[SEL] piston rings and bores.

[peter ogborne]

In this case John, removing the glaze has done it ,top compression and no 
blow back out of the breather.
----- Original Message ----- 
From: "John Culp" <johnculp at chartertn.net>
To: "The SEL email discussion list" <sel at lists.stationary-engine.com>
Sent: Monday, May 02, 2005 7:36 AM
Subject: Re: [SEL] piston rings and bores.


>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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