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Subject: flywheel gear

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Scott    Posted 01-15-2020 at 15:15:34 [URL] [DELETE]        [Reply] [Email]  
  • flywheel gear
  • I'm in the process of rebuilding a 1952 8N. This was a running and working tractor when I pulled into the garage for a rebuild. I bought the tractor in August of 2019, so I don't have a lot of history with it but it has never given me any trouble starting up. However, when I removed the engine and was dismantling everything from the block, I noticed the flywheel ring gear was welded on, and the weld had cracked and the gear had slipped about 1/2". Everything I have read up to this point does not mention welding the ring gear onto the flywheel. It is a press fit. Is this correct? I suspect I will remove the old gear, grind the welds down smooth and install a new one the proper way. Or is it okay the way it is?

    Ultradog MN    Posted 01-16-2020 at 18:36:48 [URL] [DELETE]        [Reply] [No Email]  
  • Re: flywheel gear
  • The others have given you good info.
    Yes, it's ill fitting parts from you know where that is the problem.
    I have welded a couple of those through the starter hole.
    The technique is to have someone carefully hold the ground cable to the front crankshaft pully and nowhere else or you will arc through the main or rod bearings and ruin them.
    If the flywheel is off the tractor and you can weld a bit then no big deal just weld it again.
    Remember that the flywheel is cast iron so use a rod that is made for that. One stick of special rod is maybe $2 vs a new ring gear for $? and maybe the same ill fitting part if you buy a new one. It will last for another 40 years and can be ground off and fixed again. 4 good 1/2" tacks evenly spaced is enough.
    A few years ago I bought an 8N that the PO had to have the ring gear replaced. New ring gear did the same thing. He got disgusted, washed his hands of it and I bought the tractor. I welded it through the starter hole - with good rod - then resold it. Made about $500 in an hour or two which of course I whizzed away on more parts for my own tractor.

    Tim Daley(MI)    Posted 01-17-2020 at 06:14:22 [URL] [DELETE]        [Reply] [No Email]  
  • Re: flywheel gear
  • I cut my NC Turret Lathe Machining teeth on Ford 6375 flywheels beginning in 1975. I’d turn both sides; one Warner & Swasey 2SC on clutch face side, another side by side in a cell for engine face. Then they’d go to the NATCO drilling machining for all the holes and then to a gang drill for tapping and reaming. From there went to the parts washer then to ringgear assembly. We had a gas oven to heat a stack then a worker set each one on a flywheel and pallet. Once cooled, they went back to my lathe to get the clutch surface re-faced. The cast iron flywheel ringgear diameter tolerance is ± .002” and the ringgear is tempered steel, spec’d at .060” smaller than the flywheel diameter. There is an undercut in the corner of OD and seat so gear sets flat. OEM ringgears had a chamfer on one side if one ID and had to be assembled with that chamfer facing down into the flywheel OD seat so it seated down flat. Heating expands the gear to slip onto the wheel, as interference fit process. Reface is done after so any warpage makes sure the crank bore is all square to the world with clutch face w/n .005”. Assembled flywheels then get balanced on a special machine and packed in FORD logo marked boxes then shipped to service centers all over. Ringgear slippage was mostly due to when aftermarket suppliers started making the ringgears without that ID chamfer and they would ride up. When the gear slips, the flywheel OD will get glazed and thus usually won’t hold a gear anymore. Like Ultradog said, flywheels are cast iron and if the steel gear is tacked on with the wrong welding rod, probably won’t hold. Continuous slippage only gals up the flywheel further. I learned a lot about flywheels and ringgears. I still have the OEM drawings as well as most all of the 9N tractor drawings. I spent 20 years at that company working my way up to engineering as I got my degree at night school during that time. When I left in 1995, they went out of business a year later. From there I worked at Valenite Modco Tools til 2002 when they were sold.

    Tim Daley(MI)

    mhb@ufe    Posted 01-16-2020 at 07:44:34 [URL] [DELETE]        [Reply] [No Email]  
  • Re: flywheel gear
  • I don't like to use the term "press fit" when referring to ring gears. The proper way to install it is to heat the ring gear so it swells and then let it shrink on to the fly wheel as it cools. That is what Bruce was referring to when he said ' heat it in the oven, freeze the flywheel' . Pressing the ring gear on will swell the ring gear and it won't shrink back down.


    Tim Daley(MI)    Posted 01-16-2020 at 16:42:28 [URL] [DELETE]        [Reply] [No Email]  
  • Re: flywheel gear
  • Yes, I'm with you -'press fit' not the correct term but thought I'd use the term to not confuse the poster. The correct term is 'interference fit'. A press fit involves a male part fitting into a female part with only .0003" - .0005" tolerance between them and thus are pressed into each other. A good example is pressing a bearing into a bore.

    Tim Daley(MI)

    Tim Daley(MI)    Posted 01-16-2020 at 07:02:50 [URL] [DELETE]        [Reply] [No Email]  
  • Re: flywheel gear
  • The OEM Ford flywheels were never welded on, no need to and yes they are a press fit. The issue of welding the ringgear on started when the aftermarket companies started making flywheels and ringgears and had no clue as to engineering, fit, and function as they no doubt didn't have the OEM drawings to reference and simply reverse engineered their parts. The result was incorrect dimensions and assembly. You can opt to have them re-welded or replace with new gear and wheel.

    Tim Daley(MI)

    Bruce (VA)    Posted 01-15-2020 at 17:46:19 [URL] [DELETE]        [Reply] [Email]  
  • Re: flywheel gear
  • It's easier to tack weld a slipping ring gear through the starter hole than to split the tractor and do it correctly. The spot-weld fix is usually applied when the ' heat it in the oven, freeze the flywheel' fix didn't work.

    Fix it right or have it fixed right.

    Ozlander    Posted 01-16-2020 at 12:31:51 [URL] [DELETE]        [Reply] [No Email]  
  • Re: flywheel gear
  • Be that as it may, I certainly would not replace the ring gear if it is in good shape.
    If it is, I would tack weld it in 3 or 4 places and get on with the overhaul.

    Unless of course you have to much money and need too get rid of some.
    Some people on here like to spend other people's money.

    Dn-N-Tn    Posted 01-17-2020 at 09:47:55 [URL] [DELETE]        [Reply] [No Email]  
  • Re: flywheel gear
  • A nickel welding rod is good to weld the cast iron to the steel, as the ring gear to the flywheel.

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