Minimum 1.9L machince flywheel thickness?

[Manta Rallier]

Hey all,
The Ford T5 adaptation project is moving along. Am in the final steps of locating the adopted clutch assembly. The flywheel will be machined flat; how thin can these flywheels be machined and still be good and safe? I want a good safety margin. And, any balancing issues that crop up when these flywheels are machined thinner?

Also, what are you guys doing for pilot bearing materials in a retrofit trannie situation?

Thanks,
Mark B.

[RallyBob]

Originally Posted by Manta Rallier Hey all, The Ford T5 adaptation project is moving along. Am in the final steps of locating the adopted clutch assembly. The flywheel will be machined flat; how thin can these flywheels be machined and still be good and safe? I want a good safety margin. And, any balancing issues that crop up when these flywheels are machined thinner? Also, what are you guys doing for pilot bearing materials in a retrofit trannie situation? Thanks, Mark B.

The thinnest I've dared to make any flywheel is .400" thick, at least when we're talking cast iron. That sucker weighed a bit over 11 lbs, and is currently in an Opel GT used exclusively for autocross. I've done .375" with steel billet, but even there you have to be careful about warpage if you overheat the clutch. The .400" number I arrived at gradually over the years...I would still limit myself to either 150 hp OR 7500 rpms, whichever is the lower number.

For sustained 8000+ rpms or higher hp numbers, you really should consider a steel billet or an aluminum flywheel for safety. It is ugly when they let go. I'm using an aluminum 8 lb flywheel in my rallycar for example. It used to have a lightened stock flywheel (14.2 lbs), down from about 23 lbs stock, but with the recent changes to the engine I want the security of knowing my legs will stay attached.

Cast iron flywheels need to be rebalanced when they're machined lighter, they are rarely (if ever) balanced once material is removed. I suspect the cast iron's density varies, causing this issue.

Bob

[opelnut10]

Originally Posted by RallyBob The thinnest I've dared to make any flywheel is .400" thick, at least when we're talking cast iron. That sucker weighed a bit over 11 lbs, and is currently in an Opel GT used exclusively for autocross. I've done .375" with steel billet, but even there you have to be careful about warpage if you overheat the clutch. The .400" number I arrived at gradually over the years...I would still limit myself to either 150 hp OR 7500 rpms, whichever is the lower number. For sustained 8000+ rpms or higher hp numbers, you really should consider a steel billet or an aluminum flywheel for safety. It is ugly when they let go. I'm using an aluminum 8 lb flywheel in my rallycar for example. It used to have a lightened stock flywheel (14.2 lbs), down from about 23 lbs stock, but with the recent changes to the engine I want the security of knowing my legs will stay attached. Cast iron flywheels need to be rebalanced when they're machined lighter, they are rarely (if ever) balanced once material is removed. I suspect the cast iron's density varies, causing this issue. Bob

Bob knows of what he speaks, I had one let go in the drag car at about 7500RPM that had been lightened to 18 pounds (thank God for scatter shieds) it looked like someone had put a gernade inside the bellhousing. I then proceeded to start cutting on a 1 1/8" 42 pound piece of steel plate and wound up with a 17 pound billet flywheel, which I still have, and had a whole lot better peace of mind

[GTJIM]

Always a good idea to have any cast iron flywheel crack tested before ... and after machining. Used ones can have 'heat checking' which is a pattern of small surface cracks in the friction area ... particularly if a clutch has been slipping at some time in the past.

The least sign of a tiny crack, void or porosity in the cast iron - get another one.

If you plan to run one up above 5,000 rpm or so on a regular basis as 'scatter shield' or Kevlar 'explosion blanket' would be real good insurance - as would a Titanium "Cricket Box" .... just so you know what you are saving from destruction!

Better still - an alloy or billet steel flywheel may save your legs ... or life!

[OriginalOpelGTOwner]

This discussion begs the following question. Is the GT stock cast iron flywheel robust and structurally sound such that the engine can be rev'ed to the 6200 rpm redline on a regular basis?

[Manta Rallier]

Thanks for all the input guys. My real question is, if the S10 clutch conversion requires that the stock flywheel be machined flat (which I presume it is, then some material can be removed. To get the input shaft and clutch located right, I can either back the trannie up further with a thicker adapter plate, or machine the flywheel some more, or a combination of the 2.

The objective of the query is not to get the flywheel as light as possible, but to get a feel for a minimum 'safe' thickness. I don't expect anyone here to go out on a limb and say that one can go to x thickness, and say it will be safe; just let me know how much you have machined them and how they have been used.

BTW, this is for rallying use. In almost 30 years involvement (and being a series tech inspector), I have never heard a report of an exploding flywheel, and most of the rally cars run stock stuff. Keep in mind that the vast majority of shifting in anger is done on dirt, and strong torque impulses on the driveline just break the wheels free. We worry a lot more about flying by trees 1-5' outside the car at 100 mph.......I would think a whole lot different if drag racing or road racing with wide slicks was the game here. And, if a conversion is designed then more thought (for my own piece of mind) will be given to stronger, non-stock stuff.

BTW, we've rallied these cars on about 50 events with 130-150 HP and stock flywheels and shifting typically at 7500 rpm and never had any flywheel explosions (or you would call me 'stumpy'). Again, this is on dirt so the driveline torques never can reach a very high level. But use that as a point of ref for the question about stock flywheels at 6200 on the street. If it was a problem, we would have discovered it in the 60's/70's when the 1.9L engine came out.

Regards, and any more flywheel dimension info would be appreciated.
Mark B.

[opelnut10]

Originally Posted by Manta Rallier Thanks for all the input guys. My real question is, if the S10 clutch conversion requires that the stock flywheel be machined flat (which I presume it is, then some material can be removed. To get the input shaft and clutch located right, I can either back the trannie up further with a thicker adapter plate, or machine the flywheel some more, or a combination of the 2. The objective of the query is not to get the flywheel as light as possible, but to get a feel for a minimum 'safe' thickness. I don't expect anyone here to go out on a limb and say that one can go to x thickness, and say it will be safe; just let me know how much you have machined them and how they have been used. BTW, this is for rallying use. In almost 30 years involvement (and being a series tech inspector), I have never heard a report of an exploding flywheel, and most of the rally cars run stock stuff. Keep in mind that the vast majority of shifting in anger is done on dirt, and strong torque impulses on the driveline just break the wheels free. We worry a lot more about flying by trees 1-5' outside the car at 100 mph.......I would think a whole lot different if drag racing or road racing with wide slicks was the game here. And, if a conversion is designed then more thought (for my own piece of mind) will be given to stronger, non-stock stuff. BTW, we've rallied these cars on about 50 events with 130-150 HP and stock flywheels and shifting typically at 7500 rpm and never had any flywheel explosions (or you would call me 'stumpy'). Again, this is on dirt so the driveline torques never can reach a very high level. But use that as a point of ref for the question about stock flywheels at 6200 on the street. If it was a problem, we would have discovered it in the 60's/70's when the 1.9L engine came out. Regards, and any more flywheel dimension info would be appreciated. Mark B.

Driveline stress is not the cause of a flywheel letting go is a drag car, it is the heating and cooling by friction. Just like a cast brake rotor if you heat it and cool it down enough times, it WILL fly apart and like a brake rotor heat warps the flywheel which increases friction. That friction causes heat and so on. Anyone that is working the clutch hard, in any form of racing that requires a lot of shifting is putting the flywheel thru stress and increases the chances of it failing. The Opel flywheel is made of cast nodular iron which is pretty dense so that helps, but it could still take a dump.

[Manta Rallier]

Originally Posted by opelnut10 Driveline stress is not the cause of a flywheel letting go is a drag car, it is the heating and cooling by friction. Just like a cast brake rotor if you heat it and cool it down enough times, it WILL fly apart and like a brake rotor heat warps the flywheel which increases friction. That friction causes heat and so on. Anyone that is working the clutch hard, in any form of racing that requires a lot of shifting is putting the flywheel thru stress and increases the chances of it failing. The Opel flywheel is made of cast nodular iron which is pretty dense so that helps, but it could still take a dump.

Interesting info and knowldege. So it must be due to sudden localized heating. We can argue over and over, but drag racing has a history of flywheels letting go; rallying does not. That in itself should tell us about the degree of heating going on.

But don't fear; this is good info for thought. I'm already running thoughts through the back of my mind on how to get this done. Any specific numbers on the power you were running when your flywheel let go would be appreciated.

Edit: BTW, in completing some clutch stack-up drawings last night and figuring the adapter final plate thickness, it became clear that the stock flywheel will not have to be machined down any more than to get rid of the step and the small groove between the steps.

Regards,
Mark B.

[GTJIM]

Here is a link to the most comprehensive "Flywheel" Thread on GT.com:

http://www.opelgt.com/forums/clutch-...ghten+flywheel

Check out the REALLY lightened flywheel !! :

http://www.opelgt.com/forums/attachm...g?d=1018496988

[jeff denton]

Having given this some thought, it stands to reason that a car used in racing that shifts a lot under power is going to have a bit of clutch slippage with every shift. So some heat is going to build up. Using a bigger clutch should help a bit, obviously. But how is the heat supposed to be dissipated? There is no airflow in the bellhousing. So, like in race cars that are on the brakes a lot, maybe some ducting is in order. How about an "in and out" duct, the "in" duct on the flywheel cover, and the "out" duct from the rear of the belllhousing?
Seems any airflow at all would help, when clutch heat is the problem one of the answers should be to simply remove the heat.
Also, with these clutch mods, has there been any problem foreseen or experienced with the crankshaft thrust bearing? Can it handle more release pressure?

[namba209]

Neat idea Jeff. I seem to recall a bellhousing on one of my cars that had an opening in the top center about an inch tall and 3 inches wide. Made a great hand hold moving it around. Didn't even consider it was there for heat dissipation.

[baz]

jeff manufacturers spend $$$ making rubber dust boots for the throw out arn hole and tin plates for the bottom for a reason or two
dust and water

under the car is a wet place for a road car and clutches just dont like water the thermal shock of steam in the mix is bad

the tin plate and boot also keep the dust and stones out that will eat a clutch plate in no time

no problem for a dry race car but in a general road use and rally car its a bad idea to get it in there

theres more heat going into it from the crank than from the clutch even under heavy road/race use its the stress + heat cycles in a 1/4 mile machine that does the damage as you can bet they dont x-ray the flywheel every race or change it every race like all the other bits

[jeff denton]

You're lit, baz. How could a crankshaft transfer enough heat to a flywheel to turn it and the pressure plate blue?

[baz]

surface temp gets that hot (150 odd centigrade iirc to colour steel and iron blue)when you ride the clutch or do a burn out but more heat comes in from the crank by conduction to heat the whole flywheel over the time it runs

its the old cup of coffee and a warm bath thing
the coffee is hotter but a warm bath has more heat therms in it

[opelnut10]

Originally Posted by Manta Rallier Interesting info and knowldege. So it must be due to sudden localized heating. We can argue over and over, but drag racing has a history of flywheels letting go; rallying does not. That in itself should tell us about the degree of heating going on. But don't fear; this is good info for thought. I'm already running thoughts through the back of my mind on how to get this done. Any specific numbers on the power you were running when your flywheel let go would be appreciated. Edit: BTW, in completing some clutch stack-up drawings last night and figuring the adapter final plate thickness, it became clear that the stock flywheel will not have to be machined down any more than to get rid of the step and the small groove between the steps. Regards, Mark B.

Rally racing does not product the heat generated by drag racing because you are not runnig through the gears at wide open throttle and stressing the driveline with tires that will not spin. My drag engine was .040 over 1.9 and put out 195HP at the flywheel I have seen a lot of clutch explosions and most of the time they were in first or second gear. When you are running a final drive ratio of 5:13 with a 3:44 first gear that is a gear multiplication of 17:65 to 1 and things are happening fast sitting the tach on 7000 and sidestepping the clutch then making the 1st to 2nd gear shift at the tree at 7500 will tell you real quick if you don't have the right parts

[Manta Rallier]

Originally Posted by opelnut10 Rally racing does not product the heat generated by drag racing because you are not runnig through the gears at wide open throttle and stressing the driveline with tires that will not spin. My drag engine was .040 over 1.9 and put out 195HP at the flywheel I have seen a lot of clutch explosions and most of the time they were in first or second gear. When you are running a final drive ratio of 5:13 with a 3:44 first gear that is a gear multiplication of 17:65 to 1 and things are happening fast sitting the tach on 7000 and sidestepping the clutch then making the 1st to 2nd gear shift at the tree at 7500 will tell you real quick if you don't have the right parts

OK, thanks for the info and the applications details for drag clutch use. Sidestepping the clutch was one thing I expected for a real drag launch. In rallying, the hardest use of the clutch is at a stage start, but it's not at all like a drag car. Starting on dirt in a rally car is a lot like a tractor pull; the best launch will be when you get the wheels spinning at just a certain rate, not too fast or not too slow. So you typically rev to a good spot in the torque curve (like around 4k more or less) and then feather the clutch to get a controlled wheel spin. The whle deal is limited by the dirt you are on and the tires; that grip combination limits what you can do overall.

Thanks for the data point!
Regards,
Mark B.

[Manta Rallier]

Originally Posted by RallyBob The thinnest I've dared to make any flywheel is .400" thick, at least when we're talking cast iron. That sucker weighed a bit over 11 lbs, and is currently in an Opel GT used exclusively for autocross. I've done .375" with steel billet, but even there you have to be careful about warpage if you overheat the clutch. The .400" number I arrived at gradually over the years...I would still limit myself to either 150 hp OR 7500 rpms, whichever is the lower number.

Hey BB is this minimum thickness at the outer (thickest part) of the flywheel? The inner area of the stock unit is already pretty thin. I am looking at machining down so that the dust groove is gone, to accomodate a 8.5" disc, but that requires 7.5 to 8 mm of machining from the original p-plate surface.

Thanks,
Mark B.

[jeff denton]

I weighed my "assembly as per the rulebook" on bathroom scales (not real precise, but a start) and came up with 37 pounds. I need to take about 9 pounds off, then. That sounds like a lot! No wonder I can do no better than third place against illegal 2.3 Mustangs.... Will start on the outermost regions not needed other than to hold the ring gear on.
Question, since this will be done by my machinist buddy who does not work on cars, especially race cars. How should this be chucked up in the lathe? Should it be dialed in true to the surface that the pressure plate bolts to?
It looks like the first cut should be to make a step just outside of the pressure plate bolt holes. Then flip it over and start cutting just inside from the ring gear inwards.
Or would it be better to have the flywheel bolted to a crankshaft and turn it between centers? Seems logical, since that's the way it runs. Then all surfaces could be trued up, and both sides could be cut with one setup.
I don't know, I'm not a machinist. But I've been around machine shops a lot, generally ones dealing in huge industrial parts. And this project will have to be explained properly to my machinist, who will remind me he really doesn't do stuff like this...

[RallyBob]

Originally Posted by Manta Rallier Hey BB is this minimum thickness at the outer (thickest part) of the flywheel?

I was refering to the area that the clutch disc itself actually rides on. That is the area that gets the most heat, and in cases where a flywheel/clutch is abused, it shows the most heat-cracks.

Just another FYI, but for a competition car, it's always a good idea to have the flywheel magnafluxed prior to starting any machine work, to make sure it's not cracked. And I like to have the flywheels shotpeened after machining for good measure. Costs something like $25 at the local MIL-spec/aerospace shotpeening facility, which is cheap insurance.

Bob

[RallyBob]

Originally Posted by jeff denton Question, since this will be done by my machinist buddy who does not work on cars, especially race cars. How should this be chucked up in the lathe? Should it be dialed in true to the surface that the pressure plate bolts to?

The guy that used to do most of my flywheels (before he passed away last year) machined them on his overhead mill, using a rotary table. It was clamped via the center of the flywheel, where is bolts to the crankshaft.

Bob

[GTJIM]

I guess that is to scollop out the bits between the pressure plate mounting holes on the outer edge/clutch side of the flywheel - really the only place there is sufficient 'extra' metal on the outer rim of the flywheel as the back(motor)side is already relieved on the casting. Plus the ring gear is biased to the motor side of the flywheel and needs some metal under it.

PS: Liked the way you had that area tapered away on the 'wheel with the smaller Chevette clutch!

[opelnut10]

If you know someone that has a brake rotor lathe, invest in a new bit for it and whittle away. Old trick, take the starter ring off and do your cutting when finished put the flywheel in the freezer overnight, next day turn the starter ring over from the side that was up (new tooth contact) it will slip right into the step on the flywheel and use a butane torch to heat the flywheel and it will expand back to grip the starter ring. To take the ring off, use the same butane torch clamp the flywheel upright in a vise and heat the ring going around the outside and tap it with a hammer it will come off.

[Manta Rallier]

Originally Posted by RallyBob I was refering to the area that the clutch disc itself actually rides on. That is the area that gets the most heat, and in cases where a flywheel/clutch is abused, it shows the most heat-cracks. Just another FYI, but for a competition car, it's always a good idea to have the flywheel magnafluxed prior to starting any machine work, to make sure it's not cracked. And I like to have the flywheels shotpeened after machining for good measure. Costs something like $25 at the local MIL-spec/aerospace shotpeening facility, which is cheap insurance. Bob

OK, yes you got me thinking about the 'fluxing and shotpeening. Very good ideas.

Now if those guys in SC would just pay me for that last big project, the new project can really get going. The Alltrac has it's new trannie almost ready to go, so some space will need to be filled in the garage!

Thanks,
Mark B.

[jeff denton]

Yeah, the scalloping is a neat little touch if the flywheel must be at the most ultimate "lightness".
Can you experts describe the balancing process, obviously a must after all this cutting is done?
Thank you.
This thread and the one I bumped up yesterday probably should be merged, we're kind of talking the same subject in two threads here...

[GTJIM]

Originally Posted by jeff denton 1) Yeah, the scalloping is a neat little touch if the flywheel must be at the most ultimate "lightness". 2)Can you experts describe the balancing process, obviously a must after all this cutting is done? 3)Thank you. 4)This thread and the one I bumped up yesterday probably should be merged, we're kind of talking the same subject in two threads here...

1) Scalloping removes metal from the farthest out edge of the flywheel - the bits that have the most effect when removed - best to remove them first when working to a weight limit.

2) "Static" balancing - see picture
"Dynamic" balancing - set what your local tyre store does with wheels ....
The difference is that weight (metal) is removed from the heavy side - got to figure that into the weight when working to a limit ... don't want to 'balance' it below the minimum.

3) Nay Problem-O!

4) Then how could us 'experts' post mutually exclusive and contradictory posts ??

HTH