One small change solves the two-stroke engine's biggest problems

Lineslinger · Jun 16, 2025

Progressive technology is always interesting to me...this is an interesting mod to a 2 cycle.

One small change solves the two-stroke engine's biggest problems

The defining characteristic of a two-stroke engine is to fire (combust) every time the piston is at top dead center. This makes them highly power dense, but also notoriously makes two-stroke engines dirty, inefficient, and not prone to long lifespans.

newatlas.com

hybridracer · Jun 16, 2025

One small change indeed! Rotary exhaust valves are great projects for inexperienced graduates to embark on but the reasons you don’t see them in general use everywhere are - sealing, cooling, wear, lubrication, poor combustion chamber shape - to name five. There is also the heavy and expensive supercharger that is needed. Do not confuse them with sleeve valves which , after much development work, have been used successfully in some aircraft engines.
As always, prove me wrong.

hybridracer · Jun 16, 2025

I forgot to mention that Scott used rotary INLET valves on their very advanced two stroke racing engine.

grandpaul · Jun 17, 2025

hybridracer said:
I forgot to mention that Scott used rotary INLET valves on their very advanced two stroke racing engine.

I had a 90 and 125 Kawasaki that also used rotary valves. Worked great.

hybridracer · Jun 17, 2025

The inlet rotary (disc) valves were used by several manufacturers and do work well but they are just an alternative way of controlling the fresh charge flow into the crankcase. This thread is about a design bypassing the crankcase.

concours · Jun 17, 2025

grandpaul said:
I had a 90 and 125 Kawasaki that also used rotary valves. Worked great.

A bit different

concours · Jun 17, 2025

hybridracer said:
The inlet rotary (disc) valves were used by several manufacturers and do work well but they are just an alternative way of controlling the fresh charge flow into the crankcase. This thread is about a design bypassing the crankcase.

The Rotax RV340 twin in 1975 was a potent race engine for Ski-Doo, who then went on to use them 25 years.

grandpaul · Jun 18, 2025

hybridracer said:
The inlet rotary (disc) valves were used by several manufacturers and do work well but they are just an alternative way of controlling the fresh charge flow into the crankcase. This thread is about a design bypassing the crankcase.

That's what I get for breezing thru posts to get "caught up" after being offline for a couple of days.

hybridracer · Jun 18, 2025

grandpaul said:
That's what I get for breezing thru posts to get "caught up" after being offline for a couple of days.

Sorry, I had just had a team’s meeting with Network Rail, (they are responsible for our national railway infrastructure), about our Heritage railway and was a bit tired.