Cylinder,Piston,Head Damage "Need help"
Posted February 11, 2011 - 10:55 PM
As some of you remember that I had damage to my top end when inspecting it. I want to make a new thread as per title to get more exposure then my original thread that originally had nothing to do with this issue at hand.
Ok, first here are some pictures.
As you can see, it is a mess. Shockingly, the bike ran fantastic for the 20 minutes or so I rode it when I got it "brought it into the basement for the winter the day after I got it as that was when we started getting all are snow, and I wanted to inspect things and replace things"
Ok, now onto my question. IS there any way that the Nikasil plating that chipped off of the exhaust ports could case those chew marks in the head and piston? "Also notice that the chew marks are focused on the exhaust port side of the cylinder head and piston"
Some people say that it could be the crank bearings starting to go? But I checked the crank for up and down play at the rod and it has none what so ever, it does however have a bit of side to side play but I read this is normal and needs to be that way.
I am kind of scared. I don't want to go and drop 700 on a new cylinder,head and piston kit only to know that maybe there is something messed up down there and have this happen again.
I'll admit, this is really the first two stroke engine problems like this I have ever experienced, so I am stumped. Also, the piston rings are fantastic and we're not siezed in the grooves at all. There was some rub marks on the piston, likely due to the flaking of the nikasil rubbing on the bare spots on the bore by the ports??
Basically want to know is if the plating could have/likely caused this damage?
I REALLY don't want to take apart the bottom end!
The bike in question is a 2002 CR250
Posted February 11, 2011 - 11:52 PM
Posted February 12, 2011 - 01:10 AM
Posted February 12, 2011 - 02:01 AM
Well I cleaned the cylinder head up a bit better, and it appears that there are some very very faint marks "lots of em just very small and can feel with my fingers" in the area around the plug area of the dome. I used a magnifying glass but its really to hard to tell if there is any other material other then aluminum?..
I just noticed something though. It appears that on the head, the head gasket MIGHT have been leaking? What I mean by that is that I can see exhaust/premix residue where there should not be "Please scroll up and look at the picture of the head and look at 7 o'clock in the picture to see what I am talking about.
Is that normal? I just actually noticed this myself :S. You see, I got the bike basically in winter, and only rode it for 20 minutes before bringing it into the basement.
As for the plug, I can't really comment on that as I did put some sea foam in the full tank of gas when I took it for a run to try and break up any crap inside "I have a good history with the stuff" But it looks tanish brownish and dirty like it has seen some use. Also, there was a lot of spooge coming out from where the pipe connects to the exhaust flange, so I am not sure on the lean part... but please check that picture closely for the head above at 7 o'clock and tell me if that is not right?
I am really lost, trying to figure out what caused this 100%, which I know is hard over the internet :S
Appreciate the help guys
Posted February 12, 2011 - 01:43 PM
Posted February 12, 2011 - 02:22 PM
Looks like it could have been detonating. Without seeing it first hand its all speculation but it looks like it flaked by exhaust which would indicate possible high exhaust temps. Air leaks, low octane fuels, riding in heavy loads ( mud,sand) with improper jetting or crap fuel. These are all possibilities. I would take a real close look at the lower rod bearing before throwing her back together. Crank seals for sure!
This all makes sense, someone else also said that this could have been caused by detonating as well prior. I would tend to believe he ran low octane gas in it. And we do have lots of sand and mud up this way, and it had the stock TMX carb on it as well.
I just came back from inspecting the lower connecting rod bearing, it moves smoothly, has no up and down play and from what I can see, no pins missing out of the bearing or anything to indicate the bearing had failed.
So you are saying, if in fact the bike was detonating. The temps we're getting so hot that the nikasil plating had chipped off, causing the piston crown and head damage?
It makes sense to me, I just wished I could find evidence of the plating in the head, it is hard to tell. I guess I am going to pull out the dremel and start hacking up this head to see if I can find any pieces within it embedded.
IF you we're looking at this motor in person, what would give you cause to believe it was detonating opposed to seeing pictures? Any ideas?
Posted February 12, 2011 - 03:10 PM
Posted February 12, 2011 - 03:23 PM
The nikasil probably went out the exhaust. The damage is from actual detonation, which is caused by a number of things, which Phil already described. You already said it looked to have a problem with the head gasket, that would be a pretty good air leak indicator.
You see, I have never in my life experienced detonation or the effects of its aftermath, so this is all brand new to me. The nikasil must have went out the exhaust, I cant find any traces of it. I wonder though, if the head was leaking, wouldn't it be sucking coolant? and if so, wouldn't it have smoked like crazy and the piston crown would have been clean?
Help me understand detonation aftermath.. I understand how it is caused. But how would detonation cause little round chunks to be indented in the head and piston? Am I correct to understand that it was detonating and was so hot that the nikasil chipped off and quickly was squishing between the piston crown and head, then exiting through the exhaust ports?
Wish I could find some pictures of other people who had had detonation and see their results to compare em!
Posted February 12, 2011 - 03:33 PM
Edited by Northwoodslivin, February 12, 2011 - 03:48 PM.
Posted February 12, 2011 - 03:38 PM
Detonation (also called "spark knock") is an erratic form of combustion that can cause head gasket failure as well as other engine damage. Detonation occurs when excessive heat and pressure in the combustion chamber cause the air/fuel mixture to autoignite. This produces multiple flame fronts within the combustion chamber instead of a single flame kernel. When these multiple flames collide, they do so with explosive force that produces a sudden rise in cylinder pressure accompanied by a sharp metallic pinging or knocking noise. The hammer-like shock waves created by detonation subject the head gasket, piston, rings, spark plug and rod bearings to severe overloading.
Mild or occasional detonation can occur in almost any engine and usually causes no harm. But prolonged or heavy detonation can be very damaging. So if you hear knocking or pinging when accelerating or lugging your engine, you probably have a detonation problem.
Posted February 12, 2011 - 03:50 PM
I found this here: http://www.misterfixit.com/deton.htm
The part where it says "Head Gasket Failure" really piques my interest. I think it is obvious the part of the head gasket near the exhaust ports had failed as you can see exhaust that has slipped by in that area.. interesting, but still confused that if in fact that was the case, it should have been puffing white smoke like crazy as it would be sucking coolant?
I think we're getting somewhere though. I am just happy that the crank is good:worthy:
Posted February 12, 2011 - 04:23 PM
Posted February 12, 2011 - 04:38 PM
Posted February 12, 2011 - 04:57 PM
I appreciate your advice, but I seriously doubt there is anything what so ever wrong with the crank.
I think I have come to the conclusion that this was caused by detonation which flaked off the nikasil from the exhaust ports contributing to the overall head and piston damage..
Ahh... I don't know what to do now, you all have me worrying
Posted February 12, 2011 - 05:02 PM
Edited by choppertown, February 12, 2011 - 05:04 PM.
Posted February 12, 2011 - 05:52 PM
The damage to the head & piston crown has been caused by foreign material inside the cylinder. Detonation may have contributed to the cause of it being there. It would be unwise to assume that all of it went out the exhaust. Some could equally have entered the crankcases via the transfer ports. If this were the case, damage to the crank may have been caused.
Any way of flushing the crank case with out splitting it if by chance there is anything in there? I cant see anything shining a flash light down in there...
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