138cc piston deck height

[dhz138]

yo people

whats the complete piston dimensions on the 138cc DHZ'S.. ??

ta

 

[Cactus Jack]

138 "pissed on"

Piston diameter = 54 mm (54 x 55.5 = 127 cc)

Pin height = 12 mm

Pin diameter = 14 mm

Edge of crown to base of skirt = 37 mm

Dome height = 2 mm

Overall piston length = 37 mm

I call the 54 mm piston - the 138 "pissed-on" - because everyone who bought the 127 motors thinking they were 138's - got pissed on !!!!

 

[dhz138]

yeh hahah yeh pretty much.. was only untill about 2 weeks ago i found out it was only a 127cc.. haha.

Goes way harder then any of my mates bikes though..

yo Cactus_Jack have you got any idea on the clearance between the valves and piston when at TDC ?

Because i plan on getting a High Lift Cam 7.0mm and i was just wondering how much bigger the dome on the piston can get.. ??

cheers

 

[Cactus Jack]

yo Cactus_Jack have you got any idea on the clearance between the valves and piston when at TDC ?
Because i plan on getting a High Lift Cam 7.0mm and i was just wondering how much bigger the dome on the piston can get.. ??

.........................................................................................................

No , I don't know as I've never checked but what you do is take the head off , put plasticine in the valve pockets - smear some oil on the valve heads so they won't stick to the plasticine - put the head , cam chain etc back on and turn the motor over by hand - then take it off and measure the depth between the piston and the valve imprint in the plasticine . That'll give you the stock clearance .

Then when you fit a new piston and race cam - you'll have to do it all again , making sure you have at least the same clearance as the stock engine with whatever extra clearance the cam manufacturer recommends .

The dome can be as big as what will fit in the chamber without hitting anything but you need a flame trough to allow equal flame front travel throughout the chamber ! Keep in mind that if you go too high in compression the engine will lose peak revs (unless the cam has a lot of over lap) , and will detonate more easily if you don't use high enough octane fuel and have the timing set right . You'll also most likely have to clutch it to start it because the kickstarter and cases will only handle so much before breakages occur .

 

[dhz138]

hey,

yeh roll starts allrite by me..

looks like i can only go to 57mm with the boreing.. because i aint taking my whole engine apart to bore the cases... maybe in the future when this newones near buggered ill give it a whirl..

anyway, like you said cactus_jack.. i can go 57mm w/out having the cases bored.. and that'd give me 141cc.. if i got a high dome piston and race cam, will i need metal gaskets ?

after this is done to my 138cc.. (127cc) will it flog a 140cc standard chinese engine off ebay ?

cheers

 

[Dreamah]

Ive been thinking i might get my Vavle clearences done, From what i got told after 8 hours they need to be re-set??

 

[Cactus Jack]

hey,

if i got a high dome piston and race cam, will i need metal gaskets ?

after this is done to my 138cc.. (127cc) will it flog a 140cc standard chinese engine off ebay ?

cheers

Depending on how high the compression is , you might need to use a copper head gasket !

Yes - a 57 x 55.5 (140) engine should rev out harder than a 55 x 59 (140) motor ! Long stroke engines pull great from bottom end to midrange but then they tend to drop off quickly up top . You'd need to run a bigger cam in a 59 stroked motor to get it to rev !

 

[Cactus Jack]

Ive been thinking i might get my Vavle clearences done, From what i got told after 8 hours they need to be re-set??

Yeah , you should check and adjust valve clearances often to avoid burning the valves out and also to stop the rocker and cam lobes from sgueezing out the oil and wearing quicker !

It's a good idea to use valve saver in the fuel since unleaded has no lubricating properties !