Piston Rings

[Martin Harris - Moderator]

They have my vote too.  Very often orders have arrived the next day.  Good choice of bearings too - whether right or not I’ve tended to go for C3  bearings recently (slightly larger clearance) which I’m led to believe are better for high speed/temperature use. 

[Engine Doctor]

Hi Martin . I have often wondered about C3 bearings for use in our engines. Designed to allow for heat generated especially at start up and the subsequent expansion that can cause bearing failure. I have never actually used them.

How do uou find them ? Is the extra clearance noticed in the feel of the engine? What types of engine do you fit them too? I can see a possible advantage on say a Ducted Fan Engine although they are pretty rare these days. 

With the extra clearance do you choose the sealed type for external/front bearings etc ? How do they compare to standard clearance on our applications ?

[Martin Harris - Moderator]

All I can really report is that I haven’t had any failures, problems or concerns with any I’ve fitted.  Mostly OS and clone single cylinder 4 strokes ranging from 20 to 120 and a Laser 62

[Simon Chaddock]

Surely bearing heat expansion depends on where the heat is coming from. Uniformly heated and within the capabilities of its lubrication all the bearing will expand simultaneously.

I would have expected in the average model IC engine the crankcase gets hotter than the crankshaft suggesting if anything the outer race will expand more than the inner thus increasing the ball running clearance. Just an observation.

 

Now whether the highly penetrative methanol/oil environment of a two stoke may deteriorate a sealed bearing's lubrication over time is another question.

 

  

[Martin Harris - Moderator]

We don’t normally use fully sealed bearings (there might be exceptions of course?).  Some front bearings can be replaced with 2RS bearings but always with the inner seal removed. I would normally replace like for like though - air leakage may be a problem for two strokes and four strokes without rubber seals may possibly be designed that way to encourage internal air/oilflow through the tappet area. The rear bearing would normally be open as it needs all the lubrication it can get - especially with four strokes. 
 

On the other hand, I believe that even 2RS bearings aren’t truly sealed - the seals are only clipped into place. 

[Paul De Tourtoulon]

Any idea what sort and where I can get some metal for piston rings?, I would like to have a go at making one on my little Emco SL,,,

[Engine Doctor]

3 hours ago, Paul De Tourtoulon said:

Any idea what sort and where I can get some metal for piston rings?, I would like to have a go at making one on my little Emco SL,,,

The last cast iron rod/bar I bought i found on  Ebay,  Mehanite grade. Also good for making new piston for old diesel engines. Previous to that I have used some old cast iron window sash weights. Failing that have a word with a GC piston rings Gavin might supply some.

I forgot to say. Try to find the smallest dia bar as its often difficult to find anything smaller than 30mm and thats a of waistage and time spent getting down  to size.

Edited March 27 by Engine Doctor

[Indian]

You need continuous cast bar, most of the usual suppliers sell it. M Machine, Noggin end, College etc.