Closely cowled two-strokes...

[andyb]

Has anyone got any views on the suitability of any particular make of 2 stroke, about .50 - .60 cu in capacity, when mounted in a closely-cowled environment with not much cooling? Also, are ringed engines better for this than ABC/ABN/ABL type engines?

[Russ]

Andy,

Apologies for not replying to your PM sooner, but as I have no experience of this type of installation I've been doing some research and have to say there appears very little feedback out there - surprising!

I've found plated engines to be more tolerant (less fussy) of higher temperatures and lean runs than ringed engines, so they may well be better suited to close cowl installations. They certainly like to be brought up to operating temperature quickly to straighten the cylinder bore.  Overheating them can result in over expanding the top of the tapered (at cold) cylinder resulting in some blow-by which will obviously affect performance.

The only other point I'll add as that a lot of Moki 2-strokes have been used in tight installations over the years with very good results. That said, Im pretty sure Mokis are ringed.

So I'm gonna play the Jack Straw  card on this one and sit firmly on the fence.

[andyb]

Does that mean that overheating a ringed engine will cause less damage?

[Russ]

IMO no. If you overheat a ringed engine (or lean it too much for a prolonged period) there is a good chance you'll cause permanent damage, certainly in the area of the piston and liner. The advantages of a ringed engine, assuming normal operating conditions,  are that it will maintain its piston/cylinder limit and fit over a longer period than a plated liner and it will also be cheaper to recondition.

The optimum configuration, a la Laser four stokes,  I would consider to be nikasil coating on the aluminum cylinder with a ringed piston.     

PS - Why don't you drop an email to the Australian guy who writes the engine column/tests in RCM&E.

[andyb]

PS - Why don't you drop an email to the Australian guy who writes the engine column/tests in RCM&E.

What a good idea; 'tis done.

A.

[Gareth]

Andy,

Would a heli head be any use? this has the bigger fins to allow better cooling when it doesn't have much air flow.

Gareth

[andyb]

Andy,

Would a heli head be any use? this has the bigger fins to allow better cooling when it doesn't have much air flow.

Gareth

Might be, depends how much space is available in the cowl...