2MA engine power up

[Need4speed]

might inspire..
Bore/stroke are the same for motocross - so why not..?

[tzr-v4]

Do you have more detail on the bike donor ?

I think crank case has been modified too.

[tzr-v4]

I though 4DP was the TZ250 model not YZ125.

Late motoX engines are 54mm x 54mm bore x stroke ?

seems that YZ125 are in 56 bore from 1976 -> 1989 according to wiseco piston kits
any idea ?

[mboddy]

It looks like a 1986 1LX-11311-00.



They have some new ones here:
http://www.ebay.com.au/itm/YAMAHA-NOS-CYLINDER-HEAD-YZ125-YZ-125-1986-/220228398515?pt=Motorcycles_Parts_Accessories&hash=item3346a2adb3&_uhb=1#ht_2050wt_1081

[mboddy]

How many horses?

[Noisy Cricket]

Interesting project.  Cylinders are a bit dear at nearly $700US.  Looks to have the aux exhaust ports like the 2XT and certainly must have more generous transfers.  Hope you get it to the dyno so that we can see what it nets out - could hope for mid 60's?

[mboddy]

Mid 60s. Mine with 2XT cylinders feels stronger than that.

[Noisy Cricket]

Can anybody point me to a 2XT/2MA/1KT dyno run that netted mid 60's HP?

[Toop]

nikasil on YZ 125 is from 1989 ( 1LX is iron cast added )

[tzr-v4]

Mid 60s. Mine with 2XT cylinders feels stronger than that.

A stock 2XT with a set of JollyMoto is not bad at all on track compare to standard RGV250 with pipes too. I've read (on French forum) that TZR 1KT crank is a weak point when engine is really tuned.
I'll try to get more detailed information.

mboddy you should dyno your bike and post roughly the tuning of your cylinder.

I'm interested in what to do next time I open the TZR engine (for sure squish should be reduced close to 1mm).

[mboddy]

We will be doing some dyno runs early next year and trying different pipes etc.
Hoping to have the improved powervalves first.
Squish is 0.9mm.

[Noisy Cricket]

When having the crank stroked to 56mm (to create the 400) I seem to remember most of the crank bits to be same or similarly sized to the 350YPVS bits.  If anything I would say that this crank should easily deal with 70 HP with good reliability WITH regular maintenance.  An old 350LC racer I knew said the practical limit for that crank was mid 70's with OE parts.  Indeed my 400 engine makes high 70's and at this last rebuild only needed a single crank bearing (a little out of tolerance).  I would say not to expect to go 8000 miles on a 70 horse engine without crank problems.  Certainly the Banshee guys must know how to make these cranks last.  I would just be careful how hard I spin the crank.  Nothing will last for long being regularly run to 12K.

[mboddy]

I also think the crank looks good.
But I have been racing for many years with a R1-Z crank which runs the 2RH rods.
Does anyone know how good the F3 race kit big ends and rods are?
I got my new F3 crank trued before fitting.
The rotor and Wossner pistons are very light and so hopefully that will help crank life. 

[tzr-v4]

2RH rods are also used on TZ250 engine.

TZ250 part
http://www.fondseca.com/index.php?main_page=product_info&cPath=96_103&products_id=727

2RH is a TZR125 vin code.

[Noisy Cricket]

Indeed - keeping reciprocating mass as low as is practical should extend crank life.

In the construction of the 400 the weights of the piston and rod is going up ..... way up and I have been concerned.  No problems yet!  The Wiseco piston I run is heavier even than the equivalent cast piston that is OE in the DT/WR200.  I never considered that the 400 might become a real shaker and I guess I'm just lucky as it isn't.

I have a vague memory that the big end bearing specification for the 23 x 29 x 17mm size varies by Yamaha model - the TZ's getting additional roller(s) and silver plating.  The 350YPVS / Banshee / Blaster getting the more pedestrian specification.  The "highest" specification Yamaha OE number that I have is: 9331-0523D2-00.  The OE part is going to become hard to find eventually, but perhaps the after market will keep kicking them out for the Banshee guys.....