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#4546819 - 10/18/17 06:09 AM Need to deglaze cylinder on 2-stroke outboard?
nwjones18 Offline


Registered: 11/30/09
Posts: 1052
Loc: Warner Robins, GA
I'm working on a 1975 Johnson 25hp doing a full gasket replacement. Compression was 110 on both cylinders prior to tear down, but I figure if I'm going to have the engine totally apart to replace the O-rings on the crankshaft bearings I might as well replace the rings while I'm there. The service manual doesn't mention anything as far as honing/deglazing the cylinder wall when replacing the rings, but I've read its a good idea, with people using 3 stone hones, the ball hones and even scotch brite pads. What would you all recommend? From my understanding 110 is decent but not great compression, should I just leave well enough alone?
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1988 F-150. 4.9 I6 247k. 10w-40 Castrol Syn-blend ACDelco UPF2.
2005 Cadillac STS N* 108k. 5w-30 Castrol Magnatec ACDelco Classic PF61

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#4546870 - 10/18/17 07:06 AM Re: Need to deglaze cylinder on 2-stroke outboard? [Re: nwjones18]
LeakySeals Offline


Registered: 02/18/11
Posts: 6578
Loc: Hudson, NH
Sounds like the rings and cyl walls are in good shape. Provided the rings haven't been replaced or moved, I vote leave it alone.
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#4546959 - 10/18/17 08:46 AM Re: Need to deglaze cylinder on 2-stroke outboard? [Re: nwjones18]
Eddie Offline


Registered: 12/07/03
Posts: 9569
Loc: Florida, Cape Coral
I agree with LeakySeals. The compression is good and equal on both cylinders so the walls and rings are good so leave it alone. Ed
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#4547017 - 10/18/17 10:09 AM Re: Need to deglaze cylinder on 2-stroke outboard? [Re: nwjones18]
BrocLuno Offline


Registered: 09/06/15
Posts: 5519
Loc: Kalifornia Kollective
The rings are pinned to prevent rotation, so they can come out and go back in w/o loosing index. I just take a scotch brite and some brake clean and wipe down to look at base metal condition. If no scratches running up and down the bore, you can reassemble. Liberally wet the rings and piston with good 2-stroke oil when assembling.

If you want to try, you can install new rings. Often w/o hone. Sometimes the compression comes up a few PSI. It's usually due to the spring tension being higher in the new rings. We slap new rings in 2-stoke bike engines all the time w/o honing laugh
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Formerly in marine engineering. In an earlier life I owned my own petroleum tank truck, and hauled for the majors and independent's.

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#4547030 - 10/18/17 10:19 AM Re: Need to deglaze cylinder on 2-stroke outboard? [Re: BrocLuno]
4WD Offline


Registered: 09/21/10
Posts: 6390
Loc: Texas
Speaking of rings … I have a low hour inline 4 stroke … it only gets started every month or two. If I leave the motor trimmed under (it is shallow draft tunnel so gets run flush skeg) … it will smoke a few seconds at start up…
(It runs very clean after that)
Being the pistons are sideways … I always figured a little oil leaked past the rings and having a tad bit of residual oil on the low side of bore does not hurt … opinions?

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#4547229 - 10/18/17 01:34 PM Re: Need to deglaze cylinder on 2-stroke outboard? [Re: nwjones18]
nwjones18 Offline


Registered: 11/30/09
Posts: 1052
Loc: Warner Robins, GA
Well you all are making me want to just leave it together and not worry about those last two o-rings.. I hate to split the case that doesn't appear to be leaking just to change out 2 o-rings that are most likely fine.. On this engine there are 2 halves you have to take apart to remove the crank and its just sealed with RTV. May just put it back together and leave well enough alone. I've already replaced the upper and lower crankshaft seals and all the other external gaskets.
_________________________
1988 F-150. 4.9 I6 247k. 10w-40 Castrol Syn-blend ACDelco UPF2.
2005 Cadillac STS N* 108k. 5w-30 Castrol Magnatec ACDelco Classic PF61

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#4547292 - 10/18/17 02:44 PM Re: Need to deglaze cylinder on 2-stroke outboard? [Re: nwjones18]
Panzerman Offline


Registered: 12/16/06
Posts: 4203
Loc: Port Orange, Florida
If you have good compression you could just leave it alone but 110 seems low. Most two strokes are around 120+.
I use the three stone hone and I ve used steel wool. It's really just making scratchs for the oil to get into for breaking in.
Dont feel you need to rebuild it because of all that mumbo jumbo about two strokes needing rebuilt and four strokes run forever. Two strokes run a long time with enough oil and good oil.
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#4547377 - 10/18/17 04:39 PM Re: Need to deglaze cylinder on 2-stroke outboard? [Re: nwjones18]
Kamele0N Online   sick


Registered: 02/09/15
Posts: 2041
Loc: Slovenia
It is for 56-70`s models....but nevertheless...maybe you will need that!

https://www.dropbox.com/s/doq5vtzp83e0dd...proved.pdf?dl=0
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#4547482 - 10/18/17 06:56 PM Re: Need to deglaze cylinder on 2-stroke outboard? [Re: nwjones18]
nwjones18 Offline


Registered: 11/30/09
Posts: 1052
Loc: Warner Robins, GA
So big dummy (me) flipped to the next page in my service manual and it specifically says to use a 3 stone hone to deglaze the cylinder.. Thanks everyone!
_________________________
1988 F-150. 4.9 I6 247k. 10w-40 Castrol Syn-blend ACDelco UPF2.
2005 Cadillac STS N* 108k. 5w-30 Castrol Magnatec ACDelco Classic PF61

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#4548817 - 10/20/17 12:46 AM Re: Need to deglaze cylinder on 2-stroke outboard? [Re: nwjones18]
lars11 Offline


Registered: 12/16/06
Posts: 968
Loc: Sweden
yeah, and the case seals are bound to stiffen, leak and make the engine harder than usual to start. If it is actually that old without new case seals I would be surprised if it is perfectly sealed at the axle.
So the seals alone might make it start like "new" and new seated rings may make the hole shots like new too.
(Or, you may find no difference at all but new seals and rings on a really old engine is a good thing)

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#4549474 - 10/20/17 06:27 PM Re: Need to deglaze cylinder on 2-stroke outboard? [Re: nwjones18]
Bluestream Offline


Registered: 09/13/03
Posts: 5758
Loc: Waterloo, ON
hard to chage old ways at times:

http://www.snowvalley.20m.com/bikes/dnthone.htm
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#4549984 - 10/21/17 09:10 AM Re: Need to deglaze cylinder on 2-stroke outboard? [Re: Bluestream]
nwjones18 Offline


Registered: 11/30/09
Posts: 1052
Loc: Warner Robins, GA
Originally Posted By: Bluestream
hard to chage old ways at times:

http://www.snowvalley.20m.com/bikes/dnthone.htm


Makes sense to me.. Maybe I'll just skip the deglazing and put in some new rings..
_________________________
1988 F-150. 4.9 I6 247k. 10w-40 Castrol Syn-blend ACDelco UPF2.
2005 Cadillac STS N* 108k. 5w-30 Castrol Magnatec ACDelco Classic PF61

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#4550187 - 10/21/17 01:07 PM Re: Need to deglaze cylinder on 2-stroke outboard? [Re: nwjones18]
BrocLuno Offline


Registered: 09/06/15
Posts: 5519
Loc: Kalifornia Kollective
Yeah, as far as I have observed in 40 odd years, 2-stroke run fine on new rings in old bores ... As long as they do not have longitudinal scratches, they work smile
_________________________
Formerly in marine engineering. In an earlier life I owned my own petroleum tank truck, and hauled for the majors and independent's.

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