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Cagllari HF project (picture heavy)
- Thread starter Munkul
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Cagllari HF project (picture heavy)
yamaha call it ypvs, but its used by almost every 2 stroke manufacturer. e.g. kawasaki (called kips), honda (called vtac, which is funny when you consider honda vtec), suzuki (called aetc), even my cagiva and aprilia had power valves (that are disabled to restrict them in the uk, destroying performance unless you enable them.)
back in 91 i got the brand new suzuki RM80, it was the first crosser with a powervalve (that i know of). since then it has been pretty standard on all 2 strokes.
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you learn something every day 
i have played with loads of 2 stroke engines, but they have nearly all been 20 year old designs. I also thought that YPVS was an old technology that had been given up, guess i was wrong.
i have played with loads of 2 stroke engines, but they have nearly all been 20 year old designs. I also thought that YPVS was an old technology that had been given up, guess i was wrong.
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Ok, finally got pics of the engine.
you can see the piston is scored badly, and the bit at the crown looks like it has melted rather than rubbed away....
there are also some spots corresponding to the intake ports that are carbon-free, i wonder what caused this... fuel mixture cleaning it? burning lean? detonation? im guessing mixture....
The big and little end bearings had way too much play in them. The engine had loads of things wrong with it, but it is hard to say what caused what. For example, the big/little end bearing float could have let the piston slap into the head, causing bits of head to splinter and screw up the piston. Or, it could have been pre-detonation that screwed up both the piston and the bearings.
Old cylinder (nothing wrong with it tbh) it has 3 extra ports over standard.
New cylinder - 2 extra ports over standard. Otherwise it is identical to the one above. I got this partly cos i wanted the piston in the kit, and partly because i eventually want Jordan to machine the gap between the ports to make one extra large port - same spec as the real ADA cylinders.
Bought a s/h crank case (bad idea). I put new bearings and oil seals in it, and then discovered that one of the head bolt holes had a stripped thread :bang:
I also bought a full circle crank, which lowers the volume in the crank case meaning higher vacum and therefore better top end, in theory. It will also vibrate the bike to peices due to worse balance...
Pics of old crank case versus new crank case, both bottom ends fully built up:
Rather than fix the stripped thread, i decided just to continue using the old crank case, which essentially has nothing wrong with it....
Anyway, the old timing key on the flywheel had disintegrated into nothingness, and the flywheel taper lock and keyway was knackered, bummer.
the tapered bore shows obvious signs of wear from spinning. I wonder how long the timing had been "out" for?
so.... new bottom end
...and almost complete new engine. The compression has been lowered significantly (if the squish was .44, its now .89) this is to allow for NOS to work without destroying the engine immediately. As well as that, high compression i found helps very little with power whilst killing a few hundred rpm off max revs.
you can see the piston is scored badly, and the bit at the crown looks like it has melted rather than rubbed away....
there are also some spots corresponding to the intake ports that are carbon-free, i wonder what caused this... fuel mixture cleaning it? burning lean? detonation? im guessing mixture....
The big and little end bearings had way too much play in them. The engine had loads of things wrong with it, but it is hard to say what caused what. For example, the big/little end bearing float could have let the piston slap into the head, causing bits of head to splinter and screw up the piston. Or, it could have been pre-detonation that screwed up both the piston and the bearings.
Old cylinder (nothing wrong with it tbh) it has 3 extra ports over standard.
New cylinder - 2 extra ports over standard. Otherwise it is identical to the one above. I got this partly cos i wanted the piston in the kit, and partly because i eventually want Jordan to machine the gap between the ports to make one extra large port - same spec as the real ADA cylinders.
Bought a s/h crank case (bad idea). I put new bearings and oil seals in it, and then discovered that one of the head bolt holes had a stripped thread :bang:
I also bought a full circle crank, which lowers the volume in the crank case meaning higher vacum and therefore better top end, in theory. It will also vibrate the bike to peices due to worse balance...
Pics of old crank case versus new crank case, both bottom ends fully built up:
Rather than fix the stripped thread, i decided just to continue using the old crank case, which essentially has nothing wrong with it....
Anyway, the old timing key on the flywheel had disintegrated into nothingness, and the flywheel taper lock and keyway was knackered, bummer.
the tapered bore shows obvious signs of wear from spinning. I wonder how long the timing had been "out" for?
so.... new bottom end
...and almost complete new engine. The compression has been lowered significantly (if the squish was .44, its now .89) this is to allow for NOS to work without destroying the engine immediately. As well as that, high compression i found helps very little with power whilst killing a few hundred rpm off max revs.
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