exhaust port issues

[hontrx265r]

Makes sense. I'll see what I can do about that tomorrow.

[fearlessfred]

No matter how you look at it, the aux exhaust port should not be exposed to the lower end .I have never had residew in the lower end in 27 years of riding the seems to me someone went a little too far with grinder.the angle those ports are at ,it wouldn't be hard to do.

[hontrx265r]

I agree with that fred. I will be contacting eddie to see what we can do about it. He resleeved this cylinder right after I got it because it had rotated.

[fearlessfred]

It seems to me that Eddie always does his best to make things right.please post on how it turns out.

[udontknowme]

No matter how you look at it, the aux exhaust port should not be exposed to the lower end .I have never had residew in the lower end in 27 years of riding the seems to me someone went a little too far with grinder.the angle those ports are at ,it wouldn't be hard to do.

ideally you do want the exh sealed off. but if the hole is quit small then you dont have much to be concearned with. to fix it correctly will probly be far more grief than its even worth, unless esr will strip the plating, weld up the hole then replate  all at eddies expense, but im thinking eddie will tell him the same thing i just did, it aint that big of a deal.  either way, hes not losing a bunch of power nor is any kind of damage going to occur. i guess it all boils down to who is paying the bill to fix it. any black residue that may be in the tunells or lower end is probly from what i pointed out early, a lack of adeqaute blowdown area, not the hole under the piston. its a common problem on engine combinations that arent setup well. even on a well designed engine you may see blackened tunells if the engine is continiously operated below its intended rpm range

you can ask 1000 different people and get 1000 different opinions on the matter. i happen to know that a small hole makes little difference if its there or not. hell the pic i posted above has the same kind of hole from the factory. theres no sense in diving into the reasons why because there really is no good reason but i can say those particular engines were as reliable as anything else out there.  i went to the trouble to weld the hole on one of my engines but the plating was already off and i was doing other work on it also. i certainly wouldnt go to all the trouble of tearing down a perfectly good engine just to weld that small hole. now if half the window was exposed that would be a different matter but that doesnt appear to be the situation here

[udontknowme]

if you look at this piston it intentionally drops down in the front to prevent the aux exh window from being uncovered at tdc. so ya its best to keep them covered and i dont think anybody with 2t experience would argue otherwise. but on the other hand i dont think a small hole is worth the trouble of trying to fix.

 and heres something else to think about. ya youll be keeping the window covered if you weld the corner but youll also be making the window smaller. so anything you might gain by closing the hole will probly be offset from the window being smaller. so theres a good chance youll go around in a circle and have gained nothing

[hontrx265r]

It is a sleeves cylinder so there is no plating or rewelding. Being that Eddie did the sleeve work, weather it be ok or not ok or reliable or whatever. I still want to contact him and address the issue. I do appreciate all the help though.

[C-Leigh Racing]

So I pulled my cylinder off to see how things are going inside. It has a good few hrs on it and has actually run pretty well. I noticed exhaust gas showing signs all over the lower end and transfers on the underside. Started to talk to a few people and did some rough measuring. What I have come up with is I believe the piston cutaway on the bottom of the piston is rising above the aux. Exhaust port at t d.c. and allowing exhaust gas to re enter the crankcase. Thoughts and opinions? Im going to contact eddie tomorrow if possible and see what he says but I see this as an issue. I did a rough illustration of what I believe is happening. I cant get it to load right side up the boot shape is the piston pin area and the line tagged problem is the piston cutaway.

You are correct in what you are thinking. I tried for quite a few years to get LA Sleeve & CT to change the piston design, so to stop the port linking, but it fell on deaf ears.

When I spoke to Eddie about the port linking issues, say a year after he came out with his own cylinder castings, he changed pistons & got his on design you see being used today.
The issue when your using the old design Pro-x piston, from the piston being machined to much on the sides to lighten them, lighter piston, more hp output. If it was just a slight opening or just opening up into the wrist pin hole, then the effect wouldnt be as bad, but the length of the machining on the pistons sides & the aux exhaust port window, the duration of the open area is to great during the cycle of the piston at that time in the stroke.

Do know though, the linking issues not as bad as it was a few years ago, because of the design of piston Eddie is offering today.

I'm thinking it was back in 98~99, maybe 2000, did a test on a 310 Pro-x cylinder. Welded up the aux exhaust port of the sleeve & then going back & opening up a smaller window so that there would be no way for the port to link.
That little 310 at a national TT event, was sitting in third place behind Tim Farr & Shane Hitt until the small o ring on the head dome melted & blew out the coolant.
It was part my fault, because I took time & watched the rider running the R which had a 450R as well & was spending all his attention to the 450. If the 250R had been attended to like normal, the radiator would have been checked & would have been found the coolant to be low. By it not, when it went out for the main & the coolant low in just a few laps it over heated & melted the o ring ending that little 310s life.
He ran it till it wouldnt run no more, it pure turned the crank black it go so hot, but it was gittin it done for a little while.

That test, proved to me how big of an issue that port linking ordeal was on these cylinders & something needed to be changed, but deaf ears wouldnt do anything about it until I went over it with Eddie. In less that 6 months time after our talk, ESR started offering the piston design you get today when you order a cylinder kit, so we got to give Eddie credit for doing that.

What would really be nice, if the machining on the piston sides were just like a CR250R piston, then there would be no linking at all.
Today, when I'm working on the aux exhaust port windows, I do not touch the rear part of the window, not widen it any at all so to prevent as much as I can any port linking. Its all I can do other than welding up the window in the sleeve & then re-cutting the window.
When you order a new replacement sleeve for these cylinders, should you have one sleeved, the new sleeve even after the CNC machining is complete, the window opening is cut to far around because of the angle of the cutter.

Heres something odd to think about, say your building a 270cc OEM TRX cylinder using the YZ250 piston, specially on a cylinder that is all ready ported. If you check that build when the piston is at TDC, you'll notice the skirt of the piston is uncovering the floor of the exhaust port maybe like a mm or two, but it has no affect on output & if anything its helping.
I dont know how it could be tested other than on a dyno & two different cylinders to check. My guess is, that at that part of the stroke the returning wave in the pipe is pushing some of the fresh intake charge spent out into the pipe back into the crankcase & acting like a turbo effect. I have nothing to prove this though, but I do know every one I've built that ended up with that little piston skirt gap will tote the wheels out of a corner & make for one happy rider using it.
Neil

[udontknowme]

neil is these 2 arrows pointing at the areas you guys are talking about ?   the wristpin passing over the aux window and creating a small hole isnt that uncommon. hell even the newest generation ktm are like that. theres no way around it other than a narrower aux window or a plug in the wristpin. narrower windows arent good for power and a plug is a bad idea on a mass produced bike.  

on that same note, any machined out areas on the side of the piston for lightening purposes, should be done upwards and behind the wristpin, like in the pic you see a hole above and behind the wristpin. other wise it creates a much larger void, like the esr piston. as for any small hole down in the bottom corner, just drop the front corner of the piston down and the hole is eliminated, but from the pic it appears only about a .020" gap, which i find it hard to believe its causing much problem. but all eddie had to do was look at any modern ktm piston to see what needs to be done.  :friendly_wink:

[udontknowme]

this is another way to go about it , which reduces linking holes to a bare minimum. you see the front corner of the piston is dropped down to eliminate the aux window from popping open at tdc. then the side of the piston is lightened above and behind the wristpin which eliminates any huge voids as the wristpin runs over the windows. yes there may still be a small hole as the wristpin passes over the back edge of the aux window but the linking between exh and tansfer port/crankcase is kept to a bare minimum

[hontrx265r]

Those pistons with the cutaway having that little dip would prob work perfect.  Udontknowme although I do believe this is going on and I do think its minimal. I 100% agee this could be more of a setup issue with not enough blow down. Arlan and some other reputable builders have said this is not hurting anything, but I do believe its not working at its peak.. and well that is what we are, here for. Cleigh I also appreciate your post and have read alot about linking from information you have posted. It has shed alot of light on how things are working.  As for the yz piston maybe the tiny gap isnt bad but I feel like the amount of exhaust entering my crankcase is not just from this aux port as udontknowme originally stated in some of our first posts, and is so much I cant see it working efficiently.  If its filling with old mostly burnt gas it doesnt have room for new good fuel charge. I need that greater pressure to be from intake charge. Im working things out slowly and will get this pump working good or ill start over with another..

[udontknowme]

not much you can do besides find another piston with less of the side machined out. but still you cant completely eliminate the link between exh and crankcase because the wristpin still passes over the back edge of the aux window. the best you can do is reduce the empty void in the side of the piston by using something like the pics i showed

[hontrx265r]

Yes I completely understand the linking and the fact it is what it is. I was referring to some better cylinder porting and building a more efficient setup. Lets skip subjects and address another issue I found. I was not running a reed spacer. Im running v force three. They were new less then 15 hrs on them. The upper reed pedal seemed very close to the intake roof after pulling the reeds it was clear they were hitting the roof. They have begun to chip ever so slightly. So is the fix the reed spacer to back it up a little and let it have more room? Or reshape and raise the intake ceiling?

[Pumashine]

I was not running a reed spacer. Im running v force three. They were new less then 15 hrs on them. The upper reed pedal seemed very close to the intake roof after pulling the reeds it was clear they were hitting the roof. They have begun to chip ever so slightly. So is the fix the reed spacer to back it up a little and let it have more room?

I used reed spacers on all the 350cc and below motors. Otherwise the reeds only lasted a couple of seasons. Other builders take material away where they hit. The v-force are new to me. But I have heard you can bend the tabs further with a heat gun.

[Jerry Hall]

Its not black from heat though its exhaust it wipes right off. What would cause so much exhaust blowing back though

I have not been on the site for a while and just noticed this thread.

 If the inside of all of your transfer port tunnels are black (and usually the reeds will also be black) it is from exhaust entering the transfer ports through the transfer port window. When this occurs the port will usually be darkest at the port window and the color will get lighter as the distance from the port window increases.

If exhaust was entering the hole your have pictured, the inside of the transfer ports would not be black due to the small amount flow that is occurring through this hole.  

Like Udontknowme said, the blackening is due to insufficient blown-down for the RPM where you are spending a lot of time. Increasing the blown-down will help this problem if you have the right pipe and a carb large enough to properly fill the crankcase at the RPM where the backflow is occurring.

Severely over-revving the engine past its power peak can also cause this problem even with the correct porting, carb and pipe.

Port linking (any open path from the crankcase to the export) is sometimes beneficial when the piston is near TDC on some two-strokes.  Port linking when the piston is mid-stroke or lower is seldom beneficial to power.  

On the piston up stroke, whatever is in the exhaust port close to the port link will be sucked into the crankcase from the exhaust port.  Depending on the RPM, some fresh charge may still be lingering in the exhaust port when the port linking occurrs.   On the piston down stoke, crankcase  mixture will be lost to the exhaust port.