1979 Johnson 85hp~Compression??

[WavyD]

my first post on iBoats... here goes....

so the motor had trouble starting after i would be out fishing for awhile.
would stall out in low idle or low speed.
i would have to choke it and keep rpms up high to keep running.
so my first thought was fuel.
i cleaned the carbs,rebuilt the fuel pump,and attached a new fuel adapter on the fuel hose that was leaking at motor connection,,which i thought was a major contributor to my problem.
was able to start but still dropped out at low rpm's.
then came the compression test (which i should have done sooner).
this is a V4 motor,,,,so the top cylinders on both sides read around 120+,
but the bottom cylinders are coming in at 45-50 each....ouch.
what is my next step?
i guess pulling the heads to check for blown head gasket?valves?rings?piston?
have not priced anything as of yet but i am thinking the gasket would be the least expensive?
i have the manual for this motor and do most of my own work but i'm not sure if i can do this job depending on how deep i have to go into it...
also,i'm in the Altanta (Lake Lanier) area is someone has a "reliable" shop to refer.
thanks,
WavyDavy

 

[Daviet]

Re: 1979 Johnson 85hp~Compression??

If it were mine I would pull the heads and look to see if I could see any damage, make sure the heads are not warped.
You could try another compression test, but put some oil in the cylinders and see if the compression comes up any, might be rings.
Has the engine overheated?

 

[WavyD]

Re: 1979 Johnson 85hp~Compression??

thanks Daviet for the reply.....i have had no obvious signs of overheating.

guess i was thinking pulling the heads was more involved.....that comes with reading too much of the manual about "powerhead" removal....somehow mixed that info in with the head and gasket reading and it looked major.
funny how it all boggles when you are anxious to get things done.

so i pulled the heads and yep,the left side was blown on bottom and the right side looked ok but old.
put two bolts back on to hold for the trip to a local shop.
the guy there believes that they are just aged/old and new head gaskets should do the trick.
cylinders and pistons looked ok from outside....
i will decarb,replace head gaskets,then report back.

matter of fact,,i will probably go ahead and replace the water pump for safety sake.....and on that subject,how long should it take for water to come out the port (not the pee-hole) once motor is started?
i think mine is fine but i think it takes at least 5-10 secs....will have to check again....is that too long?

 

[WavyD]

Re: 1979 Johnson 85hp~Compression??

now the question is ,,,IS IT WORTH IT ??

replaced the head gaskets and that did not do the trick.
compression on lower two cylinders still way below.

so,,,since the cylinder walls and pistons look ok (from the outside)
i am thinking the rings are gone.
being that it is a 1979 motor,is it worth breaking this powerhead down to rebuild ??
i'm sure labor costs at a shop would be way beyond what i could afford.
since i have some mechanical skills and have done the work so far myself with the help of the manual and some advice from a local shop,i need opinions on whether i am spending too much time and money on an older motor !?
it was running like a workhorse prior to this compression drop.
i think rings run around $30 a piece so that would make it another $120 for the 4 rings (or should i do them all while i'm in there??) and then add on any gaskets or other things i may find.
really wanted to keep the motor but if it's going to cost above $300 to get it back it may not be affordable for me at this time,,or future.

would be great to have some expert advice from someone out there,,,
is there something else that may be wrong that i am not taking into consideration?
is it worth trying to salvage this motor or should i just part it out on ebay or somewhere?

thanks,
wd

edit: i may be off on calculating cost of rings....they may come 2 (a set) for $30+ ???

 

[ezeke]

Re: 1979 Johnson 85hp~Compression??

You have to pull the powerhead and take the engine apart to replace the rings, so first take the lower bypass covers off so that you can see if the rings are there or not. The rings may just be stuck from rust or carbon.

You will have to replace the gaskets on the bypass covers.

 

[WavyD]

Re: 1979 Johnson 85hp~Compression??

thanks ezeke,,looks like i can pull those bypass covers without removing other components so i'll try...

anyone else have opinions on whether its worth trying to save this motor?

 

[WavyD]

Re: 1979 Johnson 85hp~Compression??

update: pulled the bypass covers and i can see no
visual problem with the pistons or the rings (i'll have someone local verify my visual findings if possible)....rings are silver and not broken and move with the piston with ease~ from my bypass cover view.
i noticed the ever so slightest movement from the front ring on the right side but i can't see a problem ....should it move? and i'm talking movement half the size of the lead on a pencil....so barely movement.

so if not the rings,i'm leaning towards a cracked crankcase since it is both lower cylinders..but if it was the crankcase,wouldn't there be some kind of leakage??there is nothing leaking from what i can see...thoughts? opinions?

 

[ezeke]

Re: 1979 Johnson 85hp~Compression??

Did you do the compression test yourself?

You might want to just button it up, lubricate the cylinders and do your compression test again. Be sure to have all of the plugs out and use a screw-in type tester. Check the torque on the cylinder head bolts first; older engines can build up enough junk at the bottoms of the bolt holes to prevent a tight seal if the head bolts bottom out.

 

[WavyD]

Re: 1979 Johnson 85hp~Compression??

yes,,i performed the compression test with a screw in type gauge.

what type lube when you say "lube cylinders" ??
the same oil i use in my 50:1 mix ??
and what method do i use to fill/lube cylinders?
i'm assuming i would just add oil thru the spark plug holes?correct?

if this doesn't work, could the reeds be stuck open for bottom cylinders ?

 

[ezeke]

Re: 1979 Johnson 85hp~Compression??

Reeds won't change the results of a compression test on the 2 stroke motors, neither will having the throttles open or shut.

 

[WavyD]

Re: 1979 Johnson 85hp~Compression??

thanks,,i kinda figured but the thought came....

am i correct on the oil/lube question above for the cylinder ?

thanks very much for your input
wd

 

[Daviet]

Re: 1979 Johnson 85hp~Compression??

Yes, squirt some oil, any type of motor oil, through the plug holes.
Rotate the engine by hand to spread the oil around and recheck compression.

 

[WavyD]

Re: 1979 Johnson 85hp~Compression??

just a follow up to close this story...

ended up having a hole the size of a bb in one of the pistons....nobody can figure out how it happened and we didn't think it was all the way thru the thick part of the piston...it was.....the rings look intact but i haven't taken the powerhead apart...
the starboard side lower piston had its problems too....in the back of the cylinder you can feel a groove or chipped spot,,,,even tho the rings look intact from the bypass covers
i have a feeling part of a ring has caused the damage.

bottom line,too much to rebuild that powerhead so i will part the motor out and hope to have another motor someday.

thanks for all the input !!
WD