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[kno3]

Hi all!
I'm looking for a good set of instructions for adjusting Stephenson's type valve gear (on marine engines). A friend has built one and wants to know the best way to adjust it, but we couldn't find much online so far.

[bbjs]

The only ones I'm aware of are Stuarts:

http://www.stuartmodels.com/downloads.cfm/the_grp/9

Slide Valve Timing

Non-Reversing Engines

Check the valve location by temporarily removing the valve chest cover. With the crank at top dead centre check that the high point of the eccentric is 90° plus the angle of advance (usually between 30° and 40°) in advance of the crank, in the direction of rotation.
Rotate the engine and check that at the extreme travel of the valve in both directions that both the top and bottom ports open the same amount. Should the port openings be unequal, uncouple the valve rod and screw the slide valve nut up or down the rod to correct the situation. This is the only way you can correct unequeal valve openings.
Valve timing is checked as follows:- with the crank and piston at the top dead centre the upper port should just be opening. If the engine is then rotated through 180° the lower port should be opening a similar amount. The port opening may be adjusted by loosening the eccentric grubscrew and rotating the eccentric on the shaft.

Reversing Engines

Valve location and timing procedure is generally similar to that required for non-reversing engines but the reversing engine has two eccentrics usually made in one piece and therefore precluding individual adjustments.
Valve location - with the steam chest cover temporarily removed and the crank turned to top dead centre carefully check that the high points of the eccentrics are 90° plus the angle of advance in advance of crank in the direction of rotation. Operate the reversing gear to bring one eccentric rod in line with the valve rod. Rotate the engine and observe bottom port openings are equal. If the port openings are unequal, uncouple the valve rod and screw in or out of the slide valve nut to required extent. Again operate the reversing gear to bring the other eccentric rod in line with the valve rod and check port openings.
Valve timing is checked as follows:- with the crank and piston at the top dead centre and one eccentric rod aligned with the valve rod, the upper port should just be opening to steam. If the engine is rotated through 180° the lower port should show a similar amount of opening.
Repeat for the other eccentric rod and ensure that similar openings are obtained. Adjust if necessary by loosening the eccentric grubscrew and rotating the eccentric on the shaft to a point where equal advance is obtained for either rotation.
Again check that the valve location is correct before replacing the steam chest cover.

Cheers, Bjorn

[kno3]

Bjorn, thanks a lot.

Is there any info or advice regarding the angle of advance?

[logoman]

Angle of advance:
To set the angle of advance, the steam port opening is measured when the piston is at
both top-dead-center and bottom-dead-center.  The desired amount of advance (advance
being the angle at which the steam is admitted to the cylinder before top-dead-center)
can be set by unscrewing the setscrew fastener which secures the eccentric, and
rotating the eccentric the desired amount.
 
 The angle of advance can be determined using the following procedure.
              a. Rotate the crankshaft of the engine until the piston is at top-dead-center.
              b. Rotate the eccentric until the valve is at its midpoint position (position A).
              c. Continue to rotate the eccentric to a new position where the head end steam port
                  just begins to open (the opening should equal the desired lead of the valve).  This
                  second eccentric position will be called position B.
              d. The angle of advance is the difference between the eccentric angle at position A
                  and the eccentric angle at position B.
              e. Typical angles of advance appear to be around 55 degrees.

for more: https://sites.google.com/site/jorgensensteamvalvegear/valve-gear-design

[kno3]

Thanks! Great info on that website.