villiers piston useable or not ?

[richard]

just purchased villiers piston but how good does a piston have to be , and can this be brought " up to scratch "

[Rob Dobie]

It depends on what you want to scratch with it. 

In the late 1950s to 60s I used to polish up the ports and pistons with Brasso every two weeks on my mopeds. To a teenager the bikes went ever so fast!!!!!  A workmate of mine had a new Velocette Venom Clubman that he stripped down and polished the piston every weekend. The bike went like stink.

[steven mandell]

I am assuming that you would not be asking the question if it was a new piston.
Firstly you must be sure that you have the right size piston.  In order to know this, you must first get a competent machinist to use a bore gauge at several different heights and orientations inside your engine's cylinder.  If out of round is not exceeded by the allowed margin, you then check the code stamped on to the piston that clarifies piston diameter as either stock or of a revealed amount of overbore, for appropriate clearance.  If allowable out of roundness is exceeded,  you must either replace or overbore your cylinder by a standard increment that is supported by your piston manufacturer, and make sure that your piston is appropriately sized for same.
After taking the above actions, you must carefully inspect the piston and ring landings for cracks and dents, as well as roundness with a caliper. 
Once past all the above checks, you should be good to go, although it might be a good idea to check the weight of your new piston against the original.  Often the weight is marked on the piston  bottom, but use of an exacting scale would be a good idea.   
If you plan on doing any piston  modifications beyond a mild polishing, it would of course be important to establish balance between the upper and lower ends of the rod and crank assembly before closing up the engine.
Also the grudgeon pin should fit with no discernable play, and piston pin be properly fitted.

Consult a good Villiers manual for specs and areas where material can be removed when balancing your piston.

[richard]

Thanks for the reply steven . The villagers around here are still using horse and cart  I had thought that the pic was clear enough to see the scour marks is it not ? The piston is the correct part it is just the condition of it that I am concerned about

[Big Al]

Taking the opposing view to Steven. The piston is there to fill a hole and carry the rings which actually do the sealing of the bore. Clearly there is a set of spacing allowing for expansion to allow for clearance. Scuffing on the side or top of the piston is not the end of the world for use in low powered units like a Villiers. It is worth checking the rings for wear. They will thin in use, but worse will ease open the groove they sit in, particularly chrome ones, and start slopping about. Also the pin stop to keep the ring from rotating into a port needs checking. Villiers later pistons are known for pin loss, I believe. A loose or flappy ring is more likely to get caught in the port, snap and naff everything up.

Taking the advice of prior postings the piston can be polished up a bit. Indeed for strokers it was not unusual to shamfure the skirt end to help oil stay on the cylinder lubricating until the bottom ring scrapped most of it down. For really poor units, like the mid of an Excelsior triple, a series of radial groves were made in the piston skirt to hold oil and aid lubing of this hot location. The marks to be concerned about are where material has been pulled off the piston. That has been a hot spot and when bad the ali starts welding itself to the bore. That then fouls the rings and naff time. So those areas need to be made smooth and if it is the same cylinder the ali on the cylinder removed. The polished piston with marks will carry petroil in the depressions.

Beyond that it is about efficiency. These engines will run with some right old growlers in, but of course you get less power for all the noise. You wear things out faster too. For mucking about that does not matter greatly but if you contemplating serious road use then the best you can afford is the way.

[richard]

thanks al i will take that on " bored " . just that they are hard to find - thanks

[steven mandell]

Right Al.
I forgot to mention to measure the spacing between ring landings, and didn't know to suggest checking for ring pins, as I have a theoretically based understanding of 4 stroke engines, as opposed to your both experiential, and theoretically based knowledge of both 2 and 4 stroke engine's fail points.
Any significant aluminum scraping off the piston/ deposition on the bore surfaces, however, would have been exposed by my suggested checking of both piston and bore diameters at multiple sites of varying heights and orientations.

[Big Al]

Indeed. I need to get a way to measure this myself. A load of engines to rebuild. Folk want a good cylinder/piston if they are paying folding so need to know the condition.

[steven mandell]

Using a good bore gauge is the only way to get accurate cyilinder diameters,  and roundness readings.