View Full Version : The old V-12

July 7th, 2014, 04:49 AM
Well it's finally time to get started on the ole V 12 ser. # 1292. I think it was probably around the early '70,s when I spotted this monster in my favorite junk yard. I didn't know much but I new I had to to have it. I have always loved machines and engines from a very early age. It was in a wrecked simi tractor at the yard so I got started getting her free to take it home.
The story was that the truck had run into the engine of a train at a remote country location. The driver was killed and some how the engineer was also killed when the rock that truck was hauling went shooting thru the air from the impact and into the cab of the locomotive. Somewhere I have a copy of the newspaper article which I will post when I find it.
So, home it went and the disassembly began. All the usual mouse nests and standing water where there (it was sitting uncovered and a carb was broken off). Got most of the pistons free except three that are still in there. The walls of the bores even with standing water seemed to still be OK (that good metal they used) and the crank looked perfect.
After some research, I don't know how I did that back then without the internet, I found that the many of the 351 parts would be the same and it looked like I would have to break those up to get them out because they would have to come out the top, so there was a school bus in the yard with a 351 so I grabbed it too. If I remember right I ran that 351 when I got it home.
Well that was then and it got set aside (35 years) for a time because of an uncontrollable problem with collecting and restoring Minneapolis Moline tractors. Well I sold the farm and I'm selling the tractors so guess what I found. So I got the 351 down off the rack to start taking it apart and found, Thanks to this great site, that is a 351M. So I said I can't tear a perfectly good Magnum apart and it just so happened there was a 351 on Craigslist St. Louis for sale (some of you saw it I'm sure) so I got that one and started taking it apart. So far it looks pretty good.

July 7th, 2014, 05:01 PM
Welcome Blackie9!

Great story on your V12. Kudos for saving other V6's. How about a pic of the V12 too?

July 7th, 2014, 11:14 PM
So tell me how do you get those pistons out with that rod in the way? And another question I have been wondering about is these numbered pistons and bores. Does this mean that the pistons are not generally interchangeable?:headscratch:

July 7th, 2014, 11:33 PM
The person you wanna talk to is CoyoteRun. He's got a V12 he put in a 50's model truck and stretched the front out to take it. Pretty cool! He knows alot about these V12s.

For the 351, post a question in the engines forum and someone with more brains than me will be able to answer you. I'm pretty sure you ahve to unbolt the bottom part of them to get them out though, you cant just pull em out the top. Kinda like a tooth where you unbolt the roots. :)

July 11th, 2014, 04:35 AM
Well this is embarrasing, I took the other head off tonight of the "parts" engine and to my surprise it was pretty clean in there too. When I picked it up it was sitting out in the weather, exposed to the elements I thought mabey there would be three or four good pistons. The rest would have grown in and become part of the block, never even thought of trying to turn it over. So after seeing the way it looked inside I put a wrench on the crank and you guessed it, it turned right over.

July 12th, 2014, 05:21 AM
So I got this engine apart and I'm looking it over and I see the block and the pistons have numbers stamped on them. 2 are marked 5 and 4 are marked 4. :headscratch:Can someone tell me what this is all about.

July 12th, 2014, 04:08 PM
The pistons are different sizes. Usually in .001 increments . Lots of engines are this way. If you look on the oil pan rail the block is usually stamped With the same # at that cylinder. Barry

July 12th, 2014, 04:15 PM
Sorry to repeat the block stamping. A good old school engine rebuilder should have a piston expander. And be able to get a piston to fit your cylinders. Or measure got replacement ones and put the biggest ones in the biggest holes

July 13th, 2014, 03:04 PM
So would I be assuming to much to think that a piston marked with lets say a number 4 in a 351 engine would be the same as a number 4 in the 702 would be the same size?

July 13th, 2014, 03:54 PM
Probably is the same.

July 16th, 2014, 03:54 PM
Barry, found this chart in an old GMC maintenance manual. Should give me some help of at least getting close to the right size. I guess a guy could get a hole bored for a bigger one if thats all he had.

July 16th, 2014, 04:02 PM
On the other hand I guess that's only 38 ten thousands between the smallest and the largest anyway on an well used engine.:ohgeesh:

August 18th, 2014, 03:00 AM
Well starting to get the parts gathered up. heres the block with 3 pistons still stuck. In the last 25 years while it has been setting they have not fallen out:headscratch:

August 18th, 2014, 03:16 AM
I have pulled the pistons from the 351 motor that I got for that purpose so I have a block, cam and crank that looks fine if anybody needs them.

August 27th, 2014, 04:15 AM
I have pulled the pistons from the 351 motor that I got for that purpose so I have a block, cam and crank that looks fine if anybody needs them.

Found Ya', Blackie:

Enjoyed the visit tonight. One thing I forgot to mention. Be sure to remove the head gaskets as careful as possible and save them. I haven't been able to find any new ones, so have reused the old ones by using lots of gasket sealer after cleaning them real good.

I'll try to keep up with your progress, here. Looks like the biggest challenge right now is getting those last three pistons loose and out of the 12.

The matching replacement pistons you have are like pure gold if you need them.


September 1st, 2014, 04:49 AM
Coyote run and or blackie are those head gaskets on the v12 the thin copper ones?. Just curious. I save and reuse the 305 ones because the are about .025 thinner and with a .035 taken off the head add about one point to the compression ratio. Barry

September 2nd, 2014, 01:27 AM
I believe mine were the ones with an asbestos layer between two thin metal top and bottom. But I like that idea to increase compression.

September 2nd, 2014, 02:05 AM
The old 305 a .and some of the truck c engines use a thin copper head gasket like old flat head fords. They are about .010 thick. They are bigger than the 351 bore. Just curious if they used them on the v12. Barry

September 4th, 2014, 03:42 AM
So you're saying that gasket would work on maybe a 379 too?