MMO Piston Soak ?

[Vikas]

To throw another monkey wrench in this discussion, the spark plug always comes out without any oil or fuel fouling. Except for red tint on the white insulator inside, it looks like a new plug. That should rule out heavy oil burning. Also I hardly ever see any puff of smoke except only when MMO or Kreen was actually being burned off.

But then why do I have to add the oil after every cut? I am sure there are quite a lot of folks (not on BITOG!) who run their OPE without checking for oil for years!

 

[OVERKILL]

Originally Posted By: Trav
I guess the problem i am having is with the word "dry".
I never thought of cold bores being dry but of course you wouldn't do a compression test on a cold engine and expect meaningful results other than it does have adequate compression to start which is a common test on no start diesels.

Vikas did say he performed a warm test and while not up to full operating temp which should have gotten plenty of oil on the bore and IMO a decent reading.
I'm going to have to reread this whole thread again, something is not fitting together for me.

It has always been my understanding that oil down the plug hole will create a temporary seal in a cylinder with worn rings or a worn bore.
This is honestly the first time in 40 yrs i have heard differently.

Check out page 46&47 this is what i was taught when i first started, course this is more modern

http://people.cpcc.edu/~fse2680e/AUT%20116A%20%20General%20Engine%20Diagnosis%20(Student%20Workbook).pdf


I think we are on the same page, my terminology is likely a tad out of whack, but that was how I was taught by my crazy french auto mechanics teacher

My points about dry versus wet were more in regards to an engine that couldn't be run to get a warm reading because either it didn't run, or wasn't hooked up (out of the vehicle) in a way that allowed it to be run. In that case we were taught that a squirt of oil down the bore (wet) will give you a reading that should be somewhat in-line to what you would get if the engine was warm, which wouldn't be the case with a cold (dry) reading.

And to further convoluted things with my exciting terminology here, a shot of oil down the bore of an engine that could be run but showed low compression, if it perked up, was, like the doc you linked to stated, a sign of a ring problem and also referred to as "wet", LOL!

I'm thinking my terminology and how I was taught may have been a little unorthodox (like the guy that was teaching it). And I'm certain your way of defining these items is more accurate than my own, even though I think we are describing the same thing.

 

[OVERKILL]

Originally Posted By: Vikas
To throw another monkey wrench in this discussion, the spark plug always comes out without any oil or fuel fouling. Except for red tint on the white insulator inside, it looks like a new plug. That should rule out heavy oil burning. Also I hardly ever see any puff of smoke except only when MMO or Kreen was actually being burned off.

But then why do I have to add the oil after every cut? I am sure there are quite a lot of folks (not on BITOG!) who run their OPE without checking for oil for years!


Start with the fuel as we discussed and go from there. It is an easy item to eliminate.

 

[Trav]

Quote:
think we are on the same page, my terminology is likely a tad out of whack

Oh we are definitely on the same page. The same thing happens to me all the time.

 

[Trav]

You said the clutch was slipping after doing a piston soak.
I assume the engine was tilted so the piston was vertical?
With no obvious sign of oil burning i would definitely suspect a leak when its running.
The oil is possibly getting blown outwards under the deck. Maybe a lower crank seal?

 

[Vikas]

Funny thing is when I did MMO piston soak, engine was not tilted at all. When I did Kreen soak, it engine was jacked up. I had clutch slippage after MMO soak but not after Kreen soak. I can not explain the clutch slippage at all.

I am going to try high mileage oil. I have picked up a bottle of Pennzoil gold colored bottle. I might add some ATP-205 reseal dosage too.

 

[Vikas]

I have cleaned the exhaust. I have fixed the exhaust bolts.

I checked the hot compression and it is showing 75 ft-lb which is pretty much right in the middle of the spec. I also did the "bogging" test as suggested here. When it is bogging down and if I spray carburetor cleaner, it wants to die even more. That rules out engine running lean.

I also looked at the spark plug after two hours of mowing. The plug looked brand new. I will later post the pictures. Nothing obviously wrong with the engine but it just does not seem to be able to handle the load.

If the engine is running rich, what could be the reason? A clogged jet would lead to lean and NOT rich. I am not sure I should start taking apart the carburetor.

Comments?

 

[steve20]

this has nothing to do with your engine issue, but might help you cut some time from your current waiting until the engine quits bogging down.
Mow 3/4 of the width you normally mow (overlap your runs down the lawn, so you are really not cutting a 22 inch width, but a 16-18 inch path)each time. It may keep it from bogging down alltogether
Steve

 

[OVERKILL]

Originally Posted By: Vikas
I have cleaned the exhaust. I have fixed the exhaust bolts.

I checked the hot compression and it is showing 75 ft-lb which is pretty much right in the middle of the spec. I also did the "bogging" test as suggested here. When it is bogging down and if I spray carburetor cleaner, it wants to die even more. That rules out engine running lean.

I also looked at the spark plug after two hours of mowing. The plug looked brand new. I will later post the pictures. Nothing obviously wrong with the engine but it just does not seem to be able to handle the load.

If the engine is running rich, what could be the reason? A clogged jet would lead to lean and NOT rich. I am not sure I should start taking apart the carburetor.

Comments?


Good to hear you at least tried it. You could always adjust the governor so that it is rev's a bit higher and see if that helps as well.

 

[Vikas]

It is already revving higher than the stock as I jacked it up. I am actually wondering if I should bring it down. May be it is running out of governor adjustment at load as the speed is too high.

Yesterday I had a different problem. A friend stopped by during the mowing, so I shut it down while talkin with him for few minutes. It just would not restart at all. I sprayed a shot of carb cleaner still no life. Finally it did start after trying many many times. It had never done this before. I was able to recreate this problem later too. Sure feels like heat soak and vapor lock to me but how would it develop this problem all of a sudden? Carburetor and exhaust are on the opposite side. Besides, doesn't vapor lock would cause engine stall? It will run as long as I don't turn it off and try to restart in few minutes.

 

[Quest]

next time when this happens: immediately pull off your plug and take a quick whiff off of the spark plug hole and also visually inspect plug gap (electrode). does it smell gasoline? is the electrode wet?

Granted that you don't small strong gasoline smell from spark plug hole and your plug electrode seems dry, (lean), assuming your coil pack is working properly, a shot of starting fluid should get it back up and running. If numerous of shots of starting fluid and still no start, your carb is plugged (assuming no intake manifold/vacuum leaks).

If your plug is wet, then it would be either an intermittent coil pack (electronic magneto coil) or carb plugged.

Good luck.

Q.

 

[TFB1]

Being bored I just reread the entire thread & something not mentioned is fuel consumption... If it's rich to the point of bogging down easily, you'd no doubt be refilling it every ½hr or so... Also the plug would be sooty with carbon, I'm still thinking it's a lean condition... Running it with the choke partly on will prove/disprove my theory...

Some years back I had a Briggs that was lazy and even a known good carb wouldn't fix it... Turned out the gasket that sealed the intake tube to the block had deteriorated and was mostly missing, a little hi-temp RTV and she was good as new...

 

[OVERKILL]

Originally Posted By: Vikas
It is already revving higher than the stock as I jacked it up. I am actually wondering if I should bring it down. May be it is running out of governor adjustment at load as the speed is too high.

Yesterday I had a different problem. A friend stopped by during the mowing, so I shut it down while talkin with him for few minutes. It just would not restart at all. I sprayed a shot of carb cleaner still no life. Finally it did start after trying many many times. It had never done this before. I was able to recreate this problem later too. Sure feels like heat soak and vapor lock to me but how would it develop this problem all of a sudden? Carburetor and exhaust are on the opposite side. Besides, doesn't vapor lock would cause engine stall? It will run as long as I don't turn it off and try to restart in few minutes.


Almost sounds ignition related....

 

[Vikas]

Heat soak ignition problem? Would that explain able to run but not start?

 

[OVERKILL]

Originally Posted By: Vikas
Heat soak ignition problem? Would that explain able to run but not start?


Yup, because when you shut it off, what was being cooled by the fan gets even hotter.

 

[Vikas]

The only thing which is different is that currently it is running with a Champion plug. This is the first time I am running anything but NGK in it. I am going to get a new OEM NGK as a first step in diagnosing hot-no-start condition.

It could be running rich as I am using quite a lot of gas. However, I just do not see/smell rich exhaust or fouled spark plug. If it is running rich, would carb rebuild fix it? And more importantly, what can cause it to run rich? I know the air filter is clean and as said before even without air filter it still bogs down.

 

[demarpaint]

Originally Posted By: Vikas


It could be running rich as I am using quite a lot of gas. However, I just do not see/smell rich exhaust or fouled spark plug. If it is running rich, would carb rebuild fix it? And more importantly, what can cause it to run rich? I know the air filter is clean and as said before even without air filter it still bogs down.


A carb rebuild can certainly help. Sometimes vibration throws the adjustment screws out of whack. Did you check the float, is it adjusted properly?