Topic: 750F2 trans vibration at 5k rpm. Need help on this UPDATE

[Bailgang]

I purchased my 77 750F2 earlier this past spring and from the start it has a vibration coming from the trans. The reason I'm sure of that is because I can really feel it from the shifter and the higher the gear I'm in the more my toes can feel it in the shifter however it only makes itself known at around 4,800 to 5k rpm and then goes away. It doesn't matter what gear I'm in either, it always happens around that rpm it's just that it really is noticeable in 5th gear and the vibration can be felt not just on the shifter but through the whole bike. The only way to avoid it is to keep it just slightly below 4,800 or slightly above 5k rpm. The best way for me to describe the sound is that of what I call a skating bearing or a galled roller bearing and between 4,800 and 5k rpm seems to be its harmonic sweet spot. It also doesn't matter whether engine is still warming up or at full operating temp.

As it stands right now I split the case last night and just did a quick visual inspection and so far all the roller bearings seem fine however they're still lubed up with oil which could be fooling me.  I have yet to start disassembling the gears for a close inspection but before I do I could use help from any of you who know their way around a 750 trans and give some tips on what exactly I should be looking for. I've already searched the topic but can't quite find a topic that fits the problem I'm having. Any help would be appreciated.

[Don R]

Look for unusual wear patterns on the dogs and gears. Shoot a little brake clean on the bearings and check them clean. That's all I got.

[scottly]

I purchased my 77 750F2 earlier this past spring and from the start it has a vibration coming from the trans. The reason I'm sure of that is because I can really feel it from the shifter and the higher the gear I'm in the more my toes can feel it in the shifter

The only time your toes should be touching the shifter is when you are shifting!?? The vibrations you are feeling may be due to the pressure your toes are applying to the shift forks; they were NOT designed for continuous load. BTW, this is true of any manual transmission, bike or car. The shift lever should only have pressure applied when shifting, otherwise the forks will wear prematurely. 

[CB750F2]

I suggest that you check the two needle bearings inside the primary sprocket assembly. The Part No. of these bearings is 91010-300-008. Pat

[Bailgang]

I purchased my 77 750F2 earlier this past spring and from the start it has a vibration coming from the trans. The reason I'm sure of that is because I can really feel it from the shifter and the higher the gear I'm in the more my toes can feel it in the shifter

The only time your toes should be touching the shifter is when you are shifting!?? The vibrations you are feeling may be due to the pressure your toes are applying to the shift forks; they were NOT designed for continuous load. BTW, this is true of any manual transmission, bike or car. The shift lever should only have pressure applied when shifting, otherwise the forks will wear prematurely.

Agreed. My toes aren't touching the shifter all the time like my comment may have suggested but there have been a few occasions where my toes just happened to be touching the shifter and I do mean just barely touching at the moment the vibration occurs and my toes definitely felt it so much so that it stung. So far the culprit seems to be #25 (6304HS) in the diagram on the main shaft. All the bearings spin freely but #25 though is sloppy, I can wiggle it's outer race a good .005"+ while the inner race is stationary. I've already decided to replace all the bearings rather than just that one simply because I don't want to be tearing it apart again because I got cheap the first time. More inspection needs to be done but I'm only working on one shaft at a time so I don't get things screwed up. I've read other post while searching and found that misplacing just 1 thrust washer can make for a bad day so I'm being patient and taking my time. I do have Hondamans book which does go into detail in regards to inspection but my kid has it now and I have to wait till Christmas for him to bring it back.

[andrewk]

I suggest that you check the two needle bearings inside the primary sprocket assembly. The Part No. of these bearings is 91010-300-008. Pat

I second checking out the primary.  Although, seems that you have a sloppy bearing too.   What do the gears and forks look like?

[Bailgang]

I suggest that you check the two needle bearings inside the primary sprocket assembly. The Part No. of these bearings is 91010-300-008. Pat

I second checking out the primary.  Although, seems that you have a sloppy bearing too.   What do the gears and forks look like?

I didn't have much time to mess with the trans today because I spent the afternoon cleaning up the lower half of the case. I'll be pulling the bearing #25 off later tonight so I can take the gears off the main shaft for better inspection but haven't messed with the other counter shafts yet other than a quick visual and so far the dogs look good, actually the whole engine seems in solid shape even the primary chain. I haven't put a mic on the crank yet but the main bearings look excellent at least from a visual point of view, I just need to get a bore gauge to make sure they're in as good a shape as they look.

[Bailgang]

I suggest that you check the two needle bearings inside the primary sprocket assembly. The Part No. of these bearings is 91010-300-008. Pat

Thanks for the part# Pat.

[Bailgang]

My kid brought back Hondman's book when he was here for Christmas for me to read up on so I finally was able to do some inspection of the trans. So far it's actually in good shape however I believe the culprit to the vibration I was having was bad roller bearings specifically the 6205nx3 bearing that sets on the main shaft directly behind the primary, that bearing was definitely shot. I goofed though when replacing it and found I had installed it with the snap ring groove facing the wrong way so off it came and pressed back on the correct way however when removing it I had to pull on the outer race to get it off and even though it felt smooth once back in place I felt an ever so slight notch from where it may have gotten indented from me pulling it off. It would probably be just fine but I'm not taking any chances so that bearing is coming back off and I'm currently waiting for another new one to replace it and this time I'll press it on correctly the first time.

I'd love to have all the gear dogs back cut however that's out of my budget but for kicks and giggles I split the case from a blown 77 F2 engine that I had setting under my bench yesterday with the hopes that maybe I could sort through it's trans and pick the best parts from it's trans and the one I'm using. No luck there though because even with an untrained eye it was clear that all the dogs had severe wear, whoever owned this engine before really beat the daylights out of it ..... which probably explains why it dropped an intake valve and destroyed the #1 piston.

At the moment I'm seriously considering polishing the gears per Hondaman's suggestions.

[martin99]

I had very similar symptoms to this on my old xjr1200. A new chain and sprocket set cured it.

[Bailgang]

I had very similar symptoms to this on my old xjr1200. A new chain and sprocket set cured it.

New sprockets and chain definitely helped but the vibration at 5k rpm was still there, it just wasn't quite as bad as it was before once the new chain and sprocket were installed.

[Bailgang]

SUCCESS!!! I finally got the engine back together and running and just got done taking it for a long test ride. The vibration I was feeling at 5k rpm is gone and the trans shifts beautifully now thanks for the most part from installing all new bearings in the trans because I'm convinced that was the culprit to the 5k rpm vibration. While I had it apart replacing all the trans bearings I lapped the gears per Hondaman, replaced both cam and primary chain not that either was all that bad but I don't intend on taking this engine apart for a while so I replaced them while I had it apart. Also new piston rings and had new valve guides installed, seats cut and all new valves and some mild porting, I basically have a bike that feels completely different now. The engine runs much smoother, pulls stronger, shifts smoother and best of all that pesky 5k rpm vibration is gone.