Cams 101

[RickR]

Which cam has more duration?
http://www.donzi.net/photos/rryan47lobes.jpg

[McGary911]

looks like the one on the right? It's hard to tell, but the one on the left looks like it has more lift.....granted i know jack about cams tho.......

[Ed Donnelly]

I like the one on the right. Its cleaner and prettier :) :) ..Ed

[RickSE]

Left. The one on the right looks like a high lift roller with less duration.

[ToonaFish]

Do high rollers typically have less duration?

[Rootsy]

ahhh a trick question :D

depends on where you are measuring that thar duration on dem dere bumpsticks... lash point, .004, .006 lift... OR .050 lift... or .200 lift... the one on the right definitely has MORE AREA UNDER THE CURVE...

it also appears as though the bumpstick on the right is a small base circle camshaft. I am also gonna feel adequately safe to say the one on the left is a flat tappet camshaft...

now if you think you are REALLY good.. tell me which one has greater JERK... yes you read that correctly... wink

[RickR]

Rootsy gets the Gold Star :D It was a trick question. They both have the same duration @ .050 but the one on the right has 7 more intake and 12 more exhaust degrees @ .200, 16 more intake and 22 more degrees @ .250.

(What does JERK stand for?)

Question #2
Why is the cam end recessed?

http://www.donzi.net/photos/rryan48thrust.jpg

[Rootsy]

the camshaft with the snout (right) is for a factory roller camshaft chevrolet block... there is a thrust plate which retains the camshaft and controls the end play. the cam on the left being a flat tapped does not require the thrust plate because the lobes are tapered and the spring pressure on the lifters keeps it forced backward into the block. on NON factory roller cam block applications with a roller camshaft installed where there is no thrust plate you have to use a cam button...

Jerk is the rate of change of acceleration (j=Da/dt).

to lead to it.... Velocity is a rate of change of displacement (v=Dx/dt), Acceleration is a rate of change of velocity (a = Dv/dt)...

JERK is what DESTROYS camshafts and valvetrain and any other moving linkage system... it is effectively a rate of change of force since F=MA and jerk is the derivative of acceleration.. therefore j= M*Da/dt or in other words j = DF/dt... it is a harsh motion and must be minimized in design...

nascar guys, Certain NHRA and circle track classes (generally anywhere there is a lift rule) are exploiting it by using extremely aggressive ramp accelerations where they literally loft the lifter off the nose of the lobe... if the lifter didnt do this it'd beat itself to death because it couldn't follow the profile of the lobe and the jerk would be too great at the inflection points on the nose...

on a seperate front jerk is what causes discomfort to passengers in vehicles (cars, trucks, trains, busses, airplanes, etc)...

Rootsy - why yes i did ace Kinematics...

[Tony]

I agree, as usual, with Rootsy.

Remember The Jerk, with Steve Martin? That was a great movie!

[Ranman]

First I got my name in the phonebook, and now it's on your ass. I bet more people see that than the phonebook.

[RickR]

Looks like Rootsy should be teaching this course.

Ranman, HUH????


Question #3 what caused this??

http://www.donzi.net/photos/rryan49chip.jpg

[Rootsy]

you mean the glare? that'd be camera flash LOL...

hard to tell from the photo but are you pointing out the chip in the nose of the lobe?... did it wipe the lobe off too? how many hours were on that camshaft...

[RickR]

Rootsy
The cam was chipped but lobe was NOT wiped out eek! Lifter was rotating and still good. Probably would not have been long before the cam failed.

[BUIZILLA]

Actually, I think the second lobe tells more of the story about how the first lobe got that way. Blow up the pic and study the lifter *track* and wear pattern.

J

[RickR]

300 hours :rolleyes:
http://www.donzi.net/photos/rryan51chipa.jpg

[BUIZILLA]

If you look closely, you were losing the 4 lobes visible in this pic. If you were to mike each lobe, you might be surprised at the wear of the one in question. In fact, the far right lobe got metal debris spinoff from the second lobe under the lifter face and ground it into the left half of the lobe. Once you lose the nose integrity, the lifter ceases to rotate. There is a .002 angle ground into the lobe nose to facilitate the lifter rotation, no taper... no rotate.

How did it get this way? dry starts.. extended nonusage.. oil quality.. excessive spring pressure.. combination of all previous..

not good in any case, but hey, Crane and COMP have some great marine grinds wink

J

what oil do you use?

[RedDog]

Refresh our memory - didn't you have problems with successfully breaking in a cam with this engine? Maybe something is being over looked with the valve train?

300 hours! I thought this was a 1 year old cam? Wow

[RickR]

Reddog
300 hrs is for 2 years :rolleyes: Since "The Boss" is back in school we are not getting much boating in wink

Buizilla
Sorry but the image make the wear patterns look odd. Wear patterns are normal except for the chip and the noses having excessive wear for 300 hours.

Comp cam out of a K kit with excessive compressed spring pressure. Single spring w/damper as per Comps recomendation :mad: And we idle alot.

Here is a better pic although is still makes the wear pattern look abnormal

http://www.donzi.net/photos/rryan52cam.jpg

[RickR]

Question #4
Why is this steel cam black on the distributor gear?
http://www.donzi.net/photos/rryan50cast.jpg

[Rootsy]

austempered cam gear on a steel roller camshaft for use with an iron distributor gear...

[Budmann]

Am I the only one who caught Ms. Toona's reply.
wink wink wink wink :p

[BigGrizzly]

The flat tapet came looks like another Comp cam failure.

[RickR]

In layman's terms Rootsy was saying
Cast Iron Distributor gear :D

Budman
Got it :rolleyes:

Griz
Correct frown

[RickR]

Question #5

What is this?
http://www.donzi.net/photos/rryan55bone.jpg

[ToonaFish]

Oo oo oo oo, I know!

A Donzi bidet!

[MOP]

Toona you even funny after the coffee wears off :D

[BUIZILLA]

aw gee, tough one..

roller lifter guide plate with a mickey mouse generic hydraulic lifter wink the clip is the mm giveaway..

J

[RickR]

Buzzilla
Yep and the lifter is OE GM.

Crane says max lift on OE lifter is .574 which brings the OE lifter even with the top of the "Dog Bone". With more lift they want you to buy their lifters which use the same pushrod but have an extended top.

I cannot see a problem if the lifter drops in to the guide slightly (pic) like .024 more.

What do you think?????

[BUIZILLA]

That lifter deal is fine, plenty of stability left. The dogbone is only there to keep the lifter from turning anyways. The LT-1 engines and Vortecs use a tin stamped lifter guide.

J

[RickR]

Buzilla
Do you have a pic of the LT1 lifter retainer?


Question #6

What is the silver colored piece in center of pic?
http://www.donzi.net/photos/rryan56gear.jpg

[BUIZILLA]

Welp, I guess someone's been in that engine beforehand wink and they drilled out the dowel hole for an advance/retard bushing, and then staked it in with a centerpunch. If you have a GM Perf parts book, look up LT-1's, or any flat tappet to roller conversion, and there is a stamped steel plate that sitts in the lifter valley to secure the lifters. Most have 2 to 4 securing screws that have to be tapped in the valley area to secure the plate. Some aftermarket plates just *snap* in place under the head bosses before the intake is installed too, depends on which brand you go with.

J

[RickR]

Buzilla is correct again :D

Bonus Question
2 camshaft degrees = ______ crank degrees.

Professor is "Gone Fishing" class is out till Feb :rolleyes:

http://www.donzi.net/photos/rryan59grouper.JPG

[BUIZILLA]

4

[Ranman]

Is that because the cam spins at half the speed of the crank? MAybe I actuall knew the answer to one of these..

[Rootsy]

yes :)