ESE's works engine tuner

[Frits Overmars]

Having some carburtion issues. Does this look too lean?

no it looks fine but dose have a small crack in the piston skirt

Looks mint, don't worry about the small crack.

I'd replace the piston as a precaution, hell you have it out so why not. If you're careful taking the circlip out you could probably use it again.

I love it! Great way to start a sunday .

[Frits Overmars]

.... the reason for my confusion about the RSA head shape is that i very recently heard a respected person definitively say that the RSA did not have a toriod design.

This kept me thinking for a while. Maybe it is a misunderstanding stemming from the way you define a toroid. The decisive factor is that the radius of the combustion dome originates off-centre; its center is offset from the cylinder center line. That may or may not lead to the spark plug intruding into the combustion chamber, depending on the radius, the offset and the plug thread diameter.

The first two pictures show the Aprilia combustion chamber with a flush plug. The third picture shows a Wobbly-head with a deeply-intruding plug. The last picture shows the turbulence in a toroid head, initially caused by the transfer streams and enhanced by the squish action.
The intruding plug seemed a logical step but tests at Aprilia have shown that an intruding plug costs power, probably because it causes a scavenging shadow where spent gases are not fully removed by the incoming fresh mixture, so Aprilia-chambers have a flat area around the plug hole.

[Kickaha]

no it looks fine but dose have a small crack in the piston skirt

You could build it up with a tig and machine it back, if you do that going by personal experience it could last up to a season being revved to 12500rpm

[wobbly]

The deep intrusion toroidal head shape was developed using flat top, so called Honda A Kit pistons.
I would opine that the end result is very similar to the flat roof dome using a convex piston.
BTW there is still some differing opinions about the circular flow direction of the squish action that is created off the sharp corner
going into the bowl.
First logical reaction that would seem to be the accepted norm, and is as Frits has shown, is that the rotation is clockwise.
But a senior/clever engineer at Yamaha told me that their CFD analysis showed it was the opposite way - and he lead the development of Yamahas 250/500 flat roof chamber when unleaded fuel became mandatory in 98.

[dmcca]

This kept me thinking for a while. Maybe it is a misunderstanding stemming from the way you define a toroid.

Ah this is surely the problem... I had made the assumption that a toroid shape always involved an intruding plug. I guess that the comments I read were based on the same incorrect definition of the design. To make this more confusing the flat roof design you posted above is the design I originally thought the RSA had, however that's the one that I incorrectly referred to as a bath tub shape which is what led to this confusion in the first place. My original question therefore should have been worded... Is an intruding plug shape better/worse than a flat roof shape?? But this has now been answered.

Thanks for being patient and taking the time to explain.

[F5 Dave]

I had assumed the intrusion plug would have had most benifit as the cylinder bore & hence chamber had become larger dropping the spark plug further into the chamber where it is closer relatively on a 54mm or smaller bore. Perhaps?

[F5 Dave]

And yes thank you all for your kinds words re my poor classic YZ piston.

I'll go up a jet size & see how it goes, if not I'll order a new one.

PS I think this was caused by excessive clearance, it did sound a bit slappy. No wear evident on bore, so it might have been bored too big to start with.

[Dutch Fisher]

D ports in a 4T are there to speed the flow up on the short turn radius, and prevent serious reversion in the area of least flow velocity,the port floor.
In a 2T we use the step at the manifold to reduce the Ex duct volume - also keeping the velocity high, and also preventing the reverse plugging wave from buggering the powerband
even more than it usually does when the pipe is too short for the rpm.
When they are designed correctly both are a useful tuning tool.
STEP AWAY FROM THE GRINDER.

...further to this, what's the informed wisdom on the half moon projections seen in the necks of these 2002 YZR500 pipes

http://www.blatawcm.com/redbull/imag...2/DSCN1996.JPG
http://www.blatawcm.com/redbull/imag...2/DSCN1995.JPG

[gamma500]

Here's some pics of rgv500 cylinders and pipes...hhmmm...

[wobbly]

When unleaded became mandatory in 98 most teams had a hell of a time keeping deto under control, having to run very rich and retarded.
The cylinders with the straighter pipes always gave alot more grief, untill a lowly dyno operator at Yamaha discovered that
when he stuck a large pressure probe into the header, the deto went away.
They managed to keep this secret for a couple of years but when teams like WCM got hold of the bikes, and left pipes lying about as you see in the pics,word soon got around.
The "things " intruding into the header take varying forms,but all do the same thing - the usually bottom "bent "pipes dont have the same issue, so dont need the so called deto buttons.
I have a couple somewhere from a Red Bull bike - I will pic them and post here .

Here is a shot of a cylinder I have been working on - its just come back from plating - the duct entry shape looks a bit familiar doesnt it.
The plating must have more Nickel in it, that would be why some of the previous shots on here look as though the cylinders have a liner, its the colour of the plating process.

[Dutch Fisher]

What year RGV500 are those from?

Y2K has more apparatus on the exh side

[F5 Dave]

. . .a lowly dyno operator at Yamaha discovered that
when he stuck a large pressure probe into the header, the deto went away.. .
. . .The "things " intruding into the header take varying forms,but all do the same thing -

Now that's queer. My only foray into using EGT probe (on my 50 so small header) but with probe position a good 6" away I fed it in & ran it up on the dyno. Oh dear, lost a lot of power & gee these EGT readings were higer than I thought. Jetting & ign don't help. Hmm wonder if the probe was causing the issue. Block it off & power comes back.

Thinking about it later I decided to retry with the probe only just inserted, think the metal outer was getting stinking hot & on small header was big issue. that was 2yrs ago & have got distracted since.

[Frits Overmars]

Here is a shot of a cylinder I have been working on - its just come back from plating - the duct entry shape looks a bit familiar doesnt it.

Quite familiar; the only give-away is the distance between A-duct and stud. And I see no provision for a powervalve. What's it for? A kart engine?

[TZ350]

And yes thank you all for your kinds words re my poor classic YZ piston.

What brand of piston were you using?

Recently we had a close call with a new PROX piston cracking up, only 20min on the dyno, pulled it out after seeing the runs losing power, it could have only been a dyno pull or two away from completely letting go.

[F5 Dave]

it was std Yamaha NOS circa 1980. Think they used ART back then which were good cast pistons. ProX used to be ART distributor under another name I think but I heard they are using Mitaka & quality is up & down. Not totally certain of any of this.

My crown was fine apart from the peppering from debris, the piston it was hard to tell where the fault started. My Std Honda piston I was running before started cracking the front of the skirt. Usually the skirt goes when there is too much clearance either through wear or incorrect bore.

But I'm guessing as there wasn't much left, clearly it fell to bits quick as I could pull the clutch.