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Submitted Article
Oliver 550 Clutch Overhaul Tips
by Greg Sheppard

I got my 1964 Oliver Model 550 (Serial 141-139-519) second-hand and used it for several years before the clutch began to slip. After taking up the pedal linkage several times I saw it was going to take more than that. The engine had been leaking oil at the rear seal and I suspected oil was causing the driven plate to slip, so I decided to replace the crankshaft oil seals at the same time I overhauled the clutch.

Allow yourself plenty of time... After buying a new clutch plate and new cork oil seals (from Korves Brothers) I pulled the engine, expecting to finish the job in a week or so. That was a bad guess. A lot of parts were caked with dirt and I couldn’t bring myself to just put them back that way. Then it seemed a shame not to paint things while they were clean and accessible, and so it went. It’s a tricky job, and this was my first one, with only a set of (sometimes cryptic) Oliver Service Manuals for guidance. On top of all that I found some problems I didn’t know I had and took time to repair them too, making a bigger job for myself than may be necessary for you, but even so I caution against tackling this job on a tight schedule.

Step by Step (This covers the clutch only):

1. Remove the center frame cover and detach the clutch cover assembly from the flywheel. Then you can either “Z split” the front and center frames (which is easier) or pull the engine (as I did). Either way, the drive shaft will be pulled out of its pilot bearing, at which point you can slip the driven plate and clutch cover assembly off the drive shaft. Inspect the inside of the clutch compartment. If you find lots of oil and dirt, consider replacing the rear oil seal. The leak is not going to get any better, and there is a risk that the continued presence of oil will ruin your new driven plate. Give the compartment a good cleaning either way. Remove the flywheel and pilot bearing hub from the engine.

2. Next, disassemble the clutch cover assembly. Remove the adjusting screw clips with a pair of needle nose pliers. Put the assembly in a press and, using a round piece of wood in the center, depress the levers. Run up the lock nuts to make some slack and take out the lever adjusting screws and washers. Mark the position of the pressure plate in relation to the cover plate by making a punch marks on both. Don’t remove the pins that hold the levers, unless you know where to get new ones (I don’t). Because they are staked in, you can’t re-use the old pins. Clean all the parts.

3. Re-assemble by setting the pressure plate on the press table. Position the springs under the levers, and squeeze the levers down with the same round block of wood used before. Hold the levers down by with ¾” hardwood wedges driven under their back (outside) edges. Release the press and move the assembly to your workbench. Inspect the springs to make sure they rest flat against the undersides of the levers and if not, use a hammer and punch to tap them outward and into place. Check carefully. If you see a spring that’s not inclined at the same angle as the others, it needs to be repositioned.

4. Put the pressure plate back on the press bed with the clutch cover on top of it, using the punch marks to get it in its original position. Position several pieces of wood (3/4” or so) around the rim to support the cover assembly but not the pressure plate. This will give you room to get the adjusting screws started.

5. Again press down on the levers with the round block of wood until you have room to work. Put the adjusting screws through the washers and into their holes, using your fingers to get them started in the pressure plate lugs. Make sure you have a half inch or so of threads engaged to avoid the risk of stripping when you adjust them later. You will need to lift the pressure plate with a screwdriver or other flat tool as you run the screws in.

6. Use a trouble light to inspect the position of the pressure plate lugs (which hold the adjusting screws) to make sure the lugs are exactly lined up with the openings for them in the cover plate. Run the locknuts down onto the washers until snug but not tight. You should have about 3/8” of thread showing between the head of the screw and the locknut at this point. Release the press and move everything back to the bench. Incidentally, if your adjusting screws are worn you can replace them with grade-8 cap screws, provided you grind off the head markings and polish the surface. The originals are 15/16” long; I replaced mine with 1”, and

1-1/8” would not be too long if you have pin hole wear (see step 8).

7. Check the position of the pressure plate lugs once more, now that you can get a good look at them. They should have been drawn into the openings in the cover plate when you tightened the locknuts onto the washers. If not, go back to the press and start over. You must get this step right or the lugs will deform the cover plate when you tighten it down onto the flywheel.

8. Now adjust the levers. The Oliver Service Manual procedure for doing this calls for placing three, three inch long pieces of .330” key stock between the flywheel and the pressure plate—not an easy thing to lay hands on, so I used the new driven plate instead—under compression it is .332” thick. Assemble the clutch cover plate to the flywheel with the driven plate (hub toward the flywheel) between the flywheel face and the pressure plate. The cap screws around the circumference of the clutch cover must be snug enough to bring the cover plate down into contact with the flywheel surface but need not be torqued at this stage. Loosen the locknuts enough to let you turn the adjusting screws and set them to bring the lever contact surfaces (which ride on the throw-out bearing) to the innermost point of their arc. The Oliver Service manual says to adjust to “1 15/16” above the flywheel face”, which is probably right for a new clutch cover, but if the holes for the pins in cover plate have been elongated by wear (as mine were, by about 1/16 of an inch) it throws this dimension off. Reason: the distance from the fulcrum (pin) to the back edge of the lever is only a fourth of the distance from the fulcrum to the lever tips which contact the throw-out bearing, so whatever wear you have will be multiplied by four at the lever tip. In my case, 1/16” of wear threw off the tips by about ¼ of an inch. To compensate for wear, set the levers so they are at the innermost point in their arc when the levers are resting on the adjusting screws, and set all three screws to the same height. For me, the correct adjustment worked out to be about 2 ¼ inches above the flywheel surface. I made a doughnut-shaped template out of cardboard, the same size and shape as throw-out bearing face, and held this under the lever contact tips to be sure they would meet the bearing face near the mid point of the template’s ring. Because spring pressure against the levers is directed slightly outward toward the circumference of the cover plate, elongation of the holes the pins ride in proceeds in the same direction. This moves the lever tips toward the outside edge of the throw-out bearing, and will eventually get so bad (maybe in another 38 years for me) that the cover plate will have to be replaced or reworked. If so, the cardboard template will warn you. When all is well, tighten the adjusting screw locknuts, replace the clips, and remove the clutch cover assembly from the flywheel. With the clips installed, the lugs on the pressure plate will be drawn into the openings in the cover plate; you should see about ¼ of an inch poking through. Put the cover plate and the new driven plate (still with hub toward the engine) on the clutch shaft. Attach and torque the flywheel and pilot bearing hub to the engine, lower the engine onto the front frame (or “un Z split” the case) backing the pilot bearing onto the drive shaft. The easy way to do this is to position the crankcase on the dowels and pull the parts together for the last ¾ inch or so using the 3/8 inch bolts which join them.

9. Now make a one last check. Operate the clutch pedal by hand, and make sure that all three levers contact the throw-out bearing at once. If not, remove the clips, loosen the adjusting screw lock nuts, and fine tune the adjusting screws. This is your last chance, and the adjustment is critical.

10. Start the cap screws which hold the cover plate assembly to the flywheel by hand to avoid cross threading. Using a wrench, tighten a little at a time all around to prevent distortion, and bring to full torque. Torque the engine mount cap screws (or the bolts you removed to do a Z split).

11. Replace the center frame cover, and put everything back that you took off to get at the clutch (no small job, but straightforward), and you’re done.

Three Months Later

1. The new clutch works fine. The only disappointment is I continue to see oil drippings on the barn floor. Not much, and only after the machine has been running, but I had expected the new seals to work better than they do. I’m going to put a small drain-hole in the inspection plate to keep oil from accumulating inside and ruining the clutch.

2. The old driven plate was not badly worn and didn’t look oil soaked. I think my slippage was caused by improper lever adjustment. After opening the case I could see that the levers didn’t contact the throw out bearing at the same time, and that two of them were making contact way out near the edge of the bearing. I believe these problems prevented the driven plate from getting even pressure all around.

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