61mm skirtless bigbore on yx 140cc

[146cc_outlaw]

hey guys i just finished putting a 61mm skirtless bigbore kit on a yx 140cc engine but when i start it up there is oil coming out of the exhaust port and a hell of alot of smoke the only thing i think it could be is the head gasket. dose anyone else no what it could be and how to fix the problem

 

[Cactus Jack]

Did you make sure that all of the cylinder studs were screwed right into the cases as far as they could go so that each stud retorques to sufficient tension ie all have the same rate of stretch ? They can back out when you remove the head ... Also the bottom right hand stud needs to have a rubber 0-ring and metal trumpet piece between the the head and cylinder to prevent the O-ring from cocking up down the stud hole ... IF the kit comes with an idiot steel shim gasket that does away with those parts then there's your problem ... Half of these kits are "engineered" by tools who couldn't design a paper aeroplane that flies ... IF the 61 mm piston is heavier than the stock piston it's replacing and you haven't had the crank assembly rebalanced to suit then I pity you ...

 

[motorman]

What's the go with these kits?? Prices etc.

Are they worth it. I have a yx 140. Wouldn't mind a bit more poke.

 

[Cactus Jack]

Yep ... they do use an idiot steel gasket up top ... LOL ... Bodgy engineering at best ... They're too stingey to supply a far superior copper head gasket which gives a reliable seal ...

Pit Bike 160cc Big Bore Kit

 

[motorman]

Seems to good to be true for $180!! Think you will need a performance head to go with it though.

Let us know how it goes after your finished. Cheers.

 

[146cc_outlaw]

ok i worked it out to be the head gasket i made a paper one which fix the problem for like 5mins then smoke again so where would i get a copper gasket from oh and the 61mm piston is 00.2 of nothing heavier than stock and i do have a fully ported head 27/23 valves and 6.3mm cam

 

[daimojay]

will be alright till the shitty jialing gearbox goes poo poo.

while it holds up there great, and i would invest in a copper or alloy headgasket from akunar... thats what i used on my jialing 182cc build and never had a problem...

 

[146cc_outlaw]

i already have a 0.5 alloy one will the copper be much better and what thickness gasket should i get it has a HC piston 7mm dome i think by the way im using this on a yx 140 so would this make it a 160cc or 166cc???

 

[Cactus Jack]

Copper is better because it can expand at different rates to close up machining and surface distortion discrepancies ... That's why it's used in steam valves etc ... Copper gaskets are also reusable many times over ... You can heat 'em up in an oven to re anneal 'em ...

IF your piston is 61 mm your bore will be - 167 cc ... IF it's 64 mm your bore will be 183 cc ...

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