Yz 250 cylinder

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10/9/2017 5:57 PM
Edited Date/Time: 10/9/2017 6:02 PM

What's best to do with this cylinder? I pulled it off the bike that broke a piston skirt. Some small scratches and nicks in it you can barley feel with your finger nail. Do you guys recommend a re-plate process, hone it or bore/hone if needed. Im guessing this cylinder has the nikasil playing? If I'm correct? First time messing with a cylinder like this. I need to clean up some of the oily residue off the walls and get better pictures maybe but this what I took wuick last night Photo

Photo

Photo

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2011 Yamaha YZ 250 -MX
1996 Yamaha Banshee 350 -Trails
1982 Chevy S10
2005 Pontiac GTO -451rwhp

10/10/2017 2:13 AM

Ive seen cylinders work perfecly fine with small nicks in the walls. I would still get it replated at millennium. Dont chance a ring getting caught up on a bur or something like that and blowing your bike up again. They have a ton of yz250 cylinders they can swap for you for quick turnaround. I sent a yz250 cylinder in and got a new one back in about a week and a half. I think the term is “core exchange” or something like that on their paperwork

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2009 Kawasaki KX450F
2009 Kawasaki KX250F
2002 Suzuki GSXR 600

10/10/2017 3:01 AM

Acidreamer wrote:

Ive seen cylinders work perfecly fine with small nicks in the walls. I would still get it replated at millennium. Dont chance a ring getting caught up on a bur or something like that and blowing your bike up again. They have a ton of yz250 cylinders they can swap for you for quick turnaround. I sent a yz250 cylinder in and got a new one back in about a week and a half. I think the term is “core exchange” or something like that on their paperwork

Yup, they're easy to work with and stand behind their stuff.

They'll swap your broken one for a refurbished one for quicker turn around times, and then repair yours for someone else.

You can opt not to I'm sure.

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If you're not mixing gas, you're not haulin ass.

10/10/2017 4:03 AM

The cylinder needs to be reworked and plated. I would also suggest taking a look at your squish as the head shows some very light signs of detonation on the edges of the squish band.

Paw Paw

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10/10/2017 6:40 AM

Paw Paw wrote:

The cylinder needs to be reworked and plated. I would also suggest taking a look at your squish as the head shows some very light signs of detonation on the edges of the squish band.

Paw Paw

I kind of thought that too. In June I sent the head to Eric Gorr (the more I've read the more I've heard that was a mistake) to have the squish tightened up for a blend of pump/race gas 50/50. I got the head back with zero info on it. I figured he would have at least said what he did and explained things. I've been running pump93 & VP C12 mixed at 32:1 with Klotz. Don't see how it would be detonation.Photo

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2011 Yamaha YZ 250 -MX
1996 Yamaha Banshee 350 -Trails
1982 Chevy S10
2005 Pontiac GTO -451rwhp

10/10/2017 7:47 AM

FYI: Most Yamaha 250cc two strokes come with a squish setup that is right on the ragged edge of self distruction right from the factory. That is why you see a lost of the owners going to a higher octane fuel to help with slowing down or stopping this. The problem is the squish set up.
If the squish is set too tight you will be reducing the fuel mix from the edge of the piston where it is needed for cooling. The result is that the piston top and the head start to erode and pit which then makes the problem get worst and finally the piston either fails or get so hot that it deforms and caused the ring to get stuck in the piston causing a loss of compression.
If the squish is set too loose than you get an incomplete fuel burn and a loss of power.
So be sure to have it checked and rest after the cylinder is reworked as some cylinder reworking involves the cutting of the top of the cylinder to make sure it is true. The result can cause the squish to be reduced.

Paw Paw

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10/10/2017 1:44 PM

Paw Paw wrote:

FYI: Most Yamaha 250cc two strokes come with a squish setup that is right on the ragged edge of self distruction right from the factory. That is why you see a lost of the owners going to a higher octane fuel to help with slowing down or stopping this. The problem is the squish set up.
If the squish is set too tight you will be reducing the fuel mix from the edge of the piston where it is needed for cooling. The result is that the piston top and the head start to erode and pit which then makes the problem get worst and finally the piston either fails or get so hot that it deforms and caused the ring to get stuck in the piston causing a loss of compression.
If the squish is set too loose than you get an incomplete fuel burn and a loss of power.
So be sure to have it checked and rest after the cylinder is reworked as some cylinder reworking involves the cutting of the top of the cylinder to make sure it is true. The result can cause the squish to be reduced.

Paw Paw

I've heard the factory squish is bad. So this isn't just a simple hone the cylinder and go deal?

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2011 Yamaha YZ 250 -MX
1996 Yamaha Banshee 350 -Trails
1982 Chevy S10
2005 Pontiac GTO -451rwhp

10/10/2017 7:30 PM

No I don't think so.

Paw Paw

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10/10/2017 8:07 PM

Eric's head design is crap and doesn't work any better than stock. He doesn't touch the factory squish band. He just cuts the head surface to tighten up the squish then cuts the bowl out to get the compression back to around stock.

I would just replate it. Only costs around $200 from millennium...

Have you checked the timing?

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10/11/2017 6:41 AM

Paw Paw wrote:

No I don't think so.

Paw Paw

Gotcha. I don't know much about the plating so that's my confusion

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2011 Yamaha YZ 250 -MX
1996 Yamaha Banshee 350 -Trails
1982 Chevy S10
2005 Pontiac GTO -451rwhp

10/11/2017 6:42 AM

Jterry wrote:

Eric's head design is crap and doesn't work any better than stock. He doesn't touch the factory squish band. He just cuts the head surface to tighten up the squish then cuts the bowl out to get the compression back to around stock.

I would just replate it. Only costs around $200 from millennium...

Have you checked the timing?

Yeah the head didn't honestly look much different from stock when I got it back from him. I'll have to send it to Millenium and let them work there magic. Can they fix the head also?

Here's how it looked when I got it back Photo

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2011 Yamaha YZ 250 -MX
1996 Yamaha Banshee 350 -Trails
1982 Chevy S10
2005 Pontiac GTO -451rwhp

10/11/2017 12:37 PM

Yes they can fix it as well when they have the cylinder.

The reason the piston broke is because it was ran to long and the cast stock pistons always bust the skirt off them when ran to many hours. Put a wiseco back in it and have piece of mind that wont happen again unless something catastrophic happens.

When you get it all back together you need to check the ignition timing.

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10/11/2017 1:21 PM

Be sure to recheck the squish which ever way you go, OEM or aftermarket piston and or cylinder.

Paw Paw

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10/11/2017 1:58 PM

Jterry wrote:

Yes they can fix it as well when they have the cylinder.

The reason the piston broke is because it was ran to long and the cast stock pistons always bust the skirt off them when ran to many hours. Put a wiseco back in it and have piece of mind that wont happen again unless something catastrophic happens.

When you get it all back together you need to check the ignition timing.

Agreed a forged Wiseco is the only piston I'll run. First time this bike has been torn into. I'd assume timing should be fine from the factory. I've never messed with it. What should I look for?

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2011 Yamaha YZ 250 -MX
1996 Yamaha Banshee 350 -Trails
1982 Chevy S10
2005 Pontiac GTO -451rwhp

10/11/2017 3:39 PM

eric513anderson,

I would send the cylinder to Millennium or Power Seal USA and have it replated.

Here is a head I did for a customer and I do this as a hobby, not my full time job. I would have at least polished the combustion chamber as this has shown on my flow bench to be an improvement in gas flow.

I tried some different velocity flow on this head during my machining, this is on a KX112 and showed some improvement on the dyno, but the rider likes it better on the track and shows better burn pattern.

Photo

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10/11/2017 3:48 PM

btroxler wrote:

eric513anderson,

I would send the cylinder to Millennium or Power Seal USA and have it replated.

Here is a head I did for a customer and I do this as a hobby, not my full time job. I would have at least polished the combustion chamber as this has shown on my flow bench to be an improvement in gas flow.

I tried some different velocity flow on this head during my machining, this is on a KX112 and showed some improvement on the dyno, but the rider likes it better on the track and shows better burn pattern.

Photo

Very nice. I'll compare prices from the two and go from there. That head looks great by the way!

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2011 Yamaha YZ 250 -MX
1996 Yamaha Banshee 350 -Trails
1982 Chevy S10
2005 Pontiac GTO -451rwhp

10/11/2017 7:11 PM

Jterry wrote:

Yes they can fix it as well when they have the cylinder.

The reason the piston broke is because it was ran to long and the cast stock pistons always bust the skirt off them when ran to many hours. Put a wiseco back in it and have piece of mind that wont happen again unless something catastrophic happens.

When you get it all back together you need to check the ignition timing.

eric513anderson wrote:

Agreed a forged Wiseco is the only piston I'll run. First time this bike has been torn into. I'd assume timing should be fine from the factory. I've never messed with it. What should I look for?

The ignition timing is usually advanced from the factory for some reason. And along with an improper squish clearance the advanced timing will make them ping on pump gas.

If you can afford to run 50/50 race /pump gas, get the head cut for race fuel run good gas and you can leave the timing advanced and it will run perfect.

Also if your looking for something else that makes a huge difference in top end power and over rev. Look up HP Race Development STIC for your carb. It might seem like a gimmick but it truly works. I was given one to test when they first came out and couldn't believe the difference it made on my yz295.

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10/12/2017 5:13 AM

Jterry wrote:

Yes they can fix it as well when they have the cylinder.

The reason the piston broke is because it was ran to long and the cast stock pistons always bust the skirt off them when ran to many hours. Put a wiseco back in it and have piece of mind that wont happen again unless something catastrophic happens.

When you get it all back together you need to check the ignition timing.

eric513anderson wrote:

Agreed a forged Wiseco is the only piston I'll run. First time this bike has been torn into. I'd assume timing should be fine from the factory. I've never messed with it. What should I look for?

Jterry wrote:

The ignition timing is usually advanced from the factory for some reason. And along with an improper squish clearance the advanced timing will make them ping on pump gas.

If you can afford to run 50/50 race /pump gas, get the head cut for race fuel run good gas and you can leave the timing advanced and it will run perfect.

Also if your looking for something else that makes a huge difference in top end power and over rev. Look up HP Race Development STIC for your carb. It might seem like a gimmick but it truly works. I was given one to test when they first came out and couldn't believe the difference it made on my yz295.

I have a little shop about 15 minutes from the house that carries VP and I get a good price on it so I've been running it for a few months now. I do a 50/50 of either VP 110 or VP C12 with 93 pump from Shell. Advanced timing and higher octane fuel made a big difference on my Banshee so I will double check the timing on the YZ. The carb thing looks interesting I'll have to look into it further. So far Powerseal USA is cheaper then Millenium and I don't think I can go wrong with either company. Plus Powerseal is in Pennsyvania and I'm in Ohio

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2011 Yamaha YZ 250 -MX
1996 Yamaha Banshee 350 -Trails
1982 Chevy S10
2005 Pontiac GTO -451rwhp

10/12/2017 6:11 AM

I can attest to the race gas in a yz especially if youre modding the squish. The one i had ran like shit on pump gas. Went with cam2 110 and it woke it up. Yamaha specifies a minimum of 95 oct anyways. And another vote for a forged piston whether its wiseco, cp, or je. Anything cast shouldnt even be considered, even oem. The yz i had blew up from the oem piston skirt shattering too.

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2009 Kawasaki KX450F
2009 Kawasaki KX250F
2002 Suzuki GSXR 600

10/12/2017 7:35 AM

eric513anderson wrote:

Agreed a forged Wiseco is the only piston I'll run. First time this bike has been torn into. I'd assume timing should be fine from the factory. I've never messed with it. What should I look for?

Jterry wrote:

The ignition timing is usually advanced from the factory for some reason. And along with an improper squish clearance the advanced timing will make them ping on pump gas.

If you can afford to run 50/50 race /pump gas, get the head cut for race fuel run good gas and you can leave the timing advanced and it will run perfect.

Also if your looking for something else that makes a huge difference in top end power and over rev. Look up HP Race Development STIC for your carb. It might seem like a gimmick but it truly works. I was given one to test when they first came out and couldn't believe the difference it made on my yz295.

eric513anderson wrote:

I have a little shop about 15 minutes from the house that carries VP and I get a good price on it so I've been running it for a few months now. I do a 50/50 of either VP 110 or VP C12 with 93 pump from Shell. Advanced timing and higher octane fuel made a big difference on my Banshee so I will double check the timing on the YZ. The carb thing looks interesting I'll have to look into it further. So far Powerseal USA is cheaper then Millenium and I don't think I can go wrong with either company. Plus Powerseal is in Pennsyvania and I'm in Ohio

eric513anderson,

I normally use Millenium for re-plating but decided I would give PowerSeal a try this last time. I used them to plate a KX112 cylinder and they did a great job.

Like you said I don't think you will go wrong with either, the re-plating by both companies is far superior of the OEM plating.

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10/12/2017 9:44 AM

Jterry wrote:

The ignition timing is usually advanced from the factory for some reason. And along with an improper squish clearance the advanced timing will make them ping on pump gas.

If you can afford to run 50/50 race /pump gas, get the head cut for race fuel run good gas and you can leave the timing advanced and it will run perfect.

Also if your looking for something else that makes a huge difference in top end power and over rev. Look up HP Race Development STIC for your carb. It might seem like a gimmick but it truly works. I was given one to test when they first came out and couldn't believe the difference it made on my yz295.

eric513anderson wrote:

I have a little shop about 15 minutes from the house that carries VP and I get a good price on it so I've been running it for a few months now. I do a 50/50 of either VP 110 or VP C12 with 93 pump from Shell. Advanced timing and higher octane fuel made a big difference on my Banshee so I will double check the timing on the YZ. The carb thing looks interesting I'll have to look into it further. So far Powerseal USA is cheaper then Millenium and I don't think I can go wrong with either company. Plus Powerseal is in Pennsyvania and I'm in Ohio

btroxler wrote:

eric513anderson,

I normally use Millenium for re-plating but decided I would give PowerSeal a try this last time. I used them to plate a KX112 cylinder and they did a great job.

Like you said I don't think you will go wrong with either, the re-plating by both companies is far superior of the OEM plating.

Good deal. I'll be having them fix the head, replate the cylinder & set me up with a racers choice wiseco. Once I'm home from work I'll have to post a picture of my reeds. I think there ok to use. Just the tip of the block has a bit of a rough edge on it

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2011 Yamaha YZ 250 -MX
1996 Yamaha Banshee 350 -Trails
1982 Chevy S10
2005 Pontiac GTO -451rwhp

10/13/2017 2:07 PM

Jterry wrote:

Yes they can fix it as well when they have the cylinder.

The reason the piston broke is because it was ran to long and the cast stock pistons always bust the skirt off them when ran to many hours. Put a wiseco back in it and have piece of mind that wont happen again unless something catastrophic happens.

When you get it all back together you need to check the ignition timing.

eric513anderson wrote:

Agreed a forged Wiseco is the only piston I'll run. First time this bike has been torn into. I'd assume timing should be fine from the factory. I've never messed with it. What should I look for?

Jterry wrote:

The ignition timing is usually advanced from the factory for some reason. And along with an improper squish clearance the advanced timing will make them ping on pump gas.

If you can afford to run 50/50 race /pump gas, get the head cut for race fuel run good gas and you can leave the timing advanced and it will run perfect.

Also if your looking for something else that makes a huge difference in top end power and over rev. Look up HP Race Development STIC for your carb. It might seem like a gimmick but it truly works. I was given one to test when they first came out and couldn't believe the difference it made on my yz295.

Piston ran too long, stock timing was advanced and head/squish wasn't set for the load and fuel you were using.
The advanced timing cost me an OEM cylinder and top-end back in 2005. Aaaargh! The power was also too abrupt for a lot of the riding a did back then. I nearly had the same issue in 2012 on my 2006 YZ250. Fuel, timing, jetting and head are all essential things to figure out on the YZ250.

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