re: Engine swap on 65 GMC 2500 305 V6
 

Both carbs have the same base, 4 studs from manifold in rectangular shape. We are thinking about using shorter studs from 305 to the 351 and bolting the 351 carb directly to manifold eliminating the governor.

I am trying to upload .jpg photos from my computer but getting a message that PNG file has the incorrect file extension.

Re: Engine swap on 65 GMC 2500 305 V6
 

Attached are the two carb bases for magnum and non magnum. The magnum trapezoid base is marked 60053 in the picture. If you have the manifolds for the 351, then the carburetor might be the only thing that wouldn't swap from 305 to your 351 without an adapter plate.

Hope that helps.
Regards
Steve
New Orleans.

Re: Engine swap on 65 GMC 2500 305 V6
 

Both carbs have the pattern of the gasket on the right side as looking at the picture.

Re: Engine swap on 65 GMC 2500 305 V6
 

You are in luck. Everything other than pistons and crank should interchange. Your 351 should be the small port version, typically a 351c.
Regards
Steve
New Orleans

Re: Engine swap on 65 GMC 2500 305 V6
 

Thank you, Steve for your assistance.

Re: Engine swap on 65 GMC 2500 305 V6
 

Pursellauto:
You are welcome. Post some pics when you get it running.
Regards
Steve
New Orleans

Re: Engine swap on 65 GMC 2500 305 V6
 

A new question about this engine swap. The clutch pivot stud that screws into the bellhousing is broken off. Any ideas on where one of these could be located?

Re: Engine swap on 65 GMC 2500 305 V6
 

Pursellauto:
There are two sizes to bell housing depending on size of truck. What size truck is it?

S few are listed on eBay, but shipping is a bit expensive. Here is one for $40 , but shipping is from Iowa, for instance.

https://www.ebay.com/itm/163995471417

Craigslist has a motor with bellhousing for $200, but it is in Colorado springs.

Bolt pattern for the engine is unique for these motors. Parts are out there, but a bit of scrounging is typically required.

Hope that helps.
Regards
Steve
New Orleans

Re: Engine swap on 65 GMC 2500 305 V6
 

This is what I am referring to.

https://www.ebay.com/i/352164203098?...xoCVn4QAvD_BwE

Re: Engine swap on 65 GMC 2500 305 V6
 

Pursellauto:
Sorry, I thought you needed the bellhousing. I don't think there is anything unique about the pivot. Seems like one from a Ch*vy would work...
Regards
Steve
New Orleans

Re: Engine swap on 65 GMC 2500 305 V6
 

I found a few choices for those, I just need to get the broken stud out to see what size it is.

Re: Engine swap on 65 GMC 2500 305 V6
 

Pursellauto:
Sorry, bug I don't know that answer.
Regards
Steve
New Orleans

Re: Engine swap on 65 GMC 2500 305 V6
 

I figured out why I could not upload pictures. Here are a few. The different carbs on the 305 and 351 and the engine that we pulled along with the one we purchased for replacement.

Re: Engine swap on 65 GMC 2500 305 V6
 

Pursellauto:
Thanks for the pictures. 351 does look like a "c" model. I would swap timing chain cover, carburetor to eliminate governor and thermostat housing. Should all bolt up on the swap. Double crank pulley on 351 I'd coveted by folks looking to add power steering.

Regards
Steve
New Orleans

Re: Engine swap on 65 GMC 2500 305 V6
 

Our thought is to also swap intake from 305 to the 351 as long as the port sizes match. and use the 351 carb on that intake minus the governor. The other idea I thought about is if possible, swapping the jets from the 351 carb to the 305 carb if the carbs match in order to get the fuel flow for the larger engine.

Re: Engine swap on 65 GMC 2500 305 V6
 

Pursellauto:
From what I can see, I think think you will find the intakes are identical. Carbs should be similar, if you want to swap jets. I am unsure if you will find much difference between the two, however.
Regards
Steve
New Orleans

Re: Engine swap on 65 GMC 2500 305 V6
 

this outfit lists pivot studs, they may have that will work.

https://pitstopusa.com/c-132367-driv...all-studs.html

Re: Engine swap on 65 GMC 2500 305 V6
 

Thank you for the link. I was actually able to come up with a GM part number that fits a whole slew of years and models. 3866568. Found a dealer in Macomb Illinois that had it and should arrive today.

Re: Engine swap on 65 GMC 2500 305 V6
 

Got the clutch pivot stud from GM. We got the broken threaded portion out of the bellhousing and this fit perfectly.

Re: Engine swap on 65 GMC 2500 305 V6
 

Here is a major difference in the block of the 305 and the 351. The 305 has a stud in the block on the right side near the timing cover that the motor mount bracket fastens to. The 351 has a pipe thread fitting in a hole in the same location.

Re: Engine swap on 65 GMC 2500 305 V6
 

As you probably know the 351C is a medium/heavy truck engine and was not used in pickups. I believe the pipe thread hole in the block was for a hose nipple for the oil return line from the air brake compressor. Large trucks had different front motor mounts than pickups too, so there was no interference with the oil return line. If the pipe thread hole is on the same center as the 305 engine mount hole, maybe you could drill and tap a pipe plug for the engine mount bolt if it's large enough or weld a stud on a pipe plug and use a nut to hold the engine mount.

Re: Engine swap on 65 GMC 2500 305 V6
 

I’ve done this exact swap over in my 67 pickup, I don’t exactly remember what I did, but after looking at it just now and the other two engines I have in my shop (original 305 and truck 351c) - I have a plug, a stud and a bolt so must have just swapped over?! Of course, swapped oil pan, oil pump, oil filter housing, and clutch, since they were larger as well as swapping the timing cover housing to get the fan in correct location - just put all the pickup parts back on the truck engine. As for the carb, I swapped over to the Holley and luckily I had the power steering, so that and the motor mounts all swapped over fine. Can’t think of much else. Good luck

Re: Engine swap on 65 GMC 2500 305 V6
 

Pursellauto:
I recall using a flush 1/2" brass plug that I got from a hardware store. The motor mount bracket then went over the flush plug. Doesn't look like I had any problem with the stud lining up, however. See attached. My engine is a 351e with magnum heads.
Regards Steve
New Orleans

Re: Engine swap on 65 GMC 2500 305 V6
 

In a situation like this when installing a bigger truck V6 into a pickup truck I'll drill a hole in the plug, tap it and install a threaded stud..

Re: Engine swap on 65 GMC 2500 305 V6
 

The 305C will also have a threaded plug, it's not so much the difference between displacement size but what application the engine is for, I have a 351E with the stud on the side of the block.

Re: Engine swap on 65 GMC 2500 305 V6
 

Pursellauto, this is Lewis Matkin. Both carbs are WW Stromburg carberators. All you have to do is to remove the Hoof Goveneror and the long studs, replacing them with the shorter studs of the 305. The main differences between the 305 and 351 carberators is the main jets and the power valve. the 305 has 0.55" main jets, and the power valve is either .62" or .65". The 351 is larger jets & power valve. Just use the 351 carberator.

Re: Engine swap on 65 GMC 2500 305 V6
 

My 351E has a stud in that location. I don't remember removing it when I rebuilt the engine, so I couldn't say what threads were on it. Might one of those oddballs with pipe thread on one end and SAE on the other.