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Author Topic: 4th gear slips and pops out-need to split the cases(NEW INFO)  (Read 2591 times)

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Offline scondon

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4th gear slips and pops out-need to split the cases(NEW INFO)
« on: May 26, 2007, 10:46:34 PM »
    Well I finally got the project bike on the road for some serious testing. Engine runs good and strong, all my wiring works as intended, and I was hoping that all that was left to do was get the carbs and timing sorted. But when I hit 4th gear it started  slipping intermtently, and if I really give it gas it pops out of gear entirely. 1-3, and 5th gears work just fine.

       The transmission worked fine before I took the motor apart and I never touched the gearing, just the shifter assembly under the engine cover. The only time I touched the transmission was when I put the cases back together and had to slip the center? shifter fork back between the gears and it only seemed to fit one way so I didn't pay any mind to it.

        Anyway, the motor's got to come out. I've got another F2 gearbox that I can use. I would like to leave the top end assembled, if possible, so my question  is.....can I split the lower case and swap transmissions without taking the top end apart (or have any of you ever done this)?

engine is a modified cb750f2
« Last Edit: June 23, 2007, 10:55:18 PM by scondon »
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Offline Sam Green Racing

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Re: 4th gear slips and pops out-need to split the cases
« Reply #1 on: May 26, 2007, 11:04:24 PM »
God man, I thought you were an expert on these motors  ;D ;D ;D.
The only work I have done was to pull off the lower crank case half to change the primary chains, so your answer is yes. ;)

Sam. :P
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Offline scondon

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Re: 4th gear slips and pops out-need to split the cases
« Reply #2 on: May 26, 2007, 11:27:00 PM »
Quote from: SamCR750 on May 26, 2007, 11:04:24 PM
God man, I thought you were an expert on these motors ;D ;D ;D.
The only work I have done was to pull off the lower crank case half to change the primary chains, so your answer is yes. ;)

Sam. :P

   The brain is very groggy from so much work lately. I've been trying to go over the bottom end disassembly in my head to see if there would be any snags, but it's making me very sleepy :D :D

    Thanks for givin' the answer I wanted to hear,Sam ;D
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Offline bryanj

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Re: 4th gear slips and pops out-need to split the cases
« Reply #3 on: May 27, 2007, 05:53:17 AM »
Swap the selector drum as well
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Offline bwaller

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Re: 4th gear slips and pops out-need to split the cases
« Reply #4 on: May 27, 2007, 06:41:34 AM »
A bit of bad luck Sean? Two steps forward, one back as they say.

Bryan mentioned the drum already, there were usually three culprits causing that fourth gear pop-out, the drum, one fork, and rounded dogs. (as opposed to rabid dogs! that'll be you if this doesn't go well) Often there would be a small chunk out of a corner of the track on the shifter drum and any unsual wear on the fork renders those junk too. It's been a long time, but check fourth gear on the countershaft closely. The dogs are probably badly rounded and the corresponding slots on the mating partner also.

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Offline scondon

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Re: 4th gear slips and pops out-need to split the cases
« Reply #5 on: May 27, 2007, 08:57:32 AM »
    Yeah, I intend to swap out the entire gearbox with one that I know is good. I had ridden this engine for 700 miles or so and did not have any problems with 4th gear before the teardown. I'll be interested to see what happened to cause this, but I'm going to give it a month or more before tearing it back down. Need to replenish my enthusiasm ;) :)
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Offline hymodyne

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Re: 4th gear slips and pops out-need to split the cases
« Reply #6 on: May 27, 2007, 11:50:57 AM »
center fork-

I'm doing a 2nd teardown on a modified cb500K1 because of a bad center selector fork. Gonna call westernhills after the holiday and get a new one.
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Offline Raul CB750K1

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Re: 4th gear slips and pops out-need to split the cases
« Reply #7 on: May 27, 2007, 01:04:06 PM »
I have the same problem, but only sometimes. I've learned to shift at the right time - I mean the right rpm range-. Otherwise, it seems the dogs doesn't fully engage and the gear slips out under load. On the same way, it's very difficult to downshift unless the engines is revving about 5k rpm, as opposed to modern bikes.


Raul
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Offline scondon

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #8 on: June 23, 2007, 10:54:03 PM »
        It hasn't been quite a month yet, but the opportunity arose for me to use a lift at my friends shop in order to tear into the Sumbich and see what was wrong with 4th gear. It turns out to be an error on my part that happened while putting the cases together. The fact that the cases went together and the engine didn't eat itself despite my error has me quite amused and the plus side of it all is that I now know how to work on a transmission :)  Here's what happened:

        While lowering the lower case onto the upper case I took a look to insure that the center shift fork was slotting into the upper gear shaft correctly, which it was. I then positioned myself above the lower case, where I could no longer see the shift fork, and wiggled, lifted, and repositioned the lower case a bit until it dropped snuggly against the upper case. During this last bit of maneuvering the shift fork popped off the shaft, unbeknownst to me. Though the fork was no longer AROUND the shaft, its bottom finger was still in the groove while the upper finger was resting against the upper case. And the bike RAN for 80 miles like this :D :D :D :D

        I can laugh about this now 'cause the actual damage was minimal and after a full days work the engine is back in the frame with just a few hours of assembly left to do tomorrow. The center fork has been replaced due to wear from being out of position. The selector drum has been replaced since the channel that the center fork rides in was very slightly worn along one side(taking no chances). The 4th gear dogs survived unscathed and there was only the slightest bit of wear visible on the mating gear where the dogs had been popping loose from, and I mean very very slight and just on the face so neither gear needed replacing.

         So, Here's to another "succesful failure".  WOOHOO!!!!!!!! ;D ;D ;D

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Offline medic09

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #9 on: June 23, 2007, 10:58:08 PM »
Good job!  Ya gotta love Honda survivability...

 ;D
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Offline scondon

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #10 on: June 23, 2007, 11:04:10 PM »
Quote from: medic09 on June 23, 2007, 10:58:08 PM
Good job!  Ya gotta love Honda survivability...

 ;D

   I am truly amazed at how well it held up, despite my best efforts to kill it :D
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Offline bwaller

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #11 on: June 24, 2007, 04:30:36 AM »
Well I think you should race out and buy some lottery tickets, you're on a lucky streak!!!

All's well that ends well.
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Offline MRieck

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #12 on: June 24, 2007, 06:00:35 AM »
 I bet that will never happen again Sean. ;) ;D
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Offline jtb

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #13 on: June 24, 2007, 06:54:09 AM »
If I'd done that, I'd have left lower case and tranny scraps all over the road!   ;D ;D ;D
Sure is great to know it's fixed, isn't it?
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Offline scondon

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #14 on: June 24, 2007, 09:02:56 AM »
    I love this forum. No matter how bad things seem there's always folks who've gone through the same, or worse, and give good advice on how to recover. "Help! My foot fell off while putting on my shoe and I can no longer walk"  "Have ya tried reinserting the bone and suturing the skin? Don't forget to use crutches while it heals. Reminds me of the time my eyeball exploded"

     You guys keep me sane :)
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Offline scondon

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #15 on: June 24, 2007, 04:56:57 PM »
     It's official. Finished putting everything back on the bike and took it for a quick spin. Engine runs strong in all 5 gears. This bike is a real joy to ride and I can't wait to get the carbs and ignition dialed in for high rpm riding ;D
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Offline joeb

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #16 on: June 24, 2007, 05:34:51 PM »
Good job Sean glad to hear you got that beast up and running . :D ;D :) 8) 8) 8) 
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Offline MRieck

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #17 on: June 24, 2007, 05:57:32 PM »
Quote from: scondon on June 24, 2007, 04:56:57 PM
     It's official. Finished putting everything back on the bike and took it for a quick spin. Engine runs strong in all 5 gears. This bike is a real joy to ride and I can't wait to get the carbs and ignition dialed in for high rpm riding ;D
Sean...is that the engine with the nice head etc???
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Offline scondon

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #18 on: June 24, 2007, 06:46:15 PM »
Quote from: MRieck on June 24, 2007, 05:57:32 PM
Quote from: scondon on June 24, 2007, 04:56:57 PM
     It's official. Finished putting everything back on the bike and took it for a quick spin. Engine runs strong in all 5 gears. This bike is a real joy to ride and I can't wait to get the carbs and ignition dialed in for high rpm riding ;D
Sean...is that the engine with the nice head etc???

   Yeah, Mike. You did this head for me back in January or even as long ago as last October. The Dyna 2000 I got from ya last Summer. And the Keihin CR 29mm's that I got off ya in 2005 will be going on the bike as soon as I get a F1 tank with the straight down petcock(F3 "elbow" petcock bangs into the carbs when mounted).

  Ya ever get those "JMR Motorcycle Porting" stickers made, I wanna stick a dozen or so on this bike ;) ;D
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Offline bwaller

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #19 on: June 24, 2007, 06:58:27 PM »
Congratulations Sean,

Don't you love it when a plan comes together! Post a pic when you get the chance.
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Offline scondon

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #20 on: June 24, 2007, 07:22:45 PM »
  Here it is in all it's unfinished glory. Most of the stuff on the bike is what I had laying around the garage. Enough to get the bike running and the motor broken in before the new tank,seat, fairing, side covers and exhaust come in later this year.   

    If anyone spots a rear Lester 18 x 2.15 w/disk brake made in '77 or '78 let me know, I've only seen one go on Ebay a few years back and "Big Pockets" Carpy snapped it up.
« Last Edit: June 25, 2007, 08:18:19 AM by scondon »
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Offline MRieck

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Re: 4th gear slips and pops out-need to split the cases(NEW INFO)
« Reply #21 on: June 25, 2007, 04:50:46 AM »
Quote from: scondon on June 24, 2007, 06:46:15 PM
Quote from: MRieck on June 24, 2007, 05:57:32 PM
Quote from: scondon on June 24, 2007, 04:56:57 PM
     It's official. Finished putting everything back on the bike and took it for a quick spin. Engine runs strong in all 5 gears. This bike is a real joy to ride and I can't wait to get the carbs and ignition dialed in for high rpm riding ;D
Sean...is that the engine with the nice head etc???

   Yeah, Mike. You did this head for me back in January or even as long ago as last October. The Dyna 2000 I got from ya last Summer. And the Keihin CR 29mm's that I got off ya in 2005 will be going on the bike as soon as I get a F1 tank with the straight down petcock(F3 "elbow" petcock bangs into the carbs when mounted).

  Ya ever get those "JMR Motorcycle Porting" stickers made, I wanna stick a dozen or so on this bike ;) ;D
The stickers are coming Sean. Don't worry....your name is on the list. ;)
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