The Stovebolt Site Forums The Shop Area Engine Shop Need 302 flywheel advice

I'm trying to install a 302 in my 51 GMC 1-ton and have a problem with the flywheel. I can't use the bellhousing that came with the 302 because it mates to a Clark 5 speed and my truck has the SM420. My 228 bell housing won't accept the thicker 302 pressure plate even when I try the washer trick. I can't use my 228 pressure plate on the the 302 flywheel because the flywheel has a raised lip where the PP bolts go such that my 228 pressure plate would be held to far away from the flywheel to engage.

My question is, can I have the ~1/2" lip machined off of the 302 flywheel and then use my 228 pressure plate? I forgot to mention that I can't just use my 228 flywheel because it is 4 bolt and the 302 is 6 bolt.

Thanks for your help

Izzy

There are a couple of ways you can go here. I presume you are replacing the 228 with a 302, so you want to keep the 228 bellhousing.

First is to find a late 248 (54 or 55/1st) flywheel with the 6-bolt crank bolt pattern. This flywheel uses the smaller clutch, which will work fine on a 302. You don't need the big 11" truck clutch used on the heavy trucks that came with 302s. You might have to swap ring gears to work with the 228 starter. A 55-62 270 flywheel will also work, if from a pickup. It will have the same small clutch pattern.

Since these flywheels can be hard to find, another way to go is to modify a V8 flywheel to work on the GMC crank. Be sure to find one where the casting number ends with "N", that denotes a nodular iron flywheel. This requires machine work to open up the crank flange diameter and re-drilling the bolt pattern to match the GMC crank. It's also a good idea to add a couple of dowel pins to the crank and corresponding holes in the flywheel. This will allow you to use any of the huge choice of aftermarket V8 clutches - both diaphragm and 3-finger style - that are available for the small block v8.

A couple of further notes - if you plan to turn this 302 more than about 3500 RPM, it will want to shake the flywheel bolts loose (and damper pulley too, but that's another subject). Use ONLY the stock 1/2" GMC flywheel bolts and either loctite or epoxy them in place. Safety wiring the flywheel bolts is not a solution here, the heads are too thin to be drilled. Also, the older style truck clutches have a lot of clamping force but won't tolerate much RPM before the retaining tabs distort, or the pressure plate flies apart from centrifugal force.

Thanks for the advice. You have brought up a couple of more questions though.

If I go the V8 nodular flywheel route is there any specific year range or motor that would have the FW I need? How will this affect my clutch linkage. Throwout bearing, fork, etc.

You mentioned vibration with the 302 shaking things apart. The motor was rebuilt with a Kantor kit so I assume it has aluminum pistons. if they are any help. I had to replace the heavy 302 2-groove pulley/balancer with the 228 pulley because of clearance problems. Will this cause balancing or vibration problems. I could probably use the heavy 302 pulley if I used a flex fan instead of the stock fan if you think it would be better.

Thanks again

Not sure of exact years, but any manual shift Chevy V8 will probably have a "N" flywheel. I think mine came from a Z28. It shouldn't cause any problems with the linkage, throwout bearing etc. If you do decide to go this route, be sure to find a machine shop who knows what they're doing. Machining and drilling a flywheel is a precision operation, and the machinist will probably ask that you provide him the crankshaft so he can do the job right.

I'm not sure how to answer your question on damper pulleys. The 228 pulleys I've seen are a press fit on the crank snout, and the 302 damper is secured by a big 7/16 UNF bolt. I also think the crank snout lengths are different (228 is shorter) so I don't quite see how the 228 damper would work on the 302, without shortening the crank snout. I've see this done, but always accompanied by drilling and tapping he end of the crank for a retaining bolt. Without a retaining bolt, a 302 WILL launch any damper pulley in very short order. I prefer to use the stock 302 double groove pulley, GM put all that damping there for good reason - crank harmonics. And the extra groove is nice for A/C or a power steering pump. This will fit if you move the radiator forward a bit, and use the outer flange of the core support. A solid Flex-a-lite fan will clear the pulley and radiator.

Steve
check your e-mail. I think there is a guy
in Denver with a 270 flywheel

I am in the process of doing this same swap, so am very interested in how things turn out. I currently have a sb flywheel at the machine shop being modified. Someone else gave me the tip on this mod, however they did not mention the "n" for the nodular metal. The machine shop I have chosen is a recognized shop for flywheel work. So far I have not heard from them. I hope this is a good sign. The block and head are at a different machine shop. They are most likely going to order some JE pistons for me next week. I hope this all comes together without a minimum of problems. I am excited about this big six. It is too cool!!