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RDJeff
...here I go again...
Group: Members
Joined: Aug. 2003
Fairbanks, Alaska USA
Posts: 133 |
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Posted: July 26 2010,11:40 |
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What do the experts say?
I have about 250 miles on a complete rebuild on my 4DP, and was going to run the top end for one more race weekend, but all my years of racing 125s made me take a peek under the heads first. Good thing I did!
One piston/head has significant damage from what appears to be a foreign object. The squish area is all chewed up/eroded, the ring is stuck at about the 4 o'clock position, where there is a chunk of piston missing from the top down to the ring. From the 2 o'clock position all the around to the 10 o'clock position, the area above the ring is all shiny. The area of the head where it transitions from the squish band to the combustion area has a few deformed areas, which to me look like debris hammered them.
The engine was running fine when I pulled into the pits after the last final. The only problem I've had is a failed power jet solenoid, on this cylinder. I jetted up to compensate, and it appear to be a touch rich if anything, the plug and piston both showing a nice brown color.
I inspected what I could of the bottom end, and all seems fine, no debris in the bottom end, it doesn't appear to be missing any bearing needles or anything. The reeds are all intact. I put new pistons, etc. in both cylinders, buttoned it all up, and did a leak test, and it only dropped 2 psi in an hour, so I think it is tight enough to run.
My theory is that a rock came off the tire of somebody in front of me, and went through the intake and up into the combustion chamber. Once it got in there, it got smashed between the piston and the head, got crushed, then the piston debris and the rock bounced around and got crushed up smaller and smaller, then went out the exhaust.
I'm having trouble posting photos, so can't put any up to look at.
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anand
...quite the collection, eh?...
Group: Members
Joined: Nov. 2008
The Netherlands, Amsterdam
Posts: 528 |
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Posted: July 26 2010,12:39 |
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or maybe bad luck and a piece of piston broke off and caused the bebris damage.
hard to say....just good you found out in time.
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dand
...here I go again...
Group: Members
Joined: Dec. 2006
Falls Church, VA
Posts: 124 |
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Posted: July 26 2010,2:27 |
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I had some debris problems int eh past, checkout the pics in this post.
http://www.tz250racing.com/cgi-bin....1;t=453
It sounds like you damage was worse though, maybe a bigger pebble/rock.
I ended up putting screening for a screen door, around the intake area (TZ125, no airbox) and I haven't had the problem since.
Dan
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vince24x
...dorkus maximus...
Group: Group-W Bench
Joined: Dec. 2002
orange county, ca
Posts: 1307 |
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Posted: July 26 2010,2:47 |
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we need a pic: from the description it could be debris (from inside or outside) or detonation. ....but a pic will pretty easily tell you which one, generally.
if the reeds are all good, it's hard to imagine something really sizeable from outside to have gotten all the way up top w/o hitting something along the way.
vince
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WSMC, USGPRU, AFM Ex #224
http://www.mobiusracing.com
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RDJeff
...here I go again...
Group: Members
Joined: Aug. 2003
Fairbanks, Alaska USA
Posts: 133 |
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Posted: July 26 2010,4:40 |
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It wouldn't have to be real big to hammer the squish area. I wish I could post up a pic, can't figure out why, maybe some network protection.
I just took it over to a local two-stroke specialty shop, and they are saying detonation. I'm still not sure...
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Mike
Blame it on the Sun.
Group: Super Administrators
Joined: Aug. 2001
Maine, USA
Posts: 2089 |
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Posted: July 26 2010,7:07 |
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| Quote (RDJeff @ July 26 2010,4:40) | | It wouldn't have to be real big to hammer the squish area. I wish I could post up a pic, can't figure out why, maybe some network protection. |
u have to watch your file size when posting pics. You'll see the max allowed size when u post an attachment. too big = no post.
check it out.
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Mike Lachance
Administrator
tz250racing.com
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RDJeff
...here I go again...
Group: Members
Joined: Aug. 2003
Fairbanks, Alaska USA
Posts: 133 |
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Posted: July 26 2010,8:35 |
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Mike, can I e-mail a photo to you for posting? The problem isn't the file size...thanks,
Jeff
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Mike
Blame it on the Sun.
Group: Super Administrators
Joined: Aug. 2001
Maine, USA
Posts: 2089 |
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Posted: July 26 2010,9:57 |
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| Quote (RDJeff @ July 26 2010,8:35) | Mike, can I e-mail a photo to you for posting? The problem isn't the file size...thanks,
Jeff |
Shouldnt have any probs, others seem to be posting pics... but regardless, yes, please send. mike@...etc
I'll post here.
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Mike Lachance
Administrator
tz250racing.com
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Mike
Blame it on the Sun.
Group: Super Administrators
Joined: Aug. 2001
Maine, USA
Posts: 2089 |
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Posted: July 27 2010,11:32 |
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Here are Jeff's piston pics
Attached Image
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Mike Lachance
Administrator
tz250racing.com
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Mike
Blame it on the Sun.
Group: Super Administrators
Joined: Aug. 2001
Maine, USA
Posts: 2089 |
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Posted: July 27 2010,11:38 |
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...
Attached Image
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Mike Lachance
Administrator
tz250racing.com
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