Engine sputtering and low static RPM?!

[Hattrick]

Hey All!
I just bought a 1952 170B last week and flew her home from Huntsville, AL. to Saint Augustine, FL. 3.5 x-c with NO problems at all... Once home I flew the wife around for 30 minutes in the new bird and washed her this weekend. When I went to start her up to taxi her back to the hangar I immediately noticed that at 1000 RPM every 2-3 seconds the RPM would drop quickly to 800-900... Noticing the weird noise and jumpy RPM I ran her up to see what my full throttle static RPM was and she's only getting around 1700 RPM. After trying to burn off the spark plugs for over a minute with zero results (this lack of RPM and sputtering at 1000 RPM and below is occurring on both MAGS by the way). After shutting down I checked the cylinders and noticed the left bank was warm to cold and the right bank was as hot as it should be.... I've had a few mechanics on the field help me look at the plane and so far we have pulled 4 of the 6 left side plugs and made sure they were firing (they are). After reinstalling the plugs we used the primer and noticed that the primer line was leaking from the intake manifold... Pulled off the copper line and had the fitting replaced (no more leaking) but the engine is still acting the same. So we plugged the intake manifold where the primer line attaches and still engine is running rough...


Tomorrow I'm pulling of the last 2 plugs on the left bank and checking those but I thought for sure fixing the leak on the primer line would fix the issue... Any thoughts from you guys would be greatly appreciated and could very much increase my troubleshooting time. The only other problems I can think of ( and I'm no A&P or IA just an instructor) is that I have stuck a valve or valves... or bad mag/s but I don't know why either of those would affect all three cylinders on the left side.... ARGH!

[53B]

Hi Mark,

I would make sure you didn't get the carb heat air intake ducts full of wash water. The flexible air ducts could have enough sharp bends to hold quite a bit of water. Hope this helps!

[Hattrick]

Thanks for the heads-up Mark. I'll look at that tomorrow as well!

[cessna170bdriver]

With one bank hot and the other bank much cooler, it sounds like you may have a loose intake connector hose, or possibly a stuck exhaust valve on one cylinder on the left (cooler) bank. I've had both, and the symptoms are similar. The coldest cylinder would be the likely culprit.

[Hattrick]

Thanks Miles...

I did check the carb heat hosing for water but there was nothing in there... After I test the remaining two plugs tomorrow I will more than likely check the intake hosing and gaskets as well as the valves on the coolest cylinder...

[Bruce Fenstermacher]

You have a stuck/sticking valve. Run the engine about 30 seconds and shut it down. Feel which cylinder is cold. That one will have no compression because the valve with be stuck open.

If the valve is only sticking and not stuck it may be a bit harder to find but that is what I bet your problem is. Been there done that.

[Hattrick]

Bruce,
Thanks for your input! I'm guessing once I identify which valve/s are stuck or sticking I just need to do the "rope trick" to reset the valve. However, I'm wondering if there is other maintenance (preventative or not) that I should do so this doesn't happen again (at least in the near future)??

[Bruce Fenstermacher]

Mark,

The "rope trick" by itself won't fix a sticking valve. It will unstick a stuck valve temporarily so that perhaps you could get home but it won't fix the problem. You need to remove and clean the exhaust valve stem and ream the carbon out of the valve guide. Lots have been written here including how to do it using the "rope trick" to hold the valves closed in order to remove the valve spring keepers.

I recommend that if one cylinder has a stuck valve others might be ready. I'd clean all the valves and yo should be good for another period of time say 300-500 hours. But who knows. Some folks here say they've never gotten a stuck valve and I sure wish I knew for sure how. Some like to use Marvel Mystery Oil (MMO) in their gas as a top end lubricant. Some use TCP religiously to help with the lead. Then there is proper leaning for todays leaded gas.

MMO is not approved yet thousands will swear by it. All the other technics and I believe MMO will help. At least it will help extend the period till the next valve starts to stick.

BTW there is a line of thought that sticking valves happen to valves and guides that are fit to tight. Certainly a looser fit would take more carbon build up to stick the valve and perhaps it would just not happen. I personally wouldn't fit my valves and guides to the tight end of the tolerance but I'd have a hard time opening them up to the loose end as well.

[canav8]

Just my .02 cents. You got water in the intake manifold. Unfortunately the left bank will injest more fluids then the right by design. A couple things that have been mentioned before. Check all connections on the intake tubes. They do tend to leak. Make sure all SCAT hoses have a pin hole to drain all water out of the scat tubing going to the heat muffs. Run the engine for about 20 min after a sloppy car wash style bath. The problems you see are normal and will disappear once dried out. A good way to fix that problem is use an STC from Challenger for the air filter(Its a K&N). The pleats on the airfilter are coated with oil. Water generally will resist passing through the oil soaked pleates. When you fly in the rain, you have to recoat the filter. It is also a small performance gain. Anyway. I would not be playing with any engine internals till you have done a compression check. Your problems are all systems normal after a bath. D

[GAHorn]

Before jumping to conclusions of stuck valves (which usually also include HEAVY vibration which you don't mention) and water in the intakes (which usually clear up in a few minutes of operation) I suggest we review what differences exist between that perfect flight home and the trouble-free flight you gave your wife.... and the troubles you experience after washing the bird.
Did you check the sumps, gascolator and carb bowl pipe-plug drain for water?
Did you wash the engine down also? Is it possible you've gotten water inside your left magneto? (the one which fires lower plugs in most installations but the one which fires lower-left/upper-right cyls in some installations?)

[Hattrick]

I did check my sumps and gascolator but the carb bowl... no water found.
I did not wash the engine down but water was sprayed into the intakes section while cleaning the cowling and prop. direct spraying was kept to a minimum obviously.
It's a slight possibility in my mind that water entered the mag...( how easy is that to do with the cowling on during a wash?) My left mag feeds all 6 lower plugs.

As for differences in eng operation before and after the wash... The eng was working wonderfully before the wash. Smooth at all RPM's and static RPM at full throttle was prob close to 2300 RPM. After the wash the eng IMMEDIATELY started to sputter at 1000RPM as stated in my OP. when leaned out there is no difference. When switching mags there is no difference. When the eng is run up to max of 1700RPM the eng runs constant speed but may vibrate a little more than normal but not drastically from what I can tell. I washed her on Sunday and have run the eng for 2-3 minutes each day since while troubleshooting, and the problem still exists.

[canav8]

Mark, Its a little hard to see and do maintenance from 2200 miles away, but, have you looked at your intake carb box with your Air filter off and looked at the position of the air box flapper? The one that is controlled by the carb heat? I suspect it is out of adjustment. A scenario I had once was: water was caught in the fresh air inlet on the right side of the cowl. It went down the scat tubing and sat. When you ran the engine the carb heat may have been still on partially and drew water from the scat tube into your intake . As I said before, left side cylinders draw more fluids through the manifold. It has been my experience, and I cannot offer an explanation except venturi effect. (I will leave that to the Physicist). I highly doubt you got the mag wet unless you have a blast tube that cools the mag, which it should not have. There are only three things that can make an engine run rough. Air, Fuel, Spark. Fuel and Spark are probably good since fuel is in a sealed system. Spark is good because no changes when doing a mag check and there are two mags, and you said you got water in the intake area. I am only offering suggestions. D

[GAHorn]

Mark, if you've been taking out spark plugs and checking them (because of rough operation caused by water)...then it's possible you've accidentally switched plug leads and gotten them firing in incorrect order. Check that carefully.

If you got water inside your plug harness, plug wells, or have porous magneto harnesses, then you could be seeing an ignition
problem until it dries out. Or, if you have a leaking magneto plug lead and have repositioned it to a nearby "ground" then you could be experiencing misfiring. Have your mechanic use his high-tension lead tester on your harnesses and dry them out while you're at it.

Pull the drain plug on your carb bowl and catch the contents, looking for water. Becareful not to overtighten it when you reinstall it or you may crack your carb bowl. (Remember, it's only gravity pressure there.)

Check your scat/sceet hoses in their routing to the mufflers and air box. Any low spots.... pierce the lower portion with an ice-pick or awl to provide a drain in the hose where water might collect. (Cessna issued a SB on that concern.)

[Hattrick]

Well guys I took off the valve covers on all three cylinders on the left bank and found #2 and #4 exhuast valves stuck in the open position... The local shop wants like 90 bucks and hour to pull the cylinders and clean the valves.... Now I'm freakin out because I'm worried its gonna cost me 1000+ dollars to fix this issue... Talk about bad luck huh... 5 hours after buying the plane.... Does anyone have any tips to help save time or money or know of anyone in the NE FL area that specializes in 170's or C-145's/O-300's??

[minton]

Any body thinking fuel venting?? sounds like "gulping" caused by plugged fuel vent(s)