Flexplate

[gophersnake]

About 12 years ago something came apart in my drive train and I had to have the truck towed home. I managed to get a good enough look between the engine and transmission to determine that the big flat, triangular piece of metal that connects the crankshaft to the torque converter had broken.

It took a couple of days' hunting around new and used parts places for a "flywheel" before I learned that the piece I needed was called a "flexplate". No one seemed to know where I could find one, new or even used. I finally commissioned a local blacksmith (that's right!) to make me one. Between my template and his workmanship, we must've done something right; the part is still in there and working.

If it should break someday, is there someplace I could get an official one or would I have to ask my blacksmith to try again? I did find a website just now that advertises, "We stock (brand) Flexplate for most makes and models" but "most makes and models" seldom seems to include '68 GMCs, especially with a 351 V6.

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'68 GMC C2500 with 351 V6, Turbo Hydramatic 400A.

My other car is an '80 Honda Civic.

[Bishops Trucks]

Flexplates are common everyday pieces. summitracing.com or jegs.com have them in stock and can have one to you within a couple days. I've always known them to be round, are the 351 V6's differant?

[gophersnake]

I've always known them to be round, are the 351 V6's differant?

The pictures of flexplates that I was just looking at were round too. Mine wasn't; it would have been a perfect triangle except that (1.) the tips were rounded instead of pointed and (2.) it wasn't quite flat; the tips were offset so they hung about 1/8" above the table when the center was lying flat. The center got bolted to the crankshaft hub and the tips to the torque converter.

I still have the aluminum template that I got it made from. I'll be happy to post a picture of it if someone will tell me how (or at least point me to the directions).

Update: I checked summitracing. For '68 C2500s they mention a 305 engine but don't seem to have heard of the 351.

I also went through 11 pages of flexplate pictures at jegs. There were a couple of listings that didn't have pictures yet. There were a couple of Mopar flexplates with four (not three) rounded tips. Sure enough, all the rest were round.

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'68 GMC C2500 with 351 V6, Turbo Hydramatic 400A.

My other car is an '80 Honda Civic.

[Longhorn Man]

You've found the problem with running an obsolite motor esp as a daily driver.
I would say the absolute bast thing you could do, would be to keep an eye on the parts pages on this board and any others you join (look on the 60 - 66 pages too, that motor was more common in them) and buy up parts that you see, that you MIGHT need in the future.

[gophersnake]

You've found the problem with running an obsolite motor esp as a daily driver.

Quite right.

I'm in no hurry to change vehicles. If I did, I'd want to keep the utility body and find something else to haul it with -- probably a slightly newer GMC or Chevy with unknown problems instead of the ones that I've already been dealing with and know something about.

I've occasionally wondered what would be involved in changing to some more common engine. It was one of the options I considered when I was having trouble finding the flexplate. Someday I might look for threads about engine swapping or even start one myself. Right now not only can't I afford it (the money or the down time) but I have no idea what would fit in that truck most easily, what it would be like to drive, what else I'd have to change. Transmission? Mounts? Power steering? Finding a blacksmith to make a flexplate (and then putting it in) sounds like peanuts compared to finding a suitable engine, getting it to fit, and maybe finding out just why the previous owner didn't want it any more.

[Longhorn Man]

in all reality, for parts avalibility both stock and aftermarket, you can't go wrong with a small block chevy. Everything you'd need can be had fairly cheap. And you could have everything you need sittin on the floor ready to go in engine, tranny and drive shaft.. allong with motor mounts and frame towers, possibly a crossmember ect, get it all ready to go in, have it in in less than 8 hrs, then rumble to the muffler shop and have your old pipes hooked up, of chop them off and get a new daul exhaust set up

[GREASEMONKEY72]

Originally Posted by Longhorn Man

in all reality, for parts avalibility both stock and aftermarket, you can't go wrong with a small block chevy. Everything you'd need can be had fairly cheap. And you could have everything you need sittin on the floor ready to go in engine, tranny and drive shaft.. allong with motor mounts and frame towers, possibly a crossmember ect, get it all ready to go in, have it in in less than 8 hrs, then rumble to the muffler shop and have your old pipes hooked up, of chop them off and get a new daul exhaust set up

[gophersnake]

Longhorn Man (and GREASEMONKEY72): Thanks for the engine suggestion. I confess I don't know my way around Chevy engines that well; I've only ever owned two, this 351 and (a long time ago) some inline 6, probably the 194. A "small block" would be a V8 somewhere around 300 to 350 CID? Are there any years I should watch out for because, oh, GM was still trying to get the smog equipment right or something?

For Bishops Trucks, here's a picture (I hope!) of the template that I had the replacement made from. If it were a complete circle it would be 12.5" in diameter. I don't remember where the ring gear was located but it must've been to the front of this. I don't think I had to disturb it at all.

[Longhorn Man]

Small block chevys span a whole lot of years, and a bunch of sizes. However, with the fact that (it sounds like) you work your rig like a rented mule... I would say ignore all the baby small blocks (262, 265, 267, 302, 307, 327) and go for a 350, or a 400 small block. If you were to get a crate engine, (rebuilt complete motor fully assemble) you could get a 383, which is a 350 with the 400 crank in it.... a stroker motor.
As far as ones to avoid, if I were doing it today, I'd avoid anything older than 1987.
There's some advantages to the older ones, you can find one with a high nickle alloy content, which wears very good (not unheard of to see a 100,000 mile high nickle block not need bored at all, even see some marks from previouse machining) however, with the new crappy oils on the market, the roller cam is almost a must.
The cam in all the old engines have a lifter that rides on the lobe of the cam, this pushes the push rod and rocker arm and then the valve, opening it up and closing it. While it is a more complicated piece than just a chunk of metal, for this conversation, we'll just call it that, a chunk of metal. This metal just slides on the metal of the camshaft. Back when oils still had plenty of zink, this kind of cam would live 100,000 miles, which, in all reality, untill the end of the 80's, that was the expected life span of most cars and even trucks.
in 87, GM went to a roller cam. The 'chunk of metal' I refered to as the lifer earlier, still does the same job, and still pushes the push rod and rocker and valve... however, instead of flat metal to flat metal, there is now a little wheel that rolls on the cam shaft lobe.
This one improvement instantly made the engines last 200 and even 300,000 miles with no major rebuild. There were some other improvements too, but this was the main thing that kept an old engine running good with plenty of power, and a good running vehicle is more likley to be maintianed and taken care of. This is why you see '90's trucks with 300,000 miles, still looking good and taken care of, and still worth 7000 bucks.
So, if you followed all that, then you see a good reason to get a later model engine. You don't need to run the fuel injection, you can install a carb'd intake on there, and everything else... only a few smal hurdles to clear on the later engines.
Some don't have provisions for a mechanical fuel pump.
As much as I hate electric fuel pumps when they aren't needed, you can run fairly inexpensive one in this aplication with minimal fuss.
must use later model fly wheel due to updated rear main seal.
No biggie... get it with the core, or source one at a junk yard or parts store when you get the crate motor.
center bolt valve covers
Again, get new or junk yard pieces. Even though many old timers or hot rodders resist the chainge and want to run there old perimeter valvecovers, the center bolt ones are way better.
If the engine has late model heads, you'll need a slightly more expensive intake.
While this seems like a pain in the 12 bolt, these heads are light years ahead of the old stuff... even the 'good' old stuff is junk in comparison.


If I left anything out, some one else can, and will, chime in on this.
There may be some other opinions, and most of what I just said is in fact my opinion, based on spinning wrenches all my adult life.

your 351 os one hell of a workhorse, and has earned respect from lots of people, but the fact of the matter is, they are obsolite, and as you are finding, the parts supply is becoming slim to none. When you have to have parts custom made, it's time to start looking for other means in my opinion.


PS. There is the chevy big block family, these engines are made more for what you do, however, price of the core, parts, and avalability of most accesories make it quite expensive. Stock for stock, even a weak big block will out perform the small bloks, but the price tag doesn't justify it if you ask me.

[rophle1]

"About 12 years ago"

If this flexplate has been running for 12 years, why do you think it'll go out now? I agree that if something big happens to your current motor I'd change it out to a more commom one, but I wouldn't loose sleep thinking my flexplate going out unless there's something else going on that you didn't mention.