From: emory!everest.Stanford.EDU!eap (Eric Perozziello)
X-Source: The Hotrod Mailing list
Date: Feb 1994
Subject: Crankshaft Keyway Repair Complete: SUMMARY
SUMMARY OF CRANKSHAFT KEYWAY REPAIR - Thanks to all who responded!
Now that the repair is complete, I thought I'd share the
experience with you all, and thank everyone who responded (list
of folks at the end- Thanks Folks!)
A week or so ago I posted the problem. A Chevy truck
was brought to me with a bad vibration that seemed to go
away when the (auto) trans was dropped into gear. The engine
is a 454 cu. in. engine (externally balanced by the harmonic
balancer) The previous mechanic wanted to replace the torque
converter for $500. The owner then handed the truck to me.
Upon digging in, I found that the harmonic balancer was not
in the right position. The woodruff key, and keyways in
the balancer and crankshaft were badly damaged. Someone had
hammered the balancer onto the crank, literally forging the
key into the crank and balancer. Fortunately, the damage is
limited to one side of the keyway on the crankshaft. Of
course, I got a new key and balancer, but I did not want to
rip the crank out and replace it. So the problem was to
repair the damage to the crankshaft. Below I will outline
the responses I received, and then tell how I fixed it.
1). COMPLETE REPLACEMENT SUGGESTIONS:
"Replace the crankshaft. If your repair fails at high RPM, the
balancer, fan, etc could fly off and kill someone."
"If it doesn't hold, the engine will go way out of balance,
and destroy the main bearings."
*** Obviously, the "best" solution, but not the most cost-
effective. I've never heard of a balancer flying off- I've heard
of FLYWHEELS coming apart. Besides, if it did fly off, it
would probably only kill ONE person, worst case... :^)
2). SUGGESTIONS FOR EPOXY REPAIR, AND REBUTTALS:
"I tried this once. The epoxy failed and ended up causing
worse damage than was originally present"
"Try Loctite Form-a-thread" Me: I picked up a card of
this stuff to have on hand, it seems to be good stuff,
but not for this sort of thing.
"J-B Weld says it can fix stuff like this :^) "
"Epoxy can not take the expansion and contraction of the
"Epoxy can not take the pounding the part will receive."
"The epoxy is going to fill the space between the key and the slot.
It's not glueing anything, just filling a void. Concrete or even
plaster would probably work."
"Use J-B Weld if you MUST use any epoxy"
"Try Devcon Plastic Steel"
"Try stuff made by Loc-tite. I've used this stuff where a
chunk of steel was thrown at the junction of a crankpin."
"Make sure any Epoxy is fresh-stock. It hardens in the applicator."
*** My reason for NOT using epoxy for the primary repair agent:
The machinist told me that Epoxy is wonderful stuff, and they've
tried it for lots of exotic repair "saves", and it CAN be as
strong as steel in some applications, but it doesn't have the same
fatigue properties as steel, and constant pounding will
eventually destroy it. The Epoxy disintegrates and falls out.
3). WELDING REPAIR:
"Fill in the damage with a welder, then clean it up with a grinder."
"Weld a new key in place."
"Weld the balancer to the end of the shaft"
"Welding will require re-heat treating the crank."
"Welding heat should not damage the crank because it's so
massive that it'll distribute the heat for the little bit
of welding that you need to do."
"Any localized heating will change the crystalline structure
of the crank in that area."
*** My reason for NOT using a welder to do the repair:
First, I did not want to weld anything in place, so that
rules out several of the suggestions. I did not want to
fill in the damage with welded material because of the heat-
treating problem. The local welder said it would severly
weaken the crank if not done under controlled conditions
(in a post-bake oven - IE: I'd have to remove the crank ).
The crank is cast.
4). OVERSIZE KEYWAY/KEY KIND OF REPAIRS:
"Machine the crank and balancer for an oversize key."
"Machining the crank for an oversize key is easy. In the
balancer, it's a different story. Maybe a flat file on
"Cut a second keyway in the crank/balancer on the other
side of the crank and balancer. IE: a secondary keyway,
placed elsewhere around the crank"
"Machine a new woodruff key that fits the damage in all its
bumps and waves. You may want to clean it up a little bit
first, making straighter sides, and then use modeling clay
to get an impression of the hole."
"Clean up the damaged area to be flat faced, and then machine
a steel insert to fill in this space, flush with the crank
surface... Then use the standard key. I used this repair once,
and it lasted six years, and it was still holding fine when I
sold the car."
*** This is close to the repair technique I decided to use. (Ya
can't argue with successful practical results!). Now the problem
was how to cut the keyway without removing the crank. (see below)
IMPLEMENTATION: Cutting an oversize key, or cleaning up the damage.
"Use a key cutter from a milling machine, mounted in a hand
Machinist: "It'll never work. The key cutter bites in, and it
will throw the drill (IE: Chatter). You could never hold it steady
by hand, it's too wild- use an abrasive....Silicon Carbide."
"Abrasives/Grinding will overheat the crank locally, and cause similar
problems to the ones you'd have if you tried to weld it."
Machinist: "Grinding it slowly with a small hand grinder will
not do any harm. Just stop frequently and check your measurements
so you don't end up with a sloppy cut."
WHAT I DID:
I ended up getting a new key, a new balancer, and a modified
woodruff key to fill in the damage. I used a small die grinder
with a silicon carbide bit to cut an enlarged keyway in the
crank, cleaning up the damage. I then modified a woodruff key
to fit into the "cleaned up" part, but not extending above the
crankshaft surface (flush with it). Then the correct sized key
was able to fit in its normal position. The modified woodruff
key was simply a steel insert to fill in the "cleaned-up"
damaged region. I then used some Epoxy (JB-Weld) to hold
the modified key in place. The epoxy is not critical, so if it
fails, the steel insert will still be doing the job, but
it sure made installation a lot easier. I then tightened the
center-bolt very tight, since this will remove much of the load
from the repair zone.
I took the truck on an abusive road-test, and it seems to hold
just fine- the vibration is all gone. I also took the time to
fix some accessory mounting brackets that (presumably) were
screwed up by the same "mechanic" that ruined the crank.
It now looks like we've inherited the truck, so I'm glad
I took the time to do it right :^)
Thanks to all who responded. Here is a list that I hope
is complete- If I missed anybody, I apologize. Any questions,
comments or criticisms, please feel free to write me. I'm the
first address on the list below.
Eric Perozziello (Me) email@example.com
John Wroclawski firstname.lastname@example.org
James Swonger email@example.com
Gary Preckshot firstname.lastname@example.org
Clive Apps email@example.com
Jens Larsen firstname.lastname@example.org
Kyle Schmidt RKSCHMID@MECHANICAL.watstar.uwaterloo.ca
Bill Webster WWEBSTER@BNR.ca
Ron Ginger email@example.com
Bill Goodman William.Robert.Goodman@acenet.auburn.edu
Roy Giacchino firstname.lastname@example.org
Bob Carrier CARRIER@FNALV.FNAL.GOV
Jim Foster email@example.com
Chris Kantarjiev firstname.lastname@example.org