# To rebuild or repower



## No Bait / Lures Only (Apr 10, 2011)

bw510 said:


> So my 99 merc 25 two stroke might have a rod knock.its been slowly getting louder and finally the other day it was having trouble idling and starting (it always starts within three pulls cold and always first pull warmed up)did a compresion check and its 100 and 110 which Dosnt sound too bad from what I've read
> Anyway I did the screwdriver in spark plug check and the bottom piston has maybe 1/32 inch of play and the top has none
> 
> I'm not sure if this is the problem or not but if it is should I rebuild? The boat is a 99 16 whipray and i really love the little light weight merc but I'm always worried about its reliability after a rebuild.
> ...





bw510 said:


> So my 99 merc 25 two stroke might have a rod knock.its been slowly getting louder and finally the other day it was having trouble idling and starting (it always starts within three pulls cold and always first pull warmed up)did a compresion check and its 100 and 110 which Dosnt sound too bad from what I've read
> Anyway I did the screwdriver in spark plug check and the bottom piston has maybe 1/32 inch of play and the top has none
> 
> I'm not sure if this is the problem or not but if it is should I rebuild? The boat is a 99 16 whipray and i really love the little light weight merc but I'm always worried about its reliability after a rebuild.
> ...





bw510 said:


> So my 99 merc 25 two stroke might have a rod knock.its been slowly getting louder and finally the other day it was having trouble idling and starting (it always starts within three pulls cold and always first pull warmed up)did a compresion check and its 100 and 110 which Dosnt sound too bad from what I've read
> Anyway I did the screwdriver in spark plug check and the bottom piston has maybe 1/32 inch of play and the top has none
> 
> I'm not sure if this is the problem or not but if it is should I rebuild? The boat is a 99 16 whipray and i really love the little light weight merc but I'm always worried about its reliability after a rebuild.
> ...


Don't sweat a rebuild, all I own is modded/rebuilt engines (3) with no issues. Just have a reputable engine builder do the work and you are good to go. I also like the light 25 hp 2 stroke motors like my Yamaha 25 @ 106#....


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## Snookdaddy (Jan 5, 2008)

Rebuild.. Merc 25hp are awesome!


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## RunningOnEmpty (Jun 20, 2015)

Check Ebay if your on a tight budget. 450 is the average cost for your powerhead used and they are very easy to find. 110 psi is low for that motor and it might be difficult to find a machine shop locally that can do a blind mercosil bore.


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## bw510 (Sep 1, 2011)

After reading a few things about rebuilding these motors and it being a problem or If for whatever reason it needs a power head 
Do any of you have any idea on a ballpark price for something like this with labor?

Also if I found a newer motor that was a long shaft how difficult would it be to swap lower units or is this even possible ?


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## yobata (Jul 14, 2015)

I think you also have to swap the mid section, not just the lower unit shaft and gear shift rod??


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## RunningOnEmpty (Jun 20, 2015)

The long shaft motor will need your short mid section and lower. The powerhead swap is very easy with basic tools and it doesn't require ripping everything apart. Mercury made some changes on the 25's and you need to be careful the motors are compatible. I'm pretty sure you can also use the Mariner/Mercury 20 hp block with your 25 hp carb without loosing any power.


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