Repairing a failed key on a cam shaft

Question by Paul Pavlinovich

My recently acquired Stover KA has a simple fault. The cam which opens and closes the exhaust valve is keyed onto the shaft which goes through the timing gear (to which it is also keyed). The woodruff (half moon) key in this shaft is badly worn so there is a lot of lash in the cam. The trouble is the end of the shaft has been peened over to hold the cam in place making its removal without making a new shaft just about impossible. I've thought of a couple of ways to repair this and am seeking opinions...

The simplest (and ugliest) is to tack weld the cam to the shaft with rod for cast iron. I don't really like this idea as I think the welds would break - conversely if the engine seized while running they might prove too strong (where as the key would be designed to fail).

The next method which I kind of like is to grind/file off the peening immediately adjacent to the keyway then using a small drill/grinder in a dremel and a lot of patience rip out the old key. Once that is done, in a drill press drill down the keyway only far enough to gain access to the existing square keyway. This would make it available from the rear. Then drive in a square gib key from the rear in much the same way as a flywheel gib key. I kind of like this idea the most because it is the least destructive.

Of course, I *could* have a new keyed shaft made (I do not have the skills for this) but I'd rather go the simple methods first. If anyone else has any ideas then I'd love to hear them.

Answer from Ray Freeman plb@plb.iinet.net.au

Paul,sounds to me the easy way is to make a new shaft then you know its all
spot on. You might be surprised how cheap it is to get a small machine shop
to do it. Failing that post it to me and I'll do it for nicks

Answer from Jack Watson jacknade2@bigpond.com

I'd be talking to Mr. Locktite. He has a grade for every purpose.

Answer from John Hall JTHALL@worldnet.att.net

I have pulled plenty of gears, pulleys and flywheels and with the exception
of flywheels on air cooled engines I have never seen a key shear. I have
seen them worn and slightly dislocated. The ones in Briggs flywheels are
aluminum and if memory serves me correct it states not to use a steel key on
the flywheel.

Having said that, tack welding may not be bad for a quick fix.
I agree re-machining the keyways or altogether replacing the parts is the
best fix.

One other idea to consider. I am assuming the cam goes against a shoulder?
Grind away the peened end of the shaft to remove and replace the key. Then
drill and tap the end of the shaft. Loctite a stud in the shaft and use a
large flat washer and locking nut to hold the cam in place? It may not look
that nice but it just may work.

Answer from William J. Pfeiffer Jr. rusty_iron@ameritech.net

Well, I would think that would cause more troubles then it is worth.  I
would just remove the peen, replace the worn out key.  How much
clearance is there on the end?  If there is a bit, why not drill out the
shaft, tap it and put a bolt and washer to hold the cam on?  If not,
just tack weld it.

Answer from Brad Soward Brad_Soward@onaustralia.com.au

You say the gear is also keyed to the shaft? Is it possible to remove the
gear and extract the shaft from the other end? It is not a good idea to
attempt to drill out a Woodruff key! Are you sure the installed key is a
Woodruff key? They would seem to be a more modern innovation, unless someone
has retrofitted it. This could explain the slop. . . . . <g> What holds it
all together and stops either end from falling off, apart from the
previously mentioned peened over end? You will not know which part is worn -
the keyway in the shaft or cam or the key itself (or all three!) - until you
get it all out and apart. The best fix is always to repair or replace the
worn piece!

Answer from Joe Prindle joe_prindle2001@yahoo.com

It does seem rather unlikely that they would have used a Woodruff key, although they were
available at that time. Cutting a woodruff keyseat takes a bit more time and a bit more precision
than a plain keyseat, and it requires a cutter ground for the job.
Regardless, I would advise against welding it. Perhaps brazing, but to get the shaft repaired and
fix it right should not pose much of a challenge to someone with the tools to do the job. I am
sure that there are lots of guys in Oz who would help you out with that, most enginemen are a bit
cantankerous, but generous!
The reason I would advise against welding it is that many cams are hard and it is tough to get
decent penetration with an arc welder. Hardened cast iron was often produced by placing "chills"
in the mold, large masses of steel that would suck the heat out of the molten iron and would cause
it to become hard. I know for a fact that Baker Manufacturing did this when they cast the cams for
their Monitor engines, because all of the blue prints for the entire Monitor line of engines are
stored and preserved at the Rock County Historical Society's Museum in Janesville, WI. I have
copies of the prints for the cams and also the prints for the chills used to produce them.
A man who is good with the lathe could easily fix you up. If the bore of the cam is wallered out,
he could most likely clean it up by holding the cam in the four jaw chuck and either bore the hole
with a carbide tipped boring tool. Then cut a piece of drill rod to length and knurl it to enlarge
the diameter slightly, and proceed to cut the keyseat. Assembling the entire works with a bit of
Loctite 609 ( or whatever number the cylindrical retaining compound is) and then staking as
original should give a good job that will last another century or so.
Just my opinion, take it for what it is worth.

Response from Paul Pavlinovich

It is a half moon woodruff all right - at least I assume it is, because the one at the gear end is and I can get at that one (the gear is held on by key and nut). The shaft will not travel through the cam lobe. The key is rooted - there are bits of it in the keyway. The lobe looks ok, but cannot yet tell about the keyway. I'll let you know.

Final summation from Paul Pavlinovich

Local fellow engine nut Stan Gunn who is a member of the local Emerald club that I'll join when I manage to get to a meeting is very kindly repairing this part for me in his machine shop. He has already turned down the peened over metal and removed the cam using a hand press. The key has been replaced by a new one and the cam pressed back on - it is nice and snug, no movement at all which should greatly help the running of the engine. He is going to drill and tap the shaft to hold a small bolt and a large washer to stop the cam travelling off the shaft when the engine is running. While it will not look quite the same as what was there before, I've seen similar on other Stovers. I do not know if the factory did that, or people have done the same repair but it will look good enough. It is really good to find someone local who is willing to help out a fellow nut

- thanks Stan.
.

This article is part of the Stationary Internal Combustion Engine Frequently Asked Questions (FAQ). This series is a combination of my views and knowledge and the views and knowledge of other people - most of them members of the Stationary Engine Mailing List (More info on ATIS). Those articles which were written by others are © Copyright to the author. Those articles written by myself are © Copyright to Paul Pavlinovich.

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Last modified Sunday, 06-Aug-2006 12:14:23 BST

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