Piston Ring Question

 Hi all,

I just finished my first engine rebuild and my bike is smoking
horribly.  I'm burning about a quart of oil every 50-60 miles.  My
pistons use three-piece oil rings, and I couldn't get the new oil
rings on with the new expander ring (the wavy one), so I re-used the
older expander.  I should have known better because the oil rings
slide in way too easily with the old expander in place.  I'm guessing
it's smoking because the old expander isn't putting sufficient outward
tension on the oil rings to seal against the cylinder walls.

So, I'm getting ready to pull the engine again.  I'm new to the whole
scheme of installing piston rings, so I'm trying to figure out exactly
how the expander and oil rings work.  If I set the oil rings on the
(new) expander ring that came with the ring set, I find that the
expander is pushing the oil rings open to make a .5 cm gap (way too
wide) which won't fit in the bore.  When I tried installing them by
hand (no ring compressor), the oil rings just wouldn't fit with the
expander in place.  This time around I'm planning on using a ring
compressor.  So, here's my big question:  Is the expander ring (wavy
one) supposed to 'compress' itself down with the use of the ring
compressor, so that it fits into the bore with the oil rings around
it, yet provides outward tension on them?  If the expander ring
doesn't 'crunch' down a bit with the use of the compressor, it seems
impossible to install.

Here's a picture of the expander with an oil ring over the tabs on
it.  Notice the .5 cm gap (5 mm) that is created by the expander tabs
pushing the ring gap open.  Although you can't see them, the ends of
the expander are butted together in this picture, just like they would
be on the piston:
http://img408.imageshack.us/my.php?image=pict0274lw8.jpg

Thanks for any help/advice!

 On Feb 20, 7:06 pm, kb1...@gmail.com wrote:


Is it the 1979 KZ650 you mentioned in earlier posts?


How much are the cylinders overbored? 0.25 or 0.50 millimeters? That's
a big gap for oil to get past, especially if you didn't stagger the
end gaps of the scrapers 180 degrees.

If you installed larger diameter pistons, you'll need larger diameter
expanders for the larger diameter rings. They would be identified by
etched numbers or painted color coding, according to what manufacturer
made them.


The shop manual, or even a Clymer's manual is better than guessing.


Maybe they are expanders for an engine with a much larger piston?


The ring expanders have to provide the tension for the oil scrapers.

The expanders must not be installed with the ends overlapping, there
must be
clearance between the ends of the expanders when installed in the
cylinder bore.

The ends aren't supposed to touch. If you have the correct expanders
and the ends touch while installed in the bore, you have to file the
ends.

When the oil control rings are installed correctly, the gaps between
upper and lower scraper will be 180 degrees apart.

You will see a diagram in any decent manual that shows how the
compression ring end gaps should be aligned.

 This is my 1979 Yamaha XS650.  Pistons are stock 75 mm (74.996 mm I
believe, standard size pistons).  I staggered the rings per the
instructions provided with them.  Everyone else has told me the ends
of the expander are supposed to be touching, but not overlapping.
That's how the old (stock) rings were installed on the pistons when I
first removed them.  I contacted the ring manufacturer (Hastings) and
they told me that although it looks wrong in my picture, it will be
right when installed on the piston and compressed with ring compressor
into the bore.  I didn't understand what they meant by that, but I
assumed the only way it would become 'right' and fit would be for that
wavy expander to compress down a little to allow the oil rings to
close up a bit and fit into the bore.

 

First question: have you tried the expander in the bore without the
ring? Just to check it's OK?

2. Have you checked the expander against the old one, to compare size?

3. Is there any chance at all that you've got some ring gaps aligned?

4. (And this is the kicker) Could you have installed a ring upside down?
Because that would certainly explain the massive oil consumption.

I've rebuilt a couple of XS650 engines, and never had the need to use a
ring compressor as there seems to be plenty of 'lead' at the bottom of
the barrels to ease the rings in.


--
BMW K1100LT Ducati 750SS Honda CB400F SH50
If you don't know what you're doing, don't do it. Workshop manual?
Buy one instead of asking where the free PDFs are
chateau dot murray at idnet dot com

 
Yes.  It fits snugly in the bore.  The old expander would just slide/
drop through.


New expander is slightly (very slightly) larger, as it exerts outward
pressure to stay in the bore by itself, while the old one just
'dropped through'.  I am assuming the lack of tension on the old one
is causing my oil consumption.


Nope, staggered them all before installing them.  Double/triple
checked.


Nope, wiper ring had a tapered edge which I made sure was installed
the right way, according to the instructions.  Top ring had no marks
on it (instructions said it can go either way).  Oil rings it said can
go either way as well.


The jugs have a taper at the bottom of the barrels.  Compression and
wiper rings went in fine.  Oil rings would either not go in on one
side or would force the spacer to pop out and overlap itself.