[Oldie]

I have a problem with the shifter on my CB250 G5 (same as CB360).


The main gearchange mechanism works fine and the pawl at the top slides left/right ok. However, itdoesn't seem to engage with the Change Pin End Plate (star shaped thing). I can get the star plate to turn and select all gears withthe help of a screwdriver turning the central cross-head screw/bolt which holds the plate to the gearchange drum so I'm thinking that the pins behind the plate (see Fig.7) might be damaged.


I don't think that Honda used this specific design in many models, as far as I'm aware, so maybe not many of you will have come across this issue.


Any ideas?


Thanks

ps. the central screw appears to have a stripped head (previous owner?) so maybe this is a clue.

 

[Oldie]

Looks like the pawl is being restricted by the bearing at the back not being flush with the casing. I've come across a similar thread on here which made me aware of this issue. Plenty of work to do!

 

[ancientdad]

It wasn't properly visible in your first picture, but I wondered when looking at the first one if the bottom end had been apart previously and the small end bearing had not been lined up correctly with its locating pin in the upper case - and now that appears to have been what happened. That bearing cap should be flush with the case, and the locating pin has cracked through the upper case in that little "mushroom" sticking up just above the arm on the shift shaft. Bottom end has to come apart to correct it, engine out of the frame to do so.

 

[Oldie]

Yes, you're right Tom, the cases have been apart before (some 8 or 9 years ago when a PO did a major renovation).

I'm not looking forward to splitting the cases but hoping that it might be easier on a bike that's been worked on fairly recently.

 

[ancientdad]

It's not that big a deal. The top end doesn't have to be disturbed at all, just the outer covers off the bottom end and the clutch and oil pump and shift shaft out, then flip the engine upside down and pull the lower case off. You'll have to repair the upper case where the pin got pushed through and cracked the little "cap" of aluminum above the locating pin, but that's pretty much it as long as there are no other needs in the bottom end like shift forks or worn engagement dogs on any of the gears due to the shifting issues. Clearly the job wasn't done quite right back then or you wouldn't be here now, but we've seen it a lot with 350s and 450s.

 

[Oldie]

Thanks for your input Tom. Very useful. Alan

 

[ancientdad]

Happy to help, as I've seen that situation a few times and repaired one myself long ago. Start a thread for the bottom end repair and you'll get all the advice you'll need.

 

[Oldie]

Ok, I've finally got round to looking at a proper fix. The engine came out easier than I expected although I probably should have removed the side cases first - hopefully that won't be an issue with the engine on the bench.

I'm still rather daunted by the next step (actually splitting the cases) but I have the shop manual, a knowledgeable internet friend and, of course, the resources of you good people to fall back on! I've also ordered some Hylomar sealant for re-assembly.

I'm interested to see what I'll find when I try and sort out this locating pin on the countershaft bearing but a few folks seem to have worked it out before, so I remain positive

 

[Oldie]

All ready to attempt the big split! Tapping away for a while hasn't made much of an impact (maybe I'm being too gentle) but I'm in no rush.

 

[66Sprint]

Did you get all 20 bolts out?..... There's one from the top IIRC.....

 

[ancientdad]

I was concerned about that too - I looked at the fiche at cmsnl and it didn't seem to show any bolts from the top, but I've never had a bottom end apart on one myself and IIRC most of the twins have a few from the top

 

[Oldie]

Think that I've got them all - one on the top and 19 below. The card in the picture is misleading as one of the upper row of 4 is missing (it's hanging loose in the case) and there's a vacant slot shown lower right where I marked a hole by mistake.

 

[Oldie]

Ok, cases split.

I've attached a pic showing the bearing / bearing cap removed and the locating pin embedded in the upper case. Up until now my thoughts have all been about fixing the "hole" but now I'm trying to figure out how to remove the locating pin first.

I've also attached a general view of the engine.

 

[ancientdad]

You may end up removing the "cap" of aluminum that has broken loose from the case above the pin and tapping the pin out. Either way, that area of the upper case is going to need attention - but the pin only locates the bearing and once clamped between the cases with the bolts tight, the pin won't have upward pressure to any great extent so a new "cap" of JB Weld would hold it just fine. I repaired a high school friend's 350 once that he did the same thing to, and at the time all I did was stake the case aluminum around the pin with a punch to help "shrink" the sides of the opening through the case to keep the pin from backing out after reassembly... he rode it for a few years after that with no issue.

 

[Oldie]

Thanks, just what I was thinking.

In the meantime I superglued a washer to the face of the pin (same diameter) and an early test shows that (if it holds in the long term) there's enough to hold the cap in place. Just trying out ideas at the moment and I'll probably read up that oil and superglue don't mix!

Anyway, going in from the top looks like a possible.

Thanks again for your input.

 

[Yendor]

What/How do you expect the washer to help your condition?

The PIN MUST stick up into the recess in the bearing cap to keep it from sliding out of position.
A washer in there is just going to cause more of a problem

? ? ? ? ? ?

 

[Oldie]

The washer just acts as an extension to the pin as it's the same diameter. The recess in the bearing cap catches it nicely. It's rock soild and there's no lateral movement whatsoever. I'm happy with the repair so I re-assembled the engine and will run it for 500 miles or so and see where we're at then. The forces on the bearing cap can't be that extreme so hopefully it will hold together but, if not, I now know more about the issues involved.

For me, the best part of the whole exercise has been taking the plunge and splitting the cases, something which I've not done before and certainly wouldn't have attempted without the good advice on this forum (thank you).

 

[ancientdad]

If you left the washer on the pin as in your picture, inside the cutout of the upper case where the bearing cap is retained between the case halves, I can't see how it would allow the case halves to come together completely without either damage or a gap between the halves. Good luck

 

[Oldie]

It all seemed to go together very nicely, with both cases absolutely flush together. I think that it will work but, of course, time will tell. If there's a problem then I'll feel more confident approaching it a second time. I've almost completed the re-assembly - just the exhausts to go on and the brake pedal spring (which has me stumped). Plenty of time to sort it all later as I have to make room for a new bike which I'm going to tidy up for my brother (space is at a premium).

 

[66Sprint]

What in heaven's name is that nasty blue stuff between (sealing?) the case halves?

A particular sealant is SPECIFIED by the manufacturer (Hondabond, which is the same as Yamabond and Threebond) and that's NOT it.......

Silicone and RTV products are a No-no as the extruded material breaks off and eventually plugs the oil passages...

I can see some areas of extrusion on the "outside" and shudder to think about what is waiting to break off "inside" the halves......