Author Topic: 8V camshaft vs diesel camshaft (gears) (Read 3802 times)

zagarus · « **on:** April 16, 2009, 12:13:57 pm »

So yesterday while putting my 1.9 together some more i was puzzled to find that the way the gear mounts to the camshaft is very different from an 8V gas camshaft.

Does anyone know why the diesel gear and camshaft are tapered rather using a key? I mean what if the camshaft were to all of a sudden lock up? The gear could still spin. Any clarification would be much appreciated.

truckinwagen · « **Reply #1 on:** April 16, 2009, 12:25:38 pm »

the diesel cam is tapered to allow small changes in cam timing to keep the valves from contacting the pistons(not an issue for gassers)

I agree that the taper is inferior to the key and had a motor fail just last year due to the cam gear spinning.

I am working on getting an adjustable gasser cam gear to work with the diesel timing belt(swapping the outsides) and using an ABA gasser cam in my next fire breathing motor.

that way I have the adjustability needed and the keyway to ensure that the gear never spins on the shaft.

Kantdrivefast · « **Reply #2 on:** April 16, 2009, 12:26:46 pm »

I though it was to compensate any minute difference in crank gear/ pump gear timing. That way you can get perfect timing and not have to worry about keyways on the cam.

truckinwagen · « **Reply #3 on:** April 16, 2009, 12:39:58 pm »

yep, it is, like I said.

burn_your_money · « **Reply #4 on:** April 16, 2009, 12:43:00 pm »

I don't think it's an inferior design. Consider how hard it is to get the gear off the camshaft. Even if the cam locked up because of something, whether or not the gear has a key or not, catastrophic damage is going to happen.

Vincent Waldon · « **Reply #5 on:** April 16, 2009, 01:20:15 pm »

Think of it this way... the poor gasser folks have to pay big bucks to get an aftermarket adjustable camshaft pulley... we get one for free! :wink:

zagarus · « **Reply #6 on:** April 16, 2009, 03:09:50 pm »

thanks for the replies guys. Here's another thought, why do they put a notch in the camshaft to allow for a key?

truckinwagen · « **Reply #7 on:** April 16, 2009, 04:36:20 pm »

I did exactly what you describe, except I torqued to 50 ft-lbs and I had the gear slip causing catastrophic failure.

it destroyed one valve, bent all the rest, sheared the keyway in the crank and sprocket, and put good size marks in all my pistons.

this time around, I have scuffed the two surfaces(not hard, just a little) cleaned with brakleen, added red threadlocker and torqued to 150 ft-lbs.

I have no intention of re timing this motor before I get my next one built with the adjustable gasser gear and cam, the current motor is just to make the car drivable for a few months while the new one is built.

burn_your_money · « **Reply #8 on:** April 16, 2009, 05:10:18 pm »

Yikes

Quote from: "truckinwagen"

sheared the keyway in the crank and sprocket,

I think this is the root of the problem though, not the cam gear.

I always go tighter then 33ft-lbs as well. 33 just doesn't seem to be enough.

truckinwagen · « **Reply #9 on:** April 16, 2009, 05:16:51 pm »

no, the cam was clearly the problem, the force of the cam suddenly stopping the belt(as the valve contacted the piston) knocked the crank pulley loose.

the crank end and pulley had no sign of back and forth wear, just a clean break in one direction, as if the damage was done in one very powerful event.

truckinwagen · « **Reply #10 on:** April 16, 2009, 06:08:47 pm »

the cam bolt is a 10.9 from the factory and I replaced it with a 12.9

lubed a 12.9 is supposed to ba able to take 100 ft-lbs, so dry I torqued it down more to apply the same clamping force.

the cam is made of very high quality material, I am not too worried about it, when cranking the bolt down it felt very solid.

as far as I was concerned the cam and pulley should be as close to one piece of metal as possible.

when I took the motor apart I found no foreign material in the piston that would have stopped a valve, and the only valve that was stuck in the guide was the one made 1/2" shorter by the piston.

as the cam gear damage was clearly an effect of the belt stopping because the cam stopped(and not the other way around) I settled on the cam gear slipping as it seems to be the only other explanation.

theman53 · « **Reply #11 on:** April 16, 2009, 06:47:51 pm »

the cam bolt is a 10.9 from the factory and I replaced it with a 12.9

lubed a 12.9 is supposed to ba able to take 100 ft-lbs,

Maybe there it is. The 12.9 ansi designation is only for SHCS not HHCS. The SHCS wouldn't have had near the surface area under the head as the HHCS. It would have had to had another washer or fit poorly in the original washer which may have given the room for error for the cam sproket to slip. Also the 10.9 will stretch and give more than a 12.9 whcih is more than likely to break than to give. The 10.9 will take more vibration before failure as well. Next is why did you replace it to begin with? If the stock bolt was messed up or messed up the cam threads then it could give a false torque, which you probably would have noticed.

truckinwagen · « **Reply #12 on:** April 16, 2009, 07:59:42 pm »

I replaced the bolt with an exact replacement except for the grade, the bolt fit perfectly in the washer, just like the original.

I replaced it as I was not sure the original bolt would take the torque I put on it(being a lower grade and old as hell)

the threads were in perfect shape and the bolt threaded in by hand fine with no undue resistance.

I understand that the 10.9 bolt will stretch more readily than the 12.9, but I figured that realistically with the treadlocker that vibration loosening wouldnt be a big problem.

also the failure I had was with the factory spec bolt torqued to 50 ft-lbs, not the new one.

theman53 · « **Reply #13 on:** April 16, 2009, 09:30:59 pm »

I still think the Socket head wouldn't have the same kind of clamp that the hex head would. Unless you have a 12.9 Hex head which in my area of the states doesn't exist, without a special order every standard stock item for 12.9 is a socket head cap screw. The SHCS puts more pressure towards the center of the fastener where the Hex is a little wider and distributes it a little more evenly...Germans being Germans they probably had thought that through before manufacturing as they tend to have a spec for everything. I probably would be a little scared of the high strength thread locker as well and if I used anything I might try a retaining compound. I don't know if they had it back then, but I know now that is what some Cummins engines do for there cam gears is the bearing and sleve retaining compound. I wouldn't recommend it without some kind of test or engineering conformation on ours though.

EDIT* If you had the fail with the old bolt torqued that high it make more sense than even the smaller dia. socket head. I edited as I didn't see that in the last post until now.

truckinwagen · « **Reply #14 on:** April 16, 2009, 09:42:10 pm »

the stock bolt was only torqued to 50 ft-lbs, well within the limits of what it can take, and far from stretching it.

we will see how well what I did this time around works.