How to compress piston rings. STRUGGLE

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rjk40
Diana
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How to compress piston rings. STRUGGLE

Post by rjk40 » Sat Dec 02, 2017 1:31 pm

Ok, this old man is really feeling stupid, trying to get the blasted three piece oil ring to stay in place while lowering the compressor over it.
Would really like some help (likely a technique...).

Bike is 1975 Ducati 860GT.

Trying to fit the vertical cylinder top end back on after refreshing (cylinder hone and valve job). Piston is still on rod, saw no need to remove, cleaned up really nice with no wear. Must, then lower the cylinder onto the piston in situ. Got new rings from Steve, and have been thwarted by the upper oil ring rail not staying up while lowering the compressor onto it. I would guess that there is something simple that I am missing, but I am durned if I can see what it is. These DeVes oil rings do not have a step on the scraper that either rail fits into; rather, the two rails ride above and below the scraper, and when all are compressed, the scraper rides smoothly between the two rails.

The struggle here is keeping the upper rail from sliding over the scraper when dropping the compressor onto the piston.

Any recommendations>

Thanks in advance.
Regards,
Richard in Florida

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BevHevSteve
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Re: How to compress piston rings. STRUGGLE

Post by BevHevSteve » Mon Dec 04, 2017 2:09 pm

"Dropping the compressor over the piston" ??

I think you may need to do some video googling to see this done. My compressor I just loosen it up to fit OVER the piston and rings, then tighten it up which compresses the rings. Tighten enough to compress rings to piston OD but not so tight that it won't slide off with some encouragement as you slip the jog over the piston (which pushes the compressor down......
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rjk40
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Re: How to compress piston rings. STRUGGLE

Post by rjk40 » Mon Dec 04, 2017 2:25 pm

Hi Steve,

Yes, I have looked at many youtube videos, and the only one that matches my scenario of doing the process with the piston in place on a vertical cylinder is for a Harley, using no spring compressor and lowering the cylinder very carefully onto the piston, compressing one ring at a time. The other videos all show putting a piston into a cylinder with the piston free of the rod.

Have you never had the rails want to both end up below the scraper when compressing the whole mess?

That's my issue. I guess I'll just keep trying until I can get lucky so the compressor closes them without the durned top rail falling down to the bottom one.

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Re: How to compress piston rings. STRUGGLE

Post by BevHevSteve » Mon Dec 04, 2017 2:43 pm

i guess I don't understand the trouble you are having.
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Re: How to compress piston rings. STRUGGLE

Post by SP3 » Fri Dec 08, 2017 2:46 pm

Oil compressor and/or piston/rings, slide compressor over piston/rings, tighten until you think it can't go any further, hold assembled mass tight against cylinder, knock piston assembly into cylinder with soft faced mallet.
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ducadini
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Re: How to compress piston rings. STRUGGLE

Post by ducadini » Mon Dec 11, 2017 12:31 am

Richard,

Try this :
1 : take all the rings and fit them into the cylinder, check gap, that way you are SURE they will fit
2 : fit the two top rings onto the piston
3 : fit the oilrings from the bottom so they don't get messed while fitting the two tops
4 : space the gaps of the two top rings according your preference (or check out a topic here)
5 : fit a full round compressor (i've seen some clamps that only push for a part of the piston)
6 : tighten compressor until it is fully closed and sits (almost) against the piston
7 : loosen a bit, fit against bottom of cylinder and gently tap in into cylinder, making sure the ends don't get caught into the gaps of crank and rod.
8 : fit pistonpen and clip (making sure to fill the gap so the clip doesn't fall into the crankcase and you have to start all over again DOUBLE)
Seen it, done it, enjoyed the results
Needless the say this is all with the piston OFF the crank

ciao
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri

rjk40
Diana
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Re: How to compress piston rings. STRUGGLE

Post by rjk40 » Mon Dec 11, 2017 10:34 am

Thanks, Ducadini,

Yeah, the biggest challenge is posed by the fact that I was doing the deed with the piston still on the rod, because, at the time, I could not find a source of wrist pin circlips, not EVER wanting to re-use the little monsters. I have since found a source for them, and will proceed the re-insertion process with the piston off of the rod. Should be easier that way.

And yes, I have no desire to fish an errant circlip out of the crankcase, and am well prepared to cover the hole whilst proceeding.

Regards,
Richard

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Re: How to compress piston rings. STRUGGLE

Post by ducadini » Tue Dec 12, 2017 8:58 am

Richard,

I understand Your reluctance to re-use a circlip, I think most of the errors and resulting damage is from the fact that they are incorrectly fitted.
When fitted with the opening down, there is (except from the rocking movement of the piston in the bore) no force to open them (or better : close them so they can get out of the groove).
Wouldn't re-use them in a 11000 rpm Pantah but in a streetbike with a redline of 7500 with standard stroke-rod ratio , a correct non-damaged circlip (check with magnifying glass) I would re-use. But over here, those things are just a few keystrokes and 2-3 days away.

When browsing through some u-toeb footage, I found a docu about the Ducati factory in the 80's, and someone fitted the piston-cylinder assy in a few seconds on the crank, using a special tool to put the circlip in place.
I sort of figured out how it works, but having some pics and/or drawings would make it easier to fabricate.

ciao
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri

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