Re: 1993 Johnson 150 - Did I blow a cylinder or worse? (based on these symptoms)
Hello Guys,
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Short version:
1. there is no wobble when placing the head on a glass desk
2. I can still not convince myself of o-ring failure
3. The head gasket for cly 6 was not pressure washed, nor was the piston
However, the cylinder was cleaned with b-12 cleaner, but I do not recall
cleaning the head with that cleaner, but I may have to try and inspect for
damage.
current theories:
theory 1 - the 'ridges' on the edge of the piston made contact with the head
and broke the seal between the head and o-ring
theory 2 - whatever caused the damage to the piston edge is much worse
deeper in the cylinder bellow the piston top and piston edges. the two
seals on the piston itself may be badly damaged and that is where I am loosing
compression.
current plan-o-attack:
Since theory 2 suxs, thinking of starting with the o-ring since its cheap.
Borrow a drimmel or sand the metal
edges from the top of the piston in cyl 6 with the piston in the fully
out(up) position. Carefully cleaning all metal shaving etc, lowering the piston,
making sure completely clean. reinstall with new o-rings, retest compression.
However, I will need to understand what caused the 'ridges' on the piston
edge as I am worried this what Joe Reeves was talking about when he
said "spells trouble with a capital "T"
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Long Version:
Guys I am sorry I lack the ability to be concise. However, I did manage a
couple of decent pictures describing the o-ring and why I am struggling
to suspect it, and the 'ridges' which have me concerned.
Didn?t get home last night till after dark, so the only test I ran was to
verify the "wobble" per Hybrids suggestion. I have a glass desk in the
shop, so I laid the head on the desk, and could detect no wobble. It felt
flush and firm when I tried to get it to rock back and forth. The head
appears not to be damaged or warped.
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compression question 1
To hit back on the question I was asking earlier and was answered but I am
still struggling with understanding. I am going to try to use a very crude drawing
to help me illustrate my question.
What I am trying to get straight in my mind is where is the piston located at the moment the spark plug fires. This is in an effort to better understand the root cause of my problem.
Case 1 in the diagram: Based on the "wear" at the top of each cylinder there appears to be a line on all 3 about 1/8th of and inch down from the top. This leads me to suspect that this is the location where the spark plug fires and presses the piston back down. If this is the case it may indicate that my piston seals are suspect along with the o-ring seal between the head and the block.
case 2 in the diagram: The piston head is curved, the head is curved and then bells up at the spark plug. case 2 would be the piston lifts to its maximum length before the spark plug ignites. Why I think may be possibly the case is it would explain the compression loss if, the build up of the 'ridges' on the piston edges reached a point where the piston was forced upwards, the 'ridge' pushed the head just enough to break the seal between the o-ring and the head (the o-ring was pressed in position since 1993 and did not expand when/if the head was pushed). The two major hurdles I have to this case though are:
- if that is true, why is the 'ridge' not beat flat, and why is there not obvious evidence of damage on the head surface.
- no evidence of o-ring seal failure either as its mounted on the block, or on the head surface (as far as I can tell anyway)
... to be continued