Mushroom Seal Replacement



The clutch arm is attached to a loose threaded post. This post is responsible for compressing the clutch when the lever is pulled. Surrounding the post and connecting to the clutch case half, is a seal that resembles a mushroom. Hence the name: the mushroom seal. This seal gets brittle over time and eventually splits. The result is that oil leaks out of the case.

This repair is not difficult, but if done incorrectly, will result in another torn seal almost immediately. It is always a good idea to have a few of these seals in your parts bin. Mushroom seals are very inexpensive - approximately $5.00. The mushroom seal is available from the Heinkel Club Deutschland.

Many of these symptoms might also be caused by a faulty clutch side case gasket. The disassembly discussed in this article will allow you to replace that gasket as well. If your gasket is old, and since you are in there, you might as well replace it.

Repair Time: 2-3 hours.

Tools Required:


Tough guy picture.

Remove rear body panel. The body panel is secured by two 10mm nuts under the seat and one 19mm bolt under the spare tire. Don't forget to disconnect wiring harness to rear lights and turnsignals.

Drain engine oil. The oil drain plug is a 14mm bolt located on the bottom side of the engine.

Remove gas tank. The gas tank is secured by two 10mm bolts on either side of tank. On an A2, the gas tank also supports the rear fender. Remove this bolt. Turn off the gas and remove the fuel line.

Remove muffler. The muffler is secured by two 14mm bolts on the right side and one 14mm bolt inside the rotating "blower" muffler cover. Loosen the blower cover and rotate it upwards to reveal the hidden 14mm bolt. Once the muffler has been removed, remove the blower cover as well.

Mushroom seal picture.

Remove clutch side cylinder shroud. The clutch side shroud is secured by five 10mm nuts. The most difficult nut will be the one behind the voltage regulator. You might need a thin wrench to complete this task. Thankfully, you only need to loosen this nut. The shroud has a slot that allows it to be removed while this nut is in place. Remove all other nuts. Once the nuts are removed, ease the shroud over the exhaust manifold.

Mushroom seal picture.

Remove clutch and gear cables. Remove cables. It is a good idea to count the number of turns the adjusters were set at prior to removal. This helps when re-connecting cables.

Remove clutch arm. The clutch arm is secured by slotted screw locked in place by a 14mm nut. Use a flat head screw driver to hold screw while loosening the nut.

Mushroom seal picture.

Remove shifting arm. The shifting arm is secured by a 10mm bolt. Once the bolt is removed, the shifting arm should slide off shaft.

Remove clutch side engine/frame buffer bracket. The engine buffer bracket is secured with a 17mm bolt. This bolt is removed from the underside of the engine.

Mushroom seal picture.

Remove worm gear. The worm gear is a strange, slotted screw object that holds the clutch arm in place. Use a narrow slotted screw driver to turn the screw inside the worm gear. Turning the screw clockwise will extract the worm gear.

Remove 10mm nuts that secure clutch cover. The clutch cover is secured by ten (or so) 10mm nuts.

Mushroom seal picture.

Remove clutch cover. The clutch cover should come free fairly easily. You might need to use a flat head screw driver in two special slots between the halves. Do not wedge the screw driver in against the mating faces. You will damage the faces and create leaks.

Mushroom seal picture. Mushroom seal picture.

Replace mushroom seal. Pull off the old mushroom seal. Most often, this will rip during removal. I generally grease up the area that holds the mushroom seal. Install new mushroom seal.

Grease up the clutch pin. I generally apply a generous amount of grease to the clutch pin to allow the mushroom seal to slide over it during installation. Notice the flat spot on the clutch pin. This is where the mushroom seal must ultimately rest when the clutch cover is installed.

Gear notches.

Verify shift rod installation. Verify that the notch on the shift rod is between the two notches on the corresponding gear. If the notches aren't lined up properly, you will not be able to set up the shift cables properly.

Replace gear shift oil seal. There is a small oil seal that surrounds the gear shift rod. This oil seal mounts on the outside of the clutch cover. I use a small hammer and punch (from the inside of the clutch cover) to knock out the old seal.

Replace clutch cover gasket. No trick here ... other than I used a lot of grease to hold the gasket in place.

Fit clutch cover. Line up all studs with the holes and install carefully. You might need a small hammer to tap the cover into place. Don't use too much force! Once installed, tighten each nut equally. Don't forget that the nut on the far right side, in the middle, also holds a bracket for the clutch arm spring.

Install clutch side engine/frame buffer bracket. No trick here.

Inspect mushroom seal. The inner diameter of the mushroom seal should be resting on a flat spot on the clutch pin. I use a small flashlight to peer into this area of the clutch cover. If the mushroom seal is resting on the threads of the clutch pin, it will rip once you start using the scooter. If I need to push the mushroom seal into place, I use a narrow bodied, long socket. I have one that will fit into the hole and can be used to push the seal into place.

Worm gear incorrectly installed.

Install worm gear. Slip the worm gear over the clutch rod. The worm gear is threaded internally and externally. The internal threads are used by the clutch rod. The external threads are for the clutch cover housing. To get the worm gear to go into position, use a narrow blade screw driver on the clutch rod slot. Turing the screw driver counter clockwise will make the worm gear go into position. The worm gear is installed when it is flush with the clutch cover.

Worm gear correctly installed.

Keep in mind that the worm gear has only one correct position. Lie the clutch lever on the worm gear. If the clutch is approximately in the 4 o'clock position, it is installed properly. Anything else, remove the worm gear turn it 120 degrees and try again.

Install shifting arm. No trick here except that the notch on gear arm must match the notch on the shift rod.

Install clutch arm. The workshop manual says that the lever must be free until it lines up with one of the case nuts (approximately 5 o'clock position). Once they align, it must have resistance. To adjust this position, use a narrow screw driver to turn the clutch rod back or forth.

Install muffler. No trick here other than I generally use high temperature sealant between the exhaust header pipe and the muffler.

Install gas tank. No trick here.

Install cables. I hope you took notes on the number of turns out your cables were set to. I think this is the quickest way to adjusting the cables. If you forgot, then you will have to set them from scratch.

Install rear body panel. No trick here.

Refill engine oil. Uh yes, don't forget this step!

Look for drips I will say that there is nothing worse than finding leaks once the cases have been assembled. Hopefully you will have no leaks.



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