ESE's works engine tuner

[ken seeber]

Piston edges. While the conversation is around radiussing, here’s something slightly different. A dude, who just came in today, over here is running twin KF engines that he sourced out of the UK. These run Dyke rings against the CI bore. Traditionally these just have the square edge on the land above the ring, see pic.

As these engines are not running under any rules, they came modified from the basic 4 deg crown angle. They were flat topped and the edge was chamfered as per pic. While not perfect in terms of carrying the radius to the full diameter, it does look like it would flow better, in that a sharp edge has been removed.

The head, which I haven’t actually seen, does not have any profile to follow the chamfer, but just has a matching 4 deg squish angle out to the bore diameter. This must result in an annular volume at the bore edge. It’s possibly why the piston was replaced, as it was detonated away at the top ring land area above the A/R pin.

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[wobbly]

53.87mm - wow surely thats not in a 54 nominal bore ?????
And yes, having a large trapped volume in the squish/bore corner is simply asking for Mr Deto to come visit.

[katinas]

And I dont intend on spending the silly money they want for pistons or heads - far rather learn how its done myself , alot more interesting as well.

After testing full rounded piston, interesting tests was with three sharp location on piston edge: near C port and two narrow sharp edges between A and EX. Even without fully matched head, on the road feels better than with full roundness, but if you have possibilities to try this with dyno would be very nice and more clear.

Add pic - rounded piston with black spots where two C ports located

[koenich]

For the 85cc mx engines, they look like this.

Those have no rounded timing edge, rather 12° squish with a flat top - insert looks accordingly.

https://www.vhm.nl/en/catalog/engine.../g+c+a+nr+view

[katinas]

Cylinder from 84' NSR 500 "low tank position".

[Muhr]

So. . When you are producing the gearbox version in significant numbers as a road- legal bike at a consumer product price. . . Make sure you export a bunch over here won't you?

This is more of a unicorn hopefully, if I not miss something so I have to make another one. Would certainly be interesting to make a geared engine!

[TZ350]

Cylinder from 84' NSR 500 "low tank position".

That is very interesting, the exhaust port bridge is fatter in the middle.

It looks like that is there to keep the area unchanged going down the duct. Not seen that before but it makes sense.

Fat Ex bridge.

[190mech]

Perhaps the fat bridge has a water passage through it?

[TZ350]

.
Yes, maybe. That would make sense too. Does anyone know for sure?

[RomeuPT]

That is very interesting, the exhaust port bridge is fatter in the middle.

It looks like that is there to keep the area unchanged going down the duct. Not seen that before but it makes sense.

Fat Ex bridge.

If its done no more it was/is probably not better....

[jamathi]

.
Yes, maybe. That would make sense too. Does anyone know for sure?

Yes, they have.

[husaberg]

That is very interesting, the exhaust port bridge is fatter in the middle.

It looks like that is there to keep the area unchanged going down the duct. Not seen that before but it makes sense.

Fat Ex bridge.

That shape a modified teardrop is also the most efficient in terms of drag. Compared to a sharp end first.

[katinas]

If its done no more it was/is probably not better....

Maybe too much material exposed to hot gases, even with cooling passage. One of the head studs goes directly to Ex divider, maybe help to finish this passage. This was the first NSR 54x54,5 and claimed 142.6 hp/ 11,500 rpm.
But after more than 30 years many things changed and who knows how it works with all new things.
Massive cooling "arc" around exhaust, maybe was first steps to what we have now, con rod -104 mm (NS 500-106mm) - looks like this engine main things became basic for all later NSR/RS models.

Interesting Yamaha late 2 Ex 7 Trans ( 2001).

[Muhr]

That shape a modified teardrop is also the most efficient in terms of drag. Compared to a sharp end first.

Think that the problem here is that the flow speed is so high that you get flow separation even though the shape is optimized

[RomeuPT]

Maybe too much material exposed to hot gases, even with cooling passage. One of the head studs goes directly to Ex divider, maybe help to finish this passage. This was the first NSR 54x54,5 and claimed 142.6 hp/ 11,500 rpm.
But after more than 30 years many things changed and who knows how it works with all new things.
Massive cooling "arc" around exhaust, maybe was first steps to what we have now, con rod -104 mm (NS 500-106mm) - looks like this engine main things became basic for all later NSR/RS models.

Interesting Yamaha late 2 Ex 7 Trans ( 2001).

Much lower port timings on the 2001?!