yx 4 valve heads?

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would it at least be better than a stock heavy flywheel setup?

I've got a brand new YX150 here and I'm not sure if I should use it, I heard as long as I kick it properly it won't crack cases?
The other option is to grab the lightweight ignition and chuck it in the lifan 140.
What do you think?
 
hmm, some people say it helps, but it'll only retard it a little bit. And it'll reduce your top end power. A proper ignition will start easier and still make full power when you rev it.
 
i wouldn't even run it without a decent ignition. All the fixed timing china ignitions are rubbish and can only cause problems.
 
tormentandglory said:
when porting, i find it easier to knock the valve guides out of the head, then you can go beserk with the grinder. Before you refit the guides you can shorten them or machine a taper on them.
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Yes this can be done. Not too keen though, only done it one time before and completely wrecked a brand new Takegawa R Stage head. I understand the principals of interferance fit, aluminium and the cast guides. Maybe you can describe a procedure to make it less scary for me. Have a couple of old heads here to practice on.
With the 4 valver the guides come out from the seat side, so I am sure they will be tight.
 
I have a set of punches that I made to suit different valve guides. I just whack em out with the correct size punch and a big hammer. If they're super tight I heat the head up a bit. Running it under hot water is usually enough to help. I like to mark them with a centre punch so they go back in the correct hole and are facing the right way. They are rarely concentric and if you put them back in wrong the valve seats will have to be machined quite a lot to get the valve to seal again. When refitting, make sure the guide has a nice lead-in so it doesn't burr up the hole. And use plenty of oil. Don't try this unless you have the right size punches for the guides or you will trash everything.
 
tormentandglory said:
I have a set of punches that I made to suit different valve guides. I just whack em out with the correct size punch and a big hammer. If they're super tight I heat the head up a bit. Running it under hot water is usually enough to help. I like to mark them with a centre punch so they go back in the correct hole and are facing the right way. They are rarely concentric and if you put them back in wrong the valve seats will have to be machined quite a lot to get the valve to seal again. When refitting, make sure the guide has a nice lead-in so it doesn't burr up the hole. And use plenty of oil. Don't try this unless you have the right size punches for the guides or you will trash everything.
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Yea no worries, but there are 4 words here that still scare me a little, punch whack, and big hammer. I have some nice punches, and will give it a go on the old heads, nothing like learning something new.

I made a little cone shaped grinding tool (machined cone with a slot cut in the side with mini hacksaw, cut holds the emry) with emry on the inside, does a nice job of tapering, and reducing the guides.
I am an electrician, that would explain a few things.
 
hey GTS 221, give mild to wild a call in Gladstone QLD he knows his shit with mini bikes and has the number one stop in the mini motard. 0749 733759. ask for richard. Mild to Wild Motorcycles is his web site...
 
yep removing the valve guides requires the seats to be recut even if you put the guide in the same hole it came out of.
and the trick to removing guides is to make sure the punch is a perfect fit and hit it good and hit square..

the punch should have a spigot machined on it the same size as the valve too. and make sure the OD of the punch isnt bigger than the OD of the guide...
 
yep used to do it for a living.. reco cylinder heads all day every day. loved doing it too...had all the flash gear to use...
surface grinders, mills, lathes, serco head machines, repco RVR machines, boring bars, k line bench..the list goes on
 
yeah i wish i was still doing it, i was forced out of it due to a back injury...lifting a diesel head onto the pressure testing bench...crushed 2 disks in my lower back... never been the same since..
but was still doing it for a bit after wards just for different companies..

i still have full access to any machine machine i need to use tho..
 
sean01 said:
milling machine...awesome...
iv been looking at getting one but its hard to find one thats at a decent price unless you settle for a china one, but apparently they have a fair bit of play in them.

what mill did you get and where from if you dont mind me asking...

im looking for 1 to setup and do case boring, piston fly cuts, seat cutting, deck machining and boring...
as well as other things...
Click to expand...

the mill itself is really the cheap bit... just get something fairly large with a tilting head... auto feed is nice in at least one axis... you can do small jobs on a big one, but not big jobs on a small one...

wait til you start equipping it :p thats when you start screaming... cutters...indexing heads... tilting vices... inserts for cutters... clamp down kits...
 
yeah but i have no need for a large one. only needs to be big enough to work on motorcycle engines.
im giving cars the flick, can work on them anymore because of my back.
and most problems can be overcome with custom tooling..

all i want it for is cutting valve seats, cutting inserts, boring cylinders and cases and facing surfaces..
there is plenty more i could do with it tho.
 
What do you boys recon of an oval intake, like the Jap stuff has on its 4 valvers ? Tapered up into the intake.

Hey you should see what an Electrician can do with a tiny .3 hp drill press, blocks of wood n some wood screws:)Ill show yas some machin
 
oval intake..hmm what intake manifold are you using?
id recon it would be a step backwards.

if anything keep it round but make it as large as you can go and make a custom intake the same size and use a carby the same size...32mm pumper is sounding awesome...because youre gonna have a sht load of torque there to use it..and after all your only after a dyno pig engine arent you, so bottom end power doesnt matter even tho it will rip right thru the rev range.

just dont make the mistake of a too radical camshaft which only gives power in the very high rev range. instant hand grenade... better off with short duration and high lift..
 
I keep looking at the camshaft, and it is 7mm lift, and of a short duration, yet to measure the duration, but looks around the 270 mark, short duration, and high lift. Sounds on the money and worth a try. Have not had any joy with the decomp cam. Akunar says he can get 330 degree 6mm lift cams for me, or pretty well anything I want really, which would be rev heaven on a small bore.

Hey the secret is out of the bag, the single most expensive part of the build, and a mini bike lifelong dream for me the "32mm KEIHIN FCR PUMPER". I hear you can run one of these, on an engine as small as 140, as long as you run a really wild cam. The only issue is that it will stick out the side of the bike. I saw once a pic of a downdraft FCR mounted pretty well on top of intake port, it also had a nice long velocity stack. This is what I will be looking to buy. Dare I ask, does any one out there know of a friendly supplier of such a beast :eek:??????? 32mm KEIHIN DOWNDRAFT FCR PUMPER ???????:eek: Or have one in a box in the back of the shed.
Dare I say that we maybe looking at 15 HP at the rear wheel
GO THE DINO PIG
 
some more pics, tassie01 211 yx 4 valve project
 
mate if you play your cards right you should see HP numbers in the mid to high 20's.

as for the decomp cam hit JR motorparts up on ebay to see if they can supply you one..then get it profiled and reground if needed..the biggest mistake there making with these cams is the lobe separation is far too big...seen some as much as 120 degree's, they perform much better if reduced to around 105-110..

also the FCR 32mm is 100% pure awesome, downdraft would be better as you can keep the carb close the the valve to promote torque but on the downside you loose air speed..can have em all i spose..
we were just talking about these the other day in chat box but you better be sitting down when you find a price, .but i d recon there'd be an extra 5+HP just in this carb if setup correctly..
sus this site out YOSHIMURA JAPAN : PRODUCTS : ENGINE
and here Keihin Fuel Systems, Inc. | Products
 
I would have gone bigger on the ports myself, and the tapered inlet is a winner. Wouldn't worry to much about making it oval. I'll post pics of my ported dirtmax 150 head when I get it back from the machinists. It's getting its seats recut right now.
 
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