That is for a water nipple and it is where the water goes into the cooling system. The 4 holes in the cooling cap are outlets so that you can position the outlet nipple or nipples wherever you want them

Looks like a place to add a water fitting according to the photo of the installed engine. Really good pictures. Is that a crimped bearing retainer I'm looking at? It certainly is not a riveted retainer or a polyamide snap on type retainer. It looks like the engine has a water cooled head & part of the cylinder is water cooled. Is this correct? Are there any pictures of the inside of the exhaust track? It looks like the head bolts are outside the liners lip & do not pass through the liners lip or the head button. Is this correct? Now that I've seen the exhaust track, there is a very poor transition from the rectangular exhaust with two eyebrows to the round shape of the exhaust flange. I wonder what effect this will have on the exhaust gas flow? Also pickets placed in the exhaust window always act like heat exchangers. They are heated by the outgoing exhaust gasses & pass that heat to the boost fuel mixture coming out & then returning. Maybe that is why QD uses only one picket in their exhaust window?

JA

The exhaust tract is certainly not the best being similar to a Zenoah or RCMK but the 1 main exhaust port and 2 sub exhaust port system is used by most high performance 2 strokes and there appears to be no issues so far with this engine unlike the single bridge used on the QD and JG. This is possibly because the TK is very well cooled and the liner is thicker than the other engines.

Speaking of the thicker liner - what is the surface treatment of the liner's bore?

Also:

Why the eight screws to secure the cooling cap? My CY cooling caps work OK with two screws.

Eight screws securing not only the cooling head but still pressed the combustion chamber to the cylinder

Eight screws are to hold down the head insert. No idea about thesurface treatment of the liner but I think meehanite is normally used as is.

Without stepping on any toes, I agree that a tri-exhaust window is something found on larger bore, bigger displacement high performance two strokes. This becomes necessary for piston ring life & adequate exhaust gas flow. However, this is not the case for our small bore engines. There are no issues with the single bridge found in QD's. Also with the QD's small bridge width & thickness, there are no heat exchange problems either.

In the posted pictures of the new engine, it appears that the pistons crown is coated. Is this correct? I have found that the best method to prevent the combustion's heat from heating the surrounding metal materials (piston crown, head, cylinder walls) & reduce high surface temperatures is to polish these surfaces that are in contact with the radiated heat. This works well since the heat is reflected. After the heat source has disappeared, there is no residual heat left on the surfaces. When people see polished piston crowns & exhaust ducts in my engines, this is not done to increase the flow!

I have posted some photos of typical tri-exhaust windows & ducts. In my opinion, the exhaust duct in this new engine leaves a great deal to be improved upon.

Jim Allen

I agree that the exhaust duct shape leaves something to be desired but as it is the first production model boat gas engine to go with one main exhaust port and 2 sub exhaust ports as used in all high performance 2 strokes then it is going in the right direction. I assume that the piston coating is a ceramic barrier coating also used on full size high performance 2 strokes which is proven to improve power output.
Dave

Does this pic label the three exhaust windows?

Looks to me like a thicker sleeve will allow these to be contoured (opened) quite
a bit and still have excellent ring guidance. Considering the absence of chrome on
the sleeve, this should be something many boaters can DIY with more predictable
results. If this design eliminates chrome and chrome flaking issues, then I see
that as a big plus.

______________________

Since the eight cooling cap screws secure the button to the cylinder then I'm
guessing those should be removed routinely as an after run maintenance. All the
more reason to always use a *reliable* 1/4 inch drive torque wrench on this type
motor and keep the eight screws coated with anti-seize.

CC,

I have used chromed cylinders bores on my QD cylinders for several years. There have been no chrome flaking or peeling issues as yet. Works very well for piston ring seating & is much more wear resistant than the original hardened liner surface. Proper honing is still required.

JA