Is this flywheel OK to use.

[Mark M.]

Re: Is this flywheel OK to use.

Joe and Don, I checked a 366861N and a 3791021. Both measure .970 disc surface to crank surface. 861N weighs about 25 LB and the 021 about 30 LB. 861N rings like a bell and the 021 has a weak ring sound. It also has a very different shape on it's engine side. Not sure if 021 is nodular or gray iron. When I get a chance I'd like to check this 021 flywheel to see if the graphite is nodular or flake form(in gray iron). A polish and magnify would tell this. 021 came in 6500 redline cars! Don if your car has a 3:08 or 3:36 rear end, the 30 LB might be best. If it's 3:55- 4:11 the 25 LB 861N flywheel would give your L79 a little more crisp acceleration once the car is rolling. The heavier flywheel helps getting the car rolling from stop better. The 861N I have came out of a 65 with 3:36 rear end and that owner had no issues. After seeing how many of that flywheel are available from a boat application which puts no wear on the friction surface, it seems an appealing choice.

[Joe L.]

Re: Is this flywheel OK to use.

Joe and Don, I checked a 366861N and a 3791021. Both measure .970 disc surface to crank surface. 861N weighs about 25 LB and the 021 about 30 LB. 861N rings like a bell and the 021 has a weak ring sound. It also has a very different shape on it's engine side. Not sure if 021 is nodular or gray iron. When I get a chance I'd like to check this 021 flywheel to see if the graphite is nodular or flake form(in gray iron). A polish and magnify would tell this. 021 came in 6500 redline cars! Don if your car has a 3:08 or 3:36 rear end, the 30 LB might be best. If it's 3:55- 4:11 the 25 LB 861N flywheel would give your L79 a little more crisp acceleration once the car is rolling. The heavier flywheel helps getting the car rolling from stop better. The 861N I have came out of a 65 with 3:36 rear end and that owner had no issues. After seeing how many of that flywheel are available from a boat application which puts no wear on the friction surface, it seems an appealing choice.

Mark------


I'm almost sure that the 3791021 is gray iron but it would be nice to confirm.

By the way, do you know that both of the flywheels you checked have never been surfaced?

[Mark M.]

Re: Is this flywheel OK to use.

Joe I checked both surfaces compared to a NOS 3991406 and they all have similar lathe type machine marks. They weren't surfaced ground but some shops will turn them. So I don't know if they have been cut. I prefer a light truing on surface grinder.

[Donald H.]

Re: Is this flywheel OK to use.

Mark,

Almost all of the 366861N flywheels I see for sale are described as Mercruiser. There seems to be quite a few of them for sale on eBay and elsewhere. They are pretty inexpensive, but the killer is shipping.

I think I'll wait till Spring Carlisle and see if I can find one of these there. With the price in the $50 range, even if I have to replace the ring gear it would essentially be a new flywheel if from a Mercruiser application.

[Joe L.]

Re: Is this flywheel OK to use.

Mark,

Almost all of the 366861N flywheels I see for sale are described as Mercruiser. There seems to be quite a few of them for sale on eBay and elsewhere. They are pretty inexpensive, but the killer is shipping.

I think I'll wait till Spring Carlisle and see if I can find one of these there. With the price in the $50 range, even if I have to replace the ring gear it would essentially be a new flywheel if from a Mercruiser application.

Don-------


I'd still be very interested to know what you hear from RAM regarding the "thickness" dimension. If it's right, then I think we've discovered a billet steel flywheel that can properly replace an original 1963-68 standard weight, 12-3/4" flywheel. That would likely also mean that RAM's 14" billet steel flywheel could replace the 14" flywheel used for most 66-69 big blocks and most 1969-81 small blocks.

Of course, the nodular iron flywheels are more than adequate for street use but billet steel "strikes my fancy".

[Gary B.]

Re: Is this flywheel OK to use.

Don,

I just uncovered the original flywheel for my '66, casting # 3791021. It weighs 29.5 lbs. The thickness from the crank surface to the friction surface is 0.970", which is that's same that Mark measured.

I don't see any heat cracks on the friction surface of the flywheel and I think what I'll do is have the ring gear flipped over, as there is some minor wear on the leading edge of the teeth. It's probably not enough to cause a problem, but the back side of he teeth are pristine as would be expected.

Gary

[Donald H.]

[Donald H.]

Re: Is this flywheel OK to use.

I got a response from RAM regarding the thickness measured from the

crank mounting surface to the friction surface.

"The 1511 is probably closer to 28 lbs.
So it looks like the RAM flywheel is at least .120 less than the OE flywheel. We have two examples, from Mark and Gary, of both the 3791021 and the 366861N castings measuring .970. I just received the 3668621N I purchased off eBay and it also measures .970.

The friction surface of the flywheel is untouched. It came from a Mercruiser setup so it was direct drive, i.e. not clutch to wear the flywheel surface.

It had a heavy coating of paint, but with that cleaned off, I really looks very good. maybe a 8-10 ring gear teeth have some tip wear, but I think they will be OK, or I can flip the ring gear.

I paid $64 for the flywheel including shipping. And yes, when I get around to addressing the engine build, I'll be sure to take this to the machine shop to balance and make sure the surface is true.

Thanks to all for your assistance. Especially Mark for steering me to the Mercruiser flywheels.

Don

[Gary B.]

Re: Is this flywheel OK to use.

Don,

It sounds like you wound up with a nice flywheel, at a good price. And your story is good for future reference to benefit others.

If I were you, I'd probably flip the ring gear. The YouTube videos I've watched suggest that's easy to do, at least in the hands of someone who does those things.

Gary