From: Dave Baker
Newsgroups: rec.crafts.metalworking
Date: 05 Dec 2000 17:32:07 GMT
Subject: Re: Proper Use of a Cylinder Ridge Reamer

>From: eea101@psu.edu  (Edward Allison)
>
>Hello,
>I am starting the rebuild of an engine and wish to use a ridge reamer
>to remove the ridge at the top of the cylinder bores for piston
>removal.   I don't want to damage the cylinders by being too
>agressive.  It would seem that if I remove the ridge completely I run
>the risk of undercutting and damaging the cylinder.  Any advise?
>Thanks.
>

I'm not sure ridge reamers have much place in an engine builders tool box. If
the ridge is bad enough to cause trouble then you really want to be thinking
about a rebore. Removing several thou of material at the top of the bore means
the new rings aren't going to have an easy time sealing at the start of the
power stroke.

For very light bore wear I dress the ridge out by hand with a fine stone on my
die grinder and then run the Delapena bore hone over the job. This means less
metal removal than a ridge reamer and to be honest it's a tool I don't see
myself ever buying.


...and then what do the robots do? asked the Krikkiter war commander. Er,
quadratic equations mostly, sir. Fiendishly difficult ones by all accounts. And
then they sulk.

From: Dave Baker
Newsgroups: rec.crafts.metalworking
Date: 06 Dec 2000 02:14:18 GMT
Subject: Re: Proper Use of a Cylinder Ridge Reamer

>From: dein2000@aol.com  (DEin2000)
>
>>I'm not sure ridge reamers have much place in an engine builders tool
>>box. If the ridge is bad enough to cause trouble then you really want to
>>be thinking about a rebore. Removing several thou of material at the top
>>of the bore means the new rings aren't going to have an easy time
>>sealing at the start of the power stroke.
>
>
>
>If the ridge is properly removed the top of the ring should not extend to
>where it was removed and you should get a good seal. the ridge ids caused
>by millions of cycles slowly moving metal upward in the cylinder and the
>new ring should be completely below the cut.

Errrrm - it's caused by the rings wearing metal away at the top part of their
travel. There's no "migration" of metal atoms going on here. I think you're
confusing this with wildebeest :)

Ricardo was one of the first to study upper cylinder bore erosion in detail and
discovered why it took place when the rings were almost stationary instead of
in the mid part of the stroke where piston speed was highest  - where one might
be forgiven for thinking initially that the wear rate would be greatest.

Hydro-dynamic lubrication protects the bore everywhere between BDC and TDC.
Wear occurs at TDC partly because of ring friction as the hydro-dynamic oil
wedge breaks down and partly because of combustion gases removing the oil film
leading to almost instantaneous oxidation of the bore walls which (rust) is
then swept away by the ring. At BDC the residual gases have lost enough heat
for this mechanism not to occur.

All that removing a ridge does is help ensure that a new top ring won't smash
against the old ridge - something that only tends to happen anyway if the new
rings are used at significantly higher rpm than when the main part of the wear
first took place (leading to more stretch of the crank/rod system and a
slightly higher travel of the ring).
It doesn't alter the fact that the bore is worn in the critical top part of the
ring's travel and won't improve the engine's performance. In any case it's only
the bottom 10 or so thou of the ridge that the top ring could possibly contact,
so dressing that bit back lightly with a scraper or emery instead of removing
the whole top of the bore does the job quite adequately.

Also - bores tend to wear mainly on the thrust side and often there is little
or no ridge round the rest of the bore. A ridge tool just removes the lot all
the way round - doing it by hand like yours truly means you only remove metal
where necessary :)


http://members.aol.com/pumaracing/index.htm
...and then what do the robots do? asked the Krikkit war commander. Er,
quadratic equations mostly, sir. Fiendishly difficult ones by all accounts. And
then they sulk.