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oil rings
10-12-2010, 07:49 PM
Post: #1
oil rings
Hello. I am putting new rings on my pistons and am wondering if, and how much, the oil scrapers are supposed to be above the pistons before compression for insertion. With the spacer in place the scraper rails bottom out with about 1mm diameter larger than bore. Is this normal? That is, will everything collapse, and safely, into place when the compressor is applied? I am concerned because this seems a bit extreme and these new spacers (the complicated wide squiggly rings) are different from my originals and will not on their own fit into a bore without overlap. The other rings (e.g. these rails and the upper compression rings) check out with good end gaps in the bores.
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10-12-2010, 10:21 PM (This post was last modified: 10-12-2010 10:29 PM by Rupe.)
Post: #2
RE: oil rings
You should consult the mfgr for details here as some rings have an overlap in the expander under the actual ring while others do not. Some rings also have locking tabs that must be "latched" for the ring to fit properly, but I have only seen that style on 2-stroke engines.

Something else to look at is proper cleaning of the ring grooves. If there is any carbon at all in there you will not get things to fit right when assembled.

The end gap you are looking to check while in the bore is only on the ring itself. If there is an expander behind the installed ring that will exert pressure but if everything is clean and lubed it should squash down just fine with a standard ring compresser.

There is a special tool available to make this cleaning task easier but it can be done with a broken piece of the old ring held tightly in a shop rag. (the edges are sharp!) Take this from a guy who has rebuilt about 300 engines over the years and never had a failure.
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10-13-2010, 07:58 PM
Post: #3
RE: oil rings
Thank you for you reply. These rings (which are very different from the originals) have the color tabs on the ends specifically so they don't overlap in the way you describe. Now with both colors showing (as the instructions that came with the rings say) it can move all over the place in the piston groove, and is larger in OD than piston diameter too. Unfortunately this set is a Beck/Arnley repackaging so there is no manufacturer I can contact to discuss this, nothing on the package or even these instructions. The only way this will assemble is if the radial portions of the corrugation in the spacer all bend and reduce the circumference that way, and bring in the shoulders that carry the scraper rails at the same time, so they can reduce to bore size too. Seems a bit complex to me.
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10-13-2010, 10:14 PM (This post was last modified: 10-13-2010 10:20 PM by Rupe.)
Post: #4
RE: oil rings
OK, what you have is a 3 piece oil ring with a combination spacer / expander plus 2 scraper rings. What you need to do is set the expander in place in the clean groove (oil drain holes clean too) and then set the scraper rings into place spaced per the mfgr's diagram, which usually shows all of the gaps staggered 1/3 of a turn. IOW, the scraper ring gaps do not line up with the expander gap. Install the remaining 2 rings, squirt some oil on the assembly, rotate all of the rings once around to assure there is no binding and everything is lubed, then space the the top ring gaps in a staggered fashion (so none line up) and install the ring compressor tool.

The reason you think this expander is too tight is because you probably took off a single piece oil ring. The 3 (and 4) piece oil rings need lots of tension to work properly. Back to the begining here... if the scraper rings have the right end gap then the whole assembly will work as designed.

BTW, pay close attantion to any pictures in the diagram for the ring shape, markings, etc. The directions may be generic and show punch marks, paint marks, taper, round nose, or other specifics for placing the scraper rings on in the right direction. Placing them upside down will create an oil comsumption issue.
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10-23-2010, 05:45 PM
Post: #5
RE: oil rings
I tried another set and these spacer/rail combinations in the pistons set up at a much lower level. and can compressed by finger pressure nearly down to piston diameter, like a compression ring. So apparently the spacers in the first set (different source) are for a larger bore (I measured more carefully and that diameter was more like 77.0 mm, 1.5 mm over bore diameter, not the 1mm I gave earlier). I could never compress those that way, and doubt a compressor could have either, at least not without damaging something. The new spacers just fit into a bore without overlap, like the originals.
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10-23-2010, 06:39 PM
Post: #6
RE: oil rings
Glad you figured it out and part of your answer was in your orignal post as you mentioned the rings would not fit into the bore without overlap. (presuming you meant the cylinder bore and not the ring groove) This why I mentioned "end gap" while in the bore.
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