YZ444 update

[pursang262]

Well another Loudon practice day got rained out, so the bike's set up for hillclimbs.Raced sunday, got second in the 600 4-stroke class,behind the defending class champ on a 600cc buell blast, and third in the 450cc class behind two very fast RD400s.This motor is awesome, and I haven't even started to play with jetting or gearing yet.Hopefully in May I can get it to the racetrack and get some time on it. To recap; the bike is a 99 YZ400 bought cheap and thrashed last winter.After cleaning,lubing and adjusting everything and replacing some hardware store fasteners, I got some bolt-on swingarm extensions so I could hillclimb it.Next was a set of 17 inch wheels and big brakes for the racetrack.This winter I was gonna freshen up the top end, but way too much time spent reading this forum changed that plan,and destroyed my wallet completely.Now it's got a new 426 crankshaft,trued,balanced and welded by Falicon to the weight of the new piston, a 97mm top end and head porting by Foreward Motion, new stainless valves with 28mm intakes, Hotcams adjustable cams still set at stock timing so far, stock carb with EKP needle, and GYT tapered headpipe with a stock 02 426 muffler that I got for free.One more hillclimb this weekend then I'll change the oil and check the valve clearance,maybe jet a little leaner and see what's next. More later...

 

[SFO]

How big a main are you running right now?

 

[MotoGreg]

SFO, I know you know a lot about the 444cc motors, I have some questions...

Does the 444 piston require race gas? What's the compression ratio? I want to update my WR400 Supermoto to this. If it was just for Supermoto races I wouldn't mind race gas but I ride on the street a lot so I want to be able to stay with pump gas. If it is a high comp piston then can I use extra cylinder base gaskets to lower the comp ratio?

I think I'll need a 426 rod and cylinder right? I can't use my 400 cylinder right? Does anyone have an old 426 cylinder for sale cheap? Even if it's got damaged Nikasil it doesn't matter since I'll be using an oversize sleeve. The White Bros catalog shows new 426 rods with crank pin and bearings from two companies... Niks/Pro-X and Vesrah. I know Niks/Pro-X is good stuff, do you know if it's OEM quality or should I stick with an OEM Yamaha rod?

I want to be as low budget as possible (well, who doesn't?) so I don't think I'll be doing any type of headwork or bigger center valve or anything like that. I'm not really interested in a huge top end horsepower gain, I'm mostly interested in gaining back some of the midrange torque that I lost with the tall street gearing.

One more thing... I read somewhere that "Hot Cams" was going to make a 426 cam with automatic decompressor. Does anyone know anything about this?

 

[SFO]

The 97mm will run fine on high test pump @14~1.
I think the combination of ignition curve and combustion chamber work together to make the yz-f very tolerant of pump fuel.
I wouldn't want to be a guinea pig for the aftermarket rod, and seeing as oem is proven, I would go in that direction, IMHO.
Yamaha sells a complete crank ass for around 300$ and I would just do that.
The headwork is really the frosting on the cake though. I would bare minimum get a good valve job done and replace your valve springs and guide seals.
I think Eric has finished 97mm barrells on the shelf, maybe you could get a core exchange for your 400 barrel, I don't know.

I'll get ahold of hot cams and see where they are at with the auto decomp ex cam.

 

[pursang262]

SFO, I just dropped from the 175 that was in there to a 168, that was the next smallest I had.I'm running the bike on C-12 because it's relatively cheap,and easy to deal with,also my other bikes like it.I don't know how that will affect the jetting compared to what you guys are running, I know you're using smaller mains, but figure I'll work my way down.I've got a track day at Loudon on the 19th, I plan on spending the afternoon playing with brass.Thanks again for all the advice.

Greg, you can get the 97mm piston in either 12.5 [stock] or 13.5 :1 compression ratios, I went with 12.5 .I didn't mind giving up a little low to midrange to get more revs on top.So far it seems to have been a good compromise.

 

[john stu]

14-1 compresion on pump fuel?that sounds scary to me!

 

[SFO]

It scared me at first too. The yz-f combustion chamber is quite dense, allowing 14~1 with a flat top piston. I ran mine on pemex with no problems. The torque peak was at 8k and it ran out of air over that.
This is a modern design and it shows. I had to rethink some of my pre existing notions on motor set-up as well. Without a piston dome to create higher compression the cross scavenging at higher rpm's isn't effected either, like in a wider valve angle 4v motor like a KLX, or a Husaberg...

 

[MotoGreg]

Thanks for the info SFO. I may have a line on a WR426 cylinder with some scratches on the Nikasil, I just have to see if we can agree on a price now.

 

[SFO]

Originally posted by MotoGreg
One more thing... I read somewhere that "Hot Cams" was going to make a 426 cam with automatic decompressor. Does anyone know anything about this?

I just heard from them that the auto decompression cam is in testing right now and is going to be available soon.
I'll keep you posted.

 

[CRboy167]

Originally posted by SFO


auto decompression cam is in testing right now and is going to be available soon.

Sweet Im in for one of those Please keep us posted!!!! :worship: :worship: :worship:

 

[MotoGreg]

I bought a 426 cylinder for $50,

 

[MotoGreg]

Sorry, some wise guy here hit the keyboard...

What I was going to say is that I bought a 426 cylinder for $50 and it should be here any day now. What are the pro and cons of boring and fitting a sleeve vs. boring and replating? I think they are pretty much the same cost-wise so I'm not sure which would be the way to go.

 

[Shawn Mc]

Id be willing to bet a considerable amount of money that the Vesrah rod would out perform the OEM rod in a duty cycle test.

Think about it, why build an inferior connecting rod for a purpose built race engine??

Dont mean to offend anyone, just my $.02 worth.

The thought of pump gas in a 14:1 motor make me cry.....it may work, but man, isnt it hard to fire?

Thank god for the compression release!!

 

[Rich Rohrich]

Originally posted by MotoGreg
What are the pro and cons of boring and fitting a sleeve vs. boring and replating? I think they are pretty much the same cost-wise so I'm not sure which would be the way to go.

The amount of metal that has to be removed to fit a steel sleeve seems to cause bore stability problems at 97mm. We saw the same things when the 400s were brought out to 417 (92 to 94mm) with a steel sleeve. Add that in with the standard deficiencies normally asssociated with steel sleeves and it's hard to recommend them. Steel sleeves are only an advantage for the guys trying to pump out a ton of cylinders. They are cheap and easy to do compared to plating.

 

[SFO]

Originally posted by Shawn Mc
Id be willing to bet a considerable amount of money that the Vesrah rod would out perform the OEM rod in a duty cycle test.

Think about it, why build an inferior connecting rod for a purpose built race engine??

Dont mean to offend anyone, just my $.02 worth.

I have a hard time recommending anything that I haven't used. I have also seen some hack crank rebuilders that are very scary.
Suggesting a guy rebuild a crank with non-oem parts and having to stand behind it is hard for me to do. My integrity is on the line with every post and I don't want some poor guy to think he is saving 100$ only to have his crank unwind and cost him a set of cases.
Cheap insurance suggesting a new oem crank set, and it is only 300$.
Fire and forget for another season.
On the other hand a qualified machinist crank rebuilder could probably get good results with these rods, but how do people seperate the wheat from the chaff as far as engine rebuilders?

Originally posted by Shawn Mc

The thought of pump gas in a 14:1 motor make me cry.....it may work, but man, isnt it hard to fire?

One of the most common comments about the 14~1 compression ratio on this motor build up is na, I just want to run pump gas and I don't want to kill the top end.
Heck, Thats what I told Rich when he suggested the 13.5~1 piston instead of the standard 12.5~1.
But I gave in.
So I built it with a tight deck height and the 13.5~1 piston thinking I could always build in less compression if the thing was too funky.
The reality of the tight chamber on the 5V yamaha coupled with a flat top high compression piston are very different than my stable data had led me to believe after dealing with domed high compression pistons and chambers on the 4v singles I have built.
I never had any detonation, PERIOD. Even running pemex down through Baja, this motor ran great. I think it would run on Tecate.
I am starting to think I could weld up the chamber some and raise the compression even more.
My only concern is valve shrouding.
BTW, in Baja I was running 15-42 gearing with a WR gearbox. It would still run right up to the rev limiter in 5th at 10,500rpm. I'd kinda like to know how fast that is.
Next time I'll mount a GPS.
Starting wise, sure you could feel the squeeze, but it almost always fired right off. There were some hot start issues once in a while but if I just did the Zoomer ritual and all was well.