1984 johnson 75 hp compression

[flyingscott]

If people can't tell the difference between a service bulletin pertaining to 56 CID blocks and not the older 49CID blocks ,I can't help you. I can only give you the facts I can't make you believe them.

 

[racerone]

Agreed !

 

[flyingscott]

One more thing I was gonna edit my last post but I waited to long. The link that was put up for adding a tell tale is wrong in so many ways. The author of that posting did it wrong he used the service bulletin for the 56 cid block to add the tell tale to the 49 CID block and he put it in the wrong place.

 

[JoshKeller84]

Sorry, i did not see the posts about the compression ring being chewed up - i believe in the picture, it was just oil reflecting the camera flash. I wiped it off and retook the pic, and it appears smooth.




The head, on the other hand, is very chewed up - is this thr likely place the 20 psi of compression is leaking?

 

[oldboat1]

Josh -- JMO, but I would be concerned about reusing that damaged head. Just think it might be tough to resurface that one and get a good gasket seal. Have you looked into finding a replacement?

 

[JoshKeller84]

Yessir, found one on a parts motor - going to go get it tomorrow - hope that returns the lost 20 psi of compression im that cylinder.

 

[Bosunsmate]

If people can't tell the difference between a service bulletin pertaining to 56 CID blocks and not the older 49CID blocks ,I can't help you. I can only give you the facts I can't make you believe them.

I know the difference between service bulletins:blah: thats not the issue:nono:, the question which you are choosing to ignore is how do airbubbles that rise to the top of a cooling jacket get out of the motor if the telltale outlet isnt at the top of the motor?

So try again:fencing:Give us the "facts" about how those risen air bubbles get evacuated efficiently from the top of the motor when the outlet isnt there :loco:.

 

[oldboat1]

[edit.]

 

[oldboat1]

Yessir, found one on a parts motor - going to go get it tomorrow - hope that returns the lost 20 psi of compression im that cylinder.

Think that's a good move.

 

[Bosunsmate]

Agreed !

The question is how do air bubbles get out of the top of the cooling jacket when the outlet isnt at the top. Its a very important question.
So how can you agree with something Racerone that hasnt even being answered?:facepalm::facepalm:
Just admit if you dont know as i cant see how that can happen unless in the world of physics you and Scott can show that in motors for some extraordinary quirk air bubbles actually sink in water!!:flypig:

 

[JoshKeller84]

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

 

[oldboat1]

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

Think it's got a chance, and it's a relatively easy fix (potential fix).

 

[Bosunsmate]

Yes your old head has enough damage to leak 20psi.
Inspect the new one and shave it down a touch too in case its warped a touch, most used ones arent perfectly flat

 

[Bosunsmate]

One more thing I was gonna edit my last post but I waited to long. The link that was put up for adding a tell tale is wrong in so many ways. The author of that posting did it wrong he used the service bulletin for the 56 cid block to add the tell tale to the 49 CID block and he put it in the wrong place.

Oh dear having a go at someone who isnt around to answer the question yet you are avoiding the main one yourself:lalala:

 

[JoshKeller84]

Can someone explain the shaving the head down process?

 

[flyingscott]

Bosunmate I am not going down that rabbit hole with you I am right and the engineers at OMC agree with me . If that topic wouldn't have been closed I would have posted on it that it was wrong.

 

[oldboat1]

Can someone explain the shaving the head down process?

Like bosunsmate says, the replacement head will probably have some warpage. Would use the resurfacing technique described in #34. (I use the cast iron top on my table saw.) You can tell by look and feel when you have it flush -- not difficult to do. Hope you get a good runner out of it.

 

[flyingscott]

Is this a new head for the motor if it is. Take 220 grit sandpaper tape it to a piece of glass and move it in a figure 8. That head is pretty big so you might just want put valve grinding compound on a piece of glass and in a figure 8 motion move it until the mating surfaces are shiny. If it's the head that you have right now in the pic take that one to a machine shop.

 

[Bosunsmate]

Bosunmate I am not going down that rabbit hole with you I am right and the engineers at OMC agree with me . If that topic wouldn't have been closed I would have posted on it that it was wrong.

:argue: ok fair enough.
Im just keen to know why on some motors it has to be on the top which is where the air bubbles would reside and then it seems on some others it doesnt have to be.:smash:

 

[Bosunsmate]

As Scott said, plus, the non shiny patches on the head as you do it on glass are the areas which are low. The high places get shaved back first. I do mine on the bathroom mirror.
As you shave it down the whole head where the gasket contacts will become shiny which indicates that head is now flat. Be careful not to push down too hard on one spot, figure 8 helps with that and periodically blow the shavings away. And dont shave off lots, just enough to get it all shiny.
Should take all of ten minutes and is a good technique to acquire.

You can also take a straight edge and put it across and diagonally across the surface to look for any warping between the edge and the head. Its got to be a strictly straight edge, i have a metal one for this