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View Full Version : Crankshaft keway repair -also posted at PM



Jim Caudill
08-16-2010, 05:32 PM
I have a friend with a 5hp Salsbury scooter that has a damaged keyway on the crankshaft where the flywheel attaches. It has "slopped out" one of the sides that is parallel with the crankshaft. I was thinking of making a copper woodruff key, clamping it in place and tig welding up along the side - while the engine is still assembled.

These engines are too valuable for me to screw up; they are ridiculously priced nowadays (think $2,000). What say ye, all you wise old salts?

MuellerNick
08-16-2010, 05:51 PM
Cut a new keyway on the other side, all else will fail.
Is the shaft hardened? If yes, welding up will completely ruin the shaft.


Nick

Carld
08-16-2010, 05:57 PM
Now knowing what the crank metal is I don't think I would weld on it. If you do weld it you need to remove the crank to do the welding.

As Nick said it may be better to cut a new keyway but you would have to cut a corresponding keyway in the flywheel. Then there is the weakening of the crank with the extra keyway.

Personally I would try to find out what metal the crank is and if I welded it I would put all of the crank except the end I was welding under water. If you weld it make the copper key narrower than needed and machine it out to size.

oldbikerdude37
08-16-2010, 06:33 PM
Cranks are not hard at all, they machine very easy, if not too easy.

Jim Caudill;s Idea will work.

His copper key core idea has worked for me too but I used aluminum clamped on the back of a big oval hole in steel, welded it closed with steel and there was almost nothing to grind on.

alanganes
08-16-2010, 06:36 PM
I have done exactly what you are proposing on two Subaru engine cranks. I did it in place, in the car. The woodruff key slot for the harmonic balancer was messed up like you describe. Got over 4 years out of the first one, and it was still running when I sold it. We would see it driving around town for a year or two after that. The second one lasted 2+ years then we sold the car due to tranny issues. Engine was still going strong.

I don't know anything about Salsbury scooters, so no advice on that from me. I was in a "little to lose" situation, and it worked for me.

ADGO_Racing
08-16-2010, 06:46 PM
I won't weld on an assembled engine. We always disassemble them before welding anything on them. Electricity takes the path of least resistance, People are always of the opinion that if the ground is right next to where you are welding it will go there and no place else. I have seen it do otherwise, a number of times. Last thing you want, is the current wandering up and down your crank and arcing over to various rod or main journal bearings. That will wipe the engine out in short order. 3-5 hours of disassembly/assembly Vs $2,000.00. Remember, no good deed goes unpunished.

duckman
08-16-2010, 06:47 PM
If the flywheel is for the ignition you need to get it right or it probably won't run right don't ask me how I know. The key way is your timing.

radkins
08-16-2010, 06:55 PM
The important thing here is to find out for sure what the crank is made of, if it is cast iron then DON'T weld it with a steel rod use a Nickel rod for iron castings such as Ni99 or Ni55. The very high Nickel Ni99 is the easiest to machine if that is going to be required but it is quite soft and while the lower Nickel rods are somewhat harder some are all but un-machinable. If it turns out that it is steel then a mild steel filler would be a good choice, welding on cast iron with any kind of carbon steel is a recipe for disaster since the weld will become so hard grinding will be about the only practical way to cut it and the likelihood of cracking will increase dramatically.



Also brazing with a Bronze rod would be another option but whatever method you decide on take steps to prevent warping from the heat.

radkins
08-16-2010, 07:00 PM
I won't weld on an assembled engine. We always disassemble them before welding anything on them. Electricity takes the path of least resistance, People are always of the opinion that if the ground is right next to where you are welding it will go there and no place else. I have seen it do otherwise, a number of times. Last thing you want, is the current wandering up and down your crank and arcing over to various rod or main journal bearings. That will wipe the engine out in short order. 3-5 hours of disassembly/assembly Vs $2,000.00. Remember, no good deed goes unpunished.




I could not agree with you more on that! I know of one case in particular where a finial drive bearing and a metal seal were destroyed in a D10 bulldozer because a guy grounded to the track and welded on the frame. Grounding to an engine case and then arc welding on the crank is scary to even think about! I can just picture the tiny arcs going on between the crank surfaces and bearings!:eek:

GKman
08-16-2010, 07:29 PM
Local machine shop used to get woodruff keys made from carbon (maybe graphite) somewhere, weld them in, chip it out, machine the OD and have a perfect new keyway.

OR...
Friend had a loose harmonic balancer on a Detroit Diesel over the road tractor. Options were remove the crank and rebuild; weld it on (it couldn't hurt the crank any worse than it was already; or the one he chose - glue it on with Catapillar brand epoxy. It had been done before and it worked for him.

Go for it.

GKman
08-16-2010, 07:34 PM
People are always of the opinion that if the ground is right next to where you are welding it will go there and no place else.

I'm one of them.

radkins
08-16-2010, 07:36 PM
Local machine shop used to get woodruff keys made from carbon (maybe graphite) somewhere, weld them in, chip it out, machine the OD and have a perfect new keyway.


I saw something similar done once and although it was not a keyway it was a guide slot in a shaft that was fairly close tolerance. In this case the guy took an old generator brush and ground/filed/sanded it to size and shape then used it in the same manner you are describing, made a perfect fit.

radkins
08-16-2010, 07:42 PM
I'm one of them.



Only if it is the same part you are welding on! Any other part may or may not work without damage, depends entirely on how well the other part is grounded to the one being welded. It does not matter how far away the ground clamp is, within reason of course, as long as it is attached to the same piece of metal being welded but it could be an inch away and cause serious damage if the current has to flow between two poorly connected parts-such as a bearing and a crankshaft separated by a film of oil? If the current has to flow through bearings to reach ground then damage is very likely.

ADGO_Racing
08-16-2010, 08:10 PM
Even if the ground clamp is on the same part, it is still possible to have problems. Not as likely, but it still happens. I have seen enough arc damage to other associated parts that I won't weld something while it is assembled. I do it right or someone else can do the damage. One think that really pisses me off is having to fix stuff that I screwed up, and should have known better. This is one of those situations where I know better.;)

What about just machining a new larger keyway, in place of the old one? Then broach a larger keyway in the hub? Key doesn't necessarily need to be a woodruff key either. Job becomes a little more complicated if it is a tapered fit, but still an alternative fix.

wierdscience
08-16-2010, 09:06 PM
Local machine shop used to get woodruff keys made from carbon (maybe graphite) somewhere, weld them in, chip it out, machine the OD and have a perfect new keyway.

Go for it.

Yes,carbon is your friend.I've done oil holes in cranks and chevy blocks that were missing half a starter mount hole.

Jim Caudill
08-16-2010, 10:03 PM
Thanks for all the input! It is great to be able to have a place to get such diverse thoughts. My friend just left, when I saw the job, I realized welding in place was not really an option. Further, the damage appeared minimal, although he did destroy the flywheel. Attempts to fit the new flywheel showed the taper next to the keyway damaged. I marked the crank and used a stone to work on the taper. When I was getting good contact all around the taper, I cleaned up the woodruff keyhole as best I could. It was only damaged about .020" deep along one side. After getting the keyhole shaped up, I made a new key by thinning out a 1/4" wide key. I fitted the key to both the new flywheel and the crankshaft. Had to tap the key in the crank with a brass punch and the flywheel fit was barely doable by hand.

When it came time to tighten the nut, he gave me an internal tooth lockwasher and a new nut and told me to tighten it to 125ftlbs. As I started to tighten the nut, the lockwasher tried to destroy itself. I said "hey this ain't gonna work", "are you sure this lockwasher goes in here?" I then took it apart and we put it together without a lockwasher. I think the lockwasher may have been why his flywheel came loose before.

Any thoughts on this?

lakeside53
08-16-2010, 10:14 PM
A tapered flywheel/crank does not even need the nut if the tapers are good. No, you do not need a lock washer...The nut simply provides the force to "stretch" the FW onto the crank. I do however leave them on :)

You also do not need the key - it does NOT stop the fw from rotating on the crank - it's just there to provide positional accuracy for timing of the magneto. I have installed dozens of FW on Chainsaw cranks without keys - modifying the timing when converting from points to electronic triggers. To stop rotation of the FW when you initially tighten, tap it (one light sharp tap is all that's required) with a socket etc and a SMALL'ish hammer.

Jim Caudill
08-16-2010, 10:25 PM
I "played" with the feel of the taper when I was stoning the crank. I could tell when I started it wasn't right, because the flywheel would "rock" slightly. I couldn't believe how little contact there was between the flywheel and crank when I started. By the time I was done, the taper fit was similar to what I fell when fitting tooling in my tailstock. The markings on the taper were pretty much being completely "wiped off" as I rotated the flywheel back and forth a few degrees. I used a deep socket and small hammer to "set" the flywheel and try to move it any way I could by hand. Then I started with the lockwasher and nut....

The flywheel had a slight countersink where it mated to the crank and the "nut surface". The lockwasher was trying to "crawl" into that cavity, and was being torn by the action of the nut.

I feel pretty good about it.

radkins
08-16-2010, 10:43 PM
A tapered flywheel/crank does not even need the nut if the tapers are good. No, you do not need a lock washer...The nut simply provides the force to "stretch" the FW onto the crank. I do however leave them on :)

You also do not need the key - it does NOT stop the fw from rotating on the crank - it's just there to provide positional accuracy for timing of the magneto. I have installed dozens of FW on Chainsaw cranks without keys - modifying the timing when converting from points to electronic triggers. To stop rotation of the FW when you initially tighten, tap it (one light sharp tap is all that's required) with a socket etc and a SMALL'ish hammer.



I don't think a lawn mower would run long without a key in the crank, they are notorious for slipping the flywheel key or no key! I also saw the flywheel slip on a Kholer 20 HP in a Lincoln welder not long ago, it was not running right and turned out to be the key nearly sheared and the flywheel nut was not loose. I have also seen it happen to Wisconsin engines on air compressors, sometimes shearing the key completely and sometimes only offsetting it. So it can occur and it would seem to me that it would be much more common if the key was left out.

Carld
08-16-2010, 10:56 PM
The only time the flywheel "slips" on a lawnmower is when the blade hits something that stops the engine or almost stops the engine. That also bends the blade and the crank most the time.

Nothing short of a sudden stop at speed will make the flywheel move whether it has a key or not. You can leave the key out of a chainsaw or a go kart racing engine without worry about the flywheel slipping if the taper fit is good and the nut is tight.

Jim, you were right in leaving the toothed lock washer out. I read an article somewhere that lock washers are not needed and often are the cause of something coming loose. Even a flat washer, if to soft, can cause something to work loose.

Most flywheel washers are Belleville washers or flat hard washers but never toothed washers.

radkins
08-16-2010, 11:12 PM
Jim, you were right in leaving the toothed lock washer out. I read an article somewhere that lock washers are not needed and often are the cause of something coming loose.




I think even Caterpillar tractor stopped using lock washers several years ago on all their bulldozers, loaders and other machinery except maybe in special instances. I read something similar a while back that said a hardened flat washer works better than a split lock washer.

lakeside53
08-16-2010, 11:13 PM
I don't think a lawn mower would run long without a key in the crank, they are notorious for slipping the flywheel key or no key! I also saw the flywheel slip on a Kholer 20 HP in a Lincoln welder not long ago, it was not running right and turned out to be the key nearly sheared and the flywheel nut was not loose. I have also seen it happen to Wisconsin engines on air compressors, sometimes shearing the key completely and sometimes only offsetting it. So it can occur and it would seem to me that it would be much more common if the key was left out.


Sure.. I've seen many case like that also... but... in almost all cases using a tapered fitting, the key is not there to stop slipping.

If the key is stopping slipping, then the taper fit isn't good, the contact surfaces were not throughly de-greased prior to fitting, or the correct torque wasn't applied. You can't believe how many guys "oil" the crank end prior to fitting - lol...

How many check the contact surfaces with some form of dye prior to refitting, or lap both for a perfect fit? It's hard enough to get people to understanding that when you use a torque wrench, the torque need to be applied as one continuous force - not stopping and "sneaking up" on the setting - that results in an under-torqued nut.

Some "keys" are now just cast as a "knob" in an aluminum flywheel - they shear in a heartbeat if there is any slip.

Carld
08-16-2010, 11:19 PM
Another thing about lawnmower flywheels, if you hit a post and shear a flywheel key the flywheel taper is distorted and will never fit correctly again like when new. I put a lot of flywheel keys in when I had a shop and I noticed when they broke the first key I would see them again more often. I couldn't sell them a flywheel but I could keep putting keys in. I loved it. $$$$$$$$$$$$$$$$$

lakeside53
08-16-2010, 11:25 PM
But sometime you never want to see the POS again... I've been known to use red loctite (with their permission ;) ) if I didn't want to ever see the engine or customer again :D :D

Carld
08-16-2010, 11:31 PM
:D I was always afraid to do that because I would always end up having to work on it again. However heat will remove anything :eek: :rolleyes: .

DougA
08-17-2010, 07:16 AM
I work occasionally on an Italian built Friggi bandsaw. The 36" blade drivewheel is held on by a taper. No key because the position of the wheel to the shaft doesn't matter. I needed to remove the wheel to repair the gearbox one day. I had to use a 10" puller on the wheel but it didn't come off until I used a large sledge hammer on the rim of the wheel and finally got the wheel to pop off.

lakeside53
08-17-2010, 11:04 AM
Luckily the fly wheels I deal with typically have some form of mount for a puller that pushes on the crank and pulls around the center. Even then, many come off with a BANG. Using an adjustable impact wrench with care can help remove the wheels without even blocking the crank rotation, but... on small engines it's a good way to break off the crank stub. Yep.. been there :(

Some steep taper fws are removed by holding the engine by the fw, protecting the crank-stub thread and hitting the stub with a hammer. Not my idea of a good design, but there are million of consumer grade chainsaws and other devices in use that use this.

Using a 3 jaw puller around the rim is a sure way to crack or break the flywheel. It tends to "bend" the flywheel and increase the needed pressure rather than apply force right around the crank stub. Every shade-tree mechanic has their favorite lever/hammer, but the best solution is to try to make a simple puller or system that works as the factory intended.

JoeBean
08-17-2010, 05:39 PM
For those interested, though this might not help the OP's problem, here's another interesting way to fix keyway screwups:

About 15 years ago As VW transitioned from 1.6L to 1.9L diesel engines they had a problem with the crankshaft sprocket for the timing belt coming loose, destroying the half keyway, and busting the valves/pistons. The "retrofit" solution at the time was installing a harder (12.9) bolt to prevent stretching & coming loose. But that was a bit of a kludge. When they released the first TDI they redesigned the crank nose to prevent this problem (otherwise the cranks were identical. Here's the old crank design:
http://media.photobucket.com/image/aaz%20crankshaft/libbybapa/trCCCCjpg002.jpg

And here was the solution:
http://tech.bentleypublishers.com/servlet/JiveServlet/download/53-8732-59901-244/Crankshaft.jpg

In other words, locate & machine a flat, and create a match on the sprocket. I did several of these mods and they work well and it's fairly easy to do if you have any of the keyway available to locate the flat. Then at the sprocket/flywheel/whatever you can either weld up & machine a matching flat, or mill out a rectangular volume and make a matching key that fits into the sprocket so that the long edge is tangential to a circle sharing the same center as the crank nose, and the edge fits the flat milled on the crank. Basically a key turned 90 degrees. I hope that makes sense.