Re-condition or new?

[rumble]

So after my first race meeting at the aus champs, ive been bitten by the power bug.

I currently have a YX150 which is about 3 years old, has the painted black head. Still in good condition, runs hard. (came 4th in chinese class :clap

Now, i either spend $500ish on a new 160 or new bore/head to give me a 160cc on the old engine, or bore the 150 to a 62mm to give me the extra cc. Remembering that i have to be under 160cc for racing motard.

Currently im looking around for a 62mm piston as i think that is my best/cheapest option.

I saw two bikes do there big ends so im a little worried about continuing using this current engine for race purposes. Although i think ive look after the engine very well with oil changes ect.

Any thought, other options.

 

[billyxxx]

v2 ???????????????

 

[sean01]

if the rest of the engine is good..ie gearbox
and it has the updated case then id go the yx160 (long) crank and a ported V2 head with a 30mm oko.

you can also go the yx160 (short) crank which is slingerless and allows the engine to spin up faster.. but you'll need to do a complete conversion on the clutch cover with a yx150-dte cover...

spose even if the gearbox needs repair it still works out cheaper than buying a new engine.
because your going to need to replace some of the new one too (clutch,head so on.)
but the key to using your own engine is to make sure it has the updated case..

at the end of the day it comes down to money for parts and if your able to do it all yourself to keep costs down.

 

[The_GDFP]

Akunar has a nice 62mm piston. I use them in a plated cylinder and they hold up well. See DHZ for a one-piece alloy slinger, if you keep the 53mm crank or swap to a 57mm sling-type. You can fab a longer transfer tube and run slingless crank with your cover, but you give up any oil filtration from the sling. 150 cranks seemed to break, here, if run with a heavy flywheel. YX's newer outer rotor, or an inner rotor should be fine. Now, I dunno how strict they are on rules, but 60x57 and 62x53 are both a fraction over 160cc.

So, as another option, maybe consider the Tak 59mm top and a 57mm crank? You'll likely want to upgrade to at least a V2, and then swap in $130+ in alloy rockers, $200 decomp cam. Legal, powerful, reliable.

Z155Ho may be the easiest. Add a V2/+R, TB manifold, 28mm carb, and rip it up.

 

[rumble]

The engine i have was a 'race' version.... came stock with a alloy slinger and IRK.

My calculations 3.14 x 31Squared x 53 gives 159.9cc is this right???

Can i bore out a sleeved stock head 2mm??

The V2 sounds like a plan. Is that just an updated head??

Gear box seems fine, again i treated it good from day one. is there free play some where to check?

 

[dafunk]

its alwayys nice to have spares .
i had my 140cc junior bike as a spare [came 3rd and liam nisbit hardly rides it!]
it ended up being used by a senior whose 160cc crank broke
so a spare complete motor would be great or bike even better

 

[The_GDFP]

pi = 3.14159265

Stock cylinder will go 62mm, but there's a little notch in the sleeve at the top that gets close to the bore. The plated aftermarket 62mm jug is reasonably priced.

Check that sling carefully. Most had a steel center, alloy cup. Prone to reverting to two pieces after high rev running.

Grab the end of the trans shafts and check for in & out play.

The V2 head, and Tak +R that it copies, have bigger valves and ports for more power. They also use roller rockers, alloy on the Tak. The roller part is mostly gimmick, but the heads make more power overall, unless you have big valves and a GOOD port job done to the stock head.

 

[Butane8]

have the yx160 gen 1, recently bent a valve so looked into tb head/ bore upgrades...
after all the sums, i pickup a gen 2 gtx yx160 comeplete engine for$ 799.[new]. have the old motor for backup/parts.. butane

 

[rumble]

Just got an email back from Akunar. They can do a head with stainless valves (any size, recommendations on size please) for around 260usd plus ship.

Email from Akunar..

Depending on the piston to be used you will need to alter the wall clearance allowance but anywhere between 0.2mm is typically more than enough for most pistons we supply. It’s just a fine balance each way with the considerations being, Is it water cooled, high compression piston, piston quality/material which will effect swelling, turbo, nitrous in which case that number will be slightly more about 0.025 more per requirement from a typical flat std setup running as low as 0.1 but mostly we run them around the 0.2mm. If you were running the engine in a boat with no drag 0.5 might work

The piston to go with would be AKPRP005G at 61.00mm and have the machine shop doing the bore for you to measure it and add about 0.2mm or slightly less and it should be fine.

No we do not deal with TB heads im sorry and do our own heads available with any valve size to suit any bore size of choice specifically because we machine/make all valves up right here. The heads we make are a non roller rocker head consisting of steel, stainless or titanium valves moved if need be and seated using a special blend all new alluminium, brass seat with matching guid, highest auto grade 5 titanium retainers, HD valve springs, rockers, shafts, porting, polishing, race cam etc… The heads we charge $250.00 USD with Steel valves, $265 for stainless or $380-420 using a titanium valve version.
Just as a guide we do bore kits for $100 USD consisting of Piston kit machined to suit, Gaskets and Cylinder $110 USD

So, if Akunar can do me a custom head for the same price as a TB, is that a good deal, quality the same???
My current thinking, get a head from Akunar, 61mm piston, stainless valves size in and out??? Cam and hd springs.

 

[sean01]

seems like his pricing is all over the show these days...

last time i got quoted for a head the starting price was 175usd and bore kits have cost me 125usd all plus post of course..

a mate of mine got 2 heads a couple of months back, both ported but in different configurations.. 1 head was an awesome job, the other the port job looked like a kid had done it and it was all assembled and had metal/allow filings all through it..

he seems very inconsistent in his manual labor items.

just quote the above problems to be sure you dont get stuck...

as for the his heads compared to a TB V2, well im not sure if anyone has done a back to back dyno test.. maybe Terry can help on this subject.

but if money is an issue it would be worth trying one and def wont be a step backwards anyways..

oh and just so you know... 61mm bore isnt worth the drama's it only makes it 154.89cc but 62mm makes 160.01cc

 

[rumble]

oh and just so you know... 61mm bore isnt worth the drama's it only makes it 154.89cc but 62mm makes 160.01cc

wont i need to hone the bore, as the bore is three years old, increasing the bore slightly bigger than a stock 60mm piston can handle? Thought while the hone is in there keep going to 61.2mm

 

[sean01]

yeah its need to be honed, but aren't you looking for a good motard engine!!!

and its not as easy as just honing out to 61.2, it has to be bored first to like 5 thou under the finishing size..

before going ahead if your set on 61mm bore size id be getting the bore measured properly first.. cause if the bore has been hot and is worn it may not clean up at 61mm... also pistons usually measure under the advertised size but with clearance there close..
i have a 57mm hispeed piston here (supplied by akunar) it measures 56.8

 

[grnman]

Akunar have some barrels for your YX

AKUNAR MOTORCYCLE BIG BORE KITS & RACE HEADS

does anyone know what there heads are like compared to a V2?

 

[grnman]

And sleeves

AKUNAR MOTORCYCLE CYLINDER SLEEVES

 

[Barnesd09]

Just a thought..... Akunar isn't "china" may want to check with Chris Jones whether you can run Thai parts in the china motard class?

 

[grnman]

ive probably got Chris' phone number if its an option you want clarification on rumble.

 

[sean01]

the barrels are china.. pistons would be manufactured in taiwan..

 

[The_GDFP]

The barrels he's sent lately have been re-sleeved OE KSR/KLX items, Thai-produced along with the rest of the Kaw engine. He had previously supplied some Chinese barrels but didn't have a source last I checked. Might ask him what's available currently.

The casting is a bit more limiting on the OE-type heads, regardless of valves installed, compared to a V2. The valve stems are 5.5mm in a stocker, 5mm in the TB, 4.5 in a Tak +R. Plus the Tak comes with the 71g alloy rockers. If limited to a Chinese head, consider sourcing valves and having the chip-chucking done by Sean or the porter of your choice.

If not limited to China-sourced components, the Tak parts are tough to beat. Maybe replace the old 150 crank with a fresh 57mm stroke 160 version and bore a KLX jug for the 59mm Tak piston? Or, depending on power curve preference, have the crank de-stroked to 49mm and use a 64mm Wiseco forging. Either would be a much lighter and stronger piston, not requiring additional notch work. I use plenty of the Akunar pistons and like the flame travel of the radius dome but they're heavier.

If stuck with Chinese engine parts, I'm sure you can find some one who's taken a new stock cylinder and piston off to build a big-bore. Then you can swap to a Zonger 155 or YX160 crank.

 

[sean01]

not so sure why they would outlaw a thai bbk and piston if you can run jap parts and not to mention V2's, oko's and so on...

come to think of it why isnt the daytona engine outlawed..

i think someone is doing to much thinking lol

 

[grnman]

only doing alot of thinking so hundreds aren't spent on the wrong part though. but when you think about it they should just label what brands you cant use.