1984 johnson 75 rebuild questions

[JoshKeller84]

j75ecrd

j5949958

i tore down this 1984 johnson 75 that came with a boat i bought to use with another motor. I figured out the bottom carb was clogged and broke the rings off of the bottom piston, presumably at the ports, due to the lack of cylinder wall damage. it had 145 psi on top 2, 0 on bottom. i checked the bore with a scope and micrometer borrowed from my auto mechanic, and it came back pretty much perfect. Honed it out, and put in a new piston and rings on the bottom cylinder only, since I just want to get rid of it.

coated everything with oil, put her back together, and hooked it up to the jump starter on my bench. top two were 130 psi bottom was 105. Put a tea spoon of oil in the bottom cylinder and it came up to 120. did I do something wrong here, or will the compression likely come up after I break it in for a few hours? whats the likelyhood that it'll run decent now?

One thing I noticed is that there are compression numbers written on the heads, and with my weak jump starter, they are coming back the same as the written numbers, which was obviously taken before it broke the rings.

 

[Bosunsmate]

You may have, did you install the piston the right way up?
It might come up once those new rings have embedded in and the honing cleared up.
Itl run fine on that, well so long as it wasnt because somethings being installed wrong

 

[Bosunsmate]

Check your lower seal too

 

[JoshKeller84]

Pulled the head again and it is oriented the correct way. rechecked the bore and it is smooth. Wiped down with some marvel oil and put the head back on. Compression was even lower. Pulled head again, wiped out the mystery oil, and coated it with some outboard oil (ran out and had to do a wal mart trip, hence the reason for the mystery oil to begin with). got annoyed, and just sat it back on the midsection to get rid of it.

Must need to be placed on the mid section to seal the lower cylinder completely? Set it back on the midsection mounted to the boat, and the compression numbers immediately jumped up to 125 bottom, 135 top two. Perhaps the fuel pump pulse line not being hooked up had something to do with it?

Put a little gas in the carbs, and cranked it a few times. Each cylinder fired when my hand was held of each carb. (homemade choke since it was cold started). after that, bump the key, and it started right up.

 

[Bosunsmate]

Must need to be placed on the mid section to seal the lower cylinder completely? Set it back on the midsection mounted to the boat, and the compression numbers immediately jumped up to 125 bottom, 135 top two. Perhaps the fuel pump pulse line not being hooked up had something to do with it?.

I suppose so if it went up after you connected that pulse line back on, as i cant see how the exhaust midsection back on would make much difference to the bottom cylinder compared to the others as you would of had the other plug holes open during that compression test too.
I wouldnt of thought that it could bleed that much out that small hole but here to learn
Dont forget new impellor

 

[racerone]

The pulse hole would leak out crankcase compression.---------That has nothing to do with compression in the cylinder.

 

[JoshKeller84]

https://www.youtube.com/watch?v=xvPifiw21wE

does she sound healthy now?

 

[Bosunsmate]

yep apart from the beginning screech

 

[JoshKeller84]

Is there a way to quiet the starter making that screech? all 3 of my johnsons do it, and no amount of grease will quiet it.