anybody have this type of leak down test failur!

[Nutwood 472]

Hey guys,building a 472 super cub,had Andy at M&M ATV hook me up on hole motor set up,great guy to deal with.but back to the story,doing leak down test and doesnt hold,has slow leak,well the first leak was intake bolt,no problem,just use some thread sealer,do test again,failed,real slow leak,sprayed every seal gasket and case,couldnt find it.grrrrr! put clutch cover back on to see if case matting surface is leaking inbetween tranny and crank case,no bubbles in the vent hoses,take motor off frame and pull cylinders off and replace base gasket,just for shits and giggles,did another leak down test,still failed!!!!Getting frustated,pissed all the above,lol start to here the leak,sounded like it was coming from in side clutch cover,lifted motor up and i really could here it better,started to spray it down and found it,its right unbetween the front crank case and the back crank case bolt,theres a molded void thats right under the crank bearing on clucth side,it has a hair line crack the bottom of that void,the size of a pincil eraser,have never seen that before,so I cleaned it out with carb spray and then rubbing alcohol,ruff it up,mixed up some fast setting J B WELD and filled the hole,I really hope it holds,I'll let it cure for 24hrs and do anther leak down test and see what happens,I've had a hard time jetting the right side so this really exsplains it all would of never have guessed it would of been there,so when you do your leak down test and can't find the leak spray the bottom of your engine,lol keep ya posted on the next leak down test and see if it passes,lol

[RagunCajun]

A very good thread! This is why everybody should do a leakdown test after a rebuild !

[Snopczynski]

FYI if you guys want jb weld to hold really well on aluminum, het it up with a torch and then put the jb weld on it. It kind of runs into the pourice pores in the aluminum and makes it seal/hold a little better.

[Larry's Shee]

That's a good tip there Snop. Thank you !!

[sleeper06]

Do the same with marine-teks epoxy

[Nutwood 472]

Do the same with marine-teks epoxy

[T_Shee]

A very good thread! This is why everybody should do a leakdown test after a rebuild !

 

absolutely. i have found leaks 3 out of 4 times i have tested mine

[Nutwood 472]

absolutely. i have found leaks 3 out of 4 times i have tested mine

Hey guy,here with the up date on the leak down test,JB weld didn't work,but I didn't heat the spot up,like you guys said,wish I would of known at the time,but its a very good ideal,I used some LOCK-TITE epoxy,it worked very well,filled the holes,because I found a leak on the other side in the same place,right under the crack bearings on the outer bearing side,looks like there was a little plug in there like the middle one has,looks like a cap shaped plug.So it passed the leak down test 6psi for 20 minutes,so now I'm passed that,its on to the tuning and jetting,should be a lot easier,since I'm not jetting for an air leak,lol So I would like to know what caused the cracks and why do they mold the cases like that,because there is'nt much material inbetween there,have never seen anything like that ever happingto the cases,so thats another spot to check out guys when you do your leak down test and cant find the leak,lol thanks for listen to my story BHQ!