- Dec 29, 2016
- Reaction score
- Viet Nam
That's why I said in my thread about the doubt: "lapping a plunger and cylinder with tight tolerances"so today I tried making a test-version of my injection pump barrel and plunger. The plunger helix came out well, as did the barrel with initial lapping. Sadly, I rushed ahead too far and began final lapping of the two parts together before getting the size close enough- the consequence was galling and seizure of the plunger in the barrel, ruining both. Lesson learned, and next time I may try hardening the barrel to minimise the potential for galling.
With small diameter cylinders and plunger : I Never lapping them together with tight tolerances.
One mistake and it will destroy your hours of work.
Before you put the plunger in the cylinder: clean them with kerosene - so clean , and then put some w20/40 oil in both before you put the plunger in the cylinder.
Your cylinder is 4mm in diameter, so use the shank of a new 4mm drill as the standard gauge. lapping the cylinder to 4mm and then making the piston (on the shank of the drill bit there is usually a a parameter engraving- sharpen it)
Make the plunger larger than 4mm (maybe 4.1mm or 4.05mm and then lapping the plunger until it slides into the cylinder only with w20/40 oil)
Or you can also use a cheap drill shank to make a plunger