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aussiecowboy

GMC 702 V12

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I've been offered one of these engines that hasn't run in about 20 years. It is in clean dry storage and has been rotated from time to time. All that is missing is the carbs and plug leads. These engines are pretty much unheard of down here in Aus, if it proves to need a rebuild, are parts obtainable?

Thanks

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I've been offered one of these engines that hasn't run in about 20 years. It is in clean dry storage and has been rotated from time to time. All that is missing is the carbs and plug leads. These engines are pretty much unheard of down here in Aus, if it proves to need a rebuild, are parts obtainable?

Thanks

I also have one of these engines that i rebuilt a few years back. They used all 351 V6 GMC part except for crankshaft,cam,block,pan,flywheel,distributor base and front cover all V12 only.I found my parts on ebay at a good price. Have mine mounted on stand and run it a few times a year. Good luck with yours if you get it

Barr

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So pistons, bearings etc were all the same? That's great news. The guy wants $1500 negotiable so might get it for $12-1300. I'm thinking of building a giant speedster along the lines of an America LaFrance based on a 1927 Diamond T truck chassis I know of that has nice steel wheels. The engine is a bit modern really but certainly has the wow factor. Bit of a shame to do it to the chassis but it is completely bare and someone has cut the back section off behind the rear springs, the section is long gone. The chassis is in a scrap yard and will be melted down and sent to China if I don't rescue it.

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So pistons, bearings etc were all the same?

Multiply 351 cu in by two and what do you get? The 702 was just two 351 V6 motors glued together.

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Not entirely true. The block was brand new and one piece, not just two v6 blocks joined together. I had assumed that a lot of 351 parts would fit but I want definite answers before I fork over my hard earned cash!

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Not entirely true. The block was brand new and one piece, not just two v6 blocks joined together.

Yeah, and they wouldn't have used "glue" either. Sorry if you missed my feeble attempt at humor. Obviously the one-piece block, crank, and cam were unique to the 702 (as noted in Post #5 above). The architecture and internal dimensions were the same as the 351, as were the intakes, exhaust manifolds, and heads - just twice as many of them!

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Seems like there's a YouTUBE video of one of those engines running?

All things considered . . . as in how they might have economically done such an engine back then . . . I suspect that you might find that, rather than build a completely new, one-off-type crank or camshaft, they discovered some way to combine each of those two respective items from existing parts. A sand-cast cylinder block would have been a different situation, though.

Seems like there's a thread, from a while back, on that engine in here? "Search" function?

Just some random thoughts,

NTX5467

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This must have been about the last all new, heavy truck gas engine before diesels took over that market. They debuted about 1960 as a V12 or V6. Immensely heavy, high torque, low HP, and very thirsty. Made to run on low octane gas and haul a heavy transport truck over the road for 200,000 miles between overhauls.

If it only had 100,000 to 200,000 miles on it, it is unlikely it would need much work to put it back in commission. I would try to find a carb and plug leads and see if it will run as is. In a light weight "special" it will just loaf.

Edited by Rusty_OToole (see edit history)

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The engine came out of an airport tug apparently so unlikely to have done too much work. I'm hoping to gear the special to the point where cruising speed is not much more than idle. If I buy the engine.

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Car Craft magazine this month has a two-page spread on the 702, and (Thunder? I think...)'s efforts to bring rebuilds to market. $18,000 an engine, and weighing 1400 pounds (!), it seems pretty cool. The article said there are fewer than 200 known to exist right now. The whole deal makes me want an old GMC V-6 for a work truck, just for the weird factor.

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