1977 1150 Piston Groove Broken

tavacska

Petty Officer 1st Class
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Jan 21, 2017
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244
Things happened on lake, please take reference the following link.
https://forums.iboats.com/forum/eng...ds/10572078-1977-1150-lose-power-when-at-load

Today, when I sync and link the carb again, I found out it too rich for idle mix, all 3 1/2, this is set for faster start. But now I know it was a mistake. When I set everything to 1 1/2. RPM increase from 800 to 1200. And all the black sooty deposit on spark plugs tell the same story too.

Also, I test all the compression after the warm up.
#1, 122
#2, 115
#3, 130
#4, 122
#5, 125
#6, 130

The idle in neutral and water tank is smoother, but still some vibrations.
When I just keep on tuning the idle mix, I heard clicking sound from engine suddenly. I know something serious happening and stopped the engine. I opened up the bypass and found out the #2 piston groove broken, and without pull up the engine, I don't know how to find where the noise come from.

How bad can it be? the second ring on that piston is good as it looks.

This is my plan for this pull up.
1. One original size piston + 2 rings
2. 3 set of reed valves
3. Crafting seal
4. Exhaust part gasket and clean

I have replaced almost every part of this engine, just can not let her go.

IMG_20180519_153616456.jpg
 

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jimmbo

Supreme Mariner
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May 24, 2004
Messages
12,944
You are going to have to split the crankcase and pull the crankshaft and pistons out to examine the damage to the cylinder wall. Piston is of course toast
 

Bondo

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Staff member
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Apr 17, 2002
Messages
70,464
Ayuh,.... While I don't do much outboard work,... one thing that's the same, regardless what motor is involved is,....

Ya can't develop a plan, 'n write a parts list, til it's torn down, cleaned up, 'n accessed to see what's still usable, 'n what parts are junk,....
 

racerone

Supreme Mariner
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Dec 28, 2013
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A lot of folks would have said compression is good.-----But here is the proof that the motor needs work.
 

tavacska

Petty Officer 1st Class
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Jan 21, 2017
Messages
244
I will work it out today.
The #2 piston had a small crack when I replaced the rings last year. But I let it be because it is only 1/8 in crack.
There are about 30 times on water since last pull out engine.
I am so surprised that it can be such a big mass since then. There must be a reason for this.

The piston self problem? because it has a small crack already for some reason.
Too rich on idle mix?

Anyhow, we will see tonight.
 

jimmbo

Supreme Mariner
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May 24, 2004
Messages
12,944
A crack never shrinks... it also affects the shape of the piston as it expands when heated
 

tavacska

Petty Officer 1st Class
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Jan 21, 2017
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Ok, here is the pictures of #2 Piston and Cylinder.
#1, 122
#2, 115
#3, 130
#4, 122
#5, 125
#6, 130


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tavacska

Petty Officer 1st Class
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Jan 21, 2017
Messages
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This piston originally has some problem. The grooves are so tight, and even after cleaned it can still stuck the rings.
My mistake was to let it be there and didn't replace it.

The rings got stuck again and broke to pieces. Some pieces are buried into the grove, some are buried into the tops of pistons. The click noise I guess is coming from the ring piece stuck into the top of pistons. It contacts with cylinder top and make that click noise.

How bad is the wall? There is some score on the exhaust port ( 2 holes). But it seems ok comparing to other cylinders which has the same kind of scoring.

Considering it has only one ring left and compression is 115. I guess I don't have to bore the cylinders? Never do the bore work before and don't know how to find the shop to do it. And I heard it is a kind of blind bore work for this kind of cylinder.
 

tavacska

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Jan 21, 2017
Messages
244
Are the valves ok?

Here are some pictures of the reed valves.
I can see the small gaps between the valves and block.

But the manual says, " Check for chipped or broken reeds. Observe that the reeds are not preloaded or standing open. Satisfactory reeds will not adhere to the reed block surface, but still there is not more than 0.007" (0.18mm) clearance between the reed and the block surface."
 

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Faztbullet

Supreme Mariner
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Mar 2, 2008
Messages
15,589
1) First motor is about 20-25psi low as those are high dome pistons......she is worn.
2) Run a rigid hone thru cylinders to see worn areas around transfer ports
 
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