Fouled Plug

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bbeep71

bbeep71

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My 66 Barracuda with 360 was running a little bad so I decided to pull the plugs and see what was going on. All plugs (autolite 65) looked good except #3. It was oil foulded. Checked plug for resistance, was OK. Checked spark plug wire for resistance,OK. What do I check to find problem? :???:
 
If valve stem oil seal is the problem, why would one be worse than others ?
The only differences I can think of.. Where the valve stems sit when the engine stops. Which ones get flooded with oil when we pour it in from bottles. Takes a wild imagination to think any of that has a bearing on it.
Replace all the stem oil seals and hope that cures it.
 
Why not do a compression test wet and dry and see what it tells???
 
You may want to see if you can barrow a scope and check the cylinder walls for wear.
You may have gotten some dirt in the cylinder and scored it.

Is there any smoke at start-up or when running ?
 
How do you do a compression test wet? Also, how do you check if the valve seal is good? No smoke on startup but sometimes it smokes after a hard ride from the #3 side.
Thanks
 
bbeep71 said:
How do you do a compression test wet? Also, how do you check if the valve seal is good? No smoke on startup but sometimes it smokes after a hard ride from the #3 side.
Thanks
Click to expand...

You do the compression test normally where you warm up the engine, disable the ignition, then wire the throttle open.

then hook up the compression gauge and see what the readings are.

Then take an oil squirt can and squirt 3 or 4 shots of oil into the cylinder and repeat the compression test.


If your readings go up with the oil, then you have a ring issue.

If your readings stay the same, any low values will be due to the valves.

If they all have good numbers and no difference wet or dry, then you should be ok....
 
To find a bad valve, you should then do a leak down test after the compression test.

You will need to buy a leakdown tester and have a source of compressed air. Then follow the instructions on the leakdown tester.


Basically, you put the cylinder at TDC and then pressurize it. Then "hold" the pressure and see if it leaks. If a valve is leaking, you can hear an intake valve leak through the carb, and exhaust valve leak through the tail pipe, and any ring leaks through the crank case.
 
Only #3 is fouled. The other spark plugs look good. Does the leakdown test check the valve seals or just the valves? Should I just check #3 for compression and leakdown or all of them? For now I bought a hotter plug RN12YC to RN14YC for #3 hoping it helps until the season is over.
Thanks Guys O:)
 
Leak down does nothing for seals, it will test valve seats and rings though.

I would test all cylinders to give you something to compare

If you dont have smoke at startup it probably is not valve seals, it could still be guides though, but it is less likely.
 
bbeep71 said:
Only #3 is fouled. The other spark plugs look good. Does the leakdown test check the valve seals or just the valves? Should I just check #3 for compression and leakdown or all of them? For now I bought a hotter plug RN12YC to RN14YC for #3 hoping it helps until the season is over.
Thanks Guys O:)
Click to expand...



It's up to you on how many cylinders you test. I would take the time and do all of them myself. You can then save the results if you have trouble later and need to know where it used to be.

The compression test and leakdown test will let you know if there is any problems with the cylinder sealing; rings, intake and exhaust valves. If you can pass both tests, then you have an engine in good shape. It should put out good power. If you fail the test, then you should fix what is causing the low readings.

The hotter plug may help, but you are just burning the build up off. You should find the root cause of the fouled plug and correct it.
 
Can you show a pix of the fouled plug..

Generally if the build-up is on one side of the plug/electrode,, it's a valve guide/seal, or intake gskt.. If the whole plug is covered,, ring..

hope it helps.
 
I already cleaned the fouled plug and put it back before I bought a hotter plug. I'll put some miles on the plug and repost a picture of the plug. Thanks for the help and suggestions.
 
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