As the crankshaft oil seals were leaking on both sides I had to replace them before replacing the pistons and running the engine. If you don't, the pistons will be toast in no time. I find it easier to work on the engine when it's on the bench so I took the engine out of the frame.
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| Taking the engine out of the frame |
But before I took the engine out I used an impact screwdriver to loosen the engine cover bolts/screws. To loosen the screw underneath the oil pump cover you need an extension for your impact screwdriver.
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| Impact screwdriver with extension |
After the covers were removed I had to take off the the alternator cover/points, rotor and sprocket on the left side and the clutch assembly and primary gear on the right side.
The alternator cover is held by three long bolts and if you loosen them you can easily pull off the stator assembly with points.
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| Stator assembly is hold by three long screws on the outside |
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| A look inside the stator assembly - Yamaha RD125A |
For the next step you need an air impact wrench to loosen the bolt with the points timing cam in the middle of the magnetic rotor. This bolt is screwed in the crankshaft. Hold the rotor with your other hand and wear a glove. Now you can remove the rotor... But it's not that simple (don't worry ..it isn't hard if you know how). You need a high tensile M10 bolt with 1.25 tread which is long enough (50 mm is long enough). Screw it in the middle of the rotor till it hits the crankshaft, grap you air wrench, hold the rotor (wearing a glove) and the bolt will push off the rotor from the tapered crank end.
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| Rotor and timing cam with securing bolt - Yamaha RD125 1974 |
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| Taking off the rotor with an M10 - 1.25 bolt and an air wrench |
Now you can see the oil seal but before you can remove it you have to remove the metal holder, just loosen the two screws and take it off.
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| Crankshaft oil seal and holder - Yamaha RD125A |
In order to remove the old oil seal I used a screw with my Yamaha LS3 but it isn't the easiest and safest way. So for the occasion I bought a handy oil seal remover tool. The seals came out really easy without the risk of damaging/scratching the engine.
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| Oil seal extractor tool |
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| Oil seal remover tool |
I also used the air impact wrench to loosen the nuts of the clutch boss and primary gear on the right side.
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| Loose clutch boss nut |
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| Primary gear and plastic tacho gear - Yamaha RD125A 1974 |
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| Primary gear removed with an air impact wrench |
It's easy to forget the thin O-ring underneath the collar behind the primary gear. Slide the collar off and take the O-ring off with a wooden pick. The old one snapped as soon as I touched it...
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| O-ring 93210-18023 crankshaft Yamaha RD125 |
Before you install the new oil seals, fill the lips with grease and use something to drive 'm in nice and even. I used different sizes of PVC plumbing pipes.
When I fastened the screws with spring in the clutch basket, one of them snapped... The screw must have had a hair crack already because the torque I used was really low... Anyway, time for some drilling.
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| Broken spring screw in clutch basket |
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| Broken spring screw in clutch basket |
The original screw is a M5 with 0.8 tread. So in this case I used a 2.5 mm cobalt drill. Cobalt drills are harder and will not quickly dull if you add some oil when you're drilling the broken screw or bolt.
Make sure you drill in the middle of the bolt otherwise you'll damage the thread. When I had a drill hole of ca. 3mm I took a screw extractor and the broken screw came out nicely.
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| Cobalt drill and screw extractor |
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| Taking out the broken screw with a screw extractor |
After the broken screw was removed I used a 5 mm - 0.8 tap to clean out the tread.
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| Cleaning the tread with a tap |
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| Broken clutch screw (137-16337-01) Yamaha RD125A |
Unfortunately those clutch screws part-number 137-16337-01 are hard to find so it will take a while before it's all back in place.
Another "problem" I had with the clutch reassembly was a mysterious "extra washer". I couldn't find it in the diagram. It seemed that I was not the only one. On the "Aircooledrd" forum I found a tread about the same problem and luckily also an answer. It seems that Yamaha has paired the needle bearing (3) with this washer as one part number ( Yamaha 93341-22302 )... very confusing. The washer goes between the inside of the clutch basket and needle bearing.
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| Clutch diagram Yamaha RD125A |
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| Part 3 ( Yamaha 93341-22302) exists of 2 parts |
Tip: Have you ever noticed the metal clutch plates have a sharp edge on one side and a smooth edge on the other side? When you're putting back the metal clutch plates make sure the side with the "sharp edge faces outside.
