Topic: Cases finally split! Pictures to come tonight.

[Lavis500]

So after all of the finaggling with work and what not, I finally found time and ability to split the cases on my '73 CB500!  My plan is too replace the primary and cam chains.  Upon inspection, it actually looks like they would have been perfectly fine (bike supposedly has around 20K miles, actual mileage is unknown) but I'll replace them anyways.  I'll replace the oil seals while I'm in there, though they still look very nice and supple.  No reason not too, though.  My bearings all seem GREAT, so I'll leave them.  I'll plastiguage the crankshaft bearings tonight, though to the naked eye there's only one that really has any significant marks on it.

So the reason for my post:  My middle shift fork looks fairly chewed up.  The place it sits between the gears looks fine, but I definitely want to clean up the metallic bits hanging off.  Can I do this without removing it by grinding, or maybe with some steel wool and just cleaning thoroughly when I'm done?  Is my only option to send it to a machine shop?  The other two look fine; one looks perfect while the other has a very tiny mar on it.

Another thing that concerned me was that on the top half there are spots on the inside that almost look like....   CRACKS??  Is this just an appearance due to the rough casting, or is this potentially something to worry about?

Sorry for the boring post.  I'll jazz it up tonight with plenty of good pics.   

[fantino]

The transmission was a big weak point of the 500 design. It seems that gears apply constant pressure on that middle shift fork, as such pretty much every one out there has burned through that middle fork (including mine, if you check out the pics in my build thread, they were GNARLY!).

You can clean up the rough edges and probably get away with it for awhile (providing the pads on the fork fingers are within spec), you can also get your fork hardwelded and ground back to spec at a speed shop for about $70 (since finding an OEM fork is essentially impossible. These fixes will only temporarily mitigate the problem, as the fork will continue to see pressure from the gears.

Undercutting the transmission will fix the wear issue and also really help with improving shifting action and positive engagement of the gears. Unfortunately, this is pretty spendy! Hope this helps, and good luck!!!

[Lavis500]

And now...  Pictures!

My middle shift fork.  This is the worst side.




The marring in the middle comes up over the edge of the fork.


Looking at the top case upside down with the cylinders away, this is the fork on the left.   Tiny mark, but probably not enough to worry about.


This is the one crankshaft bearing I'm worried about.  It's on the bottom case on the points side.


I have a question about this little bar:


Should it be able to do this?


Or this?  The other side doesn't do it.


These are the "cracks" I was talking about.  I'm starting to think they're just from the castings, but I want to really make sure.  I'd rather ask and look like an idiot than have my engine explode on me!



And after all that, I thought I'd just share my workstation!  



INPUT IS APPRECIATED!!  Hopefully people will say something now that I've delivered some goods.  lol

[scunny]

case is just casting marks
that half ring is to locate the bearing, yes you can move it around
I'd get that shifter fork out and rewelded and machined

[fmctm1sw]

case is just casting marks
that half ring is to locate the bearing, yes you can move it around
I'd get that shifter fork out and rewelded and machined

+1 on the shift fork.  It looks as bad as the one I pulled out of my CB175 and that bike wouldn't shift into 3rd gear.  And while you're at it, make sure the shaft the shift forks are on isn't bent.  I had one that was bent and spotted one on eBay that was bent (400F motor I think it was).

[Lavis500]

I'm going to go measure the fork real quick.  If it's still well above the limits then I'll just clean it and leave it.  I don't plan on putting 50,000 miles on the bike; I'd just like to ride it once in a while whenever I'm not deployed.  (army)

I'll bbs with the measurements!

Oh, and for what it's worth I've shifted it through every gear before.  Not while running, but I've done it.

[ron.cieri.313]

Replace the fork imho...for a guy who had to split the cases on his 750 twice, you do not want to mess around...why did you split the cases in the first place...was there a shifting issue?

[Lavis500]

Replace the fork imho...for a guy who had to split the cases on his 750 twice, you do not want to mess around...why did you split the cases in the first place...was there a shifting issue?

I received the bike with very minimal history and non-running.  I got her to run, but I saw oil all over the jug's fins and - this is where it sounds stupid - I've wanted to do a full teardown for a while.  This is my first time going through everything this thoroughly, and I'm very confident about it.  Bike mileage is uncertain, and I decided to tear down the top end to replace gaskets, o-rings and hardware.  I figured while I was open, I may as well go all the way and replace the primary chain.  I think the cam chain would be fine, but I've been told it's a good idea to go ahead and replace that, too.  Seals are cheap, and I'll probably replace them as well - though all of mine still seem very supple.

[Lavis500]

Measurements are as follows:  in the position the top case is in (upside down with cylinders away) the left fork is at 5.0 - within serviceable limit, the middle fork is at 5.72 - within the serviceable limit of 5.6, and the right fork is at 4.9 - within serviceable limit.

With this information, I conclude that I'm going to grind excess metal from the center fork and continue using it.  I'll remeasure after I clean it up to make sure it's still within limits.  As long as the book says it's good, then it should be good, right?

[KRONUS0100]

ok...forks are within limits................but are the straight?  What casued the side wear like that....hard shifting?   make sure that the fork shaft is straight like was mentioned above.  Tsubaki cam chain and new tensioner assembly only set me back about 100 bucks...worth it while its apart now.

[mystic_1]

Personally I'd replace that shift fork, for peace of mind if nothing else.  I'd be worried about breakage, with that much wear already present, and needing to grind off more metal to make it smooth.

mystic_1

[supersports400]

Hi,

The shift fork is a part of a "bearing", so does the gear, they work together.
Not only measure the fork, but the gear as well, and calculate the play between them.
Check the gear for damage, not only the mating area of the fork but also the splines, and the shaft.

Jensen

[MCRider]

Measurements are as follows:  in the position the top case is in (upside down with cylinders away) the left fork is at 5.0 - within serviceable limit, the middle fork is at 5.72 - within the serviceable limit of 5.6, and the right fork is at 4.9 - within serviceable limit.

With this information, I conclude that I'm going to grind excess metal from the center fork and continue using it.  I'll remeasure after I clean it up to make sure it's still within limits.  As long as the book says it's good, then it should be good, right?

The fork is almost certainly bent, that's how they get the side wear. Someone on the forum had theior forks reconditioned here.
http://www.fastbygast.com/Catagories/Products/Transmissions.asp
Worth a call to ask anyway.
PS: that's the worst, or nearly, I've ever seen and I've seen a few.

[Lavis500]

I should have included a pic of the other, much better side.



At least to the naked eye, the fork appears straight.  I'm going out of town tonight, but when I get back monday I'll do what I can to check the trueness of the the forks.  I'll check gear play then, too.  Vertical play of the middle fork bearing is virtually non existent, and lateral play is about .3 mm.

There will be more measurements to come, such as fork ID, drum OD, etc.

If I take this to a machine shop, what do I tell them?  Reweld...  what metal are these?  Aluminum?  Cast iron?  Steel?  Anyways, reweld them and grind them back to within factory specs?  Do I need any other specs other than what the factory manual gives me?  (just fork end thickness and ID)  Do I need the depth of the fork, as well as the thickness of the center of the fork which appears thinner?

[MCRider]

I was raised to consider any mark on a shift fork at all, to be unacceptable. I would replace it.

Since the days gone by when we replaced them, many have become unavailable or priced too high. So I'm in the dark as to what to do in that case.

Evidently reconditioning is possible. I don't know first hand.

Good luck.

[ron.cieri.313]

+1...I kinda cringe when I remember the realization I had to go back in again.

[crazypj]

Total waste of time to replace forks without replacing gears.
The gear dogs are worn and have rounded edges.
 That's whats causing shift fork problems, worn dogs jump out of gear and cause bent selectors, not the other way round
 you need to pull gears off shafts and replace the worn/damaged bits.
 Take some pics of gear dogs

[fantino]

Total waste of time to replace forks without replacing gears.
The gear dogs are worn and have rounded edges.
 That's whats causing shift fork problems, worn dogs jump out of gear and cause bent selectors, not the other way round
 you need to pull gears off shafts and replace the worn/damaged bits.
 Take some pics of gear dogs

I think this advice would be sound on most machines, but the 500 transmission has something else going on, evidently. My middle shift fork was TRASHED, but when I sent it and the transmission off to Fast By Gast, they said the gears all had remarkably little wear and the shift fork was nice and straight. It seems the gears in a stock 500 tranny just constantly rub against this middle shift fork and wear it down.

the undercutting is supposed to help draw the gears in to where they are actually supposed to be, which should alleviate wear and improve shifting action. Or so they say. My engine still isn't running, so I can't comment on how effective this is, but I recall reading that at least one other rider here had this done and hadn't noticed any significant wear on his parts the season after undercutting.

And yes, reconditioning is definitely possible, FBG took my fork from THIS:


to THIS:


I guess they do this a few times a year with good results. It also costs around the same or less than the parts fiche price for a new shift fork, if they were even available.

[MCRider]

Sweet!

[bryanj]

That centre fork is just about impossible to get easily now, i think I had the last one DS had some time back