Topic: Transmission feel like its slipping and catching in first gear

[Split7]

Hey everyone, I have recently come across a new issue with my k7 that I am having a difficult time pinpointing exactly what is happening. I'm hoping to tap into all the experienced SOHC4 enthusiast for suggestions om what this issues could be.

I have owned this bike for about 12 years now. I resurrected and rebuilt everything as this bike was sitting and deteriorating in a field since the 80s. I recently went thought the bike because the oil pump went out on me and ground a cam tower down. I replaced the tower and seals and put everything back together by the book. It seems to be running good. That is until I realized something was not right when accelerating hard in first gear. through all of first gear, the bike feel like it clicks out of gear then catches back into gear. this happened very quickly. It will do this several times during first gear acceleration. It doesn't do this in any other gear. Shifting feels the same as it has always been. I checked the clutch, changed the oil with new GN4, checked the shift linkage for possible issues, checked the drive chain and dampers and everything seems fine. I did order new detention springs from cycle x thinking that maybe the issue is the springs not holding arm in gear when accelerating. Im thinking maybe it wants to pop out of gear and the detent spring brings is back when more pressure is applied on pop out. I am still waiting to receive and install those. The slipping doesn't make any sort of grinding noise like I would expect if first gear was going out. Its mostly a loud cluck and a momentary lose and regain of power. Ive never really hard shifted this bike, and have always clutched it when riding. I did ask a local shop and they tell me that because it only happens in first gear, it must be the transmission. Of course I'd rather not pull the motor and split the cases, so im hoping someone might be able to shed some light on what is happening here and if this would be necessary. -  See video attached. I edited a white circle that comes up on screen when the slipping happens.
I have referred to this forum for years and it has been an intergal part of this restoration. Thank you all for sharing your knowledge here. It's truly a treasure trove of CB information!

[MauiK3]

I'm no expert but I think I'd look at the clutch closely before splitting the cases.

[scottly]

http://forums.sohc4.net/index.php?topic=86429.0

[Stev-o]

http://forums.sohc4.net/index.php?topic=86429.0

Bingo!

Quote from: GammaFlat on March 28, 2011, 09:59:19 PM

"The snap ring that holds the gear in place is not in the groove"

[Split7]

Wow this is some wild #$%*! Incorrectly installed clips moving out of place that could potentially cause the tranny to lock up and result in a bad accident. Looks like the motor is coming out  Thanks for pointing me in the right direction. You guys rock!

[Don R]

  This is a different issue, but worth a look before you take it all of the way apart.

  I had a k2 that would slip out of neutral into gear when I was trying to kick start it. I found the stud that mounts the shifter ratchet in the left side cover was loose. It had been stripped out and had a helicoil in the hole but since it had been loose so long it wore out the threads in the stud. I snagged one from a broken case and red loctited it in. It's been good since.

[HondaMan]

Another (and far more common) thing that will do this with 1st gear is a bent "L" shift fork. Like John's (Gammaflat) situation, it causes the C5-C2 dogs to barely engage, and the C5 gear pushes itself out of the barely-engaged C2 gear when this happens. In John's situation, the transmission countershaft just had to be removed, the clip flipped over, and then reassembled.

The way to tell if it is one or the other:
With the clip loose (because Honda techs installed it backward, it worked itself out of the groove) the bike will 'tap' the C5 gear against the C2 gear when the engine is hot and the bike is running on the sidestand (or leaned over, but watch that it doesn't engage and run away from you, despite being in Neutral).

If it is from a bent "L" shift fork, there will not be any 'tapping' noise when the bike is hot, in Neutral, running and leaned (carefully) over toward the sidestand.
This situation requires a new "L" shift fork to fix. The wear marks inside the C2 gear's holes will show very shallow engagement from the C5's dogs.

[scottly]

checked the drive chain and dampers and everything seems fine.

I assume that includes the sprockets, especially the front sprocket? I've seen sprockets with teeth worn to a nub that would jump a tooth under load, and first gear places more load on the chain than the higher gears.

[Split7]

So I pull the motor and took it back to the machine shop that did it originally and he suggested that in addition to changing to new clips in the right direction, I swap out the main Top Gear and the second countershaft gear. Well, I got them and had them installed. Got the bike back together and running today, and the slipping issue is still persists.  Very expensive and very frustrating to say the least. I really don’t want to take the motor back out of the bike because that’s a pain in the ass itself. I feel do defeated right now.

I did notice that the gearshift shaft is loose. Maybe that could be an issue but I guess I’ll have to look more into that  the other thing that maybe it could be is a bent shift fork? Idk where to go from here really.

[HondaMan]

It's a little unusual to just replace gears without first determining they were the cause of the trouble. Do you perchance have the old gears so some pix of them could be taken to help us see if they are showing the signs of the issue(s) we've mentioned?

This 750K7 transmission is one of the stronger 750 trannys, having the benefit of Honda's previous 7 years of testing in the early bikes. I myself have only seen 3 different problems ever appear in the K7/8 transmission, which have so far been:
1. Bent "L" shift fork from the bike being hit on the shifter lever when the engine was not running (like if the bike was tipped over and the shifter hit something on the way down, with the engine off). If run for a LONG time in this condition (5k miles, or so) then #2 happens:
2. The slots on the C5 gear get beaten up by the dogs on the C5 gear, which rounds off those dogs. Both gears show massive witness markings of this, hard to ignore.
3. The spacer(s) on the left side of the transmission's mainshaft are somehow wrong (this usually happens after someone took it apart and lost them). This causes the whole mainshaft to drift left-right while running, causing "dropout" like yours witnesses in 1st and 4th gears, sometimes also in 5th, if the mainshaft moves far enough sideways to pull the dogs of the driving gear from the selected gear. These spacers were selected on a per-crankcase basis when Honda assembled the engine in production: their purpose if to prevent the mainshaft from being able to drift left-right more than 0.1mm in use. The cases of the F2/3 and K7/8 engines were not machined for final width, but injection-molded in Honda's newer mold technology then: these shims made up for mold variations.

I haven't seen a clutch that would do what your bike's symptoms show? A slipping clutch will slip at takeoff or under heavy throttle, but it doesn't 'snap' in & out of gear like yours appears to do in the video.

One other thing that MIGHT cause this could be some [very] loose pins on the shifter drum, under the left-side transmission cover. If the center screw on the shifter drum works itself loose (sometimes they were not stamped tightly in place) then the shift drum itself will wiggle in 1st and 3rd gears, and if loose enough it can make a momentarily dog-slot dropout from not pushing the gears close enough together. This can be checked by looking into the transmission cover on the left side of the engine.

[Split7]

It's a little unusual to just replace gears without first determining they were the cause of the trouble. Do you perchance have the old gears so some pix of them could be taken to help us see if they are showing the signs of the issue(s) we've mentioned?

This 750K7 transmission is one of the stronger 750 trannys, having the benefit of Honda's previous 7 years of testing in the early bikes. I myself have only seen 3 different problems ever appear in the K7/8 transmission, which have so far been:
1. Bent "L" shift fork from the bike being hit on the shifter lever when the engine was not running (like if the bike was tipped over and the shifter hit something on the way down, with the engine off). If run for a LONG time in this condition (5k miles, or so) then #2 happens:
2. The slots on the C5 gear get beaten up by the dogs on the C5 gear, which rounds off those dogs. Both gears show massive witness markings of this, hard to ignore.
3. The spacer(s) on the left side of the transmission's mainshaft are somehow wrong (this usually happens after someone took it apart and lost them). This causes the whole mainshaft to drift left-right while running, causing "dropout" like yours witnesses in 1st and 4th gears, sometimes also in 5th, if the mainshaft moves far enough sideways to pull the dogs of the driving gear from the selected gear. These spacers were selected on a per-crankcase basis when Honda assembled the engine in production: their purpose if to prevent the mainshaft from being able to drift left-right more than 0.1mm in use. The cases of the F2/3 and K7/8 engines were not machined for final width, but injection-molded in Honda's newer mold technology then: these shims made up for mold variations.

I haven't seen a clutch that would do what your bike's symptoms show? A slipping clutch will slip at takeoff or under heavy throttle, but it doesn't 'snap' in & out of gear like yours appears to do in the video.

One other thing that MIGHT cause this could be some [very] loose pins on the shifter drum, under the left-side transmission cover. If the center screw on the shifter drum works itself loose (sometimes they were not stamped tightly in place) then the shift drum itself will wiggle in 1st and 3rd gears, and if loose enough it can make a momentarily dog-slot dropout from not pushing the gears close enough together. This can be checked by looking into the transmission cover on the left side of the engine.

Thank you for your knowledge and input it is greatly appreciated. The two gears I replaced were suggested by my engine guy. He said they were the only two that showed any signs of real ware.  Yes I have them and can send pics. I have a feeling it’s an engagement issue as I feel the first gear is not getting fully engaged and easily slipping out and back in.  the issue has become worse now since I’ve gotten the motor back from the shop, and actually drops out more frequently now in first gear.  I can check the shift from pins under the shifter cover for sure. But since everything was apart and reassembled, I know everything is been checked and tightened in that area.I never slammed gear on this bike and the bike has never been down so I don’t think it would be that issue. I’m kind of leaning towards the bent L shift fork but I’ll have to take the motor out and split the cases again to get to that and look unfortunately. In any rate, I guess I’m getting better at doing this engine removal and disassembly process lol

[MauiK3]

Sorry for your troubles, real bummer. Keep going, you will get there.

[MauiK3]

There must be someone in your area of SoCal that can zero in on this problem.

[scottly]

There is a slightly domed washer in the clutch that has to be installed with the domed side out, #16 in this drawing. A member had this installed backwards, which caused a problem with 5th gear, not first gear. It's something that can be checked without splitting the cases...
It's the dogs, or pegs on the gears that get worn that cause popping out of gear under load, not the slots like in your second picture.
Does the neutral light work properly? The neutral switch is what locates the shift drum laterally in the case, and if the switch isn't fully seated the drum can move back and forth.
What is the history of the bike? The same mechanic has had the cases apart twice now? Were the snap-rings installed correctly to begin with? If you can't find anything else wrong, I would suspect the trans was installed incorrectly, such as a misplaced spacer somewhere?

[Split7]

There is a slightly domed washer in the clutch that has to be installed with the domed side out, #16 in this drawing. A member had this installed backwards, which caused a problem with 5th gear, not first gear. It's something that can be checked without splitting the cases...
It's the dogs, or pegs on the gears that get worn that cause popping out of gear under load, not the slots like in your second picture.
Does the neutral light work properly? The neutral switch is what locates the shift drum laterally in the case, and if the switch isn't fully seated the drum can move back and forth.
What is the history of the bike? The same mechanic has had the cases apart twice now? Were the snap-rings installed correctly to begin with? If you can't find anything else wrong, I would suspect the trans was installed incorrectly, such as a misplaced spacer somewhere?

Ok ya I know the washer you’re talking about and I did install that correctly. I have done most of the work myself but splitting the cases and going into the tranny is something I haven’t personally done yet so I have my guy help me with it.  I brought the bike back from the dead about 10 years ago. I got it from a local shop for 300 bucks (see pic) and I don’t know how many owners before that. The last time the original plate was registered was in 86. I’m the only one that has had it recently. it’s interesting that you say something about the neutral switch because when I got ithe motor back this time the neutral switch is always stays on and I was wondering about that.  but you say that it locates the shift drum?? That’s interesting. I actually replaced the wire on the switch and it looks like it’s fully seated, but I’ll definitely look into that more. Also, I originally built the motor about 10 years ago and didn’t have any problems at all with the transmission until just recently it just started happening out of nowhere. That’s when I took the engine back to my guy to help me figure it out. 

[HondaMan]

About this picture: those slots are very rounded. Their engaged depth is also shallow, and now rounded out: this will need to be remachined (I can supply references of good folks who have done it for me, if needed). This tends to indicate a shallow engagement of the C2 gears' pins (see Scottly's picture above with a near-pristine C2 gear's dogs for reference).

The 3 things I know that can cause this (and the new additional jump-out you're mentioning) are:
1. Most common: bent "L" shift fork. This happens when the bike falls over to the left and something supports the shifter lever from below (like a big rock or a paint can in the garage) on the way down.
2. Second most common, following reassembly with some errors: the Neutral Switch isn't fully seated into the shift drum groove. This causes poor (shallow) engagements of 1st, 3rd and 5th gears.
3. [Very] loose shift drum top plate, which lets the pins move around when shifting. This then in turn causes shallow gear slot-dog engagements, which hasten this sort of round-out problem.

[scottly]

it’s interesting that you say something about the neutral switch because when I got ithe motor back this time the neutral switch is always stays on and I was wondering about that.  but you say that it locates the shift drum??

If the switch isn't fully seated, the neutral light will stay on. The smaller end of the switch fits into a groove in the shift drum, locating it. The faint vertical line on the switch in the pic is a "witness mark" where the side of the groove rubs on the switch. When installing the switch, install the o-ring in the case first, then the switch. If you put the o-ring on the switch first, it makes it hard to get the switch seated.
When you fixed the damage from the oil pump did you split the cases?
 

[scottly]

About this picture: those slots are very rounded.

That was the old gear, which he replaced.

[Split7]

Yes, those pictures were of the old gears. I actually found new gears online and got those. I’ll definitely look into the neutral switch and now the shift drum and in particular the pins. Maybe if I get that stuff sorted out I won’t have to pull the motor again? As far as the oil pump goes, the only thing I could tell that happened was it scored my Cam tower in one spot so I got replacement Cam towers and put all those in. Put the cam back on, timed it and did the valves and what not but there was no bottom end work done on that. I just rebuilt the oil pump. so to answer your question  no I do not split the cases for the oil pump issue. This is all really helpful though thank you guys for your info.

[Split7]

Also, here is what my neutral switch currently looks like. Looks to me like it’s fully seated, what do you think?

[scottly]

Yes, the switch looks to be fully seated. As far as the light staying on, when the trans is in neutral, the switch connects the wire to ground, which turns on the light. If you disconnect the wire from the switch, does the light go out?
It's odd that after working on the pump and top end this problem started. Maybe something got messed up under the shift cover when replacing the pump?

[HondaMan]

About this picture: those slots are very rounded.

That was the old gear, which he replaced.

That's good news!

[Split7]

[/quote]

That's good news!
[/quote]

This makes me feel a bit better knowing those gears needed to be replaced or machined anyways!

[Split7]

Maybe something got messed up under the shift cover when replacing the pump?

I rebuilt the pump and it worked great first try. Primed with Vaseline. It was on a stand so I don’t think anything would have happened to it. Another thing is when I first got it back together and started writing it. I didn’t have an issue and then about two or three weeks later I noticed it starting to do that. 

I just realized that the neutral light is just grounding out to the engine in that tight spot where it runs. the covers keep pinching it so no big deal there. Here’s a few pictures of the shifting linkage underneath the cover. everything seems real tight including the drum annd pins. The only thing that had some play is the shaft that the shift lever attaches to.  You can see that In the video attached. I’m not sure if that’s normal or not. 

[scottly]

I don't see anything that looks wrong under the cover. The play in the shifter shaft is normal with the cover off; the cover limits the play. Listening to the video again, it doesn't really sound like it's going in and out of gear, more like the clutch is slipping and grabbing? Perhaps the Vaseline packed into the oil pump found it's way into the clutch after a while and is causing the problem? Also, what kind of oil are you running?