1971 Johnson 100hp New to me.

[fire0501]

Hello Everyone. Well I bought the motor yesterday (1971 Johnson 100HP) to replace my blown 1971 Rude 60hp and I did a comp test while there at his shop. The readings are as follows

From back of motor

Top left 118 psi
Bottom Left 118 psi

Top Right 118-120 psi
Bottom Right about 135psi

I did this twice and got the same readings now I know these are not within 10% of the last one. Does this sound like an issue?

 

[Bosunsmate]

Re: 1971 Johnson 100hp New to me.

It could be ok or it could be that three cylinders have each thrown one ring. I had that happen on one lately.
You could back up the pistons and have a look to see if anything has put a dent in their dome

 

[fire0501]

Re: 1971 Johnson 100hp New to me.

Im going to do another compression test on it probably tomorrow once I get it on my boat we let the motor run for about 2 minutes before we did this test Im going to check again. The motor runs good sounds really strong too. All I know is what they seller tells me. He is an older guy and has a yard full of motors. He is retired and does this full time he told me he got 135 on each cylinder with his compression tester but I wanted to check with mine and that is what I got. The motor supposedly sat outside a wherehouse for 20years. Thanks for the insight Bosunsmate. Although I really didnt "want' To hear that lol. what do you mean by thrown ring? Broken? and as far as a dent in the dome you mean just looking through the spark plug hole?


The thing is I would pull the heads off to have a look but I really want to get out on the water this weekend and I would think I prob cant use the head gaskets again but I have read on a couple threads where guys did reuse them does this sound possible?

 

[Bosunsmate]

Re: 1971 Johnson 100hp New to me.

Yep just look through the spark plug hole. Just see if they have any dings on the surface.

If you really wanted to be sure you could ask to have the bypass ports removed and check every ring is springy.
Those gaskets are about two dollars each.
Im not sure if hed be keen to let you do it but it would firm things up for you.

 

[fire0501]

Re: 1971 Johnson 100hp New to me.

Well I already bought the motor..... I paid $450 for it and traded my old motor

 

[Bosunsmate]

Re: 1971 Johnson 100hp New to me.

Dont pull the heads as if you dont get it torqued right you could get water in here and then you will miss your old motor and the $450

 

[Bosunsmate]

Re: 1971 Johnson 100hp New to me.

Just take a kicker out, dont go to far off shore and if it goes well on your first trip then its very likely a good buy.

 

[fire0501]

Re: 1971 Johnson 100hp New to me.

Ok I will take it out tomorrow and find out he swears this motor is fine but he is the seller. He seems like a good guy. He said I could just bring it back if it craps out on me.

 

[Bosunsmate]

Re: 1971 Johnson 100hp New to me.

Thatd be good enough for me

 

[fire0501]

Re: 1971 Johnson 100hp New to me.

Oh and I only have Oars so no kicker motor lol

 

[fire0501]

Re: 1971 Johnson 100hp New to me.

Ok So I took the boat out finally this saturday. IT ran good I had it running for probably about an hour. There are a few things to work out but she runs Pretty good. First thing I noticed before I took it out was a leaky lower end... It had oil leaking out from behind the prop shaft down the lower fin Not sure what its called. So I checked the oil milky of course. It had some foamy stuff coming out of the exhaust. Like a milky or grayish foam. against my better judgement I took it out anyway. IT ran good but loaded up on the lower end which I think could just be the slow speed adjustment. it also seemed like it would have to catch up to itself like if I let it sit at a certain RPM you can feel and hear it start to burn better it took about 3-4 seconds and you could hear the rpm's get higher and then it leveled out and ran great. I also will have to check my RPM Gage as I think it might have settings for different Cyl Configurations?? The Rpm's Would rev to about 6100 and I know this motor is a 5000 RPM Range. Also it would cut out at full throttle for a second for some reason but pick right back up. Any help in which direction I should go would be Great!