1984 johnson 75 hp compression

[Faztbullet]

do you forsee the compression coming back up after putting a better shape head on it?

Maybe as depends on how much was took off old head in trying to smooth it up.... you will get a least 10 PSI

On relocating tattle tale.. This was to address 3 problems for these year engines. (1) It was the entry motor on the 28-30ft Basstracker toon and suffered water supply problems that why you always do this update on any toon. (2)The cylinder had a bridge port and if engine starved for water the bridge would expand and scuff piston (3) The lost foam design did away with water flow thru divider (49ci) and has more open area for air to possible trap.This bulletin was addressed toward toon's as these where more likely to be lugged and run in aerated water. There are THOUSANDs of these engines out there running without the mod and never had a problem and never will.

 

[Bosunsmate]

Your head gasket will likely have gasket glue on it so dont go adding anymore to it.
My 1982 60hp had everything water related replaced on it and it still overheated at idle.
It wasnt until i did this modification that the overheating instantly stopped. Ive never seen a service bulletin saying it should be done to my motor.
I think there are too many variables and yes many motors may run fine without it but for me being out in the ocean i have to maximise my chances of returning home.arty:

 

[oldboat1]

Yeah, as I read it, that 2007 thread was meant to address installation of a tell tale in a motors that don't have them, and then talk about locations -- with the general proviso that higher is better (to wit, the sevice bulletin on certain models). It seems to me the SB can be useful for anybody wanting to install a tell tale, or relocate the one they have, so has general application. I've never been a big believer of the need for tell tales in motors that didn't include them, but folks get adamant about putting them in. So it's all just a matter of choice -- including a choice to alter motors covered in the bulletin. (Actually, I'm not sure whether the blasted tell tale in those motors is part of the problem or the solution -- might be better just to remove the elbow and block off the opening, but don't think that is ever discussed as an option -- maybe for good reason.) In any case it's an interesting issue, with some general application.

(JMO)

 

[JoshKeller84]

Alright guys, installed the new head, and turned the powerhead over on the bench using jumper cables. Should be a great running motor now?

Top..


Middle


Bottom

 

[flyingscott]

Fire it up then take compression readings again otherwise looks good

 

[oldboat1]

Dead on even, to my eye. Standard first steps probably been sidetracked a little, but maybe already handled -- typically water pump, fresh fuel. Retorque after running. Good success!

 

[JoshKeller84]

yessir, went ahead and replaced the impeller while i had the jet unit off the mid section. I will be rebuilding the carbs before I put the motor back on the mid section.

 

[flyingscott]

Start the motor first with the carbs as they are just to make sure it runs. If something happens and it doesn't start you know it won't be the carbs one less thing to chase. I would start and idle it if it ran with the carbs before it will run now.

 

[JoshKeller84]

it was a fully running motor before i tore it down.

 

[JoshKeller84]

another question - on the shop2.evinrude.com parts list, it lists the correct spark plug as the champion l77j4 - i dont see any of these available anymore. have they been replaced by the l77jC4?

 

[Faztbullet]

QL77J4C

 

[flyingscott]

I understand it was a fully running motor before' but I wouldn't stick any more money into it until I ran it and rechecked the compression. Your first posts say your compression was 140/135/115 and now it is 120/120/120. You lost compression on 2 cyl maybe an issue maybe not I would just run it first just a 15 min idle then check.

 

[JoshKeller84]

Should have mentioned that i had return my harbor freight guage and get another one - it stopped holding the pressure readings. The 120 was on the new guage. Ran it for 15 minutes in the barrel, and got 120, 117, 120.

Does she sound good?
https://youtu.be/AA9cymFFF24

 

[flyingscott]

The video is private can't get to it. That explains the difference in compression.

 

[JoshKeller84]

Should be public now

 

[Bosunsmate]

From what i can hear it sounds good. You might want to button back your idle stop as if its idling that high when on the water you will chew up your clutch dog and gear teeth.
A good motor thats warm should be able to idle at a very low rpm.
I do mine until it just about stalls but never does stall

 

[JoshKeller84]

This is a jet drive motor - if that makes a difference

 

[Bosunsmate]

This is a jet drive motor - if that makes a difference

I dont know, ive never seen one. But a low idle setting saves you fuel as well

 

[JoshKeller84]

Basically, its just a driveshaft and an impeller. No lower unit gearing. Im going to clean the carbs tomorrow and do a sync n link. Then adjust idle on the river

 

[Bosunsmate]

Good luck. Get a video for everyone if you can