Crankshaft Sprocket: Replace or don't replace?

[Hector]

or something that's holding the crankshaft sprocket in place before I pull the thing out. It's been a few weeks since I 've been up in that part of the engine and don't recall seeing anything that would indicate such a thing.

[Jeff N.]

Bill and others helped my through this a bit ago. Not too hard really but I did have the engine out of my car.

- removing the sprocket. The sprocket's held on via friction fit combined with a woodruff key or slot (can't recall which) to keep it from rotating. I pulled off the sprocket with a sears gear puller centered on the crank nose. Put the puller arms on the teeth of the sprocket until I pulled it forward enough to get the arms behind the sprocket. Tapped on the gear with a ballpeen hammer to help get it moving. The gear itself is very soft metal so expect that you'll basically ruin the current gear by doing this (there's no way back once you start pulling it).

- replacing the gear. This was fun. You'll need an old qt size pot, a quart of synthetic motor oil, a campstove or similar, a candy thermometer and a good set of pliers. Basically, you'll want to heat the oil bath and sprocket to about 300 degrees (Bill- that sound about the right temp?). Grab (carefully as so not to bung up the teeth - it's soft) the sprocket from the oil bath and quickly slide it onto the crankshaft. Hold it in place and wait about 30 seconds for it to cool. That's it.

Cheers!

Jeff

[Hector]

pulling the sprocket out will be easier than installing it. I gotta go back to the car and plan a method of attack to get this thing done. Also, I just can't go banging on the sprocket with a hammer upon installation as I will definitley mess up the gear. How did you slide the sprocket back into position? Did you have something soft like a piece of wood or something over the gear to prevent it from getting all banged up from the impact of the hammer?

[Bill R.]

pulling the sprocket out will be easier than installing it. I gotta go back to the car and plan a method of attack to get this thing done. Also, I just can't go banging on the sprocket with a hammer upon installation as I will definitley mess up the gear. How did you slide the sprocket back into position? Did you have something soft like a piece of wood or something over the gear to prevent it from getting all banged up from the impact of the hammer?

[Hector]

That is too easy and shweet. Now I'm looking forward to installing this. So I was wrong, installation is easier than removal.

Yup, I see now. "Hold it in place and wait about 30 seconds for it to cool" is the give away.

Thanks Bill

[Jeff N.]

New and old cranksprocket gear side by side. You see the spots on the old one where it was damaged during removal from the hammer tapping. Note the wear on the teeth too.



Old engine front...



With new chain, sprockets, pump and guides...

[Jeff N.]

....not sure I'd suggest using newspaper quite this way..

[Bill R.]

folgers or maxwell house coffee can with about a quart of oil in the bottom
and one of those 2 burner electric hotplates with the spiral wound heating
elements to provide the heat... Temperature control was fairly simple this way...

....not sure I'd suggest using newspaper quite this way..

[Robin-535im]

....not sure I'd suggest using newspaper quite this way..

My wife gave it to me after it dropped and chipped the enamel. White Chantel 3 qt.

I used to work in a place where we assembled turbomachinery, and heated press fit was fairly common. We'd put the outer piece in an oven at 400 degrees, the inner piece in a dry-ice bath and wear big welding gloves to fit it together by hand. But if you messed up - what a mess. Hot and cold metal can come to near thermal equlibrium in seconds, and if it wasn't lined up right you practially had to throw it away and start again because once it stuck, it stuck forever.

[Unregistered]

This topic comes up periodically on Click & Clack--The Tappet Bros.: To make the gear fit more loosely to slide it onto the shaft, would it not be better to freeze it? Freezing makes the metal molecules a bit smaller, causing them to contract in on themselves, such that the hole in the gear gets a bit larger, i.e., looser on the shaft.

Last week, while rebuilding an alternator, I found the bearings and sheave would not readily fit on the shaft, until I froze the whole lot in my refrigerator. Then, while still frozen, no problemo.

Now, the crankshaft on an M30 cannot be put in the freezer. But, squirting the part with compressed gas or liquid nitrogen will cool it (latent heat of evaporation), and/or it could be wrapped with a Baggie filled with (dry?) ice.

Comments, anyone?