Can you twist a cam?

Sledpuller

Sledpuller

Comp Diesel Sponsor
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Apr 23, 2006
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Is it possible to twist a cam like an axle and throw your engine out of time?
 
the material cams are made out of dont have the torsional properties like the material axles are made out of i wounldnt think. like chris said.. i would think they would break before they would twist.
 
unless the gear would turn on the cam and break the key. I wouldnt think the cam would twist much before breaking
 
We twist the cams on single cylinder engines that have rules requiring it have a stock cam to change the LSA. I wouldn't think it would be beneficial to do so on a diesel though.
 
Yes, seen it, rear lobe was 12* off on the cam, cam was from a mod turbo/limited pro tractor.
 
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I have heard of them breaking and becoming stuck a few degrees off. This was on gassers though.
 
The chilled iron cams used in most CTDs aren't as ductile as billet cams, but they'll still windup a bit under load - won't say how much, but it's common knowledge that high seat pressures & aggressive lobes cause enough twist at higher RPM to require grinding the profile for each cylinder further & further away from the installed centerline to account for it... reaches ~30* in extreme applications.


Most folks will have to deal with a broken cam before needing to worry how much later the events are happening in #6 than #1. :Cheer:
 
XLR8R said:
The chilled iron cams used in most CTDs aren't as ductile as billet cams, but they'll still windup a bit under load - won't say how much, but it's common knowledge that high seat pressures & aggressive lobes cause enough twist at higher RPM to require grinding the profile for each cylinder further & further away from the installed centerline to account for it... reaches ~30* in extreme applications.


Most folks will have to deal with a broken cam before needing to worry how much later the events are happening in #6 than #1. :Cheer:
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The induction harden cams used in Cummins are not going to twist, any appreciable amount. The 8620L billet steel uses in pro cams will not as well. As to 30 degrees, this is not even close to being possible. The cams in any true race engine can move only a few degrees in one direction or another before piston to valve interference . If it started with 30 degrees in of pre twist it would not run.

I have seen data logs with sensors on the front and back of top fuel engine cranks and the total wind up was 1 to 2 degrees total.
What everyone if not understanding here is that as spring pressure increases, the push on the cam is countered by the same exact twist on the back side of the lobe. This counter balances the cam somewhat.

So Gene why do you ask
 
:doh: OK - edited for clarity & accuracy (mea culpa):

XLR8R said:
The chilled iron cams used in most CTDs aren't as ductile as billet cams, but they'll still windup minimally under load - won't say how much, but it's common knowledge that high seat pressures & aggressive lobes in conjunction with crank twist at higher RPM can require grinding the profile for each cylinder further & further away from the installed centerline (how much is secret squirrel stuff :)) to account for it... crankshaft deflection can reach ~20* in extreme (i.e. Top Fuel) applications.


Most folks will have to deal with a broken cam before needing to worry how much later the events are happening in #6 than #1. :Cheer:
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Cummins UGLs are poured into a chilled mold, rapidly cooling the liquid alloy's outer layer while the molten interior gradually solidifies - the hard shell created is similiar to case-hardening an alloy.
8620 isn't induction-hardenable ( a process which changes austenite to martensite deep into the core), due to it's insufficient carbon content... can't induction-harden 9310, 4820, 4320, etc. either for the same reason.
Alloys with .3% or more carbon can be successfully induction hardened (4340, 6265, 4130, etc.).
 
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COMP461 said:
So Gene why do you ask
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Local Case pulling tractor has had issues,no one can figure out.
Found out about a Ford tractor, same symptoms, twisted cam. Wondering if that was a freak, or should we check it?
 
Cams will and do twist during operation with heavy spring loads. The thing is each camshaft type is different. As a rule of thumb the smaller the core the more that it will twist, the longer the core the more it will twist, were talking front to rear. Most of the time it's a few degrees up to about a total of 5 degree. Any more than that they will break most of the time. There are plenty of top fuel and pro stock camshaft designs with a few degrees offset ground into the lobes from front to rear. The top fuel guys have it down so well that they even run different static compression in different cylinders based on the heads and what blower is being used.
 
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