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The Littlest Cam failure

New 06/01/2008


I am assembling another SHO engine and going through my parts bin of
used camshafts. I came across one which has just the "tiniest" wiggle
to it. Can't really see it, but you CAN feel it and hear it when
shaken. I'd have to call it virtually immeasurable at this point.
That's NOT my point.

Here's what I'm thinking - This could be a learning tool. :-)

I want to know what temperature range is the more critical for maximum
sprocket to shaft clearance. We've speculated that cold seems to be
likely, but have no proof. We know the sprocket and shaft are
different metals, so one could behave differently from the other from
one temp extreme to the other.

More sprocket clearance = more sprocket movement = more likelyhood of
sprocket failure. So. Is my beloved, Unwelded SHO more likey to blow
up at room temperature or highway temperature, from a mechanical
clearance point of view?

I'm proposing taking this camshaft and baking it in the oven, putting
on some baking mitts, and giving the little bugger a shake. I'm also
looking to put this nearly OK camshaft in the freezer and see if it
gets more loose or tightens up?

Group -
What do ya'll think will happen when heated, and what do you think the
hot temperature should be? 250' F ?
Will the freezer test SHO more movement? I'm NOT turning my freezer
down to Chicago Winter temps ( :-P), So we get whatever my Fridge puts
out. I WILL record the temps with a Raytech IR temp gun.

--
Eric Lehmann
97 Ebony 42k Welded - With the Angels Now so that I don't have to be.
Long Live the Garage Queen !
97 Ebony 182k Resurrected, Welded, Experiment in progress
96 Medium Willow Green Metallic 103k Resurrected, Welded, Eaton M90 inside
96 Rosemist 72k 2006 Best Of SHO, Popular Vote, 2007 Best Gen 3, Welded
96 Medium Graphite 120k - Resurrected, Welded
97 Pacific Green - Parting this one Out
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My guess is that you will need a Jig and Dial indicator to be able to tell any difference between hot and cold.
The metals are similar enough that the rate of expansion will be minimal.
This is just a guess though!
Jeff Ayers

How many failures are in colder climates?
How many are in climates with the widest temperature range?
How many have failed in hotter places?

Info might be right in front of the list.

Clare Allenby
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Eric,

Be careful, there are those that would call anyone saying temps have an effect on metals and clearances are crazy. If so, then you and I are in good company.

Problem is that I am betting it takes some pretty good scientific instruments to measure the difference. Maybe a good dial runout instrument might do it?

Don M
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Actually, I don't think it's anywhere near as simple as that.

The coldest "cold engine" temp in Toronto may be 100 degrees (F) colder than the hottest "cold engine" temp in Tempe, but "hot engine" temps can be 100-200 degrees (F) hotter than that still.

Plus there are countless more variables at play, even between my driveway and my neighbor's, that can make a difference in this kind of thing. Engine mileage, previous wear/damage, oil condition & frequency of changes, even the type of oil used, etc., you get the idea.

What Eric is talking about is a pretty direct test of just a single variable (for the most part). IMHO, that's much more conclusive than comparing statistical data (though I'm not suggesting that such a comparison shouldn't be done).

Regards,
Jon Heese
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In any case, it would be interesting to see how it plays out in your little experiment.

Dry ice isn't that expensive, if you want to later test it at a more extreme temperature variation...

Doug
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My bet is the wiggle in the sprocket is almost identical at all temperature ranges.

BUT you can't convince me that valves springs aren't harder to compress in the dead of a Minn--e-soda (can't add the accent via email too well) winter upon startup along with the syrup like consistency motor oil that is "lubricating" the cam journals and cam lobes upon cold engine startup in a cold climate.

Since your freezer doesn't go much below zero but winter startup temps certainly do (say -50). I would normally (too bad I am never normal) suggest a top end of 250 degrees but since we can't easily reproduce the bottom end and the expansion should be consistent across a "sane" temperature range. As such I say 0 - 300 degrees as in the dead of winter to the heat of summer the cams endure about a 300 degree operating swing as my ballpark guess.

Scott K
aka as Beaker
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I do not think it is that far apart.

What happens to the size of items when they get cold? (Kastanza)
I bet there is not much of a difference.
Wish I had access to my college's cold weather chamber. (part size not
vehicle size). We used to do stuff all the time.
Not good to put a cheery red exhaust manifold in there.

Ford if they took the normal car path should have cold tested the things in
Minnesota or up in Kapuskasing On.

Test is worthless if you cannot get the cold side down to anywhere near what
the thing would see parked in my driveway.

Clare Allenby
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In talking about temps and clearances, "almost identical" can be extremely important if only a couple thousands of an inch. With the minimal interference fit of the sprockets, ANY give in the fit leads to a measurable looseness, which can start the process of total failure, maybe not at that moment, but down the road.

I seem to remember someone else mentioning that cold temps combined with oil that doesn't flow as well and all the other things combining to make cold starts harder on engines in general, getting some cat calls from the gallery. Now who could that be? :)

Don M
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Dry ice is not that expensive, is it?

At -78.51░ C or -109.3░ F, carbon dioxide changes directly from a solid phase to a gaseous phase through sublimation,

I would think that your driveway does not get colder than that...

Doug
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Careful.

He IS a Canuck...
I really like the dry ice idea. Things like that are why I put this
kind of stuff to the collective wisdom of the list BEFORE jamming the
cam in the freezer.

Eric Lehmann
97 Ebony 42k Welded - With the Angels Now so that I don't have to be.
Long Live the Garage Queen !
97 Ebony 182k Resurrected, Welded, Experiment in progress
96 Medium Willow Green Metallic 103k Resurrected, Welded, Eaton M90 inside
96 Rosemist 72k 2006 Best Of SHO, Popular Vote, 2007 Best Gen 3, Welded
96 Medium Graphite 120k - Resurrected, Welded
97 Pacific Green - Parting this one Out
_____________________________________________________________________________
Some days it has with the wind-chill..

:o)

Dry ice in a cooler would work, plus good for your Ozzy impressions when you
open the cooler.

Not near me but Ontario has the coldest record temp in Canada without a
wind-chill.

White River Ontario Holds the record for -58C (-72F), also the home to the
Real Winnie the Pooh Bear that Ending up in the London England Zoo. (that is
a different Story.) I have been there and we have a photo of our oldest at
the Statue when she was 6 weeks old.

Clare Allenby
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My observation FWIW. It seems like most of the cam failure stories happened when the engine was at operating temperature. The statements were: I was driving along at a steady 55 mph and my engine died or I was just coming up to a stop sign and the engine died or started running rough or I had pulled in my driveway, I was idling while waiting for the garage door to open. I can't remember one case that stated: I live in Chicago and it was minus 20 and when I went out to start the SHO, the cam failed. The battery was dead, but not the cam failed. Others are correct when they say, it depends on how dissimilar the metals are as to how much heat/cold affects the contraction/expansion rates of the parts. But, it would still be interesting to see the reults of the test. It's possible that extra clearance on a cold start could accelerate the failure rate when the motor warmed up. A lot of variables.

John B

 


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