2 stroke tear down/rebuild

eric513anderson
Edited Date/Time 12/11/2017 7:09pm
Hey guys I’ve got a few questions about my rear down/rebuild. This is my first time tearing down a dirtbike engine. I’m pretty experienced and have built several Yamaha Banshee engines in the past with success. So I’ve been wondering...do I need to invest in a case splitting tool? Also do I need a crank installation tool as well? The Banshee cases come apart really easily. Just a few small taps here and there with a dead blow mallet and ta-da. Now obviously the YZ is a different engine. Next question is piston. I’ve always ran forged Wiseco Pro-lite pistons and that’s my intention for my YZ so I’ve been curious on either a Pro-lite or the new single ring Racer Elite piston? Just wondering what you’ve guys have experienced with these. I’ll be sending the cylinder & head off to Powerseal USA after Christmas to have the cylinder replated and the head fixed after I let Eric Gorr work on it. The head needs to be corrected for race/pump gas mix.



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Acidreamer
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Acidreamer 12/3/2017 8:28am
12/3/2017 8:28am
Yes on both tools. The yz wont come apart without them. Unless you want to fuck up your cases.

The piston in your pic is what i used on my yz250 and never had an issue. Solid piston.
Kawasaki-rider 12/3/2017 8:29am
12/3/2017 8:29am
After my first rebuild with case splitter and crank install tool, I will never do it without them.
rmoto003
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rmoto003 12/3/2017 8:35am
12/3/2017 8:35am
definitely buy them... a set of Tusk ones will work just fine and arent too expensive.
eric513anderson 12/3/2017 8:42am
12/3/2017 8:42am
Thanks guys that’s what I like to hear. Also anybody running the 8oz GYTR flywheel? I’ve thought about getting one of those also. I ride mx 95% of the time and I’m only 165lbs if that helps any

The Shop

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omalley
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omalley 12/3/2017 11:33am
12/3/2017 11:33am
rmoto003 wrote:
definitely buy them... a set of Tusk ones will work just fine and arent too expensive.
This. I bought the Tusk tools a couple years ago. I’ve done three motors so far and the tools are worth their weight in gold. Good for a few other shop uses I’ve found too.
Rockinar
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Rockinar 12/3/2017 1:48pm
12/3/2017 1:48pm
Yes get the splitter and crank puller.
kzizok
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kzizok 12/3/2017 3:01pm
12/3/2017 3:01pm
While you have it apart, check your kickstart shaft for cracks.
eric513anderson 12/3/2017 3:53pm
12/3/2017 3:53pm
kzizok wrote:
While you have it apart, check your kickstart shaft for cracks.
Will do. By the way... I can have Powerseal USA do my head mod for $75 which is pretty a common price from what I’ve seen. Anybody else have a preference or experience with another company for the YZ head mod?
FGR01
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FGR01 12/3/2017 4:54pm
12/3/2017 4:54pm
Looks like you need to replace the powervalve shaft seal.
eric513anderson 12/3/2017 5:30pm
12/3/2017 5:30pm
FGR01 wrote:
Looks like you need to replace the powervalve shaft seal.
I had it disconnected so I could take the cylinder nut off
FGR01
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FGR01 12/3/2017 6:11pm
12/3/2017 6:11pm
FGR01 wrote:
Looks like you need to replace the powervalve shaft seal.
eric513anderson wrote:
I had it disconnected so I could take the cylinder nut off
See the black spooge running down from the powervalve shaft ? That's not supposed to be there. There's a seal on the shaft that is supposed to keep that in the powervalve housing inside the cylinder.
Hcallz5
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Hcallz5 12/3/2017 7:38pm
12/3/2017 7:38pm
eric513anderson wrote:
Will do. By the way... I can have Powerseal USA do my head mod for $75 which is pretty a common price from what I’ve seen...
Will do. By the way... I can have Powerseal USA do my head mod for $75 which is pretty a common price from what I’ve seen. Anybody else have a preference or experience with another company for the YZ head mod?
I had mine done by RB Designs, he does great work.

Here is a before and after of mine: https://imgur.com/a/YvPx3
chump6784
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chump6784 12/4/2017 3:08am
12/4/2017 3:08am
eric513anderson wrote:
Thanks guys that’s what I like to hear. Also anybody running the 8oz GYTR flywheel? I’ve thought about getting one of those also. I ride mx...
Thanks guys that’s what I like to hear. Also anybody running the 8oz GYTR flywheel? I’ve thought about getting one of those also. I ride mx 95% of the time and I’m only 165lbs if that helps any
I just bought the steahly 9oz flywheel weight for mine, have not ridden it yet but will report back when I do. Planning on this saturday
eric513anderson 12/4/2017 3:32am
12/4/2017 3:32am
FGR01 wrote:
Looks like you need to replace the powervalve shaft seal.
eric513anderson wrote:
I had it disconnected so I could take the cylinder nut off
FGR01 wrote:
See the black spooge running down from the powervalve shaft ? That's not supposed to be there. There's a seal on the shaft that is supposed...
See the black spooge running down from the powervalve shaft ? That's not supposed to be there. There's a seal on the shaft that is supposed to keep that in the powervalve housing inside the cylinder.
Ahh gotcha. If I have Powerseal USA do the powervalve assembly/cleaning I can assume this will be taken care of? Might have to write that down for them to do
eric513anderson 12/4/2017 3:33am
12/4/2017 3:33am
eric513anderson wrote:
Thanks guys that’s what I like to hear. Also anybody running the 8oz GYTR flywheel? I’ve thought about getting one of those also. I ride mx...
Thanks guys that’s what I like to hear. Also anybody running the 8oz GYTR flywheel? I’ve thought about getting one of those also. I ride mx 95% of the time and I’m only 165lbs if that helps any
chump6784 wrote:
I just bought the steahly 9oz flywheel weight for mine, have not ridden it yet but will report back when I do. Planning on this saturday
Right on. I’ve heard nothing but great about the fww. My only concern is loosing the snappiness of the bike
chump6784
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chump6784 12/8/2017 11:33pm
12/8/2017 11:33pm Edited Date/Time 12/8/2017 11:39pm
eric513anderson wrote:
Thanks guys that’s what I like to hear. Also anybody running the 8oz GYTR flywheel? I’ve thought about getting one of those also. I ride mx...
Thanks guys that’s what I like to hear. Also anybody running the 8oz GYTR flywheel? I’ve thought about getting one of those also. I ride mx 95% of the time and I’m only 165lbs if that helps any
chump6784 wrote:
I just bought the steahly 9oz flywheel weight for mine, have not ridden it yet but will report back when I do. Planning on this saturday
eric513anderson wrote:
Right on. I’ve heard nothing but great about the fww. My only concern is loosing the snappiness of the bike
Rode the bike today with fww and tuned suspension and there was just a slight difference as it pulled onto the pipe. Instead of a snap it was more of a surge but in saying that the difference was slight. There was still plenty of snap to break the back end loose and I'm 20 lbs heavier than you

The bike was tracking really well on flat corners. People were commenting on how well it was hooking up. I'm not sure how much was the fww and the suspension but i felt the fastest today than i have since i got back into moto.

I actually want to try an 11oz fww but the consensus seems to be 9oz for moto. If you are thinking about getting one i would,
PTshox
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PTshox 12/9/2017 3:25pm
12/9/2017 3:25pm
Go to a 13 oz fly wheel... those YZ motors hit pretty hard... gear it down too... 48 tooth in the rear, 13 front.

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chump6784
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chump6784 12/9/2017 8:42pm
12/9/2017 8:42pm
PTshox wrote:
Go to a 13 oz fly wheel... those YZ motors hit pretty hard... gear it down too... 48 tooth in the rear, 13 front.
Gearing is pretty good for the tracks I ride on. The track I was riding on yesterday was really hard packed, kind of quarry based and I was able to hold 3rd gear pinned around flat corners that I usually had to look for a berm on. The tracks I ride on are fairly tight too, I don't want any taller gearing or I'd constantly be on the clutch
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sdhuskyrider 12/10/2017 7:40am
12/10/2017 7:40am
Going with a Wiseco pro lite piston and a flywheel weight is a bit counter productive. OEM in most cases is the best in terms of reliability and performance when it comes to pistons and cranks.
seth505
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seth505 12/11/2017 9:24am
12/11/2017 9:24am
rmoto003 wrote:
definitely buy them... a set of Tusk ones will work just fine and arent too expensive.
This is what I did years ago and the tools work great. I've split many a 2-stroke cases with those tusk tools!
BobPA
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BobPA 12/11/2017 10:35am
12/11/2017 10:35am
sdhuskyrider wrote:
Going with a Wiseco pro lite piston and a flywheel weight is a bit counter productive. OEM in most cases is the best in terms of...
Going with a Wiseco pro lite piston and a flywheel weight is a bit counter productive. OEM in most cases is the best in terms of reliability and performance when it comes to pistons and cranks.
I would take a forged piston over cast any day. Providing they are properly sized of course. OEM YZ 250 Pistons scatter from time to time...
seth505
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seth505 12/11/2017 10:41am
12/11/2017 10:41am
sdhuskyrider wrote:
Going with a Wiseco pro lite piston and a flywheel weight is a bit counter productive. OEM in most cases is the best in terms of...
Going with a Wiseco pro lite piston and a flywheel weight is a bit counter productive. OEM in most cases is the best in terms of reliability and performance when it comes to pistons and cranks.
BobPA wrote:
I would take a forged piston over cast any day. Providing they are properly sized of course. OEM YZ 250 Pistons scatter from time to time...
Ya, I always used Wiseco in my last YZ. My buddy who is pro level will shatter pistons in his YZ if he goes more than 10 hours.
Acidreamer
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Acidreamer 12/11/2017 11:11am
12/11/2017 11:11am
sdhuskyrider wrote:
Going with a Wiseco pro lite piston and a flywheel weight is a bit counter productive. OEM in most cases is the best in terms of...
Going with a Wiseco pro lite piston and a flywheel weight is a bit counter productive. OEM in most cases is the best in terms of reliability and performance when it comes to pistons and cranks.
BobPA wrote:
I would take a forged piston over cast any day. Providing they are properly sized of course. OEM YZ 250 Pistons scatter from time to time...
seth505 wrote:
Ya, I always used Wiseco in my last YZ. My buddy who is pro level will shatter pistons in his YZ if he goes more than...
Ya, I always used Wiseco in my last YZ. My buddy who is pro level will shatter pistons in his YZ if he goes more than 10 hours.
Careful with that 10 hour piston comment.....
eric513anderson 12/11/2017 1:10pm
12/11/2017 1:10pm
sdhuskyrider wrote:
Going with a Wiseco pro lite piston and a flywheel weight is a bit counter productive. OEM in most cases is the best in terms of...
Going with a Wiseco pro lite piston and a flywheel weight is a bit counter productive. OEM in most cases is the best in terms of reliability and performance when it comes to pistons and cranks.
BobPA wrote:
I would take a forged piston over cast any day. Providing they are properly sized of course. OEM YZ 250 Pistons scatter from time to time...
I won’t use a cast piston in a 2 stroke again
sdhuskyrider
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sdhuskyrider 12/11/2017 1:18pm
12/11/2017 1:18pm
The only time I ever shattered a cast piston is when the clearance was too loose. Never had an issue other than that. Ran them in watercraft at world finals a few times. Never an issue. From an engineering standpoint, swapping pistons with a different center of mass, weight distribution and thermal expansion coefficient is iffy.
seth505
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seth505 12/11/2017 2:20pm
12/11/2017 2:20pm
BobPA wrote:
I would take a forged piston over cast any day. Providing they are properly sized of course. OEM YZ 250 Pistons scatter from time to time...
seth505 wrote:
Ya, I always used Wiseco in my last YZ. My buddy who is pro level will shatter pistons in his YZ if he goes more than...
Ya, I always used Wiseco in my last YZ. My buddy who is pro level will shatter pistons in his YZ if he goes more than 10 hours.
Acidreamer wrote:
Careful with that 10 hour piston comment.....
Haha, this is specific to yz250. Pros require their own special maintenance schedule anyway. Interesting enough, he sold that 250 and says his yz125 holds up better than that thing did.
chump6784
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chump6784 12/11/2017 3:26pm
12/11/2017 3:26pm
seth505 wrote:
Ya, I always used Wiseco in my last YZ. My buddy who is pro level will shatter pistons in his YZ if he goes more than...
Ya, I always used Wiseco in my last YZ. My buddy who is pro level will shatter pistons in his YZ if he goes more than 10 hours.
Acidreamer wrote:
Careful with that 10 hour piston comment.....
seth505 wrote:
Haha, this is specific to yz250. Pros require their own special maintenance schedule anyway. Interesting enough, he sold that 250 and says his yz125 holds up...
Haha, this is specific to yz250. Pros require their own special maintenance schedule anyway. Interesting enough, he sold that 250 and says his yz125 holds up better than that thing did.
My mechanic says the same thing, the YZ250's tend to break pistons and YZ125's are bulletproof. He told me I could go 30 hours safely on a cast piston but I'm far from pro speed.
yz763
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yz763 12/11/2017 7:09pm
12/11/2017 7:09pm
sdhuskyrider wrote:
Going with a Wiseco pro lite piston and a flywheel weight is a bit counter productive. OEM in most cases is the best in terms of...
Going with a Wiseco pro lite piston and a flywheel weight is a bit counter productive. OEM in most cases is the best in terms of reliability and performance when it comes to pistons and cranks.
BobPA wrote:
I would take a forged piston over cast any day. Providing they are properly sized of course. OEM YZ 250 Pistons scatter from time to time...
Yep. YZ250 cast pistons are notorious for shattering on the intake side. Thanks to my stock piston grenading I was able to justify a full on Tom Morgan 295, new crank and bearings. Never again will I run a stock cast piston longer than starting it new at the dealer.

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