Post by mungus on Dec 2, 2019 15:37:38 GMT -6
Anyone here consider themselves an expert on the Gemini 50 / Yamaha YF1 roller latch type kick starters? I've got a weird problem with mine and I am wondering if anyone else has seen this.
I rebuilt the engine (not my first rebuild by a long way, nor my was it my first Gemini motor), then dismantled, cleaned, and inspected the starter assembly per the manual. I tested it in my hand (quick rotation to see if the the rollers lock up on the inside of the drive gear), and it was fine. Worked every time. Perfect. I then assembled the motor and bench tested the starter. It engaged perfectly and never slipped at all. All good I thought. I had NO reason to suspect anything was wrong. However when I put the motor back in the bike the starter was slipping, it only engaged and turned the motor over maybe 50% of the time, the rest of the time it slipped and the kick starter lever just goes through with no resistance.
GRRRR! Soooo out came the motor, stripped it on the bench and inspected the starter. All looks fine. The rollers measure up spot on 6.00 mm, as new. The shaft looks fine. I had a NOS starter gear and roller cage that I got from eBay so I swapped them out for the old ones this time. All the same, hand tested fine (the quick flick to check it locks up fine), then bench tested (every single attempt it worked perfectly), so I reinstalled the motor and AGAIN, the kick starter slips... This time even worse than before. It barely engages at all now, maybe 10% of the time and the end of the throw. WTF???
Now this isn't the first Gemini motor I've done and the others have all been fine. The starter assembly is simple enough and I understand them OK I think. I've measured up everything with the mic and compared them to NOS shafts etc that I have. NO DIFFERENCE. The starter shaft is only held at each end, by the capped hole that comes through the LH casing by the drive sprocket, and in the RH casing behind the seal. The internal casing holes are much bigger as they simply allow the shaft to pass through the whole rear casing set. My thoughts so far are that possibly theres a partial misalignment occurring by wear in one of those holes / bushings that only becomes evident under foot pressure. But then it does it using my hand too, so no. Or is the casing being warped when I do up the frame mounting bolts? Or is there a shim missing behind the shaft where it rests in the LHS casing? (not in my manuals nor on my other 3 Gemini motors).
None of this makes sense to me. So whats the problem I wonder?
Any ideas.
UPDATE
I found one eBay listing for a Gemini starter assembly that shows 2 washers, so that leads me to thinking one of them is a shim to space the starter towards the counter shaft. Perhaps that’s the issue. Perhaps you are supposed to lay the shafts into the LH case and space the kick shaft gear to accurately mesh with the associated counter shaft gear? In the absence of any better idea that’s what I’ll do, so out comes the motor yet again! UGGGGH
I rebuilt the engine (not my first rebuild by a long way, nor my was it my first Gemini motor), then dismantled, cleaned, and inspected the starter assembly per the manual. I tested it in my hand (quick rotation to see if the the rollers lock up on the inside of the drive gear), and it was fine. Worked every time. Perfect. I then assembled the motor and bench tested the starter. It engaged perfectly and never slipped at all. All good I thought. I had NO reason to suspect anything was wrong. However when I put the motor back in the bike the starter was slipping, it only engaged and turned the motor over maybe 50% of the time, the rest of the time it slipped and the kick starter lever just goes through with no resistance.
GRRRR! Soooo out came the motor, stripped it on the bench and inspected the starter. All looks fine. The rollers measure up spot on 6.00 mm, as new. The shaft looks fine. I had a NOS starter gear and roller cage that I got from eBay so I swapped them out for the old ones this time. All the same, hand tested fine (the quick flick to check it locks up fine), then bench tested (every single attempt it worked perfectly), so I reinstalled the motor and AGAIN, the kick starter slips... This time even worse than before. It barely engages at all now, maybe 10% of the time and the end of the throw. WTF???
Now this isn't the first Gemini motor I've done and the others have all been fine. The starter assembly is simple enough and I understand them OK I think. I've measured up everything with the mic and compared them to NOS shafts etc that I have. NO DIFFERENCE. The starter shaft is only held at each end, by the capped hole that comes through the LH casing by the drive sprocket, and in the RH casing behind the seal. The internal casing holes are much bigger as they simply allow the shaft to pass through the whole rear casing set. My thoughts so far are that possibly theres a partial misalignment occurring by wear in one of those holes / bushings that only becomes evident under foot pressure. But then it does it using my hand too, so no. Or is the casing being warped when I do up the frame mounting bolts? Or is there a shim missing behind the shaft where it rests in the LHS casing? (not in my manuals nor on my other 3 Gemini motors).
None of this makes sense to me. So whats the problem I wonder?
Any ideas.
UPDATE
I found one eBay listing for a Gemini starter assembly that shows 2 washers, so that leads me to thinking one of them is a shim to space the starter towards the counter shaft. Perhaps that’s the issue. Perhaps you are supposed to lay the shafts into the LH case and space the kick shaft gear to accurately mesh with the associated counter shaft gear? In the absence of any better idea that’s what I’ll do, so out comes the motor yet again! UGGGGH
