Camshaft

[cgwymp]

How does it weaken the cam? Seems like if anything, it would be stronger because if you do not drill directly through the exact diameter of

You are setting up for a stress failure by not distributing the forces in the shaft equally.

I'd have to see the numbers -- so far I'm not convinced.

And I'd also tend to think that if drilling it off centre does weaken it and it makes enough difference to cause failure, then the material was inadequate or the shaft too small to begin with. It shouldn't be engineered that close to the edge (pardon the pun).

..... which is exactly what this thread is all about and why JohnF is trying to produce camshafts that don't fail

So you agree the hole isn't the problem....  ;-)

Cheers!

[flywheel]

Here is a pix of a new camshaft for a 6/1, it is pre drilled and the holes ARE 180 apart.  Also shown is a new exhaust lobe. If I slide this lobe on the bare shaft the holes line up. 

The drilled holes always line up - even if I slide the lobe on backwards.  What will not line up is the tapers if the lobe is installed incorrectly. 
                                    flywheel 

[Crofter]

Flywheel, are you saying that the holes in the shaft and the holes in the lobe are all tapered for only one orientation?

[flywheel]

Flywheel, are you saying that the holes in the shaft and the holes in the lobe are all tapered for only one orientation?

That is correct!

[XYZER]

In my experience you will never drill then taper ream shaft then the cams seperatly and ever expect the holes to be in alignment for proper assembly with the tapered pin. Standard process in the machine shop world I have been would be to assemble the cams in the desired location then drill and ream while in location. I have never seen a machined part yet on a listeroid that appeared to have fresh cutting tools. All of the machined surfaces appeared to have been cut with tooling that was way past its last leg. A good tapered reamer done correctly would have a high quality finish with no tears in the surface and the tapered pin would align it and lock immediately.  

[oiler]

Today i was tinkering with my genuine lister cs and i noticed that the valve springs are quite a lot weaker than the ones on the JKson. Could it perhaps be that is the reason why our cams are failing?

On the cs i can open the valve with two fingers, on the genuine i can barely open them with two hands!

Coincidense or have someone else noticed this too?

[vdubnut62]

Today i was tinkering with my genuine lister cs and i noticed that the valve springs are quite a lot weaker than the ones on the JKson. Could it perhaps be that is the reason why our cams are failing?

On the cs i can open the valve with two fingers, on the genuine i can barely open them with two hands!

Coincidense or have someone else noticed this too?

Did you mean on the JKson, you had to use both hands?

[mobile_bob]

i see no reason for any more spring pressure than it takes to close the valve and keep them from floating at 650 or 1000rpm
depending on engine, however

those god forsaken wide seats might need the added pressure to help chop up and clear bits of carbon?

not sure how much stress it would take of the cam and idler to reduce spring pressure, or how best to do it anyway, without
replacing the springs with something a bit weaker.

it probably doesn't take much to close a valve on a relatively slow speed engine.

even if you were to reduce the spring tension, and have reduced stress on the cam/idler assembly, one still has the injection pump
and there is nothing you can do to reduce that cyclic load.

at least not easily

bob g

[oiler]

Yes i had to use both hands to open one valve

[oiler]

Bob. You are right, i forgot the pump.

[vdubnut62]

Don't forget that many of the old "Hit & Miss" engines opened the intake valve with just suction. 6 or 7 hundred rpm's doesn't take
much spring pressure.
Ron

[Crofter]

A good part of the necessary spring pressure is to reverse the mass of the rocker arms, pushrods and cam followers. Lighten that part of the package and I think you could use much lighter valve springs to affect valve sealing. As Vdub mentions, the valve spring on the hit'n mis intakes are pretty light. Probably the exhaust with lifters, pushrod and rockers are heavier.

We need Xyzer to make us up some titanium or carbon fiber valve train components so we can lilghten the valve springs waaaay up and save the cam shaft breakage on the twins.

[vdubnut62]

Go down to your favorite Wally-world and grab a couple composite arrows, cut to length, epoxy ends on 'em and there are your lightweight pushrods. Aluminum rocker arms and you're all set, wonder if a set of big block chevy roller rockers could be adapted?
Ron

[Crofter]

Go down to your favorite Wally-world and grab a couple composite arrows, cut to length, epoxy ends on 'em and there are your lightweight pushrods. Aluminum rocker arms and you're all set, wonder if a set of big block chevy roller rockers could be adapted?
Ron

Yes, and I think the cam followers could be fabbed hollow. I think the reciprocating mass of the valve train could easily be cut in half. Probably save enough friction to show a minute fuel saving. I think you would want to maintain a reasonable safety margin on valve float in case of incidental governor overrun. The valve keepers are not a very sophisticated fit to the stems or the spring cap so it wouldnt take much to shake them loose with bad results.

[oiler]

Crofter. I see your point, but on a genuine Lister pushrods and rockers are at least as heavy as the ones on an 'oid.

Perhaps valve float could add a little safety in an overspeed situation...