yzr long rod

[dub250]

iv got a chance too buy a complete kit for a 90-96 yz or wr id like too put this kit on my 96 wr 250 lets hear some feed back on it like benifets and disadvantages

[RCannon]

You shoudl get the kit, especially if it is a good price. I believe it will only go up in value.

I dont recall it having any drawbacks, other than the cost and difficulty of installation.

[CaptDan]

I fully agree with RCannon on all counts. ?

But I was under the impression that the long rod kit was only for the '96-'97 YZs, as the earlier bikes (and WRs) already had a rockin' motor.

The addition of the long rod kit to our '96 YZ really filled in the bottom of the powerband. Still not as grunty or electric as the '94 (and '99+) motors, but a great improvement.

[dub250]

the 94-96 wr cylinder is a 94 yz cylinder but the 97 is differant i believe but its not the same as 95-98 cylindeof a yz

[jsantapau]

the only disadvantage is that with a longer rod you have greater chance of rod failure just because there is more of it ..... talking the difference between a 125mm rod and a 130 mm rod....... in fact at the time 1989 / 1990 yamaha was using the 130mm rod in 89 and went to the shorter rod in 90 to prevent rod breakage.....

by putting the 5mm spacer under the jug with 2 base gaskets you are effectively raising the ports the distance of 1 extra base gasket that and with the decrease in primary compression you are tending to smooth out the bottom end power and favor towards the top end with an emphasis on wider and smoother powerband.....there is a lot of talk of changing rod ratio and piston speed due to geometry changes that I dont quite understand but it is to favor higher rpm....... maybe on the 96 motor the spacer helps unshroud the rear boost port for better cylinder filling to improve bottom also as CaptDan states

a complete long rod kit should include ; 89 rod kit,5mm spacer,2 base gaskets, 89 powervalve to governor rod, 2 longer studs and 2 longer dowels for the cylinder to rest on.

[CaptDan]

After checking part numbers, it seems ALL 250cc 1990-1998 Yamahas share the same rod (5X5-11651-03-00), so I guess a long rod kit could work on the '94- style motors. ?

It was the lack of bottom end on the '96/7 YZs that made the L.R. kit so popular. Everyone was after that '94 powerband!

[CaptDan]

...a complete long rod kit should include ; 89 rod kit,5mm spacer,2 base gaskets, 89 powervalve to governor rod, 2 longer studs and 2 longer dowels for the cylinder to rest on.

Don't forget the longer power valve rod cover. I never did figure out what year to use, probably '89:bonk:

[adam728]

the only disadvantage is that with a longer rod you have greater chance of rod failure just because there is more of it ..... talking the difference between a 125mm rod and a 130 mm rod....... in fact at the time 1989 / 1990 yamaha was using the 130mm rod in 89 and went to the shorter rod in 90 to prevent rod breakage.....

.....there is a lot of talk of changing rod ratio and piston speed due to geometry changes that I dont quite understand but it is to favor higher rpm......

I highly doubt Yamaha made a 5mm change to the rod length to fight breakage. It was most likely for those things you don't quite understand, piston acceleration, peak speeds, changes in the way the cylinder fills at BDC, changes how cylinder pressures rise and effect the moving piston near and at tdc, slightly changes port timings, reduces thrust against the cylinder wall, etc etc.

[jsantapau]

yes your right an 89 cover ..... forgot about that since that on dont really fit that well either

I would assume that the power characteristics<sp> for each style of engine and powervalve would vary greatly in that 90 /98 set up but I am sure if they all share that same base gasket it would work

[jsantapau]

I highly doubt Yamaha made a 5mm change to the rod length to fight breakage. It was most likely for those things you don't quite understand, piston acceleration, peak speeds, changes in the way the cylinder fills at BDC, changes how cylinder pressures rise and effect the moving piston near and at tdc, slightly changes port timings, reduces thrust against the cylinder wall, etc etc.

they if I remember correctly went to a shorter rod to "increase reliabilty"

[dub250]

i believe it has all the contents that were stated before, it is an old factory off road bike and is way faster and smoother than all my previous wrs. im curious as to what this kit will produce as far as power