Author Topic: The Grinding Lean transmission (Read 4486 times)

Industrial Cafe · « **on:** December 28, 2008, 11:41:17 AM »

first off let me say, the motor is out of the bike right now.
OK, here's the story, I was riding around one day and, coming to a stop, I noticed this crunching sound coming from the transmission.
sorta like an unevenly spaced "grunka-grunk....grunk-grunka-grunk" sound. It sounded like 2 gears lightly touching each other you get the picture.
I looked down and my chain was slightly slacked, so I got off and adjusted it with some tools I had in my backpack.
That wasn't the problem. Still grinding. So I got it home and noticed I could make it stop grinding if I leaned it to the left, I lean it to the right and it grinds like crazy. So I took the clutch apart and left the basket in. started it and it still made the sound. the pan had a large amount of plastic shavings, gasket material, wire wheel pieces, a pebble, and a piece of broken steel.

I hope someone can help.

paulages · « **Reply #1 on:** December 28, 2008, 11:57:34 AM »

bent shift fork maybe? what kind of bike?

Industrial Cafe · « **Reply #2 on:** December 28, 2008, 12:11:21 PM »

oh yeah sorry, the profile editor isnt working for some reason

1971 cb750

Industrial Cafe · « **Reply #3 on:** December 28, 2008, 12:24:02 PM »

WHALEMAN · « **Reply #4 on:** December 28, 2008, 04:55:59 PM »

How in the hell a rock that big get in the sump? I can see how they get in the oil tank but not the sump. The primary chain tenisioner is chunking somewhat but not that much. If the part on the left is steel I fear you are going to have to tear it down and find out what broke. A closeup of the steel chunk might help. I am lost. Dan PS If it is a gear I might have an extra.

paulages · « **Reply #5 on:** December 28, 2008, 06:41:19 PM »

ouch. that looks bad.

Industrial Cafe · « **Reply #6 on:** December 28, 2008, 07:59:54 PM »

yeah... about that chunk, one of my kids picked it up and lost it for me...

It had curved wear on the side you can see in the picture, like it was a shift fork or a piece of an end cap for a rod. the straight sides were broken off and the round side was cast. The back is convexly rounded and rough cast steel.
one of the sides was broken a long time ago, the other side had a new shiny clean break to it.

fuzzybutt · « **Reply #7 on:** December 28, 2008, 09:28:05 PM »

sounds like a shifting fork to me too.

mark · « **Reply #8 on:** December 28, 2008, 11:05:30 PM »

Quote from: Kickstand on December 28, 2008, 07:59:54 PM

yeah... about that chunk, one of my kids picked it up and lost it for me...

It had curved wear on the side you can see in the picture, like it was a shift fork or a piece of an end cap for a rod. the straight sides were broken off and the round side was cast. The back is convexly rounded and rough cast steel.
one of the sides was broken a long time ago, the other side had a new shiny clean break to it.

Based on your description and photo, I will say it is a piece of a transmission gear.... part of the slot where the shift fork rides.

I may have a nearly identical chunk on the bench from some kid's pitbike that I worked on a while back. That was the one I found inside. There was another that got caught by the kickstart gear and punched through the case.

Quote from: paulages on December 28, 2008, 11:57:34 AM

bent shift fork maybe? ...

I'd check that too.

Bottom line.... I'd scatter it now before the chunk you haven't found yet does something really bad.

paulages · « **Reply #9 on:** December 28, 2008, 11:40:46 PM »

i thought i had reposted after you described the chunk, but apparently it didn't work...

i'd say it looks like the tip of a shift fork, and that would fit the description of what was happening... if the shift fork was broken, the associated gear could float in and out of the gears it meshes with while another gear was selected. however, the entire end of the shift fork would have to break off for that to happen. maybe it's the knobby other end of the fork that rides in the groove on the shift drum?

paulages · « **Reply #10 on:** December 28, 2008, 11:48:37 PM »

if you can zoom in on this, it looks a lot like one of the tips of the shift forks.

mark · « **Reply #11 on:** December 29, 2008, 12:01:20 AM »

ten bucks says it's off one of the sliding gears.

I'm guessing that you found 'A', and that 'B' might still be in there somewhere.

Industrial Cafe · « **Reply #12 on:** December 30, 2008, 03:59:08 PM »

yay... i split the case.
OH GOOD GOD! is there supposed to be sand in the main bearings?

The shift fork on the top set of gears is worn about a millimeter or so through.
and -oh great!- there's some sweet rainbow heat treatment on the fork race and a blackend gear.
Also there's burnt up flakes of metal stuck to the worn fork... damn it, my camera is at a friends house.
I'll post some pics with my #$%*ty backup camera.
still no sight of the missing chunk, but the diagram above me here, looks about right.

the bike sat for 12 years before i got it, and the case hasn't been split before.
I hear horror stories of hard times getting bolts out, I had no trouble whatsoever. the bike has 26000 miles on it and it was stored in a shed.
the head was removed for head work in the 80's. Maybe that's where the rock came from.
i dunno.

Industrial Cafe · « **Reply #13 on:** December 30, 2008, 04:58:37 PM »

Look at the second gear in the top rack, and the fork.
They're blackened, maybe they're jamacan gears.
Mmmmm, I havent tasted them yet to see if they're spicy or not.

I don't know if there was some sort of clogged oil port in there or what
i'll get more into it tomorrow.

Industrial Cafe · « **Reply #14 on:** January 04, 2009, 01:47:14 PM »

fifth gear (closest to the outside) on the secondary shaft, and the two secondary shaft forks are very new.
the old gear must be where that chunk came from in the bottom of the pan.

Industrial Cafe · « **Reply #15 on:** January 09, 2009, 11:42:27 AM »

A thousand words.

paulages · « **Reply #16 on:** January 09, 2009, 06:33:09 PM »

Quote from: Industrial Cafe on January 09, 2009, 11:42:27 AM

A thousand words.

whew, boy. i knew there had to be a shift-fork problem in there somewhere. ouch!

MRieck · « **Reply #17 on:** January 09, 2009, 06:53:07 PM »

That crank has been modified. That rod small end looks bushed too but it's hard to tell (could be the lighting).

Industrial Cafe · « **Reply #18 on:** January 09, 2009, 07:18:27 PM »

what makes you say that? it looks pretty stock, it's got holes drilled in it, but it looks factory-ish... (no knife)

MRieck · « **Reply #19 on:** January 09, 2009, 07:26:22 PM »

Quote from: Industrial Cafe on January 09, 2009, 07:18:27 PM

what makes you say that? it looks pretty stock, it's got holes drilled in it, but it looks factory-ish... (no knife)

The oil galley hole has been chamfered.

paulages · « **Reply #20 on:** January 09, 2009, 07:28:48 PM »

Quote from: MRieck on January 09, 2009, 06:53:07 PM

That crank has been modified. That rod small end looks bushed too but it's hard to tell (could be the lighting).

it does look bushed. look at the edge... looks bronze.

Industrial Cafe · « **Reply #21 on:** January 09, 2009, 08:30:50 PM »

i wish it was bushed, thats just the color they are inside...
part way inside ...aw

do the journals look wore out, or is it just me?

paulages · « **Reply #22 on:** January 09, 2009, 09:18:16 PM »

they look pretty bad in the pictures. you might check the color of the bearings and mic the journals.... there may be room for a regrind or polish.

Industrial Cafe · « **Reply #23 on:** January 09, 2009, 09:51:48 PM »

I'll definitely do that.

thanks

bryanj · « **Reply #24 on:** January 10, 2009, 01:13:27 AM »

There is never room for a re-grind but a light polish might work. to be honest with all the used engines/cranks out there is it worth it?

Classic "Dirty Oil" pictures

News:

Author Topic: The Grinding Lean transmission (Read 4486 times)

WHALEMAN

fuzzybutt