What to check…..there are three main things to check. Do your crank webs have "coaxial axis" ???? What does that mean ? Well if the webs have rotated around the crank pin then they are out of alignment. The two pics below show the two webs mounted on a dummy crank pin and then rotated about that crank pin. One pic is with the webs way out of alignment and the other is with them rotated back into alignment.
There is no way that your crank will come out that misaligned but it will have some misalignment so it will have to be corrected. That is done by hitting the outer web with a copper hammer so that it twist itself back on the crank pin until it is aligned. The drawing below shows this coaxial misalignment and the other two ways your crank could be out.
I indicate on the surfaces that the outer bearings will be put on. The specs for a 1979 RD400 are shown below
Maximum deflection (S) : 0,03 mm Small-end deflection (P) : 0,36 - 0,98 mm Big-end side clearance (D) : 0,25 - 0,75 mm Width (F) : 52,00 - 52,05 mm Width (A) : 153,90 -154,05 mm
Now which way the "high spot" on any shaft is moving will show you which misalignment you need to correct. I will try and explain what you see at the indicator for each different misalignment. But if you have got this far you should be able to work it out yourself. I will do that write-up at later date.
Remember that this is only the way that I build my cranks. Other people might not agree with how I do it but it works for me.
I have put this info up so the people can see that it is not really a black art this crank building and if you have the tools and a bit of knowledge then you can rebuild your own cranks.
If you are not confident then there are plenty of good firms that will do a great job for a good price.
But I have always wanted to do as much of my own work as I can and now that I have got this info from the internet and other sources I want to make it easily available to my fellow two stroke owners.