yx 4 valve heads?

[themountain]

mmm...its very nice and interesting to see a build like this, but makes it really sense with the weak cast quality of the engine?? I do not only speak about the cases, the main problem I think will be ,to avoid the input and output shaft from bending, chipping all this low quality sprockets in there...next will be clutch...if you can`t find a slipper clutch setup for the bike, the first turm on gas will be the end of it....thought about that...?? Then the gear box must be treated in some kind of way , otherwise it will be gone in no time even with oilchanges after every ride!!

It need much more than some polished intakes and a stroker pin to make a turd a good engine!!

 

[dafunk]

the 4 valve set up allows a much better shaped combustion chamber . given the same valve area .
letting the tuner increase the performance before detonation occurs .
i would also let the clutch slip during acceleration to ease the load on the gearbox .
like sean said ,hope the 4v head has a decomp . although push starting and kick starting it correctly may reduce the chances of case breakage .
looking forward to see your results!!!!

 

[tassie01]

I care not for the box, or casings, clutch, input shaft, bla bla, it only has to last for the dyno run. I got a day out of my last monster engine, alas no dyno run
But yes, I take on board all of your notes. My uncle is an engineer with his own induction hardening oven, and a rockwell hardness tester, maybe I should take the time to speak to him.

 

[tassie01]

Thats a big engine. What ignition are you gonna use? I'd recommend a lifan 150 ignition, or you'll be cracking cases like eggs. If you're going to that much trouble, is it possible to fit bigger valves to the 4v head? I can't remember how much room there is between the inlets. That head should work well on a sensible size engine, but 200+cc is getting pretty serious. I don't think it'll flow enough. As a rule, in a 2v engine, the inlet valve diameter should be close to 1/2 the bore size. If you do the maths to relate that formula to a 4v setup, I reckon you'll be down about 10% of what is ideal. I'd recommend 23 or 24mm inlets.
It'll be an extreme grunter, but not much rev. Be careful with compression to, I wouldn't be going much higher than 9.5:1. 10:1 max or you'll be leaving a trail of broken engine parts and oil on the track.

Yes indeed,,,I have a lifan 150 small outer rotor kit, and am chasing a switchable digi cdi.
I have been studing 4 valve combustion chamber notes, and there is quite alot of work to do on the head in that department. The ports are conservative, as you suggested, and a mm or 2 will come out here and there, particularly the exhaust.
Larger valves are a possibility but there is also the cost, and with the likelyhood of engine failure, I am not going there. But 1mm bigger intake, and 2mm exhaust valves would increase valve area by a fair margin. Somewhere around 5%. And yes I agree that keeping the compression ratio down a little is a great idea. I intend to only run avgas, that may help a little.

 

[tassie01]

the 4 valve set up allows a much better shaped combustion chamber . given the same valve area .
letting the tuner increase the performance before detonation occurs .
i would also let the clutch slip during acceleration to ease the load on the gearbox .
like sean said ,hope the 4v head has a decomp . although push starting and kick starting it correctly may reduce the chances of case breakage .
looking forward to see your results!!!!

Is there a decomp cam for the YX ? Maybe the little extra cost here would let me start the thing at least one time. Do you know a supplier ?
And Yes 4 valves are better than 2, particularly for the combustion area, valve stability, and also(slightly)longer cam duration. Slipping the clutch on the dyno is not an option.

 

[sean01]

if the head runs a normal 2 valve cam then you can get one from dhz DHZ Mini Moto - PITBIKE DE-COMP RACE CAM DHZ D25 Grind YX 150,160cc
sometimes if you chase them up on his ebay you can get them for as little as 140 plus post...

should help alot

 

[tassie01]

pics are posted in Tassie01 photo gallery, yx 4valve 211

 

[sean01]

looks like theres a bit to do on the ports hey.
bowls need a good tidy up and knife edge the intake.
but yeah they do look nice

 

[tormentandglory]

dammit i'm jealous! I really wanted to try that sucker out. I've started porting a dirtmax 150 head instead. Boring!

 

[themountain]

...Larger valves are a possibility but there is also the cost, and with the likelyhood of engine failure, I am not going there. But 1mm bigger intake, and 2mm exhaust valves would increase valve area by a fair margin. Somewhere around 5%...... .

Its not only the size of the valves ...its how they sit in the combustion chamber

... I intend to only run avgas, that may help a little.

Avgas will do zipp to help...read the post on race fuel in PM...says it all!!

 

[tassie01]

china 4 valves pics

 

[tassie01]

more port work pics posted, intake, and combustion chamber
Points to remember when porting, no polishing the intake tract, this will cause fuel air mix to bead on the walls of the intake, 120 grit is or coarser is the go.
Turn off the porting grinder on entry, and exit to the valve side of the port, one slip here, and the valve seat is stuffed. Generally try to not expand the port at the valve seat, no less than 0.8mm, this will bugger up fuel air fan propagation during valve opening, and closing times(80% of the time)
95% of the port work will be done, raising, and smoothing air flow around the valve guide. Generally keep away from the bottom of the port tract, clean up only, and usually only to tidy up in the port behind the valve seat. Grinding off the valve guide, inside the port will not help valve stability at high rpm, and can cause low valve seat, valve guide and valve life.
At the intake port opening (carb side), match the port to the intake manifold, not the gasget. Keep the manifold walls parallel to the intake tract, not a good idea to have an expantion area here.Taper out as far up the manifold as the port tool will go.
Highly polish and smooth iregularities in the combustion chamber, this will limit carbon sticking and decrease turbulance around sharp bits.
Highly polish the exhaust port, and only remove material of similar amount to the intake. Polishing helps prevent carbon build up.
Always keep in mind, bigger is not necessarily better, accuracy in finish, and improvements to flow are what you want, you can expect up to 10% increase across the entire rev range, better overrev ability.
Be careful with jetting, maybe a size bigger on the main, and probably no change on the idle only mixture. Try raising the needle a clip or two before anything, and plug chop.
Make sure you have the correct tools, a well lit area, and plenty of patience.
Note, flow bench testing is obviously the way to go, but experience and practice works well also. Chineese heads are cheap, porting heads is fun.
Ride on.

 

[tassie01]

10:1 on a 200cc engine will require a 22cc chamber volume. Is that even possible?

Yes chamber is not measured yet, I am going to have to modify the top of the piston, machine some off the top, and make new relief cuts.
Chamber and piston to top of cylinder will be measured, when I am finishing off.

Hey did I see that you have a switchable digi ignition box, if so maybe you can unload it on to me. You sell and build some nice gear. If I won the lotto, I would give you a blank check to build Vtwin Gorillas. Then we will take on Takegawa.
Cheers for the input

 

[tassie01]

yeah i can now tht you say it like that,
i thought the 11mm pin height was including the pin and pin bushes..
so really its a 12mm pin height working off the conrod small end..

also whats happening about valve reliefs in the piston.
and what compression are you chasing..

its going to be a case killer for sure unless you get yrself some sort of decomp setup.

Case killer it will be for sure, one backfire will smash the kick gears, cases, and anything else in the way. Memories of a worked ducati 900ss that I used to have, near broke the thing in half one day when it decided to backfire when I was kicking it, not only did it put a hairline crack straight down the middle of the cylinders, on the LHS case, but also tore a mighty hole in my shin, and cost me 5 grand to fix.
Decomp cam will be ordered, when I get to measure up a standard one. Havn't got an engine yet. SSSSSH don't tell Mummy I'm spendin money on the mini again.

 

[tassie01]

mmm...its very nice and interesting to see a build like this, but makes it really sense with the weak cast quality of the engine?? I do not only speak about the cases, the main problem I think will be ,to avoid the input and output shaft from bending, chipping all this low quality sprockets in there...next will be clutch...if you can`t find a slipper clutch setup for the bike, the first turm on gas will be the end of it....thought about that...?? Then the gear box must be treated in some kind of way , otherwise it will be gone in no time even with oilchanges after every ride!!

It need much more than some polished intakes and a stroker pin to make a turd a good engine!!

Dear Mr The mountain, I respect your input very much and have acted upon this.
My old uncle the mechanical engineering teacher said it would be easier to make a gearbox than to treat the gears, shafts ect. Firstly you need to know what materal is first berore you can do anything. If you do know what it is then all the "bits" have to be anealed before any treatment could take place.
He suggestion was to completely renue every supporting bearing with a quality one. Oil is another factor that should be looked at, stripping the engine and looking for wear, where it is on the gear face, and shafts, can influence what type of oil used. One suggestion was to correcty run in the engine, for at least 20 hours, this will help the gears naturally work harden, and reduce stress across the meshing teeth, oh, then added, make sure you buy a heavy duty cam chain, dont trust the china one. Restricting throttle opening to half should work here. De buring the casings, relieving oil gallerys, and a light beed peening process should make the cases a little better.
De compression cam, new kit of bearings, case matching, blueprinting, beed blasting, new cam chain, case boring to a slight interference fit with the cylinder will all help. Please keep in mind that this engine will not have to rev hard to make massive amounts of grunt, compression ratio will be below 10:1
Needless to say there will be more than shiny ports, and a stroker pin, going into the turd
The dyno report will not lie.

 

[tormentandglory]

yes, i still have 1 digi ignition left. It only has one profile which gives about 13deg extra advance after about 4000rpm. The backplate is adjustable which helps a lot. I run em on all my bikes. My 165 V2 engine has 11:1 comp but can still be kickstarted, as long as you're careful.

 

[DvDRip]

torment and glory, do you know if the ORK style ignitions on the old YX 150's have digital ignition? it looks just like the lifan ORK except the backplate is not adjustable and the cdi is not the same

 

[tormentandglory]

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.

 

[tormentandglory]

nope, the original yx150 ork's are junk. Hence the smashed cases. You need the original daytonas or the lifan copy.

 

[DvDRip]

ok thanks for that info, what if I modded the pickup the retard the timing a bit?