55.2-59 Flywheel and Starter Combination GMC

[ses427]

Converting from L6 to V8 in a 56 GMC. Think I have the right bellhousing but no luck figuring out which flywheel to use. 166 or 176 tooth? I tried the 176 from a Pontiac but the flywheel just hits the clip at the end of the bendix. Trying to keep it stock, any wisdom would be appreciated. Thanks.

[mr48chev]

What V8 are you using? plus what bellhousing are you using.

[ses427]

A GMC 288 V8 and the stock GMC bellhousing

[IamBrian]

That’s a Pontiac engine then, usually installed in the 1955 GMC - the 56 had a 316 - but no matter. Why can’t you use the original flywheel for that engine? Which trans are you going to use? Stock GMC or trying to modify?

[mr48chev]

You have to use the correct flywheel for that Pontiac made engine, a Chevy flywheel won't work.

Unless they are just hellbent on keeping the truck appearing "original" most guys who pull the six out of a GMC go to a small block Chevy and Chevy V8 bellhousing. Far less headaches and parts are way easier and less expensive to get.

[ses427]

Yes, guess I am one of those hellbent people, I want to keep it stock. If I fell off the wagon, I would probably go LS but that is another story.

I am trying to find out how many teeth the flywheel should have and if there is a cross reference to another vehicle. Tried the early Pontiac route but those are nowhere to be found either.

[mr48chev]

I'm not finding a 288 engine in any year of GMC exactly what do you have?

I'm finding a 55 only Pontiac engine that is a 287 that is actually 287.2 if you get down to the nitty gritty and that is one year only.

According to this 55/57 Pontiac flywheels should be the same but an hour's searching does not bring up one ring gear for a 55/57 Pontiac to be able to know how many teeth one has.

That is the trouble with odd ball stuff that most guys threw in the scrap pile years ago, there are no parts available for them unless you pay an absolute premium and even less information.

The Best I can suggest is contact Wallace racing and see what they have to say. Or go on the Pontiac Registry and tell them you have a 55 Pontiac with a stick and ask what flywheel will replace your flywheel and what fits and what ever you do don't tell those guys you put the engine in a truck.

I have very honestly spent the past hour searching for a 55/57 Pontiac ring gear and none exist to even get you a part number or a tooth count. You may have replaced your six with 700 lbs of scrap iron.

[IamBrian]

Hahaha yes the early Pontiac powered GMCs are different - guess that’s why I like them too. My 55 one ton has the 288 (Pontiac calls them a 287 and the 56 came w a 316) but GMC calls it the 288 and the 317. No biggie.
Any way, it sounds like you’re installing a stick shift tranny, not the early hydramatic - they came both ways. I’m not sure I can still look at my flywheel to count the teeth but I have my engine sitting in my shop w the bell housing installed. I also have a hydramatic sitting around with the ring gear I took out.

[IamBrian]

There are usually aluminum flywheels being sold on eBay for these engines - current ad says it is a 176 tooth. These engines are around but you need to find a running one cuz rebuilding them is expensive. I bought mine right out of a running Pontiac nearby and there’s a 316 north of me and an early 389/tranny just east of me so you can find them.

[mr48chev]

When I searched last night I couldn't even find a replacement ring gear for one. Not for a GMC or Pontiac.

What I was reading last night said 58 and later had a larger diameter flywheel than 55/57.

[dsraven]

to each their own, I get it, you want to build something that you can say is stock GMC stuff and it was only built for x number of years and came in x cars etc. that's cool. BUT, it's gonna cost you waaay more than normal stuff and you're gonna spend a bunch of time searching and cobbling together parts when you could be driving. that part is up to you, it's your truck. I get how you go to shows or hear of guys building something and it seems like a broken record or they all bought the same parts from the same supplier and the only difference between them seems to be what they polished or painted. same same. you want something different but built with stock parts. again, very cool. just not cheap or quick. good luck on finding the parts you need and hopefully they are still serviceable. post up a few pics of your rig, would love to see the progress.
it's called hotrodding because we build what WE want out of parts WE find and don't have to answer too anybody but ourselves on how it looks, runs or drives (up to a point-safety first)

[ses427]

hey, thanks for all the efforts and suggestions. I never give up so I will find some combination that will work. Wallace might be a good avenue. Thanks for your time. Let you know what happens.

[mr48chev]

The big problem is that I just flat am not finding anything on those engines or flywheels or clutches for that setup. My Hollander interchange doesn't go back far enough as far as I know but I'll dig it out of the garage in the morning.

There is a somewhat active 55/59 GMC group on Facebook if you are on facebook Some aren't and so be it but if you are https://www.facebook.com/groups/50sgmc Mixed bag of folks just like here with some restoring and some going pretty wild on their builds but a resource is a resource. Someone there may be able to point you in the right direction.

[paulspickupparts]

There is a new ring gear listed on Amazon for Pontiac GMC that shows it as 176 tooth . They also have some of the dimensional specs . With that being said I would not put a lot of faith in the description of something found on Amazon without a second source of verification.

https://www.amazon.com/176-Tooth-Pon.../dp/B07MMHYFGX

For your pickup with original V8 there were only two flywheels made . One for a manual transmission and one for a hydramatic transmission . The pickups with manual will interchange 100 150 250 and 300 series . The hydramatic has a bigger interchange even into the bigger series .

However 350 370 400 410 450 and 500 had two different options as far as v8 manual flywheels . Possibly (not sure) but maybe larger because of being more heavy duty in that application torque etc.

Running of memory here but I think when you ordered a flywheel from GMC it was also paired with the correct housing . So pretty sure the pickup with V8 would have had a smaller housing that say a 450 series .

Sure you know this but 6 cylinder flywheels or housings do not interchange .

I hope not the case but someone may have paired a big truck flywheel with small pickup bellhousing. Thanks good luck