yx 4 valve heads?

Shop deals on ebay
Advertise with us
Find deals on amazon
Mini Dirt Bikes & Pit Bikes Forum

Help Support Mini Dirt Bikes & Pit Bikes Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
it dropped the exhaust valve from smahing the piston...im not sure what piston it is because thts a 63mm bore and i havent seen the V2 heads advertised with 63mm piston...
 
KABOOM! Nice pickup for $20, easy fix for the right guy ;) The older V2 kits were 63mm, I have one on my z50j engine.

I wonder if they're still available? Its an iron liner, so it can be bored to suit the 64mm skirtless piston.
 
yeah i was told that the damage in the pics was all that was wrong... lol i took off the clutch case and bingo...cracked case...
so i used the gearbox and standard barrel to repair a yx150 i had..

but i plan to get an upgraded case kit for it in the future..

oh and this 63mm bore is the ceramic type.. you can see a small chunk out of the bottom of the skirt.. im yet to inspect with a magnified glass and see if its still usable...

the head will be repairable.. theres no biggie in tht...
 
I went to buy bearings for my yx150 the other day, and almost all of them are odd sizes. The dude at the shop says he can get them but it'll take a few days. I have the updated case with the needle roller bearing. Its ****. Poor quality bearing, hard to find a replacement. There must be 0.2mm radial movement in it and its barely even worn. Interestingly enough, there is a standard size ball bearing with a 15mm I.D. and a 32mm O.D. (2mm smaller than the old style yx bearing) Its a bit thinner to. I'm gonna machine my roller cases to take one of those.

TB must have made many different variations of those cylinder kits!
 
tormentandglory said:
There are 4v engines around with tuliped valve stems. The zx2r valves that i used in my 4v are 4mm stem, necked down to about 3.25mm. I've seen plenty of car engines with the reduced stem diameter to.
Click to expand...

Ok , Sean said they maybe 2 piece valves, and If I get into the stems I may find one rattlein around the combustion area, not pretty
Best to make new ones.
 
lol... costly but worth every bit... and stainless are stronger and lighter. or find a car engine tht runs the same head size and stem and then machine it down and add the collet groove..
 
Check the valves with a magnet. Inlets are rarely 2 piece. Exhausts often have a stainless head welded to a non stainless stem. If one end is magnetic and the other isn't, its 2 piece. If its all magnetic, its one piece.
 
wow, you guys ammazze me with what you know. And I have to say thanks for your time, and infinate wisdom,,,,,,,,,oh, and that beautiful CHINA XY 4V HEAD
Oh both inlet and exhaust valves do not stick to the magnet, so I guess that they are(all 4) 2 piece.

I rang up OOR in the UK tonight, he is sending me a camshaft, cam sprocket, new valve springs.
He said that with their camshaft(modified overlap like Sean suggested, a correctly ported head, and a properly jetted 28mm VM Mikuni will deliver up to 29HP in the 4V head at 172cc. Apparantely they raise the compression also by taking a little from the top of the cylinder. They will send me the specs.
Tiz all waiting now,,,,,,,,,,,,all good things come to those who wait.

Been reading all the blog on carb tuning, no one mentions anything about the emultion tube around the needle, and the influence it can have on bottom end in a flat slide 28,
My example/question is, if I were to make the air holes in the bottom of the tube smaller(solder and re drill) would that in turn richen the mixture off idle, and give me back the power that I had when the carb was way over in main size ?
Has anyone done any work here ?:cool:
 
never had the joy of fiddling with emulsion tubes. but i know that they are the main reason everyone's tuning is so different..
i have an oko 28mm with 8 holes in the emulsion tube and other keihin 28mm with only 6 holes, they are completely different to tune.. the 6 hole one needs hugh pilots..

and as for if they need bigger or smaller holes im not sure.. but i think also the postion up the tube plays a little too as it reflects on needle postion during rolling the throttle on...

only emulsions i have ever played with were the ones on my datsun 1600 with twin 45mm sidedraft webers. spent a day on my mates dyno till we got it right..ended up with 179hp...pretty quick for an aspirated 4cyc

29hp man tht thing is gonna rip ya arms off
 
tassie01 said:
wow, you guys ammazze me with what you know. And I have to say thanks for your time, and infinate wisdom,,,,,,,,,oh, and that beautiful CHINA XY 4V HEAD
Oh both inlet and exhaust valves do not stick to the magnet, so I guess that they are(all 4) 2 piece.

I rang up OOR in the UK tonight, he is sending me a camshaft, cam sprocket, new valve springs.
He said that with their camshaft(modified overlap like Sean suggested, a correctly ported head, and a properly jetted 28mm VM Mikuni will deliver up to 29HP in the 4V head at 172cc. Apparantely they raise the compression also by taking a little from the top of the cylinder. They will send me the specs.
Tiz all waiting now,,,,,,,,,,,,all good things come to those who wait.

Been reading all the blog on carb tuning, no one mentions anything about the emultion tube around the needle, and the influence it can have on bottom end in a flat slide 28,
My example/question is, if I were to make the air holes in the bottom of the tube smaller(solder and re drill) would that in turn richen the mixture off idle, and give me back the power that I had when the carb was way over in main size ?
Has anyone done any work here ?:cool:
Click to expand...

hahahaha i just spit my dinner on the keyboard reading that lmao. no way in hell your getting that out of a single cam 4 v lmao.
 
HACKMUNCH said:
hahahaha i just spit my dinner on the keyboard reading that lmao. no way in hell your getting that out of a single cam 4 v lmao.
Click to expand...

No, I thought it was a bit out there. Just what I was told. Im happy with anything over 15HP, at the rear wheel.
Got any more of those 28mm pumpers for sale ?
 
Hey, :) My Stroker pin split main bearing, piston and cylinder turned up today. The cylinder still has 111cc cast into the side of it, It is 67mm. The boys have inserted a sleeve
Will post pics tomorrow,,,,,,,too busy playing now
 
thought some of you guys migh enjoy these. yx 4 valve with 23.5mill ti intake 19.5mill ex ampco seats and guides and custom valve springs

head008-1.jpg

head016.jpg

finshed intake
motor005.jpg


almost stock exhaust
motor012.jpg


worked exhaust
exhaustport002.jpg



almost stock exhaust left port
motor014.jpg



worked exhaust left port
exhaustport004.jpg
 
storminnorman07 said:
thought some of you guys migh enjoy these. yx 4 valve with 23.5mill ti intake 19.5mill ex ampco seats and guides and custom valve springs

head008-1.jpg

head016.jpg

finshed intake
motor005.jpg


almost stock exhaust
motor012.jpg


worked exhaust
exhaustport002.jpg



almost stock exhaust left port
motor014.jpg



worked exhaust left port
exhaustport004.jpg
Click to expand...

is it me or camera flash... they look like brass valve inserts...

thts a sweet looking setup there mate... please tell who supplied the head to you?
im about to pickup a couple of these and not sure how many versions there are and if ppl have had back experience from certain sellers..
 
You must log in or register to reply here.

Latest posts

Back
Top