Need Advice on Chrysler 140HP Missing/Vibration

[gjh1967]

After some advice Folks.
Im in Australia and own a 1978 Chrysler 140HP outboard.

The 140 was running great last weekend as my videos on Youtube can attest to. Took it out yesterday afternoon. Starts great.

Problem raised its head after 5 minutes. Took it up to a bit over half throttle and it started to vibrate and lose power. I throttled back to idle. That's ok but engine didn't feel right. Small vibration. So i Took it home.

Flushed it out and tested idle and part throttle. Vibration appears worse on higher idle.

Checked plugs (NGK BUHS) all good with no differences in color. Tested electrodes with Multimeter. No leaks and good resistance 0.01 Ohms average.
Checked Fuel and filters. Spotless.

Compression test. Wide open throttle test. engine cold
cylinder 4 at bottom 115 PSi
Cylinder 3 110 PSi
Cylinders 1 & 2 zero.Needle just fluctuates.

Did a test on water temps last weekend.
Water temp at exhaust telltale was 59 Deg Celcius
Temps on overheat sender 53 Degrees.


Today i pulled the transfer port covers off at Cylinders 1 & 2 to see if there was anything out of the ordinary.

Couldn't spot anything broken. Could see part of the bore on each cylinder and no harsh scoring noticed.

Taking into account the engine is 40 years old and i cant be sure if its ever been rebuilt..
1978 140HP 1407H8A

Whats your thoughts on possible causes of the vibration. Would a crap Reed valve on that carb do this or head gasket.

The vibration seems like a car when it misfires under load. No backfiring was noticed either.

Cheers Glenn.

 

[jerryjerry05]

Since it has no compression on 2 cyl that are next to each other??
I'd check the head gasket.
The reeds shouldn't have any effect on the compression.

 

[gjh1967]

Thanks Jerry. Kelly B said you'd be the Guru that could help. I'm pulling the head off tomorrow. I'm a qualified motor mechanic in Oz but 2strokes are a complete mystery to me. Cheers Glenn

 

[kbh121956]

Thanks Jerry. Kelly B said you'd be the Guru that could help. I'm pulling the head off tomorrow. I'm a qualified motor mechanic in Oz but 2strokes are a complete mystery to me. Cheers Glenn

I knew that Jerry would chime in for you. Good luck and happy boating.

 

[pnwboat]

The temperatures that you indicated are pretty normal.

When you have the head off, check for any damage to the outer top edge of the pistons. A broken ring will often damage this area of the piston.

Rotate the motor to move each piston all the way down to inspect the cylinder walls for any obvious scoring or damage.

Hopefully you'll see a problem with the head gasket.

I've attached a photo of an example of a piston damaged by a broken ring as viewed from looking down into the cylinder.

 

[gjh1967]

I took the head of This afternoon and couldn't

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​ really see anything out of the ordinary. Attached are pics of cylinder 1 & 2.Cyl Head and head gasket on fire ring side and head side. This doesn't mean that the head isn't warped though. As the problem has only occurred over a 15 minute time-frame, im thinking the problem has just started.

 

[jimmbo]

Now that you have 3 posts you should be able to post pics

The upper cylinders are the first to show issues when an engine is not getting enough cooling water. How old is the water pump impeller?
Check the head for warpage, small amounts can be removed by lapping the head in a figure 8 motion on an abrasive on a flat surface

 

[jerryjerry05]

jgh1967 the pics didn't show up??
Sites like Shutterfly or another photo sharing site can help load pics.

 

[gjh1967]

Ive ended up stripping the powerhead down for a freshen up. Depending on the bore size it may only need hone and re-ringing.

 

[gjh1967]

Here's a Pic of Piston 3. Its started to scuff from carbon build-ip in the rings.It looks like the Engine has been worked on before as its 10Thou over standard. This to me doesn't look like a factory piston but i could be wrong. Has anyone seen a piston like this before with the stripes on it.

 

[jerryjerry05]

Can't really tell how bad it is?
Try to clean it and see if the scrapes go away.

You can try to re-use but I'd get a new one.

FSA474260 .010 over rings

The stripes mean nothing.
That looks like a regular Chrysler piston.

Be careful when buying rings, some aftermarket(Wisco) won't fit right.

 

[gjh1967]

Thanks Jerry. Its Bad. The scrapes on the side of the piston have made it a bit flat either side. This is going to be a trophy and put on a Plinth to admire. From my measurements i have double checked again and it looks like its been oversized 10Thou. The good pistons are 85.66 Avg at skirt and 85.46 Avg at top of pistons. Bores are 85.94 at skirt and 86mm at top of block. I may be wrong but im sure this is 10 though over from standard. 3.375" being standard. Cheers

 

[jerryjerry05]

The oversized usually have the size marked on the top of the piston.
It should have .010 stamped on the top.