Grenaded GasGas 2 Stroke

edot504_
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11/28/2023 6:54pm
lumpy790 wrote:

How many base gaskets are you running to get the proper squish clearance when you replaced the top end? Clearance Looks pretty tight

We just did the 1, that’s how the bike came from the dealer so that’s how we did it

edot504_
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11/28/2023 6:54pm
crmx105 wrote:

Piston intake skirt may have hit crank? Was new piston OEM Vertex?

burn1986 wrote:
If the wrist pin bearing and stuff was in the exhaust, it might’ve been the circlip that came off, but the piston and head should’ve been...

If the wrist pin bearing and stuff was in the exhaust, it might’ve been the circlip that came off, but the piston and head should’ve been scratched up. The head shouldn’t have broke under any circumstance. I’ve locked up soooo many two strokes and have never seen a head do that. When you rebuild, I would suggest an aftermarket head like vhm.

We’re definitely going to do that

1
edot504_
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11/28/2023 6:55pm

That’s insane. I’m assuming from the fact that you are posting that you are relatively uninjured? Glad you’re ok. 

Yeah I didn’t crash haha happened close enough to the ground that I was alright 

2
FGR01
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11/28/2023 6:58pm
edot504_ wrote:

Yeah we’re just going to find a way to buy a crate engine, if we can find somewhere to buy it from haha

langhammx wrote:
These are brand new bikes, taken apart and sold as parts, I’ll try and find a link to his eBay page, but he posts on here...

These are brand new bikes, taken apart and sold as parts, I’ll try and find a link to his eBay page, but he posts on here as well. 
 

Mav ~ help me out here… he’s posted on the for sale section several times. 

4

The Shop

langhammx
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11/28/2023 7:13pm

That’s him. 
 

A buddy of mine does the part out business, but he didn’t have a 2-stroke 250/300 motor on his site. 
for anyone else needing new/like new take-off parts, this is his eBay page as well. Great guy to deal with, he’s in Burbank, Ca. Alex
https://www.ebay.com/str/socalmotorecycling 

 

9
crmx105
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11/28/2023 7:15pm Edited Date/Time 11/28/2023 7:35pm
crmx105 wrote:
If there is any intake skirt left measure the thickness of it versus the original piston. Vertex had a quality control issue with some pistons. It...

If there is any intake skirt left measure the thickness of it versus the original piston. Vertex had a quality control issue with some pistons. It was talked about in the 300SX thread. The inside of the skirt can hit the crank. Maybe the 250 as well?

FGR01 wrote:
This is a carb bike, not a TBI bike.   There is no known issue with piston to crank contact on the carb bikes.  Also when the...

This is a carb bike, not a TBI bike.   There is no known issue with piston to crank contact on the carb bikes.  Also when the piston does contact the crank it does not usually present in this manner (head blown off).    My initial guess is this is more likely a rod failure.

Same piston and rod for carb, TPI and TBI so if the new piston had a skirt out of spec it could most def hit the crank. Counter balanced motors all pretty similar. There was pics of a TBI bike where the skirt hit the crank and the rod broke on the small end, split the part where the wrist pin goes through almost in half. There is a big cut out on the rod  for lubrication of the wrist pin bearing which would make it a weak spot.

3
-MAVERICK-
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11/28/2023 7:32pm Edited Date/Time 11/28/2023 7:35pm
edot504_ wrote:

Yeah we’re just going to find a way to buy a crate engine, if we can find somewhere to buy it from haha

langhammx wrote:
These are brand new bikes, taken apart and sold as parts, I’ll try and find a link to his eBay page, but he posts on here...

These are brand new bikes, taken apart and sold as parts, I’ll try and find a link to his eBay page, but he posts on here as well. 
 

Mav ~ help me out here… he’s posted on the for sale section several times. 

I don't know if he has the parts for OP's bike but here's the guy:

https://www.vitalmx.com/community/cmill987,61692/all#all

Edit: Checked his posts and it does not appear that he has 250 2 stroke parts. 

2
Joko
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11/28/2023 7:44pm

Can consider buying the BRC 500 kit $6300 (www.BRCracing.ca in Canada), I believe you just need the donor transmission, kit includes cases, cylinder, etc.

Also Tom Morgan Racing does a good job weld repairing damaged cases, maybe a cheaper option than new, if not too wasted…

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2
Warlock
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11/28/2023 7:53pm

That is some ugly looking metal for such a new bike. Almost looks like it's crystallized. 

8
1
11/28/2023 8:11pm

           I am anything but a motorbike tech, but there may have been some porosity in those castings.  Otherwise, glad to hear that you are OK .  Good Luck with the rebuild.

4
NSP139
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11/28/2023 8:19pm

You said 100 hours on the frame does that mean bottom end also with pump gas?

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edot504_
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11/28/2023 8:29pm
NSP139 wrote:

You said 100 hours on the frame does that mean bottom end also with pump gas?

Yes

1
edot504_
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11/28/2023 8:30pm
Gary Duck wrote:

Ready to race?

GasGas is actually #getonthegas but I guess I got on it too hard

12
11/28/2023 8:34pm
Warlock wrote:

That is some ugly looking metal for such a new bike. Almost looks like it's crystallized. 

Heads are cast, looks like a typical cast fracture.

7
Chance1216
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11/28/2023 8:36pm
FGR01 wrote:
langhammx wrote:
That’s him.    A buddy of mine does the part out business, but he didn’t have a 2-stroke 250/300 motor on his site.  for anyone else...

That’s him. 
 

A buddy of mine does the part out business, but he didn’t have a 2-stroke 250/300 motor on his site. 
for anyone else needing new/like new take-off parts, this is his eBay page as well. Great guy to deal with, he’s in Burbank, Ca. Alex
https://www.ebay.com/str/socalmotorecycling 

 

Just scrolled through your guys site. It’s nice not scrolling through a bunch of old garbage. 

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NSP139
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11/28/2023 8:46pm
NSP139 wrote:

You said 100 hours on the frame does that mean bottom end also with pump gas?

edot504_ wrote:

Yes

These bikes love leaded fuel I would never go past 50 hours on the bottom end with Japanese two Strokes new to the KTMs not sure about the Austrian quality yet🤷‍♂️

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Vet57
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11/29/2023 2:23am

Hydraulic lock? 

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CPR
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11/29/2023 3:49am

Only 2t I’ve seen break everything- both cases, barrel and head, was a rod failure in a YZ125. But I have seen a few KTM’s crack/ break cylinder heads due to big end failures. Their outer casting around the insert is very thin.

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FGR01
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11/29/2023 4:36am
crmx105 wrote:
If there is any intake skirt left measure the thickness of it versus the original piston. Vertex had a quality control issue with some pistons. It...

If there is any intake skirt left measure the thickness of it versus the original piston. Vertex had a quality control issue with some pistons. It was talked about in the 300SX thread. The inside of the skirt can hit the crank. Maybe the 250 as well?

FGR01 wrote:
This is a carb bike, not a TBI bike.   There is no known issue with piston to crank contact on the carb bikes.  Also when the...

This is a carb bike, not a TBI bike.   There is no known issue with piston to crank contact on the carb bikes.  Also when the piston does contact the crank it does not usually present in this manner (head blown off).    My initial guess is this is more likely a rod failure.

crmx105 wrote:
Same piston and rod for carb, TPI and TBI so if the new piston had a skirt out of spec it could most def hit the...

Same piston and rod for carb, TPI and TBI so if the new piston had a skirt out of spec it could most def hit the crank. Counter balanced motors all pretty similar. There was pics of a TBI bike where the skirt hit the crank and the rod broke on the small end, split the part where the wrist pin goes through almost in half. There is a big cut out on the rod  for lubrication of the wrist pin bearing which would make it a weak spot.

Yes, I am aware of the common parts.   However, the carb and TPI bikes went a solid 6-7 years on those parts with no common issue of skirt to crank contact.  I've never heard one report of it.  That issue did not begin until the TBI bikes came out.  So, that makes us ask, what changed?  Well, it's an all new cylinder to start with.  Maybe something going on there.  Also, the TBI bikes have a rev limiter.  Maybe cutting the ignition or fuel on a two stroke at max rpm makes some weird things happen with piston vibrations or fluctuations?  

1
mikelawlor
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11/29/2023 5:14am

I’m in the proses of doing the top end in my 23 300sx and when I checked the deck height it was 0. And that’s what the manual says. I haven’t checked the squish yet as it’s still apart but I will let you know what it is. As far as the parts. My dealer gave me a top end kit for a 2017 300xc. I was super skeptical at first but after some research pretty much any 250/300 crank and piston is the same since about 06 on. Even the gaskets are the same. The only difference in my cylinder compared to an old one is on the left side cover there is just a hole with a o ring in it to accept the servo motor. The rest of the covers are the same. I have heard the piston clearance issues but even both physical pistons have the same part number stamped in to them and physically look identical. I even checked the skirts with a caliper and they measure identical. If he has 100 hrs on a bottom end that’s not uncommon but failures can happen. If you blew the lower or upper rod bearing your gonna smash the piston in to the head and that’s likely what happened. 

2
11/29/2023 5:18am
NSP139 wrote:

You said 100 hours on the frame does that mean bottom end also with pump gas?

Are these bikes really fragile enough that you can expect a failure this severe if you put 100 hours on an engine?  I have no idea how fast the OP is, but if he’s racing a Gas Gas 2 stroke, he ain’t qualifying for Supercross.  In my 30+ years of racing, I’ve never rebuilt a crank before 100 hours no matter what brand of bike.  I just put the first piston in my KX450 at 90 hours, and I mostly did it out of cold weather boredom.  

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sandman768
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11/29/2023 6:03am
lumpy790 wrote:

How many base gaskets are you running to get the proper squish clearance when you replaced the top end? Clearance Looks pretty tight

edot504_ wrote:

We just did the 1, that’s how the bike came from the dealer so that’s how we did it

I have done only 5-6 250/300 top ends, all were 2 stacked base gaskets to get required  X dimension . Did you measure X ? Or maybe coolant leak into combustion chamber? Could be upper/ lower rod bearing or rod itself but 100 hrs on oem crank is usually not an issue unless a Pro is riding it. 

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NSP139
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11/29/2023 6:11am
NSP139 wrote:

You said 100 hours on the frame does that mean bottom end also with pump gas?

Are these bikes really fragile enough that you can expect a failure this severe if you put 100 hours on an engine?  I have no idea...

Are these bikes really fragile enough that you can expect a failure this severe if you put 100 hours on an engine?  I have no idea how fast the OP is, but if he’s racing a Gas Gas 2 stroke, he ain’t qualifying for Supercross.  In my 30+ years of racing, I’ve never rebuilt a crank before 100 hours no matter what brand of bike.  I just put the first piston in my KX450 at 90 hours, and I mostly did it out of cold weather boredom.  

I've always thought it was a good idea to rebuild the cranks before they fail not after to prevent this kind costly repair and also what possible injury could be caused from the bike locking up! They're all kinds of factors involved the riders speed his weight the terrain he rides in the weather how well is maintenance is! I might be a little excessive but I like the Peace of Mind that it brings LOL

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crmx105
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11/29/2023 6:27am
FGR01 wrote:
This is a carb bike, not a TBI bike.   There is no known issue with piston to crank contact on the carb bikes.  Also when the...

This is a carb bike, not a TBI bike.   There is no known issue with piston to crank contact on the carb bikes.  Also when the piston does contact the crank it does not usually present in this manner (head blown off).    My initial guess is this is more likely a rod failure.

crmx105 wrote:
Same piston and rod for carb, TPI and TBI so if the new piston had a skirt out of spec it could most def hit the...

Same piston and rod for carb, TPI and TBI so if the new piston had a skirt out of spec it could most def hit the crank. Counter balanced motors all pretty similar. There was pics of a TBI bike where the skirt hit the crank and the rod broke on the small end, split the part where the wrist pin goes through almost in half. There is a big cut out on the rod  for lubrication of the wrist pin bearing which would make it a weak spot.

FGR01 wrote:
Yes, I am aware of the common parts.   However, the carb and TPI bikes went a solid 6-7 years on those parts with no common issue...

Yes, I am aware of the common parts.   However, the carb and TPI bikes went a solid 6-7 years on those parts with no common issue of skirt to crank contact.  I've never heard one report of it.  That issue did not begin until the TBI bikes came out.  So, that makes us ask, what changed?  Well, it's an all new cylinder to start with.  Maybe something going on there.  Also, the TBI bikes have a rev limiter.  Maybe cutting the ignition or fuel on a two stroke at max rpm makes some weird things happen with piston vibrations or fluctuations?  

Yes but when and for how long were pistons produced out of spec? Not trying to be stubborn but if it was my bike would def want to know why it came apart? 

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wrc777
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11/29/2023 6:28am
crmx105 wrote:

Piston intake skirt may have hit crank? Was new piston OEM Vertex?

Any thoughts on how any bike could run for more than a minute with skirt to crank contact let alone 20+ hours?

2
crmx105
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11/29/2023 7:12am Edited Date/Time 11/29/2023 7:25am
crmx105 wrote:

Piston intake skirt may have hit crank? Was new piston OEM Vertex?

wrc777 wrote:

Any thoughts on how any bike could run for more than a minute with skirt to crank contact let alone 20+ hours?

Doesn't happen immediately. Typically happens when the bike is pushed hard. Its due to the inner intake skirt of the piston being to thick. Google it or search the 300 SX thread, its on there. I am not that skilled on the computer to find it and attach it to my post. Lol

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NLMB150
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11/29/2023 8:09am Edited Date/Time 11/29/2023 8:11am

I’ve seen this happen to 4 bikes I know off.   2 of them were under 20 hours…

and was told by a shop owner the new efi bikes do the same thing.       It’s not you.  Just a reoccurring issue.       

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MxAddic
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11/29/2023 8:25am Edited Date/Time 11/29/2023 8:33am
wrc777 wrote:

Any thoughts on how any bike could run for more than a minute with skirt to crank contact let alone 20+ hours?

Can't tell you how but they will. Sometimes forever. 2 Strokes are awesome.

Going to need to see the rest of the carnage to determine exact cause here. I can see a couple scenarios.

2

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