Discussion and questions related to the course Practical Engine Building
Hello, do you guys have any video where you show the correct way to verify if the oil ring (spacer) is the correct diameter? for example if you use custom piston like 85.25mm and the rings set are 85.50mm how do you know if the oil ring (spacer) is too big or too short? It happened to me that with a type S oil ring (spacer) when placing it in the cylinder it enters very tight, almost it is deformed and with the same block the Type F oil ring (spacer) get's very loose, so how to know when it is correct? I understand that the oil ring (spacer) cannot be modify, in addition there are several types of oil ring (spacer) that would be good to clarify their correct installation.
Hello good question te oil spacer ring is a radial spring so it will generally have a fair amount of tension on the bore I do not know how much you can get away with as far as what Is too large or small but my own rule of thumb is .001 tho bore change adds about 0.005 to the ring gap on a 88m bore but as i say that is my own theory, so keeping that in mind I have removed material from the end of the spacer when I have been forced to fit a ring kit like you did
If it is the corrigated/square wave shaped expander (spacer), it should be fine, with the rails (the thin scraper rings) given around 20-30 thou end gap. The 0.25mm diameter difference is just under 32 thou' at the end gap and I don't recall any beint too tight to be unable to accept that - but might well be wrong, anyone?
What I suspect is happening is a very common mistake in assembling the ring package - it is CRITICAL that the ends of the spacer butt up against each other, with some designs it is possible to overlap the ends and this will force the side, scraper rings to stick out, especially if the wave in up and down, rather than sideways in the groove. Many manufacturers actually have coloured ends, so you can clearly see if they are properly placed after the rails are fitted. there is quite a lot of info' on the interweb about this very thing.
As an apprentice, doing my first engine, I was actually caught out by this, so it can happen, but just the once...