Thanks to David Deines - updated 9/8/01
Gang,
I am now in receipt of Don Harold's camshaft. Or the 'collective camshaft' as it
were. Remember, I have very little 'hands on' knowledge of these things but I
will offer my observations.
1. The bearing on the outside of the failed sprocket has a groove about
1/32" deep. Does anyone know if that is supposed to be there?
2. The sprocket moves about 1/16" side to side between the 'nut' on the
inside and the race on the outside. I understand where the clicking comes from
now. I can see the splines are still intact on the tube, and cannot turn the
sprocket more than about 1/16" by hand.
3. ALL of the bearing surfaces have a raised land in the center of the surface
and score marks all over. It takes a fingernail to tell that there is a
difference, but it is easily seen.
4. This thing is DENSE! Frankly with all the talk about how low weight it should
be I was surprised. I expected this to weigh half what it does. I have held
hi-performance cams for 350 chebbies, and they only weigh about twice this.
5. The cam lobes look as clean as a baby's bottom. No marks, no wear. Don's car
had almost 100,000 miles on it.
I'm going to have my father-in-law take a look at this, then I'm sending it to
Kirk for his examination. The last time I spent any quality time inside a motor
was in 1981 with a 352 Thunderbird Y-block.
FWIW
David
'98 TR
$1000 piece of pipe in hand
PS: No signs of overheating. All the lobes and bearing surfaces look normal, no blueing.
Groove in bearing may be a an oil groove? Paul Nimz - does yours have one?
Tim Wright
What's interesting is I would have expected strictly radial wear/grooving as the sprocket attempted to turn on the shaft. Once it let go I could then see it threading, corkscrewing or whatever. Seems that there is some linear exertion being placed on the sprocket. WRT to the wear factor. Don't forget that the lobe mat'l and shaft mat'l are and have to be different. Yamaha could make the lobe as hard as req'd to negate wear without anything else to worry about. The shaft had to be designed and heat-treated keeping in mind that a deformation/expansion process had to take place to secure the lobes and sprocket in place. Therefore the mat'l selection and the degree of hardness probably was not optimum but satisfactory in their minds. If the shaft was hardened to the same degree as the lobes, say 65 RC, then it would be impossible to put it through the expansion/assembly process. It would probably just explode like a piece of porcelain. I wonder why they didn't heat treat the entire assembly after installation. Probably warpage, parts moving etc. It would be real interesting to find out the hardness values are for the individual parts. That would go along way in determining the logic that was employed during the process.
When you rock it back and forth, is there more play at one end of the sprocket
relative to the other. I know that is not an easy question to answer. But you
might notice more of a gap between the sprocket and shaft say at the end with
the sprocket located directly over top vs. the end that has the hub only. Just
wondering if having the sprocket being offset on the hub is causing a small
amount side force/load. Out of curiosity, where are you guys located.
Hammy
John Hamilton
The cam you have is the "exhaust" cam, on the left or front head.
It has not yet totally failed. I caught it in time. The way the cam sprocket is
loose, tell you why I could hear a ringing sound coming from the front of the
engine. I thought it was a timing chain, but I now believe the noise was the cam
sprocket starting to go. As David noted, the cam lobes look like new for an
engine with 105,000 miles on it. I was not impressed with the cam journals
though. They look a little rough, like an oiling problem, but I don't think
there was a "bearing" like a main bearing on a crank. Can any of the
rest of your verify that. this surprised me...It was like the cam rested right
on the head casting and was restrained by the top clamp ??? Anyway, other
problems existed and, timing chain, guides, tensioners on timing chain as well
as the tensioners on the slave chains were replaced. All other cams were tight
and did not need replacing. Cost....1671.00 on parts....22.5 hrs labor. I now
feel good about the top end of this engine. When do the rings go ???? on a
105,000m engine.....can I go another 100,000m now ??
Don Harrold
David,
Hardness can be determined at any time using a hardness tester. Most basically
look like a small drill press. It has an interchangeable "penetrator"
instead of a drill chuck. The part or location on a part is cleaned if req'd,
then placed under in the machine on an anvil just under the penetrator. Rockwell
"C" (RC) is the most common scale used for general purposes. For RC a
120deg. conical diamond penetrator is inserted in the machine. The part is
brought up to meet the penetrator by means of adjusting/raising the table. The
table is then raised a bit more until the penetrator has just started to
penetrate the part and the weight scale on the front of the machine reads that
10kg of preload is now being applied. A handle is flipped and 150kg of weight is
applied to the penetrator further pushing it in to the part. The load is removed
after the needle stops moving indicating full penetration allowed, downward
movement has stopped. Voila, whatever the dial indicates is the hardness of your
part (depth that diamond has penetrated). There are even portable hand held
units. We have some at work, but their accuracy, repeatability is not that good.
From what very little I know about motors, a regular camshaft is hardened to say
55-60 RC, then ground to final dimension. At this time we don't know anything
about our camshaft wrt hardness or mat'l composition. I suspect that the shaft
is still relatively soft, which would account for the marks on the shaft bearing
surfaces. These marks on a normal "hard" shaft would not be present
unless there was a problem. The reason I think the shaft is still soft is the
assembly process used. From what I can gather, all parts were made individually
and then assembled (not a revelation I know). Lobes were probably hardened to
req'd hardness that all cam lobes require 55-60 RC? This hardness is obviously
required for wear, but also req'd because in the swaging process one part has to
be sacrificial, or soft and the other hard. Same goes for the sprocket. It had
to be hard wrt wear, so it might as well be hard for the assembly process as
well. That leaves the shaft. The shaft has to be somewhat soft for two reasons.
First, to allow the cam and sprocket spline to bite into it in the swaging
operation. Second, to remain soft (ductile) enough to allow it to be expanded
during the assembly operation and keep it's integrity wrt cracking, flaking,
shrinking, profile
etc.
This is speculative on how they assembled the parts. A fixture (jig) was made to
accurately locate all the components in a very rigid manner. An anvil was
hydraulically driven up through the shaft thereby expanding the shaft and
causing the interference fit at the lobes and sprocket. If hardness testing
revealed that the shaft was say >50 RC, one would assume that the assembly
was subjected to heat treatment after assembly. I would think that to be a risky
affair, warpage, part movement etc. They would almost surely have to re-grind
the assembly after such a procedure. So I bet it wasn't done, Yamaha trading off
the premature wear of the shaft bearing surfaces to allow them to do this
process.
It would still be nice to know though. If the shaft is indeed hard, then wear
marks would not be good. If it is still soft, it would account for the wear
marks. And if there is an oiling problem which again I'm not in any way
discounting, then the wear would be even more premature. Maybe this could be
adding unforeseen friction/load on turning the camshaft. That load would be seen
at the sprocket.
So why did they use this process to make the camshaft? Money? Does it allow for
higher RPM's? Did Yammy feel like experimenting with an engine they would not be
held accountable for?
It would be nice to hear from a gearhead as to why they think or know what the
advantages of this style of cam are.
If it's strictly a production/cost related shortcut, I'm going to be really,
really pissed!
Sorry for the major ramble, just thinking out loud. I was only going to talk
about hardness testing. But in true brainstorming, all concepts are laid out on
the table. There could very well be someone sitting back taking all this in and
connect all the dots for us.
Hammy, caffeine level now pegged!
John Hamilton
'97 ES
90k km
Multi-ported Airbox
HAMS*SHO
What exactly failed?
Do the little teeth fracture? Or does the bond between the teeth and tube fail?
How tall are the teeth?
If the teeth are very hard and brittle, and can't take any motion (rocking
caused by the oscillating loads) then welding them may not be the best fix? If
the teeth fracture in shear then weld will have to connect tube to the lobe
above the teeth.
Are there little bits of teeth still embedded on the tube?
Anybody catch what I am trying to ask?
Tim Wright