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1990 Johnson 140 compression

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rusty34

New member
Hi all
have been searching for a used boat, thought I'd finally found "the one".
haines hunter 1990 5.6SL with a 1990 model 140hp outboard .
did a wet test and motor and hull performed as well as I could tell.
agreed on price with it being based on compression test being ok.
did the test yesterday.
130,120,130---100.

ive backed out of sale but what could the low cylinder reading mean?
obviously it could mean a number of things but could it be as simple as a new set of rings in that cylinder?
or is it 3-5k fix up 12 months down the track?
any advice would be greatly appreciated.

rusty
 
A decarbonizing could bring the bad cylinder back up to specs, Bad rings, Scored cylinder wall, A bore scope would show imperfections inside of cylinder. Until head is pulled there's no telling, it is 26 years old. Some times a rebuilt powerhead is the cheaper route than rebuilding yours, But it's like a box of chocalates u never know what your going to get!! I think backing out was wise
 
johnnygjr said:
A decarbonizing could bring the bad cylinder back up to specs, Bad rings, Scored cylinder wall, A bore scope would show imperfections inside of cylinder. Until head is pulled there's no telling, it is 26 years old. Some times a rebuilt powerhead is the cheaper route than rebuilding yours, But it's like a box of chocalates u never know what your going to get!! I think backing out was wise
Click to expand...


Cheers Johnny!
 
Rusty..... I am assuming that the compression readings you obtained of 130,120,130,100 pertain to the numbering of the cylinders, standing in back of the engine and facing the spark plugs, the cylinders would be numbered as follows:

2....1
4....3

Meaning: Starboard Cylinders 1 & 3 = 130 psi... and... Port Cylinder 2 = 120 psi with Port Cylinder 4 = 100 psi.

If this is the case, the Port bank has failed. The compression shows a difference of 20 psi between the lowest and highest reading (not acceptable) which normally indicates that the powerhead needs replacing or rebuilding. There is nothing on the market (cleaning agents) that could possibly close that 20 psi gap.

At a minimum, the cylinder heads should be removed in order to inspect the sealing surfaces of the block and cylinder heads, the pistons, cylinder walls, etc.... $$$$$$!
 
joereeves said:
Rusty..... I am assuming that the compression readings you obtained of 130,120,130,100 pertain to the numbering of the cylinders, standing in back of the engine and facing the spark plugs, the cylinders would be numbered as follows:

2....1
4....3

Meaning: Starboard Cylinders 1 & 3 = 130 psi... and... Port Cylinder 2 = 120 psi with Port Cylinder 4 = 100 psi.

If this is the case, the Port bank has failed. The compression shows a difference of 20 psi between the lowest and highest reading (not acceptable) which normally indicates that the powerhead needs replacing or rebuilding. There is nothing on the market (cleaning agents) that could possibly close that 20 psi gap.

At a minimum, the cylinder heads should be removed in order to inspect the sealing surfaces of the block and cylinder heads, the pistons, cylinder walls, etc.... $$$$$$!
Click to expand...


joe
i wasn't sure how the cylinders were numbered.
the compression reading was as below.

2- 130. 1- 130

4-120. 3-100

what would this mean?



thanks a lot for your response.
rusty
 
rusty34 said:
joe, i wasn't sure how the cylinders were numbered. the compression reading was as below.

2- 130. 1- 130 ........... 4-120. 3-100 ........ what would this mean? thanks a lot for your response. rusty
Click to expand...

To me, that would strongly suggest that the bottom carburetor was running lean and caused damage to the two bottom cylinders.

I wanted to add a [EDIT] here: The compression shows a difference of 30 psi between the lowest reading (100 psi) and highest reading (130 psi) which is not acceptable. This normally indicates that the powerhead needs replacing or rebuilding. There is nothing on the market (cleaning agents) that could possibly close that 30 psi gap.

Previously I had stated a difference of only 20 psi which was/is obviously incorrect.
 
Last edited:
joereeves said:
To me, that would strongly suggest that the bottom carburetor was running lean and caused damage to the two bottom cylinders.

I wanted to add a [EDIT] here: The compression shows a difference of 30 psi between the lowest reading (100 psi) and highest reading (130 psi) which is not acceptable. This normally indicates that the powerhead needs replacing or rebuilding. There is nothing on the market (cleaning agents) that could possibly close that 30 psi gap.

Previously I had stated a difference of only 20 psi which was/is obviously incorrect.
Click to expand...



Cheers mate, I'm glad I didn't buy this boat now that's for sure!
 
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