So....You want to rebuild a GMC 702 engine.

First off, congratulations on the rare find!

Now for the reality check.

A vast majority of these engines that are "found" have set outside and have  bores that are ruined from rust.

The distributors were usually yanked to use in another engine and rain has ruined the exposed cam. The distributor has 4 gears in it that are not available.

Or worse yet, water was left in the engine and it froze causing the block to bust. Many of the stationary engines were used seasonally and were drained at the end of the season. In 50 years it only takes one time to forget to drain the water and that guy has a 702 he wants to sell you cheap. Another failure mode from freezing is a small crack in the head that allows water to enter the cylinder while sitting. the next time the engine is started the piston hits the water (which is not compressible) and bends the rods and cracks the main bearing webs. From all outward appearances, this engine could be unscrupulously sold as a good engine.

The list of parts no longer made for this engine are staggering. When trying to get parts, there were 2 different blocks made and some parts don't interchange between the two.

Was your engine missing any parts? Did it come with the waterpump, flywheel, starter, distributor or manifolds? I hope so as these parts are no longer available. Rod and main bearings have been discontinued by all three companies.

Are the bores good? Are the pistons and skirts good? Are they within weight tolerance?  Hope so. Oversize pistons haven't been made for over 25 years. Are all the lifters good? Yup, no longer made. Valves? Cam bearings? You got it. No longer made. And as for the distributor.....don't ask.

ThunderV12, LLC has jumped these hurdles to bring these engines to market. 

Here is the formula to build your own V12.

Buy three core engines at $4,000-$10,000 ea. (per ebay listings).

Tear all three down and pick the best block crank and heads.

Perform $5,000 machine work on the block, crank, cam, (4)heads, rods.

Buy 12 custom tall CH pistons ($3,000+)

Buy all the unavailable parts and upgrades on the ThunderV12 web site ($8,000+)

Spend hundreds of hours. 

There, you did it! And only $30,000-48,000!

All we can say is, if you plan on restoring a 702 V12, or buy a "rebuilt" 702, check its condition before you buy and be careful out there.

At ThunderV12,llc, we have no interest in selling a bargain priced engine.

We will only sell the best GMC V12 you can buy. Period.

The effort required to bring these engines to market is immense and expensive. It does no one a favor cutting a corner and creating a long term headache  for the customer.