[SEL] piston rings and bores.

[guitronics]

Hi: I'm a newbie to the list,and will ask a question that's probably 
been asked many times before.

Anyone have good results with "Gapless" rings?

John Culp wrote:

> I dunno, I've put new rings in totally glazed old bores that weren't 
> hugely enlarged or out of round and had good results. The glazing 
> itself isn't a problem with gas sealing so much as it reduces the 
> oil-holding capacity of the cylinder wall and can cause problems with 
> ring and piston lubrication. A much bigger problem is if your bore is 
> worn till it's not round. The rings may have worn and turned as the 
> bore wore so they sealed fairly well in it, but new rings won't. 
> They'll bridge between high points across out-of round sections and 
> you'll get tremendous blowby.
>
> On pulling a piston out, I always look where the ring gaps are. In a 
> perfectly round bore with free rings (not pinned), there is no 
> preferred orientation and the rings will rotate randomly over time 
> running in the engine. The gaps won't be found oriented the same way 
> when you later pull the piston as when you put it in. (That's why 
> orienting them in specific ways isn't critical.) Often you find the 
> gaps all lined up on one side of the piston. That means the bore has 
> worn to an egg shape, with the gaps lined up on the pointy side of the 
> egg. That bore will have to be rebored.
>
> John
>
> On May 1, 2005, at 6:38 PM, peter ogborne wrote:
>
>> I just rebuilt a small single cylinder ,four cycle engine. .....short 
>> cuts ,don't take them ! Because i could not readily buy new rings i 
>> made some ,no problem there but i did not take the glaze off the 
>> bore. When reassembled there seemed to be lots of compression and 
>> start up was easy . After an hours run absolutely no 
>> compression...first thoughts it was the valves . I did the usual and 
>> shot some oil down the spark plug hole....compression !That 
>> eliminated the valves as the problem . Pulling the barrel off and 
>> examining the bore showed considerable glazing ,there was evidence of 
>> blow by ,oil coming out of the breather. So now it out with the hone 
>> ...................
>
>
>
> John Culp
> Bristol, Tennessee, USA
>
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