Crankshaft disassembly

[teazer]

Conbs, you raised an interesting issue of crank pitting.

It's that old philosophical question - If crank pitting can't be seen, did it really happen?

I have only stripped a few cranks and some had minor pitting that would probably last for years in a street motor and some were so bad that they were bound to fail sometime soon. In a race motor, we can't afford to use pitted pins because they will fail and because the loads are much higher and for longer.

For example a street motor turns at say 9k max and spends most of its time at say 4-6k. A race motor reaches say 12k and spends all of its time above say 8/9k. So that race motor experiences forces 2-3 times higher than a street bike and it's continuous load. No cruising time.

But how rusty, if at all are all those street motors? Your hypothesis that maybe most of them are pitted, may be accurate. The problem I have is that once I strip a crank I can't very well reassemble it with bad parts.

I recently had a GT750 crank that the seller claimed was OK to use but it looked a little suspect to me so we had it stripped. The rust was such that it would not have lasted to the end of the drive, and the only usable parts were the oil slingers. No pins, rods bearings or wheels were usable.

For a street motor, I'd suggest that it it all moves smoothly with no rough or tight spots and no obvious signs of rust or wear, then it's probably OK for a few years in a street motor. That has to be teh call of teh guy that owns the bike based on their own experience. BTW, that was not a professional opinion on any particular crank - just a personal opinion that cannot be used in a court of law. ;-)

[jerry]

Well put Teazer. The subject of loads can still end up out hand with road motors if the revs end up too high. My new race project will have piston conrod assemblies of approx. 350gms (0.77lbs) which is not too heavy I believe. Running at a piston speed of 4300ft.p.m with a 2.32 conrod ratio (relatively long) to reduce loads at expected peak HP that little weight has become over 5000lbs due to G forces at Expected max. rpm and as you well realise it sort of becomes pretty stressful for the various components including bearings. For a CB72 12000RPM equates to 4252 ft.p.m. piston speed. All good fun in the pursuit of reliable road and race engines. All the best Jerry

[conbs]

Jerry and Teazer,

I think we are all tracking here, except you guys already know a bunch of the things I am about to learn. My point is that for just-for-fun bikes (no high loads), a guy needs to know how to make the best guess at which crank will last to the end of the drive versus which one will last for years - without taking them apart.

Teazer, I think you hit the nail on the head. If we assume that crank pitting really DID happen (in 70% of the cranks out there), whether we look or not, then how does a guy discern as best he can, if the crank he is looking at will give him reasonable service. First check the service limits in the Honda shop manual and dial guage everything. If its out of limits, better look for another crank. Second, even if it is within limits, check the bearings for rough or tight spots. If either of those are present, better look for another crank. Finally look for "problem" rust. It may be a little harder to quantify what is a "problem", but significant rust on the counter weights or center shaft warrants in-depth investigation.

On the crank I am trying to reclaim, I noticed that the counterweights had some rust, but it was toward the outside of the weights and not real bad anywhere. Wire brush in a drill took it off and I used some naval jelly to get it down to bare metal to make sure the rust did not end up in my oil later on. One of the center bearings can slide to the side enough to see the pins. I couldn't see any rust or pitting on the pins. Flushed it real well in the parts washer and blew it out with air. Repeated to make sure everything was very clean.

In my case I am only removing the starter/rotor end of the crank so I will get to see the con rod bearing and shaft on that side. If there are problems in that bearing, it will be decision time. Teazer, I will be like you and have a hard time putting it back together if there are rust problems. But if it looks good, I will be able to (hopefully) put it back together with pretty good (but not perfect) confidence about the whole crank.

The centrifugally compressed crud inside the crank is another story. Taking just the end of the crank off will disturb some of it making it subject to going through the bearings and the rest of the motor. Decision is whether I want to try to clean all of it out with some Berryman's or other cleaner, put the crank back in the parts washer with the pump squirting through the crank oil passages or ?????. I haven't seen it yet, so I don't know what I will be dealing with. Anyone else have any thoughts?

I got the jig made to press the end off the crank. Its not going to win any beauty contests, but should get the job done. Please excuse any ugliness that shows up in the pictures. For reassembly I am going to scribe a mark on both cranks along the centerline of the con rod shaft at an angle that intersects the centerline of the crank. It should be pretty close if I get those lined up when pressing it back together. Then lead hammer and dial guage for final adjustment.

These are just the thoughts of a newbie to crankshaft disassembly. If anyone thinks I am on the wrong track, I would appreciate you sharing it with me. BTW Jerry, at 57 I am not really a "young feller" but someone could easily be confused because I don't necessarily act my age. My youthful exuberance on this whole crank thing is partly because of the grand adventure, partly because I am learning alot about a new area (late in life) and partly because it has been a pretty cool project to share with my big brother, who may well be the best big brother a guy ever had.

Off to the shop. I would appreciate your prayers.

[teazer]

That hard crud is packed into the annular oil slinger which is machined into the inner faces of the inner two wheels and in my limited experience, it has to be gouged out - it's hard. And on average there will be about a teaspoon of crud per crank wheel.

[conbs]

Teazer, thanks for the description of the crud and where to find it. I am not planning to take my crank down that far, so I guess I won't have a chance to gouge it out. Sounds like its too hard to get out with some kind of solvent or parts cleaner so maybe that means it just stays put. Hmmm.

I spent the evening in the shop taking my own advice. First I put the dial guage on everything again just to be sure I am sure. This time I was very anal about making sure the guage was precisely placed. I confirmed what I found the first time, everything is well within tolerance. Second step looking for binding or rough spots in the bearings. Nothing. They are not new, but are all fairly smooth. As I said in the last post, I had already removed the rust on the counterweights. I looked at it a little more closely and still didn't really see anything that bothered me. Looked at the one inner bearing that slides apart part way and the rollers look like new as does the cage.

I guess I will have to get the outside counterweight off of it to see what I can see regarding the crud. The problem with the crank is the surface where the starter sprocket rides. Apparently didn't get enough oil and the PO just kept riding it. So....I wonder why it didn't get enough oil..... Maybe plugged up with crud? I hope to make it to big brother's tomorrow to perform the operation. We'll see if the patient survives.

[conbs]

I have a number of pictures that I have been trying to load into a post for 2 hours. I can't get the pictures to load in the right order and can't cut and paste text to put things in the right sequence. Can anyone explain how I can get this done?

The patient is on life support awaiting your help.

[G-Man]

Bill

Upload them to 'Flickr' http://www.flickr.com first and then you can just paste the links in your text in the right order.

Use the 'grab html / bbcode' option then paste it in your post.

G