Do I have a stuck valve?

[robshepherd]

Greetings!

This is my first post, though I've been lurking for a while. The volume of information here is impressive, if not a bit overwhelming. I am posting today to ask for advice on what I think may be a stuck valve. I have a late model A4 in a Sparkman & Stephens Yankee 30. The engine has developed an intermittent knocking sound, and if I pull the plug wires one at a time while idling, each results in significantly rougher running, with the exception of #3. No. 3 is firing, but it seems like for practical purposes this motor is intermittently running on only 3 cylinders. I have not performed a compression test (don't have the guage), but each cylinder will blow my thumb off the hole, including #3. My exhaust is pretty clean at idle, but there is obvious blow by at higher rpms. From the log book I'd estimate that this motor has 1000-1200 hours on it, and it is fresh water cooled w/ a heat exchanger.

Does this sound like a sticky valve? If so, would it be good to begin with MMO in the hole, or perhaps Kroil?

I originally thought I had fuel issues due to the occasional rough running (and ultimately I may have...) so I rebuilt the carb and the mech. fuel pump. They didn't look very good inside, but now they are nice and clean and this motor fires right up almost as soon as the starter engages.

For a bit of background, I am not a mechanic (yet!), but I am learning a lot and hope to learn more.

Kind regards, Rob

[Dave Neptune]

Rob, first welcome to the Afourian Forum! If it blew you thumb off the hole it's not stuck but maybe sticking intermitantly. A bit of MMO or a spray of penetrating oil, my preferance into the plug holes when you shut down.
Run some MMO in the fuel at around 100:1 mix and it will slowly loosen it up in good time.
How do your plugs look, especially #3? Could be as simple as a bad plug, idle adjustment or even just needs a tune!
Try some of the above and run for a couple of hours, then do a compression test with a gage, both dry first and wet after if the problem persists.

Dave Neptune

[robshepherd]

Thank you Dave for your input.

Plugs look decent and the engine is freshly tuned (New: wires, coil, pts at .019, rotor, condenser, R45 plugs at .035, and timing adjusted).

I do have access to a gauge I can borrow, and I will report back with dry and wet numbers after I give #3's valves some treatment with the penetrating oil.

Thanks! -Rob

[Al Schober]

Rob,
I've seen problems that I attribute to MMO in the fuel - deposits on the intake valves. I do recommend that you add some MMO to the crankcase.
I'd also check your valve tappet clearances to make sure #3 isn't running tight.
Looking forward to seeing your compression numbers.

[robshepherd]

Thank you Al,

Today I sprayed some Kroil into #3, let is sit for a while, and turned it over a few times with the plug out. Also added some MMO to the hole, cranked it a bit, and letting it sit.

I have not added anything to the fuel. We'll see tomorrow if I've made a bit of progress. I'm starting to think I might have more than one issue going on (surprise, surprise), but I don't want to say more until I've had a chance to investigate further.

What a great resource this forum is. Amazing. Regards, Rob

[CalebD]

Clogged carb can be because of dirty fuel.

It is hard do know what is lurking in your tank (if it hasn't been checked in over 10 years).

The picture below is the last one gallon of stuff I pumped out of our 20 gal. fuel tank.

Ethanol is not your friend.

[ArtJ]

Rob,
I've seen problems that I attribute to MMO in the fuel - deposits on the intake valves. I do recommend that you add some MMO to the crankcase.
I'd also check your valve tappet clearances to make sure #3 isn't running tight.
Looking forward to seeing your compression numbers.

Hi AL
Are you suggesting that MMO in the fuel caused issues? Could you please elaborate
for us amateur engine people?
Best Regards

Art

[robshepherd]

Success!

So for a couple of days I've been running the motor for 15-20 minutes periodically after adding some MMO to the oil pan. I also supplemented this treatment by spraying Kroil into the cylinder hole with the plastic needle nozzle aimed at the valves, hand turn it a bit, and spray some more.

Today #3 started firing reliably and she's running smoothly at idle, and under load against the dock lines. I'm planning to change the oil again, and perhaps run with a bit of MMO in the pan as a precaution, at least until the next oil change.

I will also borrow a compression gauge next week and report back with those numbers for any feedback.

For now though I'm signing off for a few days to go sailing with my wife here in our local cruising grounds, the San Juan Islands. Anybody on the board from the Pac. NW? Bellingham, San Juans, Anacortes? Just curious.

Thank you everyone for the feedback. I really appreciate it. Cheers, Rob

[lat 64]

For now though I'm signing off for a few days to go sailing with my wife here in our local cruising grounds, the San Juan Islands. Anybody on the board from the Pac. NW? Bellingham, San Juans, Anacortes? Just curious.

Thank you everyone for the feedback. I really appreciate it. Cheers, Rob

You lucky dog you!

My brother is on Bainbridge I. He sails out of Pt. Madison Y.C. I may get there next year to borrow his boat and bop around a bit.

R.

[robshepherd]

You lucky dog you!

My brother is on Bainbridge I. He sails out of Pt. Madison Y.C. I may get there next year to borrow his boat and bop around a bit.

R.

You'd love it! Come on the shoulder season. Everybody's gone home now that school has started again. We've got wood heat on the boat, so the season is "just starting" as far as we're concerned!