Two Stroke Motocross

Two Stroke Motocross Forum => Technical => Topic started by: cnrcpla on May 29, 2012, 06:51:24 PM

Title: What are those black lines inside the cyliner?
Post by: cnrcpla on May 29, 2012, 06:51:24 PM: I opened up my top end today to make sure everything was alright, and I have been noticing this one prominent black mark, very skinny, almost looks like a scratch in the bore, but it is smooth. Is it ring blow by? I hope not because I only have like 3 or 4 hours on a brand new top end... Any thing I can do to stop it?
Title: What are those black lines inside the cyliner?
Post by: cnrcpla on May 29, 2012, 07:10:12 PM: I kind of answered my own question. I am pretty sure coolant is getting in the cylinder on the down stroke. The O rings seem fine so that points to only one thing... A warped head. How can I be sure the head is warped, are there any tests I can do to make sure the head is or isn't warped?
Title: What are those black lines inside the cyliner?
Post by: Recovered on May 29, 2012, 09:14:20 PM: take your head to a machine shop they would be able to clamp it down level and then mich it or anybody in your area that builds any kind of race engines would be able to check it out for you
Title: What are those black lines inside the cyliner?
Post by: cnrcpla on May 29, 2012, 10:22:11 PM: Thanks man, I just took it to me neighbor who owns his own machine shop. He can do it for me, he said he could see the warp just by looking at it With a planed head, am I going to have more compression? And with more compression, it is to my understanding more power?
Title: What are those black lines inside the cyliner?
Post by: SachsGS on May 29, 2012, 11:57:08 PM: Heads often "collapse" in the exhaust area rather then warp.I made a fixture that clamps to the cylinder head and then mount it in my lathe and use a dial indicator to determine the damage.
Title: What are those black lines inside the cyliner?
Post by: cnrcpla on May 30, 2012, 12:07:23 AM: Oh, that's cool. It was warped on the ends of the head from the port sides. I knew it was warped when I put a straight edge on it and I could see sunlight...
Title: What are those black lines inside the cyliner?
Post by: scotty dog on May 30, 2012, 02:29:39 AM: you can also get a plate of glass, stick some sandpaper to it and do figure 8 movements on it with the head that will show up any warpage and you can get it flat again. Obviously you dont need to seeing as your getting yours machined though, just a handy thing to know if ya need to do it quick
Title: What are those black lines inside the cyliner?
Post by: cnrcpla on May 30, 2012, 02:57:32 AM: I actually did try that, but I only had really fine emery paper on me at the time, so that didn't show up to well.
Title: What are those black lines inside the cyliner?
Post by: scotty dog on May 30, 2012, 03:20:49 AM: haha yeah that would take a while
Title: What are those black lines inside the cyliner?
Post by: cnrcpla on May 30, 2012, 02:46:22 PM: So am I right? Planing the head would give me more compression and more compression means more power, right? hahaha
Title: What are those black lines inside the cyliner?
Post by: riffraff on May 30, 2012, 02:58:28 PM: Quote from: cnrcpla on May 30, 2012, 09:46:22 PM
So am I right? Planing the head would give me more compression and more compression means more power, right? hahaha

you want to take off the least amount as possible, taking off too much could give you clearance/squish issues and higher compression would require higher octane fuel possibly
Title: What are those black lines inside the cyliner?
Post by: cnrcpla on May 30, 2012, 03:23:04 PM: Yeah, I just want enough taken off to get the warp out and make it flat again. The lines I am referring to are apparently light seizure marks, which is a direct result from coolant leaking into the engine in the down stroke. That is also where the little dingers in the top of my piston have been coming from.
Title: What are those black lines inside the cyliner?
Post by: cnrcpla on June 01, 2012, 01:19:53 AM: Update: I got the head back today, he had to take off .004 to make it all flat again. I put it all back together and turned the gas on, then it started pissing gas all over the floor out of a vent hose. Apparently the raised tube inside the carburetor was bent ever so slightly (I have no idea how) but I put it straight and it stopped. I finally went to kick it over, and the first kick it almost started, the second kick the starter fell OFF because the compression DENTED the roll pin...
Title: What are those black lines inside the cyliner?
Post by: Jeram on June 01, 2012, 02:04:36 PM: Quote from: cnrcpla on May 30, 2012, 09:46:22 PM
So am I right? Planing the head would give me more compression and more compression means more power, right? hahaha

not always,

higher compression = cooler exhaust gases (T1/P1=T2/P2 and cooler exhaust gases mean the pressure waves in the pipe move slower, meaning the pipe is more efficient at lower revs.
which is why there is also a general misconception about high compression heads being for bottom end power gain. Because thats what it does when you keep the same pipe.

If your someone who likes to use the bottom end and midrange of your bike, you should like the subtle change it will make.
such a small change shouldnt change your comp ratio by much tho, So I doubt it will be very noticable.

be sure to plug chop and check jetting tho
Title: What are those black lines inside the cyliner?
Post by: cnrcpla on June 02, 2012, 02:07:10 AM: Oh ok, I see what your saying. I do use bottom and mid a lot pulling out of turns on the track, so it should come in handy.
Title: What are those black lines inside the cyliner?
Post by: cnrcpla on June 06, 2012, 12:35:55 AM: Update: I got the throttle cable in today and put it all together. I do notice the compression increase, I also bumped up the octane. I started it up and it had a perfect idle. It was nice and slow, but strong. It sounds pretty good too, but I couldn't ride today because of the weather. Hopefully tomorrow I can, I want to see if it makes a difference.