Yz250 Top end inspection

Kenny Boy
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Kenny Boy
Edited Date/Time 12/4/2015 7:55am









what happened? this piston only has about 8 tanks of fuel on it.


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slackinoff
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slackinoff 11/7/2015 8:42pm
11/7/2015 8:42pm
What was the cylinder bore measurement before piston install?
Kenny Boy
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Kenny Boy 11/7/2015 8:50pm
11/7/2015 8:50pm
slackinoff wrote:
What was the cylinder bore measurement before piston install?
Good question. I took the cylinder to my local engine shop and they told me it looked ok to buy a "standard" piston ( he insisted it just needed to be honed) from what I have read I shouldn't of let him do that, then I took it to my local Yamaha dealer, they said the same thing. Standard piston, so I put a 66.4 wiseco in it. it seemed to have excessive engine noise which is why I took it back apart.
mb
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mb 11/7/2015 10:23pm
11/7/2015 10:23pm
Piston to wall clearance? Rind end gap? Compression? Cyl probably needs to be replated.
Kenny Boy
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Kenny Boy 11/7/2015 10:23pm
11/7/2015 10:23pm Edited Date/Time 11/8/2015 12:55am
I'm trying to figure out if I want to get it replated or just buy a new cylinder, I think they are $400. I guess I Could get $100 for my cylinder? I just don't want to have it re-plated only to have a problem. Looking for some guidance, I really love the bike it's my first but have been afraid to really ride because the engine has had a weird noise since I owned it... going on 3 years.

The Shop

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Kenny Boy
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Kenny Boy 11/7/2015 10:28pm
11/7/2015 10:28pm Edited Date/Time 11/7/2015 10:34pm
mb wrote:
Piston to wall clearance? Rind end gap? Compression? Cyl probably needs to be replated.
I checked ring end gap it was within Wiseco's recommendations, I'm not sure if it was the right way to do it but I measured piston to wall clearance with a feeler gauge at the skirt, was in specs also. From what I can tell I thought it looked good on the intake and exhaust sides, it just has a lot of blow by on the sides of the piston... but I'm no expert. I wanted to check compression but don't have a gauge, one is on my list of things to buy before I run it again though. Felt pretty high kicking it. Started the 1st kick almost every time even after sitting a few months.
slackinoff
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slackinoff 11/8/2015 3:12am
11/8/2015 3:12am Edited Date/Time 11/8/2015 3:44am
Kenny Boy wrote:
I checked ring end gap it was within Wiseco's recommendations, I'm not sure if it was the right way to do it but I measured piston...
I checked ring end gap it was within Wiseco's recommendations, I'm not sure if it was the right way to do it but I measured piston to wall clearance with a feeler gauge at the skirt, was in specs also. From what I can tell I thought it looked good on the intake and exhaust sides, it just has a lot of blow by on the sides of the piston... but I'm no expert. I wanted to check compression but don't have a gauge, one is on my list of things to buy before I run it again though. Felt pretty high kicking it. Started the 1st kick almost every time even after sitting a few months.
The bore could be out of round just slightly...but if the bike runs good??.....you could just ride it. What are the symptoms the bike is showing, other than allot of blowby?

EDIT*
The easiest/cheapest way get a decent measurement of the cylinder is to procure a set of TELESCOPIC dial bore gauges and also a caliper to measure them.....or take the cylinder to a machine shop and ask them to measure it at the specific locations identified in the service manual.

I sent my used, torn up barrel and a new OEM piston kit to Ken Oconnor racing. http://www.kenoconnorracing.com/Cylinder%20Plating.html

He made sure the plating was done for my specific piston I sent him, he cleaned and installed the PV's, and made sure that the rings were gaped properly. He then boxed it all back up so could I assemble. He will make sure all is in spec and ready to bolt up. I loved working with him on my recent build.

He even rebuilt my crank and did a dang good job on it too.

IF you are really just tired of Screwing with it. Pack it up in a igloo cooler, tape it up good, and ship it to him for a rebuild.
Falcon
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Falcon 11/8/2015 5:28pm
11/8/2015 5:28pm
Is that a crack in the piston skirt on the intake side, or just a wear mark?


You should also know that Yamaha has different piston sizes to match different cylinder gauges. The total bore of the cylinders varies very slightly and they use A, B, C, and D to compensate. (A is smallest, D is largest.)
Make sure your piston matches the letter stamped on the rear portion of the cylinder (on the outside) for the best seal.
Kenny Boy
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Kenny Boy 11/8/2015 6:03pm
11/8/2015 6:03pm
Falcon wrote:
Is that a crack in the piston skirt on the intake side, or just a wear mark? You should also know that Yamaha has different piston...
Is that a crack in the piston skirt on the intake side, or just a wear mark?


You should also know that Yamaha has different piston sizes to match different cylinder gauges. The total bore of the cylinders varies very slightly and they use A, B, C, and D to compensate. (A is smallest, D is largest.)
Make sure your piston matches the letter stamped on the rear portion of the cylinder (on the outside) for the best seal.
I will have to take a better look at it when I get the chance, it may be a few days. I know they have A,B,C, and D pistons. The stamp was gone on my cylinder. I plan on running a forged piston unless you guys know something I don't?
Kenny Boy
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Kenny Boy 11/8/2015 6:06pm
11/8/2015 6:06pm
Kenny Boy wrote:
I checked ring end gap it was within Wiseco's recommendations, I'm not sure if it was the right way to do it but I measured piston...
I checked ring end gap it was within Wiseco's recommendations, I'm not sure if it was the right way to do it but I measured piston to wall clearance with a feeler gauge at the skirt, was in specs also. From what I can tell I thought it looked good on the intake and exhaust sides, it just has a lot of blow by on the sides of the piston... but I'm no expert. I wanted to check compression but don't have a gauge, one is on my list of things to buy before I run it again though. Felt pretty high kicking it. Started the 1st kick almost every time even after sitting a few months.
slackinoff wrote:
The bore could be out of round just slightly...but if the bike runs good??.....you could just ride it. What are the symptoms the bike is showing...
The bore could be out of round just slightly...but if the bike runs good??.....you could just ride it. What are the symptoms the bike is showing, other than allot of blowby?

EDIT*
The easiest/cheapest way get a decent measurement of the cylinder is to procure a set of TELESCOPIC dial bore gauges and also a caliper to measure them.....or take the cylinder to a machine shop and ask them to measure it at the specific locations identified in the service manual.

I sent my used, torn up barrel and a new OEM piston kit to Ken Oconnor racing. http://www.kenoconnorracing.com/Cylinder%20Plating.html

He made sure the plating was done for my specific piston I sent him, he cleaned and installed the PV's, and made sure that the rings were gaped properly. He then boxed it all back up so could I assemble. He will make sure all is in spec and ready to bolt up. I loved working with him on my recent build.

He even rebuilt my crank and did a dang good job on it too.

IF you are really just tired of Screwing with it. Pack it up in a igloo cooler, tape it up good, and ship it to him for a rebuild.
It has been having a slight knocking noise at low rpm which went away when I gave it throttle, recently I noticed a rattling sound as I was getting into the powerband while in 5th.... I may send it to Oconner, not sure if I want to buy a new cylinder yet.... I need to sell this trinity exhaust I have for my raptor.
WileCyot
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WileCyot 11/8/2015 6:21pm
11/8/2015 6:21pm
Let me know when you're ready to order a new piston or any other parts. I can get you a killer deal.
Kenny Boy
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Kenny Boy 11/8/2015 7:41pm
11/8/2015 7:41pm



the ring gap was in specs, wish I would of tried this before running it .
mb
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mb 11/8/2015 8:46pm
11/8/2015 8:46pm
Cheapest is going to be a re-plate.

Power seal USA $184 plus shipping
http://www.powersealusa.com/prices/

Rocky Mountain ATV OEM Yamaha
Piston
Rings
Wrist pin and clips
Needle bearing
Head o rings
Base gasket

$181.50
Say $50 at worst to ship your cyl there and back.

=$415.50

project racer 11/9/2015 5:25am
11/9/2015 5:25am
How many hours on the crank / lower end since the last freshen up ?

Would suck to tie up half a grand in a new top end, only to see a needle or thrust washer come marching up through the new stuff.

Personally, I never hone plated cylinders. Basically ,you just want to break the glaze from prior run time off of the cylinder walls. A piece of 600-800 wet or dry sand paper, along with some WD 40, and a careful hand, will get the results necessary.

The plating is thin. No need to tax it by running a hone through it.

The last picture shows some serious run out in the bore.

Have it measured for run out, along with taper from top to bottom if you plan to use it , if it is usable at all.

With the amount of wear on it, a C or D sized OEM piston would be the best likely replacement.
WileCyot
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WileCyot 11/9/2015 5:48am
11/9/2015 5:48am
I can get you a new OEM cylinder for $350 plus shipping. As for the other parts as mentioned above,

Piston - $80
Rings - $35
Wrist pin and clips - $20
Needle bearing - $14
Head o rings - $9
Base gasket - $18

Total $176
Kenny Boy
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Kenny Boy 11/9/2015 10:43am
11/9/2015 10:43am
Don't anyone know why it wore the side of the cylinder? I would of thought it would of been the front. Or back of the cylinder.
WileCyot
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WileCyot 11/9/2015 12:01pm
11/9/2015 12:01pm
Kenny Boy wrote:
Don't anyone know why it wore the side of the cylinder? I would of thought it would of been the front. Or back of the cylinder.
Out of tolerance big end rod bearing and/or crank bearings.

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mxtech1
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mxtech1 11/9/2015 2:03pm
11/9/2015 2:03pm
I would be leery of the crank. You haven't made any comments regarding how many hours it has. I would recommend having the crank rebuilt and trued.

I have had very good luck sending all my cylinders to Millenium Technologies. If you buy your piston ahead of time, you can send the piston with the cylinder and they will repair the cylinder to the exact tolerances that piston will need. They will also clean your cylinder so well it will come back looking brand new. Companies like this take all of the guess-work out of it for you if you do not have a thorough understanding of engine tolerances.

If the cylinder really is worn to the point where it is of round, you will need to have it bored first size over, re-plated, and then match a piston to that accordingly.
Kenny Boy
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Kenny Boy 11/9/2015 3:26pm
11/9/2015 3:26pm Edited Date/Time 11/9/2015 3:39pm
mxtech1 wrote:
I would be leery of the crank. You haven't made any comments regarding how many hours it has. I would recommend having the crank rebuilt and...
I would be leery of the crank. You haven't made any comments regarding how many hours it has. I would recommend having the crank rebuilt and trued.

I have had very good luck sending all my cylinders to Millenium Technologies. If you buy your piston ahead of time, you can send the piston with the cylinder and they will repair the cylinder to the exact tolerances that piston will need. They will also clean your cylinder so well it will come back looking brand new. Companies like this take all of the guess-work out of it for you if you do not have a thorough understanding of engine tolerances.

If the cylinder really is worn to the point where it is of round, you will need to have it bored first size over, re-plated, and then match a piston to that accordingly.
Yeah I should probably rebuild the crank or buy a new one, I have no idea how many hours are on it. What's a good price for a new OEM one? Looking like it's going to be a full rebuild.Huh

I seen a tusk case splitter and crank installer/ or puller? for $120. Is that my only option? This will be my first time splitting a bottom end. I might do a gear swap also, I'm only 140 so the bike spins like crazy, the gears feel like they should be spaced farther and the top speed is to low.. If anyone has any suggestions that would be great.
WileCyot
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WileCyot 11/10/2015 7:44am
11/10/2015 7:44am
mxtech1 wrote:
I would be leery of the crank. You haven't made any comments regarding how many hours it has. I would recommend having the crank rebuilt and...
I would be leery of the crank. You haven't made any comments regarding how many hours it has. I would recommend having the crank rebuilt and trued.

I have had very good luck sending all my cylinders to Millenium Technologies. If you buy your piston ahead of time, you can send the piston with the cylinder and they will repair the cylinder to the exact tolerances that piston will need. They will also clean your cylinder so well it will come back looking brand new. Companies like this take all of the guess-work out of it for you if you do not have a thorough understanding of engine tolerances.

If the cylinder really is worn to the point where it is of round, you will need to have it bored first size over, re-plated, and then match a piston to that accordingly.
Kenny Boy wrote:
Yeah I should probably rebuild the crank or buy a new one, I have no idea how many hours are on it. What's a good price...
Yeah I should probably rebuild the crank or buy a new one, I have no idea how many hours are on it. What's a good price for a new OEM one? Looking like it's going to be a full rebuild.Huh

I seen a tusk case splitter and crank installer/ or puller? for $120. Is that my only option? This will be my first time splitting a bottom end. I might do a gear swap also, I'm only 140 so the bike spins like crazy, the gears feel like they should be spaced farther and the top speed is to low.. If anyone has any suggestions that would be great.
What year is the bike? I'll look up a crank for you.

I can get an 04 YZ250 Crank (5UP-11400-10-00) for $325 + shipping to you brand new from Yamaha.
mxtech1
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mxtech1 11/10/2015 10:04am
11/10/2015 10:04am
mxtech1 wrote:
I would be leery of the crank. You haven't made any comments regarding how many hours it has. I would recommend having the crank rebuilt and...
I would be leery of the crank. You haven't made any comments regarding how many hours it has. I would recommend having the crank rebuilt and trued.

I have had very good luck sending all my cylinders to Millenium Technologies. If you buy your piston ahead of time, you can send the piston with the cylinder and they will repair the cylinder to the exact tolerances that piston will need. They will also clean your cylinder so well it will come back looking brand new. Companies like this take all of the guess-work out of it for you if you do not have a thorough understanding of engine tolerances.

If the cylinder really is worn to the point where it is of round, you will need to have it bored first size over, re-plated, and then match a piston to that accordingly.
Kenny Boy wrote:
Yeah I should probably rebuild the crank or buy a new one, I have no idea how many hours are on it. What's a good price...
Yeah I should probably rebuild the crank or buy a new one, I have no idea how many hours are on it. What's a good price for a new OEM one? Looking like it's going to be a full rebuild.Huh

I seen a tusk case splitter and crank installer/ or puller? for $120. Is that my only option? This will be my first time splitting a bottom end. I might do a gear swap also, I'm only 140 so the bike spins like crazy, the gears feel like they should be spaced farther and the top speed is to low.. If anyone has any suggestions that would be great.
You can get away without a crank installer/puller if you have a shop press.

You will absolutely need....
A case splitter
A Flywheel puller
A clutch basket holder tool
Seal removers are nice
feeler gauges
A blind bearing tool kit
A seal/bearing driver kit
Torque wrenches

I believe everything else can be done with standard tools
WileCyot
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WileCyot 11/10/2015 11:05am
11/10/2015 11:05am
I would look at getting tools from RM ATV Tusk brand. I can get a bit of a discount if interested.
WileCyot
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WileCyot 11/10/2015 11:08am
11/10/2015 11:08am
I can get a Tusk Splitter for $65 and The Crank Puller Installer for $65 as well.
Kenny Boy
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Kenny Boy 11/10/2015 12:13pm
11/10/2015 12:13pm
WileCyot wrote:
I can get a Tusk Splitter for $65 and The Crank Puller Installer for $65 as well.
Ok. I will let you know if I want you to get me something.
Kenny Boy
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Kenny Boy 11/10/2015 12:15pm
11/10/2015 12:15pm
mxtech1 wrote:
I would be leery of the crank. You haven't made any comments regarding how many hours it has. I would recommend having the crank rebuilt and...
I would be leery of the crank. You haven't made any comments regarding how many hours it has. I would recommend having the crank rebuilt and trued.

I have had very good luck sending all my cylinders to Millenium Technologies. If you buy your piston ahead of time, you can send the piston with the cylinder and they will repair the cylinder to the exact tolerances that piston will need. They will also clean your cylinder so well it will come back looking brand new. Companies like this take all of the guess-work out of it for you if you do not have a thorough understanding of engine tolerances.

If the cylinder really is worn to the point where it is of round, you will need to have it bored first size over, re-plated, and then match a piston to that accordingly.
Kenny Boy wrote:
Yeah I should probably rebuild the crank or buy a new one, I have no idea how many hours are on it. What's a good price...
Yeah I should probably rebuild the crank or buy a new one, I have no idea how many hours are on it. What's a good price for a new OEM one? Looking like it's going to be a full rebuild.Huh

I seen a tusk case splitter and crank installer/ or puller? for $120. Is that my only option? This will be my first time splitting a bottom end. I might do a gear swap also, I'm only 140 so the bike spins like crazy, the gears feel like they should be spaced farther and the top speed is to low.. If anyone has any suggestions that would be great.
mxtech1 wrote:
You can get away without a crank installer/puller if you have a shop press. You will absolutely need.... A case splitter A Flywheel puller A clutch...
You can get away without a crank installer/puller if you have a shop press.

You will absolutely need....
A case splitter
A Flywheel puller
A clutch basket holder tool
Seal removers are nice
feeler gauges
A blind bearing tool kit
A seal/bearing driver kit
Torque wrenches

I believe everything else can be done with standard tools
I have every thing except the case splitter and bearing tools.
Kenny Boy
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Kenny Boy 12/3/2015 10:32pm
12/3/2015 10:32pm
WileCyot wrote:
I can get a Tusk Splitter for $65 and The Crank Puller Installer for $65 as well.
i can get both for $120 on ebay.
Kenny Boy
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Kenny Boy 12/3/2015 11:05pm
12/3/2015 11:05pm


I guess the next step will be to take the cylinder to my local dealer to measure how bad the cylinder is worn? i would hate to pay to have it shipped to Oconner to find out it's no good.
WileCyot
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WileCyot 12/4/2015 6:45am
12/4/2015 6:45am
Kenny Boy wrote:
[img]https://p.vitalmx.com/photos/forums/2015/12/03/113720/s1200_1204150137_1.jpg[/img] I guess the next step will be to take the cylinder to my local dealer to measure how bad the cylinder is worn? i would...


I guess the next step will be to take the cylinder to my local dealer to measure how bad the cylinder is worn? i would hate to pay to have it shipped to Oconner to find out it's no good.
If it's outside dims he can have it stripped, replated, and honed to finish diameter for that piston. He will measure the piston anyway and finish hone the cylinder to what it needs.
xnationalwrench 12/4/2015 7:55am
12/4/2015 7:55am
Just another observation: Measure the clearance just before reassembling, if you measure then run a hone thru it you have changed the measurement how ever slightly.

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