I finally got around to advance the timing on my motorhome and didn't have the proper timing tools so I decided to do it a way that I read on this forum.
I delayed it doing it for about a year because the MH ran good.

I pinned the motor and then checked the pump and the pin slipped in. The timing was 12.5º stock.
I then painted a area on the balancer and scribed a line across it and set up a pointer for 12.5º. I then pie-d the diameter of 9.25"- dividend by 360 and that came out to .0805, times it by 2 for 2º more degrees of timing and scribed another line .161 clockwise.
I then unpinned the motor and pulled the timing gear the rotated the motor CCW further than the 2º mark then CW to the mark. I cleaned and popped the gear on and tightened it some and then unpinned the pump and rotated it CCW - then CW to the 2º mark and checked the pump and the pin went tight in. I then torqued the pump to 170 ftlbs using a new nut and washer.
I rotated the motor CW two revolutions stopped on the 14.5º mark to check the pump again and the pin went right in.

I noticed that when I pinned the motor that it had about a degree of slop. I centered the slop before I started scribing the lines.
Now for the road test...
I just came back from a road test and the MH does seem to have more power. EGT's on the flats runs 50º cooler at the same speeds I test at and I pulled a hill in 6th that would shift down to fifth before.
I feel that timing the motor this way is probably as accurate as with the proper tools because of the pin slop.
I feel that if your timing can be set back to stock- you can reset your timing anywhere you want doing the way I did it. I'm sure I'm not the first to do it this way and won't be the last.
I can afford to buy the tools but wanted to try it this way and found out that it was easy.
The only thing that was a problem for me was draining the oil from the pump without splashing on the concrete driveway.!
If you can do the math and scribe straight and accurate lines- you can save the cost of the tools.
JMHO

 

I like it. It almost seems simpler then with the tools. next time I bump my timing im gonna do it your way and then check it with the gauge and see how accurate it is.

 

Only downside is you don't always know where the pin is set in the pump. Those are moveable, so it won't neccesarily be at 12.5 or 13 or what have you. Thats the nice thing with the dial, but thats only good if you have the correct timing chart. A timing light is real only way of finding out what your real timing is. But for quick and relatively easy, your way is hard to beat.

 

A lot of the shops with very experienced techs do it your way but always check with a timing light afterwords.