Tired of breaking camshafts

[jdperform]

These are sprint engines. Everything we now build new have 55mm journals and hence a larger barrel size. We have seen no failures with that size. The cams in question are the standard roller bearing size of 1.875 and they are split 50/50 into which block they go into std height cam or raised cam (+.391). Manufacturer of block maters not. I under stand there are many SBC cam cores and barrel sizes available. I would love to us a 50mm core and grind it down nice big barrel etc. The problem is the grinding the lobes past suffiecent heat treat depth.
Installing a 50mm cam in a standard cam height block although doable requires grinding bottom of the sleeves to install the bearings unless the cam tunnel is relieved adjacent to sleeve bottoms. And still you can get into the con rods hitting lobes. I'll get the cam out today and report the findings , (again)

[Newold1]

Hey jdperform:

Are you really looking for an answer or are you just pissed, blowing off steam and venting, because some here who have a lot of usable knowledge and experience asked for information as to cam core, base circle size, etc., etc, and you don't provide the information for some here who might help solve your problem! Communication, valuable tool! should be on every ones bench or tool box!

[pamotorman]

what about sharp corners where the break happens. when my son was racing motorcycle 4 hour hare scrambles he was breaking transmission gears. i machined radius into all the sharp corners on the gears and the problem went away

[CamKing]

From my notes, I see 2 different barrel diameters available for the 1.875" journal cams. .850" or .900".
That's why I asked what the barrel diameter was. If the ones you're breaking are the .850", then the first thing to do, is go to the .900". IF you're breaking cams with the .900" barrel, then the fix is going to be a little more involved.

[In-Tech]

what about sharp corners where the break happens. when my son was racing motorcycle 4 hour hare scrambles he was breaking transmission gears. i machined radius into all the sharp corners on the gears and the problem went away

I'm curious of this as well. Castings and heat treat depth make me wonder if it is doable or futile It sounds like Mike knows.

[jdperform]

I don't live on this website.
Mike it is a .900 barrel. I was told today when I ordered the new cam that is a constant problem with the smaller barrel cams. Again I was told there is no bigger barrel available for the 1.875 journal. The team that runs this deal has an big checkbook but not so big as to put a new 55mm block, cam, gear drive plate, pushrods, lifters .904 from .842, front cover etc.
I talked to core suppliers and the guy who was tutered by Harvey, and I got the same answer.

[CamKing]

I don't live on this website.
Mike it is a .900 barrel. I was told today when I ordered the new cam that is a constant problem with the smaller barrel cams. Again I was told there is no bigger barrel available for the 1.875 journal. The team that runs this deal has an big checkbook but not so big as to put a new 55mm block, cam, gear drive plate, pushrods, lifters .904 from .842, front cover etc.
I talked to core suppliers and the guy who was tutered by Harvey, and I got the same answer.

Here's what I would do. Take an 8620 steel, 50mm journal core with a barrel diameter right below the max base circle size you can run, rough the journals and lobes to .020" above the finished size to make it a 1.875" journal cam, re-carborize the cam, then finish grind it.
This should only add about $150 to the cost of the cam.

[Newold1]

This may be a situation where you come to the realization and truth that "none of us can create miracles nor walk on water"!

I am pretty sure a lot of us who have tried to work miracles for our customers finally come to the fork in the road where we "as the experts" inform the customer no matter how big their wallet that there is going to be only one way we can create and build an engine for them that will maintain their needs is to draw that line in the sand and say "if you need that and we are going their, its gonna be "my call"!

I am curious in this case when these cams broke and necessitated redos and rebuilds including time and labor would the cost after that still be that much cheaper than the block with 55mm and stronger cam core?

[PackardV8]

Some good suggestions here, but my question is back to what causes OP's engine builds to continually break the SBC camshaft right in front of number eight exhaust lobe and most here don't seem to have that failure mode. Do most sprint car SBCs with medium aggressive lobes turning close to 9K break the cam there?
What is unique to his build that puts too much stress in that location?

Details which might also be relative, what and how are the oil pump and ignition driven? What's on the front and rear of the crank; balance damper/flex plate/flywheel? What balance factor? Gear drive for the cam or chain? Whose? Fuel pump driven off cam nose?

[CamKing]

Some good suggestions here, but my question is back to what causes OP's engine builds to continually break the SBC camshaft right in front of number eight exhaust lobe and most here don't seem to have that failure mode. Do most sprint car SBCs with medium aggressive lobes turning close to 9K break the cam there?
What is unique to his build that puts too much stress in that location?

They normally break before the #7 or #8 exhaust lobe, because that's about dead center of the widest gap between bearings.
On a sprint car engine, the rear of the cam is drilled and tapped to run the power steering pump. This adds to the problem.
The opening ramp on the lobe design, also adds to the issue, but it's not my place to critique someone else's designs.

[PackardV8]

Some good suggestions here, but my question is back to what causes OP's engine builds to continually break the SBC camshaft right in front of number eight exhaust lobe and most here don't seem to have that failure mode. Do most sprint car SBCs with medium aggressive lobes turning close to 9K break the cam there?
What is unique to his build that puts too much stress in that location?

They normally break before the #7 or #8 exhaust lobe, because that's about dead center of the widest gap between bearings.
On a sprint car engine, the rear of the cam is drilled and tapped to run the power steering pump. This adds to the problem.
The opening ramp on the lobe design, also adds to the issue, but it's not my place to critique someone else's designs.

Thanks, Mike. As usual, I have the questions and you have the answers.

[pamotorman]

Some good suggestions here, but my question is back to what causes OP's engine builds to continually break the SBC camshaft right in front of number eight exhaust lobe and most here don't seem to have that failure mode. Do most sprint car SBCs with medium aggressive lobes turning close to 9K break the cam there?
What is unique to his build that puts too much stress in that location?

They normally break before the #7 or #8 exhaust lobe, because that's about dead center of the widest gap between bearings.
On a sprint car engine, the rear of the cam is drilled and tapped to run the power steering pump. This adds to the problem.
The opening ramp on the lobe design, also adds to the issue, but it's not my place to critique someone else's designs.

do RO-7 blocks have the standard 5 cam bearings or do they have 7 like pro stock blocks ??

[jdperform]

Thanks Mike, I do have 2 questions though. 1) I assume they will face the front of the cam after 2nd carburising and 2) Is it possible to do what you say AND keep the rear drive concentric?
Years ago I destroyed a cam trying to drill and tap the rear after it was heat treated .

[user-17438]

Some good suggestions here, but my question is back to what causes OP's engine builds to continually break the SBC camshaft right in front of number eight exhaust lobe and most here don't seem to have that failure mode. Do most sprint car SBCs with medium aggressive lobes turning close to 9K break the cam there?
What is unique to his build that puts too much stress in that location?

They normally break before the #7 or #8 exhaust lobe, because that's about dead center of the widest gap between bearings.
On a sprint car engine, the rear of the cam is drilled and tapped to run the power steering pump. This adds to the problem.
The opening ramp on the lobe design, also adds to the issue, but it's not my place to critique someone else's designs.

do RO-7 blocks have the standard 5 cam bearings or do they have 7 like pro stock blocks ??

R07 has 6

[CamKing]

Thanks Mike, I do have 2 questions though. 1) I assume they will face the front of the cam after 2nd carburising and 2) Is it possible to do what you say AND keep the rear drive concentric?
Years ago I destroyed a cam trying to drill and tap the rear after it was heat treated .

Yes, you would pull the dowel, and face the front of the cam.
Since the rear "Center" on the cam is the rear drive, it will be concentric when they finish grind the journals.