February 3, 2018

YPVS repair, Yamaha 34X IC chip transplant

Another one interesting repair job that got me scratching my head for a while. The below RD/RZ500 YPVS unit belongs to Mark(UK) and needed a repair job to be done.

The IC chip was badly corroded and lots of the pins didn't made contact with the PCB due to the oxidation. This is not rare on Yamaha YPVS units but I'm not sure I have ever seen one at this state. 
Any attempts to clean the pins and put new solder on them was at least discouraging as the pins cracked in half by only slightly touching them. There are some tricks that can been done as to trigger the circuit from different pins but this proved to be inappropriate in  this situation as well.
After hopelessly looking at the YPVS unit for a while, I accepted my defeat and I informed Mark that there is nothing that I can do as to repair his unit. 
A few minutes passed by and while randomly searching at my "junk" box, a possible solution caught my eye. I'm not sure why I always find solutions among things that I should had thrown away years ago.
The "possible" solution was a highly damaged YPVS unit that had almost broken in half though the IC chip looked to be intact; I successfully removed it from the PCB and the transplant was now ready to be used on Mark's ypvs unit.
The highly damaged and long forgotten little YPVS unit actually had a final role to play. I take it that it's more to do with luck and stubbornness than real skills though Mark's unit is now in full working order and ready to serve for years to come.

January 22, 2018

Piston, Drill Lubrication Holes

A couple months back I installed a fresh top end on a friend's bike, a '99 Cr125. The piston came without lubrication holes at the exhaust side. So, I thought it wouldn't make any harm to add a couple holes, quite the opposite I reckon.

The piston was temporarily placed in the cylinder with the piston ring just above the exhaust port roof and the exhaust bridge layout was then scribbed on the piston skirt.
Two marks were then punched on the piston, from memory it was about 8mm and 18mm below the piston ring. The punch marks were then spot drilled on the Dore Westbury miller and then drilled through with a 1.5mm drill.

The holes seem a little bit too large due to the chamfering. A drill of 1 or 1.5mm is adequate enough for this modification. 

For more info on the subject, check out this older blog post
2t-racelab.com - piston preparation
and also this nice article from the Wiseco blog
blog.wiseco.com - relieving the exhaust bridge and drilling lubrication holes