head leaks

kelly dean

Active Member
Oct 3, 2019
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rebuild on triple forty 69cc, a new gt4 cylinder and a gt5 piston set. Been through a number of motors and what persueing this hobby and thought id seen or done every wrong thing there is, surprise exhaust and head leaks and i've never had either of those, always more lessons lol. Ive sorted out the exhaust leak now on to the head problem. i have a cdhpower cnc 6cc chamber compression head. ive used this head on several cylinders with no issues and as best i can check it without prescion measuring tools im fairly certain its not warped its a heavy chunk of aluminum. quilty once again of getting lax. Im thinking 2 things, the head has a slight ridge of the cush band any extra after gasket should go in the bore and maybe thats not lining up or the cylinder is too tight for it. im useing a good copper gasket not sure the exact thickness its a tad less than stock aluminium. second thought is perhaps the top of this new cylinder isnt true. easy aint worth nothin onward and upward.
 

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curtisfox

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Dec 29, 2008
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Cylinder may be warped? One way to check is to sand them on a piece of glass or heavy saw table, or the like. Use fine wet/dry sand paper circle motion, can use permanent marker on it, till it is sanded away.......... Curt
 

kelly dean

Active Member
Oct 3, 2019
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Cylinder may be warped? One way to check is to sand them on a piece of glass or heavy saw table, or the like. Use fine wet/dry sand paper circle motion, can use permanent marker on it, till it is sanded away.......... Curt
thank you Curt i had that in mind Ive got a glass table and some 400 wet/dry but i hadnt thought of the marker was gonna paint it or something lowriderl
 
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kelly dean

Active Member
Oct 3, 2019
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I've got it broke down and i see a couple things i should have been more aware when i assembled this motor. The top of the cylinder is really quite rough im going to true too 1000 wet/dry. the other issue is the ridge of the cush band does not seat down in the bore. Can i chamfer the edge of the bore the little bit it will take to seat the cush band in the bore. it's a tiny amount and at TDC there is room enough frrom the piston.
 
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curtisfox

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Dec 29, 2008
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Glad you found some defects, time to sand and make it even better, don't have a china engine myself, just years of being a member. So when you start talking about cush band, i would have to study LOL...........Curt
 
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indian22

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Dec 31, 2014
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You guys have it going in the right direction for sure. I'd go easy on the chamfer Kelly, nothing wrong with taking the sharp edge off,one of the great things about copper gaskets is their ability to conform to head and jug once all surfaces are flat, smooth and parallel. I've used that same head on a couple of builds and like it. 6cc chamber and a medium thick copper head gasket is a good combo. I replace the stock kit head studs "butter bolts" with high grade steel fasteners.

Rick C.
 

kelly dean

Active Member
Oct 3, 2019
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kentucky
i looked at an old cylinder last night and sure enough its slightly chamfered to allow the cushion or also called the squish band into the bore enough to bring the mating surfaces together. Oddly this new cylinder is pretty much squared off at the top of the bore so the mating surfaces arent coming together to seal. Ive got a good copper gasket im not sure the exact thickness very slightly less than a stock aluminum one. I'm going to carefully chamfer it with a half round file enough to let band down and getting the mateing sufaces to come together. this little is another first for me.. live and learn ;) and hey thank you guys for your time and help i appreciate it .
 
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kelly dean

Active Member
Oct 3, 2019
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kentucky
it came down to the head i tried a stock head no leak.. so i trued the head for better or worse. just test rode and no leak and it ran really well for a new top end. all the way up until i ran outta gas ... HAHA
 
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indian22

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Dec 31, 2014
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Reasons vary for 4 stroke Kelly, but often it's just running a heavy mix for a given motor. Once broken in some of my motors want 40 to1 others 32:1 or 36:1 that's using NGK plug & same heat range etc. Lucas semi synthetic & premium fuel no alcohol added. Stock CDI on basic stock engines with a few bolt on perf parts but the more highly tuned motors get an after market CDI. So were talking both same and different here, but all mine run with a little 4 stroke action and that's ok to me 'cause it says the motor is being lubed and cooled as well. Air temp and atmospheric pressure are also factors. Altitude here is about a quarter mile above sea level so my recommendations for fuel mix at sea level or even a half mile high will likely be off even if the motors are setup exactly the same including jets and float setting.

Four stroking that's not just momentary & occurring in a small rpm band needs addressing because it makes the bike less fun to ride and it's inefficient to operate. If you get to a certain low rpm say 6,000 and that's it with a 44 tooth cog and the motor has just stopped four stroking or still is...that's a problem because your not hitting the pipe, even the stock kit pipe should bust through 6,000 like you just shifted gears.

Take recommendations with a grain of salt though they be true for one, they're not for others. Motor setup and performance wildly vary for so many reasons and that includes factory of production for each of the major engine components. Sometimes the answer is simple, but then there's the rest...

Rick C.
 

kelly dean

Active Member
Oct 3, 2019
139
174
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kentucky
thats all typical 2stroke lol...its a lil rich and thats probably mixture.. its running pretty well.. its a 11/44 gear with a 20 inch wheel thats not a top end setup its really pulling good low end through mid range with excellent throttle response and thats what i want on this bike. i do appreciate you all and your time and experience thank you.. kelly...
 
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kelly dean

Active Member
Oct 3, 2019
139
174
43
60
kentucky
Reasons vary for 4 stroke Kelly, but often it's just running a heavy mix for a given motor. Once broken in some of my motors want 40 to1 others 32:1 or 36:1 that's using NGK plug & same heat range etc. Lucas semi synthetic & premium fuel no alcohol added. Stock CDI on basic stock engines with a few bolt on perf parts but the more highly tuned motors get an after market CDI. So were talking both same and different here, but all mine run with a little 4 stroke action and that's ok to me 'cause it says the motor is being lubed and cooled as well. Air temp and atmospheric pressure are also factors. Altitude here is about a quarter mile above sea level so my recommendations for fuel mix at sea level or even a half mile high will likely be off even if the motors are setup exactly the same including jets and float setting.

Four stroking that's not just momentary & occurring in a small rpm band needs addressing because it makes the bike less fun to ride and it's inefficient to operate. If you get to a certain low rpm say 6,000 and that's it with a 44 tooth cog and the motor has just stopped four stroking or still is...that's a problem because your not hitting the pipe, even the stock kit pipe should bust through 6,000 like you just shifted gears.

Take recommendations with a grain of salt though they be true for one, they're not for others. Motor setup and performance wildly vary for so many reasons and that includes factory of production for each of the major engine components. Sometimes the answer is simple, but then there's the rest...

Rick C.
the motor is running good. triple 40 69cc 6cc compression head speed carb, the bigger OZ coil 2 piece performance cdi NGK b6hs plug on a good wire and the banana expansion chamber. Im thinking another gear it does 30mph full out id like to cruise at 30 with out pushing that hard, i wonder what would be best a 38 or 40t sprocket ?
 
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