1988 johnson 120 powerhead removal

[muddyfishin]

if I had a digital caliber im sure itd be easier however mine is labeled in inches, so 3.5 would be 3 1/2 "

 

[muddyfishin]

I just converted my 3 11/16" online and it came to 3.6875

 

[muddyfishin]

also ive just looked up the specs on iboats for my engine and it claims the bore size is 3.68.. so it seems im spot on at the top of the cylinder. as I said I dont feel any wear around the lip,

 

[racerone]

Sorry, your measuring technique is just not good enuff to determine wear and tear !!

 

[muddyfishin]

how would you recommend? digital caliber?? im here for one thing, knowledge

 

[Bosunsmate]

Looks like some partial blow by on that piston. Digital caliper is what you really need to check it all out properly as you need it precise.
I dont worry about bearings myself- but if you get a good deal on them then sure do them.
Id do rings/seals/gaskets and also pay close attention to that piston, it may need to be replaced due to that blowby area getting worn, so compare its diameter very closely to the others

 

[Bosunsmate]

How do the head channels look, filled with salt?
How about the exhaust cover area? You may find a cause for localised heat in that piston troubled area

 

[muddyfishin]

I will get a digital one before I start ordering parts, and honestly the bearings all seem good, I haven't made up my mind on them yet, the head channels have some salt but nothing crazy I was able to get most of it out. still have to do the other side,, the exhaust cover area on this model is not the removable cover it is part of the block so I believe ill have to take the cover off the top where the wiring is to see in there or look through the bottom port.are you talking about the crank seals?, the top crank bearing and seal look very good haven't looked at the bottom yet , will I have to hone to clean up the marks left by the blow by?

 

[Bosunsmate]

Yes the crank seals. I always replace them, sometimes even though they look good they for some reason arent when shes spinning.
Id hone, safer than sanding and a honer is cheap $15 ish
Those piston heads will all need a good soak and clean, cleaning everything, as you are likely aware is so important on these

 

[muddyfishin]

you mean to soak the whole pistons to remove the carbon?what would work best for cleaning.

 

[Bosunsmate]

yep thats what i do, and get the ring grooves shiny too.
Easy job even if its raining too
I normally leave the wrist pins alone, but when reinstalling dribble some two stroke oil over them so they arent dry on start up.
Checking the pin in the piston head tpo, make sure they arent missing as unlike a four stroke they are important to stop the rings rotating and catching the ports

 

[muddyfishin]

what do you use for the soak? seafoam? and on the piston I pulled, on the bottom ring that pin seems like it is pushed in compared to the top ring,, and I can spin the ring around although it isn't compressed, the top one doesn't spin like that

 

[Bosunsmate]

Seafoam would do, petrol/diesel. Any solvent you have hanging around.
That bottom pin sounds something to look into further. How does it compare to the other pistons (When you have pulled them)?
I havent taken apart that particular model before so cant be exact but if its not the same as the other pistons id be getting that sorted, it may be why you had something catching on the port

 

[muddyfishin]

I did just go check it out again, and in general that bottom ring is just really loose compared to the top, I know its not compressed however, the pin does catch the ring if closed

 

[muddyfishin]

sometime this week ill compare it with the others to be sure

 

[Bosunsmate]

When you get your new rings it may change things as it may of had the ends worn off that lower ring making them looser

 

[muddyfishin]

ok so ii pulled the other pistons today, and ive found that all cylinders are getting a little blow by on the exhaust port, although only the top port side had low compression the others were all at 120 psi, both starboard pistons had a stuck lower ring causing the blow by id assume, but overall the cylinders look good no gouges. the low compression piston obviously has the worst of the blow by wear on the piston, im going to compare diameters shortly other than that I believe its time to hone, soak clean and put in a parts order. I will post some pics shortly

 

[muddyfishin]

id also like to point out that when pulling the pistons, the top port which is the low cylinder, came out a lot harder than the others, all three just slid out nice where as the top port needed some persuasion

 

[Bosunsmate]

Sounds good. Id consider replacing that lower piston if you are not sure its totally in shape

 

[muddyfishin]

been a little while but I am waiting for my order of parts to show up, in the meantime, im soaking the pistons in a gallon of parts cleaner,, just curious as to whats acceptable for cleanliness on these pistons,, most of the carbon is coming off however there is little traces Im having trouble getting out of the ring grooves, its been the 2 that had one stuck ring where the build up is being a pain any tips?? and hopefully these parts show up soon, the weather is getting nice