balancing act
 

I will be getting my new OS JE pistons put in at some point in the not-too-distant future. Given that the new parts do not weigh the same as the OEM parts that are coming out (are lighter), I am still debating about getting everything (ie. crankshaft) balanced when I get it re-built. Regardless of that, however, I just bought a small digital scale (0-600 g in 0.1 g increments) and will be weighing the pistons and pins to make sure that both pistons and both pins weigh the exact same. Although I imagine the weight difference (if any) is minor, I will make sure that both the front and rear piston and pin combo are identical in weight. This should make it run fractionally smoother.

Quick question, where is the best place to remove weight from the piston and pins if need be. I was thinking the inner par of the bottom of the skirt on the piston and the inside of the pin (just grind away slighty with dremel). Sound ok?

cheers

sounds good to me. If you're having the engine rebuilt, do it right and balance and lighten. I wouldn't think twice about it and then you won't have to look back. it's not like something external that you can change easily and inexpensively. Let them balance the pistons while you're at it and check them when you get them back.
Off the subject, is your rear PVM a 6"?

I wouldn't thin out the skirt. Could result in collapsed piston and piston slap. You shouldn't have to remove that much anyway. Maybe from the inside of the pin boss.

Parts balancing is good.
Crankshaft balancing as you may know is a whole other concept.
If you can find a shop that has balacing equipment for cranks ( most likely does a lot of cars too ) and they balance it for you, ask for it to be welded.
When rebuilding porsche engines, we never rebuild an engine without the crank and crank cases going to Atwell engines here in dallas.
In all of the great city(s) of Dallas / Fort Worth, theres only 2 or 3 buisnesses that can truly balance crankshafts the right way. And I only know Greg Atwell among these personally, so I send all my work there. I would recommend having this kind of work done by his shop if you really want the real stuff... and are in texas.
the work is verifiable, and you feel it in the engines when they are balanced.
They get rough again if not welded... so theres the "seal" on the expensive balancing.
You only TIG weld about a centimeter on each pin to lock its position in place, preventing rotation.
Stock motors run in a constant state of imbalance, unless you do the fine balancing and weld it(lock it) they never stay strait. Every crank and rod pin has the free opportunity to twist a little when the engine backfires or farts, if not welded. ( ahem .... superhawk! )
Most of the real benefit goes to multi cylinder engines, but on the V-twin, its only an issue of the balance of the crank weights them selves.
You get the center balance of the crank and all your assembly parts weighed like you are doing, it will feel noticably smoother.
You can really make engines last longer by balancing just the crankshaft.
The only difference between a Toyota bottom end and a Lexus Bottom end is the Lexus crank gets balanced, and the Toyota crank comes right off production and into a box with no extra goodies.

I would (and did with mine) get it all done by a professional. They will most probably want all the assembly anyway.

thanks

Just called around and found a local shop who can weld and balance my crank (to the new bits) for $225 (CAN). I think I will go ahead and get it done, it will surely pay off in smoothness and longevity....

Nice, that will be one sweet motor when you're done with it:)
RC

I hope so. In the end, some will surely be quicker on top end as I building an engine with particular focus on the mid-range but you`ll be hard pressd to find one with more grunt :) I want the thing to literally leap forward every time the throttle is turned (never use top-end anyhow but I use the mid-range every single time I go out).

Am still waiting on some parts to come in (including CCT`s from Truck). The tricky part will be holding off until after riding season is over to get it all done. I thought of dropping it off at the shop before leaving for (family) vacation (2 weeks) but worry about some stupid delay (like a back order) throwing a wrench into everything. At least if that happens in November, it`ll have until March to come in without robbing me of riding time (mind you I have my DT200R to bomb around on but it`s not the same as the VTR).

My next RC51 engine will be lightened and balanced for sure.

My VTR engine had tighter budget restrictions.

Thats a very good price dude.

Quick question: while I can easily understand why one would weld up a crank with multiple journals (I had a friend with a Yamaha three-cylinder two-stroke snowmobile engine have his crank go out of phase slightly, for example) but in the case of the VTR, both conrods run on the same journal. Is welding needed?

cheers

What's the story with welding the rod throws? Where does the twisting of the crank occur? I can't see it bieng an issue on a short crank. But I don't know anything about it.

There are two counterweights with a conrod journal. Sudden torque inputs to this can cause the non driving (flywheel) side to twist relative to the driving (pto) side of the crank. This can really only occur on an assembled crankshaft typically found in two strokes. Our crank, which on fiche appears to be a cast/forged one-piece unit, shouldn't have this as an issue. The conrods are bolted on and are not assembled as part of the crankshaft from what I can tell.

That's kind of what I was thinking. But there may be more to it.

The VTR crank is a one-piece casting.

You are right, if its a one peice casting. Im not sure it is. I will check, Im intersted now.
It may be that the crank is one peice on the fische because its an assembly from honda.

I threw that out there for generality. Now you guys know some good tidbits at least.

Balance it and if its a one peice crank, go with it.

On many other bikes its not a single casting and will twist like Autoteach described.

Cars and 4 cyl bikes are affected by this more than V twins.


The XR750 harleys that our shop used to race mile flat-track with ( not I ) all had to be welded. but a harley that makes over 150 HP is a self destruct machine anyway.
The team spent over 30,000 dollars ( in 1986 money ) on each bike.
They would kick a superhawks ass on a road racing course. (with Charlie Orr piloting at least)
He won the 1987 Austin Texas "Aquafest" road race (down town streets race course) on this bike, racing against GSXR and other dedicated road racers. When I can find the pic I will post it of him sideways in 1st place sliding the rear thru the 3rd from the last turn ... on city pavement! Can you imagine what the riders behind him were thinking ? lol
( Those two XR750s were the loudest and most violently fast bikes I ever rode , period. holy shit they were fast )
[not friendly and very hard to ride]

you're making that up right? I didn't know such things existed, lol

I swear it would be the most terrifying thing you ever rode, lol.
Not at all a Novices bike as it has a 1/4 turn throttle and an explosive power band like a 2 stroke.
It was so little and skinny it felt like you were riding an XR-80 with a rocket motor.
They rebuilt the top end after each race. Spent big $$ on them.

In essence its not really a harley, but in fact it is still a harley , if that makes any sense.

And... bubba shoberts VT-750 honda he rode against the harleys was even more powerful.

Getting anywhere close to 200 hp/L out of a Harley (except perhaps the V-ROD) must require some SERIOUS modding ($$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$)

BTW, I did some research on the VTR1000.org site and one chap had the crank dynamically balanced on his built-up VTR and he said it transformed the bike (much smoother and revved up much more quickly). Sounds exactly like what I'm looking for...... :)

They pissed $$ away so fast it made me sick.

Picked up a cheap digital scale on eBay (weighs to 600 g, 0.1 g increments) and weighed the JE pistons and pins. Results:
piston 1: 392.5, piston 2: 391.6
pin 1: 116.6, pin 2: 116.4

small differences to be honest but they'll be the same before they go in....

Nice Mikstr, now you're officially a "weight weenie"...LOL!

You may want to weigh yours too Rick. While you may not want to go whole hog and get your Stage 1 engine balanced, doing the pistons and pins wouldn`t hurt and is quick and easy to do.
As far as the balanced engine is concerned, have a look at the comments made by delmeekc (?) on the VTR1000.org site (site is down at the moment unfortunately), it may change your mind....

will do, Mr. Weight Weenie:)

That`s Mr. Torque-meister to you son :)

LOL!