Camshaft Breakage

[RMS Performance]

Hey guys, long time lurker, first time poster. Great information here!!!

I do a lot of high performance diesel engine work in the Tractor Pulling field. Anyway, last night I had a customer call and said that the new camshaft that he bought from me broke. He was not real angry but wanted to know why.

Here is what happened. He has been to a few pulls and has had trouble getting the turbo spooled up coming off of the line. His slipper clutch adjustment was too tight and would engage before the turbo would be spooled. Last night he was adjusting his clutch and tried the new setting. The engine slowly came up on rpms and at 4000-4250 hit boost and almost instantly hit 5500 rpms. He off course let off the throttle instantly. When the engine returned to idle everthing was not right. He pulled it into the shop and pulled the valve cover to find the rear two cylinders had no valve movement.

Lobe Specs of the Cam:
I: 214 @.050 Lift: .375
E: 232 @.050 Lift: .375
LSA: 110
Intake Centerline: 100
Rocker Ratio: 1.75
Valve Spring Seat Pressure: 210
Over the Nose: 470

Anyone have any ideas? This is a reground stock core. They do have to turn down the shaft some when they reduce the base circle. It is not much though as you can see the casting is places yet.

I have never had this happen before. A more typical break would be at the nose of the cam where the gear is pressed on. I am suspecting that a high RPM, No load, and sudden release of the throttle were the contributing factors.

Possibly a fluke though.

How about some thoughts!!!

Thanks,
RMS Performance

[OldSStroker]

What engine? Where was the failure? Next to a journal or a lobe or?

What is rpm for the stock engine?

Cast cam, right? Are steel (billet) cores available?

[RMS Performance]

Engine: John Deere 466
Stock Specs: Bore 4.56" Stroke 4.75" RPM 2400

Currently: 585 Cubic Inches
Bore: 4.75" Stroke 5.5"

Don't know fore sure where the failure was. Still waiting for the engine to be torn down.

Billet cores are available but are high dollar for this customers budget. Around $1000 difference between the two options. We have had good success with the stock cam in this application but that may be changing as we continue to increase performance and RPM.

[OldSStroker]

Engine: John Deere 466
Stock Specs: Bore 4.56" Stroke 4.75" RPM 2400

Currently: 585 Cubic Inches
Bore: 4.75" Stroke 5.5"

Don't know fore sure where the failure was. Still waiting for the engine to be torn down.

Billet cores are available but are high dollar for this customers budget. Around $1000 difference between the two options. We have had good success with the stock cam in this application but that may be changing as we continue to increase performance and RPM.

$1000 sounds like a lot for just a billet core. The demand must be pretty small.

You might consider machining all the as-cast surfaces between the lobes and journals on a stock cam prior to (or after) regrind. Try to get rid of all the irregular surfaces which are stress risers. You should be able to do this on a lathe. At least use abrasive strips to polish down the as cast surfaces and especially the fillet areas next to the lobes and journals.

Consider doing the above work on a stock cam, and then having it Magnaflux (magnetic particle) inspected for cracks BEFORE sending it out to be reground.

Are the stock lobes surface hardened? Does the cam grinder reharden the lobes? Is so, this might screw up the torsional strength and fatigue resistance of a cast cam.

Obviously at twice the stock rpm with lots more spring load you are really pushing the stock cast cam. Of course, if the 5500 was a one time high rpm, and the valve springs aren't able to control the valvetrain at that rpm, you might not see the problem again if you don't see that rpm.