The SC 61 story continues, it has run well since the rebuild, but started to get bored with it. So, with "advanced rc model boats" by John Finch in one hand, and engine in the other, I ported it.
For anyone interested, here is the timing data:
Standard: Exhaust 154 deg, Intake 187
My targets, which I achieved, were:
Exhaust: 172 deg, Intake 200.
All measurements were done simply using a degree wheel and a piano wire pointer fixed to one of the head bolts.
I was really easy to do, just took my time with a dremel. I was advised to lighten the piston (Thanks Dave), and after seeing how much metal there is on the standard piston gudgeon pin bosses I can see why my con rod failed. So after much grinding the piston is much lighter.
I have for now left the squish clearance alone, it is measured at approx 0.25mm.
I left the exhasut port "bridge" in place, for no other reason than it was there before I started. The exhaust ports were widened and matched to the crankcase at the extreme edges.
Schneurle and transfer ports were tapered to try to get the fuel "up" rather than "across".
Engine washed off and reassembled. I refitted the stock carb for the tuned motor and removed the restrictor from it.
Back into the boat for some testing, starts as easy as ever, ran it with a 2024 prop, took off and ran OK, revving more easily and higher than before. unfortunately a leaking tuned pipe put paid to any more extended running, so ten minutes is all I have on it so far since the work, and I have not had the chance to play with tuned pipe lengths yet. I think I am slightly struggling to get enough fuel into the engine now too, but more testing soon.
Still running Duralgo 16% nitro.
Has anyone from Elmbridge got any hot set up tips for this motor to take it further that they are willing to share?
Glenn