yz 250 cylinder wear?

[mike-evans]

Hi Guys, bought a 01 YZ 250 2t last October that was fuly rebuilt last summer, inc cylinder. I took the head off the cylinder earlier to check it out. I noticed the top of the piston was lightly covered in carbon which wiped off, and the same on the head, jus about half of the head was lightly covered and the rest was a light brown colour (colour of material). The cylinder stil has the criss cross pattern on the wall from when it was replated, I noticed a few rub marks around the cylinder, they cant be felt at all, and 2 rub marks, 1 either side of the powervavle, again cant be felt, is this normal? There is very slight left to right movement of the piston whilst stil in place in cylinder, again is this normal? Piston had 66.36 stamped on it, is that standard size?

 

[whenfoxforks-ruled]

You really need a bore gauge to properly check the cylinder, or take it to someone that has one and knows how to use it/trusts. How is the ring end gap and piston skirt clearances? My 97 CR250 has a piston/ring life of 7.5 hours. That means, that properly used with the correct oil ratio, it may last 7.5 hours, give or take a few minutes. I will take it apart at that point and check it. Vintage Bob

 

[_JOE_]

Like Bob says, you need to check your clearances. Rub marks can be caused by several things including too little or too much clearance. Pull it apart and take measurements.

 

[mike-evans]

what about the tiny left to right movement of the piston in the cylinder, is that normal? Once I have tore it all down and everything is within spec (should be, only has about 3 hours on it), i wil get a bore gauge from work. it is stil ok to put the same piston and rings back in? How do i then remove the rub marks?

 

[_JOE_]

You need some room for the piston to expand or it will sieze in the bore when it heats up. If there is too much clearance the piston will rock and the skirt will wear the cylinder. Was the cylinder replaced with a brand new factory cylinder or was the original part repaired?

As far as removing the marks it really depends on the severity. Some good pictures would help alot.

 

[whenfoxforks-ruled]

Reuse nothing, more than likely. The rings is a big no-no never, like clips. And head gaskets on water cooled bikes, no-no. If the rub marks are from an exhaust bridge, it needs to be bigger, the clearance. Are they normal wear marks, or seizure marks? If the skirt clearance is still with in spec it may be able to reuse, depending on them marks. Are they through the rings? Tiny left to right does not sound good either, unless its the top with the rings off? That would mean nothing, the piston has a smaller diameter up top. Plated or sleeve job on the bore? Vintage Bob

 

[mike-evans]

It was a repair, not a new cylinder. How do I tel if it is a sleeve or replate? Also how do I tel the diference between normal wear marks and sieze marks, pretty sure they are normal wear marks as I cant feel ANY depth of the marks, wont a hone remove the marks?

 

[mike-evans]

just rang the shop who done the cylinder work, and its a liner in there, not plated....he said to jus rub the marks with very fine wet and dry paper, as it is not scored. Are rub/wear marks common?

 

[_JOE_]

You DEFINATELY need to take several measurements. Sleeves need to be machined to the proper clearance when installed. It's very possible it is too loose or too tight. You should find a new shop for your high performance 2 stroke stuff, you can't hand sand a cylinder. You shouldn't see any wear marks, especially inside of 10 hours.

 

[mike-evans]

ok, so I need to check piston ring wear, by removing cylinder, fitting rings inside cylinder and using feeler gauges, measure the ring gap, correct? Also bore gauge to check cylinder spec? Wil have to read manual on how to check skirt gap? How do I remove rub marks? Anything else to check?

 

[whenfoxforks-ruled]

Dang sleevers. I have one also. Done by others, not me! Its a seemingly cheaper method of fixing the bore? It probably needs a hone ran through it to clean up the aluminum flashing off. Plated, oven cleaner and a scotch brite pad, not a liner though! Then all the port edges need to be chamfered. If it has an exhaust bridge in the middle of the port, it needs to be relieved more than the bore. The sleeve bore needs a little more clearance than the stock plated bore. Its a YZ, so I am not for sure about the exhaust, and I do think it has a huge intake bridge? It does not move as much as the exhaust, the exhaust gets hotter. To check the skirt clearance, place the piston without the rings into the bore, where the piston normally travels, and check it with the feeler gauge. What ever the hours are on the stock bore, the sleeved bore wears out quicker. The only advantage that I can see, running long on re-rings will not oval the liner. Vintage Bob

 

[mike-evans]

ok so not end of world or bike for having a sleeved cylinder.....phew...it has 1 big exhaust port in the centre and 2 smaller ports either side, so 2 bridges in total joining to the centre port...i cant put pics up as my computer is broke.

 

[julien_d]

Nope, the exhaust bridge that would need relieved would be right in the center of the main exhaust port. cylinder wall between the main exhaust ports and sub exhaust ports doesn't count ;).

J.

 

[mike-evans]

when I measure the piston, if it is in spec, wil it be ok to re-use the piston and get 2 new rings for it? As the cylinder has a sleeve, does that mean the wear limits in the manual are now not tied to my cylinder due to it not being standard? What limits do i measure this sleeved cylinder to? It has 66.36 stamped on the piston...

 

[whenfoxforks-ruled]

Piston with in specs is good. Because its a liner, the tolerances need to be a little looser. I do not know the EXACT amount, I am pretty sure .001" more will suffice, skirt and ring gap. You will also have a shorter hour limit on the top end. How much, I think not being the top racer in the country, assuming, that if you tear it down and check it at the normal time, you can get a good idea how YOU are wearing the engine. You can also check it after break in with a compression gauge, and keep checking it till there is a drop, then ring it. I have a 97 CR250 with a sleeve, and this is about my plan on it. I do not know for sure, but I think its the safest route. Other than getting it over bored and plated, or another jug? Double check all the ports are beveled, its their job, but they may not know it. Vintage Bob

 

[mike-evans]

Piston with in specs is good. Because its a liner, the tolerances need to be a little looser. I do not know the EXACT amount, I am pretty sure .001" more will suffice, skirt and ring gap. You will also have a shorter hour limit on the top end. How much, I think not being the top racer in the country, assuming, that if you tear it down and check it at the normal time, you can get a good idea how YOU are wearing the engine. You can also check it after break in with a compression gauge, and keep checking it till there is a drop, then ring it. I have a 97 CR250 with a sleeve, and this is about my plan on it. I do not know for sure, but I think its the safest route. Other than getting it over bored and plated, or another jug? Double check all the ports are beveled, its their job, but they may not know it. Vintage Bob

so when checking skirt and ring gap, 0.001" ontop of manuals limits wil be fine? Am I understanding this correct?

 

[whenfoxforks-ruled]

Pretty sure its .003 on the skirt and .018 on the ring gap. Vintage Bob

 

[whenfoxforks-ruled]

I am still trying to find out where I got them numbers from? If it was on here, or talking to Eric? I would feel bad taping conversations, maybe crib notes? The expansion rates are different, the surface wears the piston and ring quicker. And the thing I am unsure of, is if the clearance was more! The search function is working pretty good again. All the stuff I dug up gave no specific numbers. I do not want my 250 to seize the piston the first time out either. On the phone or in his books, gives no insight to how it is dealing with Eric in person, priceless. Hopefully I can give him a call today, as long as I can have an hour or so of nobody bothering me! Vintage Bob

 

[whenfoxforks-ruled]

Found 1 close: http://www.thumpertalk.com/forum/archive/index.php/t-774009.html . And I will be darned if I did not find the guy, that had me sucked in back in the day, 78~81, and still used the dark ages sale pitch before he sold out his company: http://www.streetdirectory.com/travel_guide/print_article.php?articleId=60323 . I am still getting even with him, plus the smoking deal he gave me on my Fox Forks! Sucker! And I found some stuff I have been yapping about for awhile, my composite cylinder and piston! I did not see the no rings technology coming though? What clearances on that bad boy? http://www.techbriefs.com/component/content/article/2258?start=1 . I should have taken the sissy typing and computer skills back in the day also! It takes a while searching and what not, when you really do not know the basics. 1 missed key and the page disappeared?? I am getting better. Now to categorize all them points of good information. I was taken aback finding Wiseco posting on Thumpertalk, and not here! Vintage Bob

 

[mike-evans]

My manual gives PISTON DIAMETER of 66.352-66.367mm (2.6120-2.6129in), RING GAP, standard 0.40-0.55mm(0.016-0.022in), limit 0.95mm(0.037in), CYLINDER BORE, standard 66.400-66.414mm (2.6142-2.6147in), wear limit 66.5mm (2.618in).... Piston clearance=cylinder bore-piston diameter. The piston in my bike has 66.36 stamped on it. Is it just the three measurements mentioned that I have to take? But as said, what limits are relevant to my sleeved liner? Is the skirt clearance mearured from piston diameter-cylinder bore? Im getting confused with all there figures :yikes:

 

[_JOE_]

Did you read the TT link Bob gave you? Wiseco gives a bit more detail.

Why are you confused? Take all the measurements you have specs for and compare them. Not too difficult.

 

[mike-evans]

Did you read the TT link Bob gave you? Wiseco gives a bit more detail.

Why are you confused? Take all the measurements you have specs for and compare them. Not too difficult.

my confusion is because I have never measured pistons or bores on my bikes before....3 measurements needed, ring gap, cylinder bore and piston skirt? Correct? Why does piston skirt need measuring? Does the piston wear? Wiseco said add 0.001" ontop of limits for iron liners, but that wasnt a difinative answer....

 

[_JOE_]

my confusion is because I have never measured pistons or bores on my bikes before....3 measurements needed, ring gap, cylinder bore and piston skirt? Correct? Why does piston skirt need measuring? Does the piston wear? Wiseco said add 0.001" ontop of limits for iron liners, but that wasnt a difinative answer....

Never had a bike with a sleeve eh? ;)

The final machining is critical. Usually it will be honed until the tolerance is where the machinist wants it. The tools used to take the bore and skirt measurements must be good quality, known accurate peices for the readings to mean anything. If the liner was slammed in by some hack in a shed somewhere chances are good it's going to need some finish machining. If you don't have the proper tooling I would suggest taking the parts to a reputable machine shop to be measured. Bore guages can be quite pricey.

The piston skirt will wear over time as the piston rocks slightly in the bore as it travels through it's stroke. Wiseco is basically saying that one thousandth should be enough for most applications but you should keep an eye on it incase you're one of those applications that needs one and a half thousandths. They can't tell you that will be fine and have you seize it up, these days that would leave them open to a law suit.

 

[whenfoxforks-ruled]

The piston and your book say .002" of skirt clearance, its got a sleeve so you need .003". Mike the od of the skirt, about 1/4" above the bottom, from exhaust side to intake side. Add the .003" to the piston od, and have someone qualified knock her up. They should need the piston to check. A bore gauge is the only accurate tool to measure the bore with. For safety and ease of mind, triple check it by fitting the piston and checking the skirt clearance with a feeler gauge. Then the rings. And the ports, they have to be chamfered, check it. Did you read all the links? Pop quiz? Vintage Bob

 

[mike-evans]

The piston and your book say .002" of skirt clearance, its got a sleeve so you need .003". Mike the od of the skirt, about 1/4" above the bottom, from exhaust side to intake side. Add the .003" to the piston od, and have someone qualified knock her up. They should need the piston to check. A bore gauge is the only accurate tool to measure the bore with. For safety and ease of mind, triple check it by fitting the piston and checking the skirt clearance with a feeler gauge. Then the rings. And the ports, they have to be chamfered, check it. Did you read all the links? Pop quiz? Vintage Bob

Yeh I read the links, thank you. I have internal micrometer rods which read to 0.0001" i wil use to measure the bore, and a digital vernier which also reads 0.0005" which i wil use for piston measurement, i have feeler gauger to double check skirt clearance. All i need to do know is strip it down, measure and hopefuly be able to use the piston with new rings....