*This message was transferred with a trial version of CommuniGate(tm) Pro*
Yes sir:
>Would you please decribe the difference between passive and positive
rotators.
A passive rotator allows the valve to freewheel when it is opened. The
latter M38s uses
passive valve rotators. A cap, a little larger in diameter, than the valve
stem is fitted
over the valve stem end. The lifter pushes on this cap, not the valve stem.
The
tolerances were such that when the valve opens, you can rotate the valve by
hand. The vibration and the slight turning, from the spring being pressed
down caused
the valve to reseat in a slightly different possition. By constantly
reseating in a different
place, there was a cleaning action taking place between the valve and seat.
Positive rotators have a ball bearing cap that fits over the valve stem. As
these are actuated,
the valve is forced to rotate as it opens, an initial scruffing between
valve and seat takes place.
TRW wrote an article some time back when the issue of unleaded gas came up.
They generally prefered passive over positive. They seemed to think
that this scruffing and lead free gas adds to valve recession. But again,
not all
rotators are this brutal.
The M715 motor is an example of positive valve rotators.
I tend to prefer the passive but I am having very good experience with the
positive ones
as well.
Many diesels use some form of rotation for valve longevity.
All these examples, I need to add, are using harden seats.
>MB has both tapered and square valve spring retainer keepers and I assume
that the square >ones allow rotation.
That may be. I've forgotten, and do not have my info in front of me.
Regardless, you'll
still need those caps.
> The valvetrain appears to be assembled with whatever parts were laying
>around at the time. >Fortunately a previous owner installed hardened
exhaust valve seats.
I hope so, for all that effort. But you may have to have that checked.
There were and maybe
still are "soft" valve seats. These were used just to save the head/block. But
the material isn't suited for unleaded gas use. I tripped over that one
myself. Had to reorder
the right seats.
Those keepers are a function of the spring retaining cap. Be sure of these
parts.
You wouldn't want those parts coming loose in there. Least the valves
wouldn't drop
into the cylinder bore on an MB.
I hope this is helpful.
I'll be helping my only half with her GPW motor, so this is a good
refresher for me.
Ted.
This archive was generated by hypermail 2b29 : Thu Mar 02 2000 - 22:30:38 PST