shustack Posted June 12, 2013 Report Share Posted June 12, 2013 Well after melting my first as cast 421 cub, i put a weekend on this new top end as cast 421, somebody noticed a stud was broken on the stator side, along with i thought it wasnt running right well that was y. Well i tore it down to replace the stud and found this on the clutch side of the motor. Squish was .37-.38(which i know is tight) kicking psi 150. I was mixing some 112 with 93 Looks like something was flying around in there but everything else seems fine. The left side dome has some very very very small marks. From the pics i researched on here detonation is usually the whole piston and dome, but i cant find anything blown apart. Also since the cylinder was off i was kicking around a serval cylinder, the light switch power for hills if fun but a fuckin pain in the balls to work with. Is it better to port cub for more mid or port a serval for a lil more top end. Im looking for a in between. Also running straight pump Any input is appreciated Thanks Joe Quote Link to comment Share on other sites More sharing options...
Tedder Posted June 12, 2013 Report Share Posted June 12, 2013 Been there done that. I have a piston and head with those exact markings.... Was a small chip off the crank bearing that did it. The race cracked when our alky motor went lean. Better tear it down now or It'll cost you more later. Quote Link to comment Share on other sites More sharing options...
2strokeshees Posted June 12, 2013 Report Share Posted June 12, 2013 Something let loose and found its way up there, Id tear down and figure out what it was before you surprised mid hill climb. Did it hold 150psi both cylinders after the fact. I have had a ring break and work its way up there. Quote Link to comment Share on other sites More sharing options...
Finch Posted June 12, 2013 Report Share Posted June 12, 2013 weak. could be worse. Quote Link to comment Share on other sites More sharing options...
Finch Posted June 12, 2013 Report Share Posted June 12, 2013 if that plug pictured is the one you were running when it happened i wouldnt think lean/deto somethings in there. Quote Link to comment Share on other sites More sharing options...
J-Madd Posted June 12, 2013 Report Share Posted June 12, 2013 Crank bearing would be my guess. Or did the porcelain ever crack on the plug? Could also be the crank trying to separate and the wheels rubbing the case. Especial if you had a case stud loose. That is not deto. Not to say that deto wasn't involved. Quote Link to comment Share on other sites More sharing options...
n2otoofast4u Posted June 12, 2013 Report Share Posted June 12, 2013 The linear direction spots are not deto. Deto will speckle. Not to say that deto wasn't the root cause of some other failure but those marks are foreign material. I as well would agree with some issue in the crank area. Quote Link to comment Share on other sites More sharing options...
Finch Posted June 12, 2013 Report Share Posted June 12, 2013 Crank bearing would be my guess. Or did the porcelain ever crack on the plug? Could also be the crank trying to separate and the wheels rubbing the case. Especial if you had a case stud loose. That is not deto. Not to say that deto wasn't involved. thats what mine was crank seperated but then a ring snapped and all hell broke loose. Shus id split the cases for sure. Quote Link to comment Share on other sites More sharing options...
m671054 Posted June 12, 2013 Report Share Posted June 12, 2013 Any chance you fogot to clean your pipes after the first motor died? Quote Link to comment Share on other sites More sharing options...
shustack Posted June 12, 2013 Author Report Share Posted June 12, 2013 I didn't bother testing it when I seen the stud broke. The plugs looked good as you can see, I couldn't find any cracking of the sort. I was leaning towards something other than deto but knew that involved tearing down so was hoping for the easy way out. The last motor was melted due to overheated on a drunk in night. Not much carnage just the rings melted to the piston and smoked the nikasil, so I didn't both to clean the pipes out. Just dump upside down. I appreciate the info guys and will be back hopefully tomorrow with the root of the evil. After I tear the rest of it down. Thanks joe Quote Link to comment Share on other sites More sharing options...
JUSTWANNARACE Posted June 12, 2013 Report Share Posted June 12, 2013 How does the wrist pin bearing look? I would venture to say its a wrist pin bearing or lower rod bearing cause by the deto u see on the center of the piston.. jmo Quote Link to comment Share on other sites More sharing options...
J-Madd Posted June 12, 2013 Report Share Posted June 12, 2013 I've never seen a wrist pin bearing go bad. I did have one that fell apart upon disassembly though. Did you replace those in the rebuild? Builders are bad about not suggesting new ones with new pistons. And FFS new pistons don't come with them. I always replace them. I agree it could have been one Of the rollers out Of that. And on second look at the piston it looks like some deto there, but it's usually not in the center like that. Quote Link to comment Share on other sites More sharing options...
Zillaguy Posted June 12, 2013 Report Share Posted June 12, 2013 Those marks are not caused by deto... Deto will look like the you sand blasted a divet or a hole in the piston, it won't be clean dents like that... That looks like a chunk of bearing or ring was getting smashed between the head and piston... did the ring line up pin(s) fall out of the piston? If so those may have come loose due to deto.. I'd tear the motor down to inspect everything... I'd also loosen up that squish to at least .040 if not .045 Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted June 12, 2013 Report Share Posted June 12, 2013 Any chance you fogot to clean your pipes after the first motor died?People never mention this, but it is definitely the reason for my buddies blaster burned down twice. Quote Link to comment Share on other sites More sharing options...
BANSHEE HP Posted June 12, 2013 Report Share Posted June 12, 2013 Well after melting my first as cast 421 cub, i put a weekend on this new top end as cast 421, somebody noticed a stud was broken on the stator side, along with i thought it wasnt running right well that was y. Well i tore it down to replace the stud and found this on the clutch side of the motor. Squish was .37-.38(which i know is tight) kicking psi 150. I was mixing some 112 with 93 Looks like something was flying around in there but everything else seems fine. The left side dome has some very very very small marks. From the pics i researched on here detonation is usually the whole piston and dome, but i cant find anything blown apart. Also since the cylinder was off i was kicking around a serval cylinder, the light switch power for hills if fun but a fuckin pain in the balls to work with. Is it better to port cub for more mid or port a serval for a lil more top end. Im looking for a in between. Also running straight pump Any input is appreciated Thanks Joe if you need another 9768 68mm piston I have a decent used one. pm if your interested. Quote Link to comment Share on other sites More sharing options...
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