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Competition Diesel racing, sleds, dynos, power tuning and max performance.

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Old 11-22-2006, 12:43 AM
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6.0 Crank/Cam Thrust Load Issues

After having a few cam followers come apart and drop needle bearings through the oil pumps on a previous engine, discovery of the real reason behind the chain of events has led to the opening of another can of technical crap-worms in the 6.0 racing world.

As some may know, the rear timing gears of the 6.0 are helical cut-meaning they are cut at an angle. Any helical gear generates a certain amount of thrust load at a given speed and torque level. In the case of the 6.0, this thrust load pulls rearward on the camshaft, and forces the crankshaft and the pump shaft of the HPOP forward. Increasing engine speed and/or output torque (both are a factor in these applications) will amplify these forces. While traditionally this is not an issue, this engine has seen upwards of 5500 RPM and 1000+ pound-feet of torque.

Interestingly enough, the force of this was actually enough to PULL the pressed-on gear of the camshaft part of the way off the rear of the cam, all the way up to the flange on the rear crank. This caused the camshaft to have endplay- a significant amount of endplay ( a measured .128 inches, over an 1/8th of an inch) and the walking back and forth twisted on the lifters, causing them to fail.

You can see in the pictures the amount of camshaft movement. I don't know how long the lifters were exposed to this over-tolerance (I'm sure it grew as time went on) but it did cause catastrophic failure.

There are two potential solutions to this problem- one being to TIG-weld the cam gear onto the shaft, and two to engineer and install straight-cut gears for the rear. I don't particularly care for solution one because as I see it, it is a band-aid for the real problem. Solution two is an issue because the crankshaft is a two-peice crank, with the rear of the two containing the gear. This rear peice cannot be removed without throwing the crank out of balance and the rear main seal surface out of round, so the new peice would have to be installed on the crankshaft before machining, then the entire assembly would have to be rebalanced after the final cuts were complete- which will get very expensive very quick.

Any of our resident techs or engineers have any thoughts on the subject?
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Old 11-22-2006, 12:44 AM
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Old 11-22-2006, 10:00 AM
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if you do straight cut gears then you will have excessive whine. the main issue is you have excessive rpm and i feel like thats your problem. more rpm, more centrifugal force pulling and pushing. the only thing i can come up with maybe use a preload bolt stop to keep pressure on the cam. then again, you may just find another weak spot.
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Old 11-22-2006, 02:10 PM
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Quote:
Originally Posted by BowTieHatr
if you do straight cut gears then you will have excessive whine. the main issue is you have excessive rpm and i feel like thats your problem. more rpm, more centrifugal force pulling and pushing. the only thing i can come up with maybe use a preload bolt stop to keep pressure on the cam. then again, you may just find another weak spot.
The whine doesn't bother me a bit, I'm actually quite fond of it.

You are certainly correct about the excessive RPM; but I will not drop the powerband in order to save parts. What breaks can be fixed and at a certain point (I guess when there isn't an international part left in the engine? ) it will eventually become reliable under the stress I put upon it.

The preload bolt is actually a very good idea and might be something I should try before going to the expense of the gears. I'm sure the crankshaft can handle the thrust- not sure about the HPOP pump shaft but an HPOP is a hell of alot cheaper than those gears so if I toast one finding out, no big deal.
I knew I posted this for a reason
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Old 11-24-2006, 02:13 AM
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adrian.erks.harris adrianerksharris
I wouldn't go to the extreme of.... hang on... who am I talking to here...

As for gear whine, the tip velocities you will be seeing aren't too bad... certainly not approaching supercharger gearbox levels.

All you need to do is work out what the centredistance is (centreline of crank to centreline of camshaft). Your ratio obviously is 2:1.
Now, I hate your bloody imperial gears, because I can't understand them. But essentially you will need to go through a catalogue, and work out 2 gears that will give you exactly a 2:1 ratio, and still give you the centredistance you are after.

You will also want the same face width... and make sure the gears are manufactured out of something along the lines of EN36A, and get them flame hardened too - b/c helical cut gears are stronger than straight cut ones...


Now, honestly is it all worth it?
- I know you are like me, and overkill just ain't even enough, and there is no way you are going to weld something when you can introduce all other sorts of pain
But, you will need to at LEAST find some gears of the shelf, and get splines cut to suit, if not, get the gears custom ground... and the splines cut.
And gear and spline cutting ain't cheap... You will also need to get them to measure what type of splines you need.

Honestly, unless you are a complete utter sadist like me, get it welded...

However, if you can find me the centredistance, I can work out what size gears you need (I might even do it in imperial too )



On edit. Can you just machine a recess in the camshaft and somehow fit a thrust bearing to it?
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Old 11-24-2006, 02:21 AM
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Quote:
Originally Posted by BigF350
Honestly, unless you are a complete utter sadist like me, get it welded...

However, if you can find me the centredistance, I can work out what size gears you need (I might even do it in imperial too )
I think we are on the same page

I'll be emailing you shortly.

I can't have them TOTALLY straight, or otherwise there will be nothing to prevent the crank and cam from walking to and fro as they please....im figuring somewhere between 3 and 5 degrees should be enough to keep things firmly planted but reduce the thrust load to neglible levels.

For strength, what about something along the lines of a slightly biased herringbone (double helical) gear? 10% length bias? Just throwing out some ideas...Those are even harder to get cut and even more expensive...

edit- just so happens that I found a pretty highly recognized custom gear company; CM Gear only about 2 and a half hours from where I live....

Last edited by PSD 60L Fx4; 11-24-2006 at 02:29 AM.
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Old 11-24-2006, 02:23 AM
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Old 11-24-2006, 02:36 AM
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adrian.erks.harris adrianerksharris
Quote:
Originally Posted by PSD 60L Fx4
I think we are on the same page

I'll be emailing you shortly.

I can't have them TOTALLY straight, or otherwise there will be nothing to prevent the crank and cam from walking to and fro as they please....im figuring somewhere between 3 and 5 degrees should be enough to keep things firmly planted but reduce the thrust load to neglible levels.

For strength, what about something along the lines of a slightly biased herringbone (double helical) gear? 10% length bias? Just throwing out some ideas...
Ok, you just introduced another relm of hurt... if you want "slightly helical" gears, they pretty much have to be custom ground.

I assume the standard ones run a 45deg helical angle?

A herringbone gear would be your best solution, but we are talking $$$ and what kind of real estate does this thing have to fit in anyway?
Because they usually have a pretty wide face width...

Oh, and don't forget we can start playing with pressure angles on your gear teeth to reduce your shaft loading... which in your situation could be very handy. That is if it is greater than 14.5deg already...



As for gear companies, they are usually everywhere - there is probably one in your town, not all are capable of doing helical gears though, and even fewer are capable of doing herringbone.
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Old 11-24-2006, 02:40 AM
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I have not carefully measured the angle but as far as I can tell, they are right about 30 degrees. I will find out for sure.

The face of the gear is 1.15 inches, so thats about how much room we have to work with. I could get away with making it a LITTLE thicker toward the back of the gear, but anything more than about .100-.105 is going to put it up against the flange of the rear main seal.

I had actually brought this issue up in a discussion me and Maxium4x4 had a while back (before this problem occured) but we had both chalked up the situation to me being a paranoid wanna-be engineer...that is, until I actually yanked the gear off...then we both had to take a second look

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Old 11-24-2006, 03:25 AM
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1.15 - a herringbone should be fine...
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Old 12-11-2006, 09:19 PM
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I just stumbled onto this thread and the new competition forum. Excellent
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Old 12-11-2006, 09:32 PM
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Forums slow...

Go the herringbone route if you have the time and $$$
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Old 12-12-2006, 10:16 PM
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I have the solution for replacing the crankshaft gear for you Matt, that is an easy one, have a split gear made. (a company in Baton Rouge patented a split gear that drives a blower on a Cooper intergral compressor which used to mean pulling the crankshaft out of the engine to change the bull gear out, after over 70 swaps without incident, its pretty much bullit proof) Porta band the old one about 2/3 of the way through and smack it with a big hammer, it will break and fall off in 2 peices. I would say when having the new one made it needs to have .0005"-.0015" of interference fit per inch of diameter. The balance factor should not be all that hard as have them oppose the bolts that will get you close enough to final balance the assembly pretty quick. (balance was not an issue inthe coopers as the crank turned a mightly 300 rpm's) As for the problem up top, on the cam side, a tilt pad bearing (turbine application in exactly this scenario...active vs. inactive thrust surfaces caused by opposite direction pinion loading due to the single direction helical drive gears in the gearbox) comes to mind. I would stay with whats in there as a 30 degree bevel gear (standard in most american gearboxes) is a tried and true design of over 50 years. Machining the block for an active thrust pad bearing will porbably be much cheaper than having herring bone gears cut.

Now after having said all that, I have a tig machine in my garage, I do not however own a gear hobb. Guess which route I would take? Besides you never know til you try it, why go the most expensive route first?
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Last edited by mrxlh; 12-12-2006 at 10:23 PM.
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