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Webster IC Engine build log.
Bogstandard:
Chris,
Now you are starting to slow down a bit and take your time, it is very noticeable in your work.
Compared to your earlier builds, this one is exceptional. Keep it up.
Bogs
raynerd:
Thanks John!
I`m still struggling to find data for the groove width and depth on this piston for the piston ring! The table that was posted would have been perfect only it doesn`t include a 3/32" cross section! I`ll have to try and work it out based on that data unless anyone can lend me a hand!
Chris
NickG:
Chris,
As Doug said, I believe the ring is technically supposed to roll slightly in the groove so it pushes against the groove wall and seals. This is maybe to get the lowest friction. I don't know whether the groove dia is supposed to be size for size or slightly larger than the id of the o ring. I would think, like you it's supposed to be marginally larger.
Might be worth checking if Marv has a program for this?
Nick
Bogstandard:
Chris,
Whenever I fitted o-rings as piston rings I looked at them in a slightly different way, in that I didn't want them rolling up and down in a wide slot. To me that stinks of maybe getting twisted up and uneven wear.
My way for a 3/32" (0.094") cross section ring would be to just cut a square section slot a couple of thou wider and the same shallower.
So 0.096/7" wide by 0.091/2" deep.
That way, the ring, by being pushed into the groove, would take up an oval shape, giving a nice side pressure to form the seal. As the ring wore away, it would slowly form a flat where it rubs on the cylinder wall and gradually return to it's original round shape.
Your bore does need to be rather smooth, otherwise it will wear away an o-ring fairly quickly.
I am sure that other people have different views on the subject, I just told you mine that worked for me.
John
dbvandy:
I agree with Bogs... The fitment of the o-ring is important, but not critical.... from all the information I read on the subject, the important thing is that you have pressure on the dynamic surface (cylinder) at all times. The engine is very low compression, about 4 to 1 where a car is about 10 to 1, so you are not going to get much blow-by either way. Jan Ridder does not even use o-rings in his engines, just a tight fit.
It is starting to look like something now! I love that feeling!
Have you decided on ignition? If I had seen this, I would have done it without a doubt...
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=13767
This CDI unit will make for a really clean install. You still have to lug around a battery, but it will make a reliable spark. Or you can go the route I did with the trimmer coil as it works beautifully and does not need anything else to run. On the Otto, I used some neo magnets on the flywheel, so you don't have to use the finned flywheel from the trimmer.
Just some food for thought....
Doug.
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