I am hoping to not have to do all the experimentation from scratch.

Can anyone share with me what they have found to be the Ideal crankshaft Balance Factor for

1975 DT125
1975 DT250
1976 DT400

My DT400 is first on the list to get the vibrations as low as possible but without a reference Ill have to split the case and make modifications over and over, hoping someone can save me a few tries.

Thanks

Etienne

I'll kick it off to bring it back to the top. But it's too hard basket for me although an interesting subject. I just true them up so they spin accurate & away we go. Big thing is to have the engine mounting bolts very tight as a jamgling around motor vibrates like crazy. Some more modern 175-200's have the swing-arm bolt through the rear of the motor & that's very important to keep tight. But old 360's are notorious for vibes & mine fleet were no exception. But just to be different [or stupid lol] i fittes YZ250A short stroke crank in my 360. Was a bit of jiggery pokery but it worked well & was silky smooth. Crank is wuite different to a trail 250 crank. I've got no idea on ballance factors though. That bike was 80x64 bore & stroke, so a heavier 80mm piston swinging on a crank ballanced for a 70mm lighter piston. funny what works sometimes. Normal 360 is 80x70. & 250 is 70x64.

I appreciate the bump, and I'm glad that you mentioned keeping mounting bolts tight. Its true even frame rigidity affects what the ideal balance factor might be

The vibrations on my DT400 would make my hands numb after 30 minutes of riding. Makes the 500 mile 3 day trips through forest service roads less than pleasant. 

500 mile 3 day trips through forest service roads. Man you'd be a tiger for punishment.

First thing to check might be crank runout. 

I can't speak for the bigger bikes but the 125/175 is sewing machine smooth up to over 10,000 rpm when crank is trued to near perfection AND care is used to install it properly. 

About 20% of that are paved roads connecting the route together, but its a blast with a group of vintage bikes

Thanks for the input I appreciate it

Et,
There is no ideal factor for a single. It's just a matter of what plane the secondary balance is desired, for/aft or up/down.
Usually the primary is 100% and one lives with the secondary for/aft off balance.

cliff

If i could add a few things related to this.
In regards to the 400. I think setting the crank up in the lathe or on mag centres running two clocks on the lands is certainly the best way to get well within the ball park.
Other factors are you have the piston weight doing it's best to escape the confines of the cylinder ,prehistoric ignition and a ruddy great rotor on the end of the crank.
The other thing is the bearings. Careful what you buy in regards to where they're made. I only buy Koyo and IKO and if it doesn't say made in Japan on the outer, it don't go in. I'll take German but nothing else.
On top of that you have assembly methods. I don't hammer bearings in. I have a hot plate and heat the cases to 150°C .Everything just either drops in or pushes in with a graft. Everything spotless.
Not saying you don't do those things or trying to insult your intelligence. I have seen it so many times. People going to extraordinary lengths to get stuff bob on then you see them buying okay bearings and then battering stuff in to casings with a socket and hammer.
What's your objective ?
You obviously have one to ask a technical question like that and i'm curious .
Regards Shyted

Using the centers is usually problematic for me because puller bolts and/or hammer usage has often damaged the centers.  It doesn't take much to throw things off when you're trying to get within 0.0005" of perfection...  preferably as close to 0 as possible.

Factory method of using v-blocks on a surface plate or better yet a specialty crank truing stand is the way to go in my experience.