I am finally getting engine back together. Scat crank new main shaft and new drums. Got flywheel and main shaft on. Bolted it up. And after rotating them 180, I’m down to .001 so I’m set there. I bolted driven plate to brake drum. All the bushings were done at high end machine shop and up to this point everything was great. So I checked runout on the output shaft and friggin .036 of runout!!! Took apart, checked to make sure drum turned true, it does. Tested driven plate alone and still .036! I looked carefully and put dial up under plate just to see if entire things is wobbly. I wanted to be sure the runout is in the bushing and not a bent plate. Sure as shit the whole damn thing wobbles! I knocked out bushing, bolted the plate back to drum and after rotating position just once I’m down to .010 so a little more work to find a good index. Now I need to find a local guy who can machine bush straight this time! I guess that why they call it test fitting! My question is can this be done in a lathe and expect to come close?
David, Yes, The driving plate bushing can be bored in a lathe. I’d even say its one of the easier ones to do since it’s readily accessible to measure and you can keep the boring bar short. A few tips:
- Make sure the plug that fits in the bore is installed and tight before proceeding. If not, install it. The fitted bushing can’t be pulled out to correct this later…
- The shaft (Called the “driving plate sleeve”) should pilot in a small lip on the driving plate. This is critical since it aligns the sleeve with the lip that mates to the brake drum. Make sure the rivets are tight.
- The collar (Called the “clutch shift”) that normally rides against the clutch fingers (there’s 3 of them) works well to keep the fingers from moving around during machining. The lathe chuck can also be used, the key is just keep them restrained or they will fly out during machining.
- If you chuck up the driving plate assembly on the sleeve (i.e. shaft), indicate the shaft to get “0” runout. I prefer a 4-Jaw or adjustable 3-Jaw chuck to get it dialed in. You’ll only be able to indicate a short section beyond the chuck, and the fingers will be in the way. But it can be done!
- Before machining, check the runout of the inside of the lip that mates with the brake drum. If you find excessive runout,stop and figure out why. Also check the face runout of the surface that mates with the brake drum as well. The interface of the driving plate to the brake drum is intended to be completely concentric and perpendicular to the driving plate sleeve.
I was able to find the just right position of the driven plate to the drum. I am down to .004 total runout. So I know for sure the end of the output shaft is true. I will have my machinist index on that spot and true to zero runout to bore the bushing. I talked this over with several t guys that do almost everything themselves, and they all match what Mr. Martin says. Who ever knew that the model t emotional roller coaster was measured in thousands of an inch
I finally got the runout to just between 2 and 3 thousands! It took pressing in several bushings until I was happy with how straight it went in. Then I took driven plate and brake drum assembly to a machine shop. Instead of indexing on the driven plate sleeve, I had them true to zero on the brake drum sleeve. I then had them unbolt the brake drum and true the driven plate bushing. Thus brought the runout down to about .011 and not good enough. I sent the plate out to j and m machine and they were able to remove the extra amount from the mounting surface of the plate. I can finally move on and assemble the engine! Thank God!