Cam Profile...That's what I thought you were referring to.

But how does cam profile have anything to do with the discussion at hand, specifically with the concerns of operating two valves with a single rocker arm?

Makes zero sense to me.

 

Great, everyone's LS7 heads, and now this...

 

When the cam opens the and closes the valve, the opening and closing ramp will make a difference in how hard the valve get yanked off or hits the valve seat. Hot cams like the crane and woods cams drop the valve pretty hard on the seat.. Others are nice and easy. HD has very long set down ramps compared to the hotter cams. Makes em quiet.. Some HD owner feak out over valve reain noise. This is a picture of a stock TC and M8 cam. The brighter one is the M8. You can see that the M8 is a little slower. With a rocker arm ratio of 1.625 to 1 on both cams.. The ramp only needs too be 0.0031 higher(and it ends up being a little longer) at the end of duration to set both valves down on the seat at the same velocity if there is a difference of 0.005 in valve clearance.





Hope this makes sense.

 

BTW, If the issue was simply how hard the valve hit the seat that was causing the issue, There would be a ton of TC heads with loose valve seats. Crane, Woods and possibly Leinweber would be the culprits.

 

Max,

Ok then. We're talking about two completely different things.

You're talking about shock loads imparted on the valve/valve seats based on cam profile.

The discussion I was involved in was in reference to a concern others had of one valve never fully seating because of the single rocker arm design.

The two are completely unrelated.

Thanks for the clarification.

 

Sorry I thought the valve not seating was already debunked. If not it should be..

Add:
What sets the lifter position will be the tightest valve..

 

I was wondering how long it would be before something like this came up with the 4-valve motors.

Even the Beemers provide for individually-adjustable valve clearances in their 4-valve twins by using variable thickness semi-spherical shims in the rocker tips. Did the MoCo actually believe that it could produce parts that were so accurate that they could bypass any kind of provision to match the clearances? Also, that all the individual parts would wear EXACTLY the same amount over time?

That's nuts - even for the MoCo - and that's sayin' a helluva LOT! Without being able to match the clearances, one valve will always open & close slightly before or after the other (depending on which one you're looking at), and that will cause a slight difference in the overall valve timing for each head as a result.

However, I can't really see how this could possibly cause any damage or excessive wear to the valve train components. All it does is affect performance.

 

So do the 4 valve beemers have hydraulic lifters?

 

No, but the lifters have nothing to do with whether the valves open and close together.

 

I don't see one valve slightly lagging behind the other as a problem. Max is right that tightest valve sets the lifter, if there is only .0005-.001 difference between both valves it wouldn't be noticeable.

I wonder what the specs are on this, how much difference would be too much?