[brubor2015]

MY 1970 CB350 has problems shifting when hot. I split my cases to inspect the tranny. I have never been in this deep so I do not know what to look for. Please look at my pics and let me know what you think. One thing I question is the swirl marks on the second to the right shift drum channel. The others do not have these. The shift fork pin for that channel shows no wear different from the others. They all look shiny and new. I think these swirl marks are actually original machining marks. Has anyone else seen these before? Another thing I question is the slight wear (rub marks) on outer shift forks shown in the second pic. Obviously something caused these surfaces to rub. Again let me know what you think. My current plan is to put it all back together with new clutch friction plates, clutch springs, gaskets, oil seals and Rotella T6 5W40 synthetic.

 

[Boomer343]

I just took a look at my 3 spare shift drums and none of them have anything like the marks your drum has. Since I have spares I would probably swap one like yours out.

On the shift forks that is common and compared to some I have quite minimal.

I only use the Rotella T6 in my builds as well. You should check the wear on the gear selector arm and the roller that keeps the shift drum in a particular gear. Both are prone to wear and can cause shifting problems. You might also consider removing the multilink gear shift lever and go with the direct lever that was first on the 73 model.

 

[ancientdad]

I've never seen a shift drum with marks like that. It's almost as if the pin got pushed into the drum with some force, certainly odd. Personally, I don't like the looks of the rub marks on the 2 shift forks, particularly the one on the left. Rub marks like that usually indicate that the fork is slightly bent and the gear it moves is rubbing on the side the force came from - often caused by missing a gear under load too many times. Closer inspection of the gears might reveal some wear on the dogs of the gear involved as well. I'd replace the forks so you wouldn't have to go there again, but that's just me.

 

[mike in idaho]

Rub marks usually mean bent shift forks. What condition are the engagement dogs on the sides of the gears? Rounded-off dogs will cause the gears to be forced apart under acceleration, bending the forks. Shifting gears with a dragging clutch or bashing on the lever, instead of shifting normally, doesn't help either.

 

[brubor2015]

To ancientdad and Mike in Idaho, thanks for your observations. I have added some pictures of the gears and the dogs as best I can get. You might not be able to tell anything from the pictures, but if so, please let me know. When I look at the gears and the dogs, I would say everything thing looks normal. I do not see anything that is excessively worn or damaged. Even the forks to the eye look straight and not worn other that for the rub marks I indicated. I know that this no substitute for measuring them against a specification, but I do not have the tools to do so. I still think that the swirl marks in the channel--as unusual as they are--could still be factory machining marks. There is absolutely no sign of the pin wearing funny in that channel. All three pins measure the same diameter and length and have no wear marks on the ends. I'm thinking that the pins only contact the channel on the side and that is why there is no sign of wear on the end.

All I have is a digital caliper. Is there anyway to measure the straightness of the forks with that?

Thanks for any help.

 

[brubor2015]

Boomer343,

Thank you for your help. What exactly should I be looking for on the gear selector arm and the roller? Will this wear be obvious to the eye or do I need to measure against a specification? To the eye I see no visible wear on any of these parts.

I might just try the direct shift lever thingy too. That multilink thing seems squishy.

 

[Boomer343]

The wheel that tracks in the star wheel that is on the end of the shift drum gets sloppy and can hang up. The pins that the shift lever mechanism pushes against can wear as can the parts of the mechanism itself. Make sure the screw that holds the star wheel in place is tight, on the early models it usually is but particularly on the 73's it would back out.

On a recent engine rebuild I found there was rust on the shift drum and on the insides of the bore on the shift forks. That transmission also had the worst wear marks on it's forks I have ever seen. The PO told me it was shifting with no issues but does say that after my rebuild it shifts much better..... guess that's what happens when you replace just about everything in the tranny. The rust occurs when a bike sits for a long period of time.

BTW that engine had the clutch push rod seal blow out at highway speeds dumping all the oil and seizing the cam. He admitted to having had the seal push partially out and simply pushing it back in .... expensive lesson. When I am putting the cases back together I put a light coating of the Honda bond onto the seal edge as well as the mating surfaces of the cases. Watch also the locating pins that are in the case that fit into the shaft bearings..... nasty damage occurs when they push through the case.

 

[mike in idaho]

All I have is a digital caliper. Is there anyway to measure the straightness of the forks with that?

Lay the forks on one side on a flat surface and compare the height of the fingers. Re-assemble the shift drum assy. and the transmission shafts back into the upper crankcase. Now turn the shift drum into the various gear positions to see if the dogs engage correctly. In each gear, try to pull the mating dogs apart by hand to see if the dogs stay engaged at least 50%.