Inliners International Forums General Discussion Engines help with gmc flywheel

help with 270 flywheel. I have some 235 and gmc parts mixed and I need a gmc 270 flywheel. So I find one in my pile its got 1/2 holes spaced 2" for the flywheel to crank mount. It takes an 11" disc and has B38663-5 cast into it. Now the ring gear has 168 teeth, i'm almost 100% that this is a GMC and not CHEVY. but is it 6 volt or 12 volt.
THANKS JD

I think 4 bolts is 6v and 6 bolts is 12v. I'm not totally sure.

168 tooth is 12V, 139 tooth is 6V

6 bolt and 4 bolt cranks were used in 6V trucks. A 6V starter works fine on 12V.

Beater still think a right up of info on flywheels and starters is needed in tech tips

Yea, We need one for the early Chevy 216-261 & GMC 228-302 and one for the 194-292. Both should include what after market flywheels are available and what flywheels can be adapted.

yep, a tech write up would be great. i'm sure all GMC fly wheels are the same other than the 4 bolt and 6 bolt holes. And I believe they were 6 volt to 55 maybe, then they were 12 volt. Its the number of teeth on the ring gear that makes the difference and I don't know what that is.
JD

It comes down to large diameter vs. small diameter. The large flywheel/flexplates have 168 teeth on the early Stovebolts and late 250/292 engines and require the correct starter nose for engagement of tne bendix to spin it. The small fylwhweels with the 139 teeth for the Stovebolt and 153 teeth for the 250/292 take a different starter nose. Not sure how to look at the Stovebolt starters to tell what they fit since they all bolt to the bellhousing and I haven't paid that much attention to them, but the later block mounted starters have the straight across bolt pattern for the small 153 tooth flywheels and the staggered bolt pattern for the larger 168 tooth flywheels.

I have 168 and 139 tooth flywheels for GMCS; both are the same diameter. When using a 168 with one of the "little" starters the Chev V8 is correct for the drive gear.
If you want to use one on the 139 tooth, the original Nissan starter drive gear will be correct. I had 2 adapters made 25 years ago for the 2 hole starter mount on stock bell housings using the "little" starters and RB starters in Long Beach told me the stock gear was correct. I used them for years prior to purchasing on of Buffalo's plates.......Good Luck

I'm still unclear on the 139 tooth option here. The 139 was the 6v? What Nissan starter drive works? Does it fit a 12v GMC starter or do you use the Nissan starter? Also are you saying that a V8 gear on an L6 starter for the 168? Thanks for this input I had not heard this before.

If they're the same OD, just different tooth count, then the pitch of the teeth on the pinion drive is different then. GMC must have had some Ford engineers working for them back then.

Here is proof that my original information was wrong. Here is a GMC 6v 139 tooth flywheel with 6 crank bolt holes. When did they start using 6 bolts? If I had known this my pickup would probably still be 6v. Picture lifted from eBay.

so I'm assuming that 168 is 12 volt late style like a 57 pickup. I would like to use the 57 12 volt style starter as I already have one and I will be using a 54 bell housing.

After I get this figured out I need to focus on the clutch plate and press plate. My flywheel had an 11" clutch and no way will I need that much clutch in the 31. But I do need the right parts to use my t5 trans.
thanks Jay D

The clutch plate will depend on the spline on the trans input shaft. An 11" won't hurt you.

I believe the 6 bolt flywheel started with the 302. 302s never had 4 bolt cranks. Somewhere around 55 or so they all went 6 bolt. It's a bigger bolt pattern than chevrolet and I've always wondered if it was the same as Pontiac which also used 1/2" bolts.

I see my picture...

You have to be careful where you leave your stuff.

Wish I could remember the year for the 4 to 6 hole change, but I can't. I used the 6-volt starter with a solenoid (not kick) on 302 for years with a 139 tooth gear. Just ran it on 12 volts. Never had a problem. How may flathead Ford have you heard at a car show with 12 volts to their 6 volt starters? let me guess....all of them.
The starter shops told me there are very few starter gears.(not ring gears) All these Hitachi starters we see for today hot rods were started in Japan on small engines as I have heard it. The 240-260-280 ZEE cars had them and they were strong enough to start our V8's. On the ZEE cars the pinion gear is the same as the one used on a 139 tooth ring gear of a GMC. I liked the 139 because it turned the engine over faster. When I started having trick flywheels made the manfacturers were haveing a hard time getting 139's so I went with 168's which are the same diameter. All my staters were for 139 so I put in the gear for the ones on the Chev V8's it went right in. When I'm at a swap meet and see a Hitachci (nissan) starter for a few $$ I buy it knowing I can just change the mount for a Buffalo 6 (Chev V8), stock 2 bolt I had made, and put in the right pinion and I done for a few $$. Good Luck

Am I reading that correctly?

you can use an inexpensive starter (Hitachi) to crank a High po GMC?

A fellow inliner local to me would love that as he has had no end of trouble with his starters at the compression and cam he runs.