just what IS that "dust" on the cyl fins

C170Driver · Post by **C170Driver** » Sun Oct 05, 2003 11:21 pm

Anyone care to help out a lowly 180/former 170 owner/flyer? Out flying the 180 (O-470-L) the other day and picked up a sudden and audible increase in vibration - like someone threw a switch; once the floats were back over water - I tried various things to see if it would go away: one mag, less throttle, less/more rpm, etc. But no avail. It was of the same frequency as normal engine vibration, but greater magnitude, and frequency varied with rpm. Didn't go away until I pulled the throttle way back on final.

Until the hangar is available - i changed oil (sampled) and cut open the filter, so far so good. Mounts all look good, accessories are snug. One thing I found was a gray powder (ash) dusting the fins under the bottom plug on both #1 and #6 - made the more obvious on the new CHT probes recently installed - still shiny on the rest of the cylinders.

Question: what is the powder from? blown exhaust gasket? cracked head? diaper change? Would either produce that kind of vibratio?

Next thing in a row once the hangar is MT is compression check looking for stuck valve (though not expected to occur in flight?) and further dis-assembly. Any ideas? No crack in spinner or plate found, either. Appreciate you sharing any ideas! Thanks! (missing the 170).

mit · Post by **mit** » Mon Oct 06, 2003 4:54 am

Pat
You sold the 170? how could you? Well I wish I had a 180 also, sigh....

Robert G. White · Post by **Robert G. White** » Mon Oct 06, 2003 5:29 am

I also fly behind a O-470-L engine... I had a the same symtoms several times before I overhauled the engine... it was missing due to fouled spark plugs on one cylinder... This missing also can be caused by a bad or stuck exhust valve. A bad intake valve will affect more than one cylinder by firing back thru intake... and thus engine very rough.

C170Driver · Post by **C170Driver** » Mon Oct 06, 2003 4:01 pm

Tim, it took two years for my father-in-law to shame me into selling our wonderful 170 sports car and throw in with him in the 180 suburban. I still miss the light controls and second-nature flying of the 170. The 180 and I still have spats now and again - but we will adjust.

Bob - what are the chances of a valve sticking in flight? I was thinking they typicaly balk at start-up, but have no experience with stuck valves (i know i just jinxed myself). Still waiting on the hangar to empty out so I can take more stuff apart...

spiro · Post by **spiro** » Tue Oct 07, 2003 9:16 am

hey Pat,

interesting seeing your post here after seeing it on the 180/185 list! My initial thoughts are fouled plug or bad wire, or possibly an intake leak indicated by the EGT's - I noticed you said you found some loose. Mags current? I'd look at ignition & intake before thinking it's a valve.

the grey dust is probably exhaust - just got to look to see where it's coming from.

my 180's got an L also, but it's just an overgrown O-300 as far as the troubleshooting goes.

btw, if you're still looking for a good sheet-metal guy, drop me a line, I can recommend several.

- paul

Robert G. White · Post by **Robert G. White** » Wed Oct 08, 2003 7:36 am

Hi Pat:
Yes, I doubt it was a valve sticking in cruse flight... although one may have started leaking. An exhust valve will affect just it's own cylinder, an intake leak valve leak is very noticable as it makes the engine run very rough from the compression blowing into the intake system. The dust you mention may not have any connection to the vibration or roughness you experienced. A compression test, even just pulling the prop thru each cylinder, will be a good start. If OK, then pull the plugs and check them for fouling or indication of not firing, either wet with fuel or oil. If all OK..then look for other causes. Plenty to choose from... crank counter weights, cam lobes, prop and spinner, engine mounts, and so on.
Blue skies to you, Bob

C170Driver · Post by **C170Driver** » Thu Oct 09, 2003 6:50 pm

I was really pulling for something simple like an ignition anomoly - but did not experience the relief I desperately desired by switching from one mag to the other during the episode! Could it (ignition) still be the case?

I tightened up the hose clamps on a few of the intake manifold risers quite a bit - some took three+ complete turns of the screws to tighten; that should make some kind of difference. It was remarkable that all the cylinders on the left side of the engine were running cooler in cht and egt as a group compared to the right side - that's what made me think about some fault inthe induction system on one side compared to the other.

Hangar finaly cleared out - should have the thing in there tonight. I truly appreciate the input. You folks are GREAT!

I also have another dilema - been invited to ferry a DHC2 Beaver on floats to ANC from JNU and return with a C206 seaplane - might cramp my maint. schedule.

4-Shipp · Post by **4-Shipp** » Fri Oct 10, 2003 1:27 am

Does your primer enter at the left intake manifold like on the 170? If it does, and it is leaking, that could account for the cooler temps on the left - they are running rich. I just had the same problem on my 170 evidenced by a sooty stain out the left stack but not the right.

Bruce

Post by **GAHorn** » Fri Oct 10, 2003 4:08 pm

To answer your question Pat, ...it IS possible that ignition could cause the problem. Besides a bad plug or two, you could have carbon tracking inside the mag dist. caps. You might also have harnesses in trouble. A high-tension lead tester will tell you that pretty quickly. (Most shops have them. They are small boxes similar to mag timing/sync. boxes.)
If both your mags of of similar vintage, both might exhibit ignition problems.
I owned a 206 that would do this from time to time. It turned out to be one cylinder had a cracked valve guide. The guide would allow the valve to occasionally wobble out of perfect alignment and be a big leaker. A little while later, the engine would smooth back out.
I found it by removing the rocker covers and attempting to "wobble" the valves. (I was doing it just out of curiosity as a check for worn guides.) Imagine my shock when I was able to move one valve and watch it's valve guide stub move along with it!!
Since it was a mid-life engine, I just exchanged the entire cylinder with a rebuilt chromed one.