In article ,
Larry wrote:

No valves. Intake ports and exhaust ports open as the piston
passes over them near BDC when the blower recharges the air and
blows out the dead gases. Piston rises cutting that off,
approaches TDC, cam rack in the head opens injection just as
compressed air reaches 1200F and KAPOW!, we're on our way down
again after this god-awful loud knocking noise also indicating
compression is great, making enginemen smile...(c;

Well it is obvious that Larry has never wrenched on a Scream'in
Jimmy of any kind, or he would have known, that they ALL have
Exhaust Valves, in the HEAD, under the VALVE COVER.... where the
Injectors ARE......


Me

Wayne,

The only way to check the compression is by removing the injector,
their are special tools for this. It's not a difficult job, but you do
have to reset the rack, which can be a little difficult if you've never
done it before and don't have the tools for it. By the way, two cycle
Detroit Diesel's have exhaust valves in the head (usually four valves)
and an intake port cut into the side of the cylinder (no intake
valves). The blower builds pressure in the intake manifold and when the
intake port is open that pressure, along with the open exhaust valves,
is what forces the exhause out.