Gear shift fork damage?

[sgd37]

Happy Friday everyone!

So I've slowly begun my reassembly when I noticed that the central gear shift fork has two ridges and other marks from what I think was some serious friction. She was really hard to shift past 2nd when I got her so might this be the cause?

Here's a picture:

http://imgur.com/g4LciLX

As far as I can tell there is no damage on the rest of the transmission but I'll check again before reassembly.

So can I just grind off those ridges or do I have to replace it?

Much appreciated

[hairygit]

To be safe, it needs replacing, and the cause investigating. The hardened surface looks to be scraped away, and it wont last long as it is, and 500's in particular and to a degree some 550's these failing are a known weakpoint. Just to let you know how bad things can get, a mate had a 500/4 back in the 70's, started jumping out of 3rd, then one day it somehow engaged 2 gears at once, and locked the back wheel solid at about 40 m.p.h. While he was recovering from his injuries the Police mechanics stripped the engine and found a bent selector fork had caused the accident, therefore he didn't get prosecuted, but he never rode a bike again. Never underestimate what seemingly small amounts of wear to gearbox parts on a bike, and I certainly wouldn't waste time or money putting that back in an engine! They can be difficult to find, and quite pricey, but what price your life?

[Bryanj]

Would that be the centre selector by any chance? known fault and now very difficult to find. From memory the same part is in a 250/350/450 twin but you can check on motogrid.


EDIT NOT 450 but (Note US never had 250 but gearbox same).


 CB350A MOTORCYCLE, JPN, VIN# CB350-1000001   

 CB350GA MOTORCYCLE, JPN, VIN# CB350-5000001   

 CB350K2A MOTORCYCLE, JPN, VIN# CB350-2000001   

 CB350K3A MOTORCYCLE, JPN, VIN# CB350-3000001   

 CB350K4A MOTORCYCLE, JPN, VIN# CB350-4000001   

 CB500A MOTORCYCLE, JPN, VIN# CB500-1000001   

 CB500K1A MOTORCYCLE, JPN, VIN# CB500-2000001   

 CB500K2A MOTORCYCLE, JPN, VIN# CB500-2100001   

 CL350A MOTORCYCLE, JPN, VIN# CL350-1000001   

 CL350K2A MOTORCYCLE, JPN, VIN# CL350-2000001   

 CL350K3A MOTORCYCLE, JPN, VIN# CL350-3000001   

 CL350K4A MOTORCYCLE, JPN, VIN# CL350-4000001   

 CL350K5A MOTORCYCLE, JPN, VIN# CL350-5000001   

 SL350A MOTORCYCLE, JPN, VIN# SL350-1000001   

Post a better picture and I may be able to find you a better one. If you can get a new one expect at least £60 plus postage

[sgd37]

Cheers

I don't know if these are any better, but yeah it's the central fork.

http://imgur.com/OIchp7a
http://imgur.com/SiKymq4

Tell me if you want a specific angle. Also would really appreciate a good used one.

Edit:

I assembled the tranny and there seems to be no damage on the gear that the central fork sits on. I also cycled it through the gears with no problem but I don't know how conclusive that is. The only wear is some chipping on the counter top gear without any wear on the corresponding gear. Can I get away with this?

http://imgur.com/N0aHfch

[mickwinf]

i had the same problem with my 500, i ended up getting one from  USA via ebay, had to order a used set of 350k which are common in america and includes the correct item.

[hairygit]

As regards the gears themselves, I would take a guess that something has let go previously, and somebody has swapped for a part gearset from another bike, as there should be corresponding wear/damage to the meshing gear, so it probably hasn't done many miles since. There looks to be an amount of the gear damaged, and obviously it will only get worse with use, too much of the surface hardening has been damaged for me to want in my engine. It may last a while, but it will "let go" sooner or later, all depends how much of a gambler you are, it's a lot of work to do again, and if it does let go other parts will get damaged. Sorry, but that's how I look at it, but your choice!

[sgd37]

Damn, was hoping for some good news.

Am looking for american cb350 parts. Any other sources would be appreciated

Cheers

[totty]

Could you get it welded and machined? Plenty of places can do cranks and cams so you'd think this would be possible.

[hairygit]

You could probably get it welded and machined, but it's probably bent, which is the most common reason for that kind of damage, and then it needs to be hardened properly, but getting it back to the shape it should be won't be easy. You'd need a new one for comparison, and the work involved would cost far more than a new one. Looking at that gear on a 32 inch monitor shows how badly damaged it is, and it will need replacing for safety and peace of mind.

Sent from my X6pro using Tapatalk

[sgd37]

As far as I can tell it has never been opened up before, but yeah I'm sourcing a new gear, thankfully they're easier to find.

Are you sure it's hardened, what would explain the colour difference? To my mind it would make sense to not have it hardened to prevent damage to the tranny. 

[hairygit]

Just the tips of the fork are hardened, that's why I suspect it is bent, the non hardened portion is what appears to be damaged, and that part would never normally contact anything else. What makes me think its been apart before is the damage to the top gear in the pic, but not a mark on the gear it is meshed with, how else would that have happened.

Sent from my X6pro using Tapatalk

[Bryanj]

That wear pattern I have seen on just about every 500 box I stripped, can you give me pics of the tips of the fork both sides as that is the most important part, Gear damage could be not enough oil changes with a small amount of swarf from somewhere. I have a new selector but also a job for it I also have some used gearboxes but not at home and can't get to them till next weekend

[sgd37]

The tips don't look too good either. But they measure from 5.6mm at the bottom to 6mm at the top which I believe is within spec.  Anyway here are the pics

http://imgur.com/Kf72FF7
http://imgur.com/tCzd5mn

I've been building this thing since last june so what's one more week to wait . If you could have a look that would be great.

Cheers

[Bryanj]

In the words of my engineering long dead uncle that is well crodged mate, I will have a better one but not new somewhere,

[sgd37]

Haha I tend to agree yeah. I did see it before but was focused on other things. Good thing I didn't put it back in. Any idea what might have caused such damage. Seems excessive for a 22000 engine

If you do have one how much would you want for it? and would you also happen to have a counter top gear as well?

Cheers