FX-1 Piston blown what is the usual cause?

chadetroit

chadetroit

Get Wet
Location
Bay Area, CA
a6cd8a67-421b-e7e4.jpg


I have about 45 minutes on this engine. I was trying to get the carbs dialed in on the low end and after a few runs I lost one of the cylinders. Nothing was overheated. No sizzling pipe, no smoking head, pissers running clean. Plugs were not scorched. Was running full 110 octane with 38:1 mixture.

Ski is 62t top and bottom
Komander Head
Domes are suppose to be pump gas but I gotta find out the cc's
lightened stock flywheel
Epic ignition
Dual mikuni 46's
Factory Mod Pipe
Bored to 760 wich I think is 84mm pistons
Epoxied and Freestyle ported
VFIII reeds
Riva intake
144 sj pump
10-16 hooker


Before I fix this I gotta make sure history does not repeat it self. The one thing I did not check was compression (I don't own a gauge, but I think one is in my future) Any opinions?
 
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Billybo455

Billybo455

Location
Central FL
usually blown ringlands are from detonation. one thing you may want to check is the squish. your setup doesn't seem like it needs 110. but if the squish is to tight it will detonate no matter what. don't forget when you go to a bigger bore you also gain compression because you're compressing more air into the same chamber on the head.
 
Freakrider

Freakrider

X247
Location
Tampa Bay area
You have 84.25 mm pistons there and lost piston on the intake side the cooler side and front cyl which runs aprox 20 degrees cooler ...hmmm.
 
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Waternut

Waternut

Customizing addict
Location
Macon, GA
Looks like the exhaust side to me. Were the ports chamfered properly? If not, the ring could've snagged the sharp edge of the port.
 
E

egbrig

The ring end gap which was located in the exhaust allowed the gas to travel down and through the ring gaps and heat up the gaped ends which then in turn got hotter until they became little glow plugs and began the detonation cycle. The ring ends don't look as if they got snaged otherwise they would be bent and their not. Its amazing how much gas pressure develops in the cylinder.
 
W

Watcon

Location
Near Seattle WA
The rings snagged in the ports on the downstroke,and the energy from the rotating mass didnt allow the piston to stop. When the piston couldnt stop, the ring acted as a lever and snapped off the top of the cast piston.
 
chadetroit

chadetroit

Get Wet
Location
Bay Area, CA
Love waking up to all the responses thanks guys.

I did check the squish which was about 50 or 60 thou from what I remember. It was a little above optimal. I remember asking the builder if he thought I should take some off the bottom of the jug.

Just went and checked and....

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You guys were spot on. The clean piston is pointing towards the exhaust side the blown up one is pointing toward the intake side.

So I guess the good news is I now know the cause and the fix. Unfortunately I gotta tear everything down to clean up the piston shards. I'm hoping I can get away with just honing the jug.

Thanks again for the help, the X once again proves itself invaluable.
 
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chadetroit

chadetroit

Get Wet
Location
Bay Area, CA
You know I'd be more frustrated if I built the engine but I bought one already built to save myself the hassle. That being what it is I never took the head off since I bought it and even if I would have I don't know enough where I would have noticed the arrows pointing in opposite directions.

Not sure how long the repair will put me out for, that is the frustrating part. 45 minutes of riding is just a cruel tease
 
Waternut

Waternut

Customizing addict
Location
Macon, GA
chadetroit said:
I'm going to keep that between myself and where I purchased it from as I have not had a chance to talk with him on it yet.
Click to expand...

If it was a company putting your engine together then they owe you a new top end because that's gross negligence to put a piston in backwards. If it was a friend just helping out, maybe they will help you out again but that'd be a tough one to deal with.
 
swapmeet

swapmeet

Brotastic
Location
Arlington TX
That sucks man. I've had nothing but trouble out of my build but at least the mid-top power band works so I have gotten some ride time in.

Hope you get it fixed quickly. GL!
 
chadetroit

chadetroit

Get Wet
Location
Bay Area, CA
Yeah this thing has been fighting me the whole way between bad electronics, the wrong pipe chamber, and now a backwards piston I can't seem to catch a break. I'm hoping this is the last of it since bad things happen in 3's this should do it.

Just have to unhook the starter cable and the engine will be free again. I get why a ready to run freestyle ski is so expensive now.
 
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