Resurfacing Nodular Iron Flywheel

[JohnnyB]

So, I have a GM Nodular iron flywheel. Resurfaced it at work on a regular Grinding wheel / table. This is the third resurfacing cut on this flywheel since I have owned it for 31 years. I thought it looked terrible, and felt terrible where the disc rode. However only took about .006" of an inch to clean the face up to where it looks new.

A friend ( my boss ) insists that the flywheel HAS to be blanchard ground, and that doing it on the regular grinding table we have is a big NO-No....He could not tell my why it is a NO-No, just that it is.

My question is, is a blanchard grinding of the flywheel mandatory, or is a regular grinding table OK ??? Looks good to the eye, feels good with my fingers, and checking flatness/runout on a granite table it is less than .001" total indicated across the entire flywheel.

[rustbucket79]

So long as the surface is reasonably smooth, I can't think of a reason where this would be a problem.

[PackardV8]

A friend ( my boss ) insists that the flywheel HAS to be blanchard ground, and that doing it on the regular grinding table we have is a big NO-No....He could not tell my why it is a NO-No, just that it is.

In Blanchard grinding, a grinding wheel is placed on a vertical spindle and then moved counter to the rotation of a magnetic chuck, which holds the piece in place. The process leaves a telltale finish pattern on the surface of parts.

Not clear on what you mean by a regular grinding table - are you using a unidirectional surface grinding machine? If so, it isn't the best process and your boss may be correct. However, check any automotive machine shop which grinds flywheels every day and there's no true Blanchard grinder in sight. The processes are somewhat similar except the workpiece/flywheel is bolted down and the finish is essentially invisible. The advantage of an automotive machine is it registers the flywheel off the same center hole as mounted on the crankshaft and spins the flywheel in the same manner as it will be operating in the car.

checking flatness/runout on a granite table it is less than .001" total indicated across the entire flywheel.

Checking it on a surface plate isn't using the same registration. The flywheel is only located on the crankshaft by the small area around the bolt holes, which may or may not be precisely in the same plane as the full surface area of the back side. A properly ground flywheel will show essentially zero runout when rotated off the mounting surface.

Bottom line, you're probably OK, but your boss has a valid point.

jack vines

[JohnnyB]

A friend ( my boss ) insists that the flywheel HAS to be blanchard ground, and that doing it on the regular grinding table we have is a big NO-No....He could not tell my why it is a NO-No, just that it is.

In Blanchard grinding, a grinding wheel is placed on a vertical spindle and then moved counter to the rotation of a magnetic chuck, which holds the piece in place. The process leaves a telltale finish pattern on the surface of parts.

Not clear on what you mean by a regular grinding table - are you using a unidirectional surface grinding machine? If so, it isn't the best process and your boss may be correct. However, check any automotive machine shop which grinds flywheels every day and there's no true Blanchard grinder in sight. The processes are somewhat similar except the workpiece/flywheel is bolted down and the finish is essentially invisible. The advantage of an automotive machine is it registers the flywheel off the same center hole as mounted on the crankshaft and spins the flywheel in the same manner as it will be operating in the car.

checking flatness/runout on a granite table it is less than .001" total indicated across the entire flywheel.

Checking it on a surface plate isn't using the same registration. The flywheel is only located on the crankshaft by the small area around the bolt holes, which may or may not be precisely in the same plane as the full surface area of the back side. A properly ground flywheel will show essentially zero runout when rotated off the mounting surface.

Bottom line, you're probably OK, but your boss has a valid point.

jack vines

Thanks Jack- What I should have said when I mentioned checking it on the Granite table is, we used 1 -2 - 3 blocks under the flywheel bolt mounting surface holding the flywheel off the table. So we did register off the flange/bolt mount surfaces. And went around that with a dial indicator mount on a machined block and checked the actual flywheel surface all the way around about one inch in from the outside edge while the flywheel was sitting on the 1 2 3 blocks.

The grinding machine is just a flat table that holds the flywheel down by magnetism, and the grinding wheel moves back and forth automatically over the top. I have never paid much attention to the actual make and model as I am one of the shop electricians and service tech, not a machinist. Guess I could ask We dressed the wheel first to insure it was true, and also did a light skim cut of .005" on the back of the flywheel first using the front as the register as it was flat as far as we could tell. so essentially we trued up the backside by using the front as a register, then cut the front face using the fresh cut back as a register for the front. As long as the original front surface was parallel to the mount flange I was hoping I would be OK.

That seemed to be proved out by sitting the flywheel flange mount surface on a couple of 1-2-3 blocks then running the dial indicator all around the front face. I know it wasn't the fastest method, but it was FREE, and seemed to check OK. I was asking about the blanchard grinder as it leaves a different finish verses what our surface grinder does. Was wondering if the disc would actually 'know' the difference after a couple of little "burnouts" ??

[JohnnyB]

So long as the surface is reasonably smooth, I can't think of a reason where this would be a problem.

It is extremely smooth, hopefully not too smooth.

[PackardV8]

From what you've told us, you didn't do a best science flywheel regrind, but you did it as well as it could be done wrong. I doubt there will be any problems.

jack vines

[JohnnyB]

From what you've told us, you didn't do a best science flywheel regrind, but you did it as well as it could be done wrong. I doubt there will be any problems.

jack vines

Gee, not sure how to take that Jack...

But it looks pretty.........

Actually The only thing I might be wary off is the surface finish as it is really smooth, but definitely not looking like a blanchard ground surface. I was just wondering if the disc and pressure plate would be able 'to tell' the difference. And how critical the run out typically is. Is it's tolerance in tenths of a thousand, or is within .001" Ok. I can always have it blanchard ground later if so. This flywheel is for a second (back-up ) engine and might not get used for a couple of years.......

[hsutton]

If you subject that IRON flywheel to any great amount of heat it will blow up like an IED. I had a friend blow one up in a 375 h.p. - 396 cu. in. Chevelle and the damage was unbelivable. It pulled all the bolts out of their bosses in the back of the block, sheared the input shaft off the transmission, sawed the passenger side header into, dropped the transmission to the ground, bent the driveshaft and blew up the engine. It also took out the distributor cap and put a big dent in the car's hood. Any iron flywheel is as dangerous as any part of a car. Trade it for a good steel flywheel and you'll have piece of mind. If you never put a tire with any traction on the car your iron wheel may be O.K.

[JohnnyB]

If you subject that IRON flywheel to any great amount of heat it will blow up like an IED. I had a friend blow one up in a 375 h.p. - 396 cu. in. Chevelle and the damage was unbelivable. It pulled all the bolts out of their bosses in the back of the block, sheared the input shaft off the transmission, sawed the passenger side header into, dropped the transmission to the ground, bent the driveshaft and blew up the engine. It also took out the distributor cap and put a big dent in the car's hood. Any iron flywheel is as dangerous as any part of a car. Trade it for a good steel flywheel and you'll have piece of mind. If you never put a tire with any traction on the car your iron wheel may be O.K.

Yeah, I am aware of how bad an Iron flywheel can be. This is Nodular Iron which is slightly better, .......but still iron. This is for a second backup motor that may not even get used. Only if I toast my main motor which does have a Brand 'spank me' new Hays billit steel wheel. And if do do ever use it, it is inside a lakewood shield with a block plate.

[JohnnyB]

From what you've told us, you didn't do a best science flywheel regrind, but you did it as well as it could be done wrong. I doubt there will be any problems.

jack vines

Was done on a Okamoto wet surface grinder Model #1632N using a 14 inch wheel, (vintage 1987 ) . table is 16 x32 inch. dont know if the accuracy of this machine is equal to what the blanchard grinder is or not. Anyone out there know????????

[JoePorting]

At around $200, steel flywheels are cheap insurance.

[hsutton]

If you subject that IRON flywheel to any great amount of heat it will blow up like an IED. I had a friend blow one up in a 375 h.p. - 396 cu. in. Chevelle and the damage was unbelivable. It pulled all the bolts out of their bosses in the back of the block, sheared the input shaft off the transmission, sawed the passenger side header into, dropped the transmission to the ground, bent the driveshaft and blew up the engine. It also took out the distributor cap and put a big dent in the car's hood. Any iron flywheel is as dangerous as any part of a car. Trade it for a good steel flywheel and you'll have piece of mind. If you never put a tire with any traction on the car your iron wheel may be O.K.

Yeah, I am aware of how bad an Iron flywheel can be. This is Nodular Iron which is slightly better, .......but still iron. This is for a second backup motor that may not even get used. Only if I toast my main motor which does have a Brand 'spank me' new Hays billit steel wheel. And if do do ever use it, it is inside a lakewood shield with a block plate.

The Chevelle had a Lakewood Scattershield and a block plate and still looked like a bomb had gone off. Pulled all six or seven bolts right out of the back of the block, block plate and all, then all the pieces came through the hole between the block plate and the scattershield. Another friend of mine blew up one of those special "nodular iron flywheels" in a Ford. It mushroomed the outside of the Lakewood about 1" behind where it was attached to the back of the engine. There is no safe iron Flywheel explosion.

[vetrod62]

Ouch!

[autogear]

A friend of my dads is missing half his foot from a blown iron 'wheel in a 55 chev gasser style car with a 283 that had a serious atitude problem. That aluminum bellhousing went to pieces, dad was able to yank a chunk out of the drivers door.

Sell that to some resto nut and get a steel one.

[GRUBBY]

Ouch!

My dad had that happen in a 55 Chevy. It took out the trans tunnel, dash, cowl, windsheild and part of the roof. Those iron 'wheels have no place nowadays in anything but a dumptruck...lol