Rough running engine

[gliderman]

I am having an issue with my 1951 170A, with a C145 installed. Recently a rough running engine occurred at idle with a general lack of power. After engine run I found a cold # 6 cylinder. Suspecting a stuck valve and not wanting to do the "rope trick" I removed the cylinder and had an engine overhaul shop check it out. They claim to have found a sticking exhaust valve and reamed the guides and did a general clean-up. Found the piston corroded lightly on the rings lands so convinced me to purchase a new piston and ring set (after all it is only money right!).

I have also had the mags checked and subsequently overhauled and re-timed to engine after cylinder re-installed. New plugs installed, ignition harness checked out OK with high tension lead tester.

On engine run after re-installation of cylinder same issue continues; rough idle, lacking power, cold # 6 cylinder. Mag drops about 75 RPM per side. Curiously, application of carb heat at about 1000RPM seems to smooth out operation but only slightly. So now what? We have checked the induction system for overall tightness etc., and found nothing unusual. The engine has about 1100 hours since overhaul and has given no trouble since purchase 5 years ago. Oil consumption is about 1 liter per 6 hours flying.

Anyone with ideas, hints, tips, or general suggestions greatly appreciated.

Mike

[canav8]

Have you done a compression and a leak down check?
Doug

[GAHorn]

If a cylinder is dead (cold) ...I mean really cold.... then you can probably rule out ignition, although you might first replace or at least test those two spark plugs, and there's certainly no prohibition against watching those spark plugs "spark" while cranking the engine with the mixture in shut-off.

If you just redid the cylinder, you can probably rule out compression, but performing that test is still not dis-qualifying.

It points to induction/fuel. You've looked at the intake plumbing (externally I take it) so there might be an obstruction internally or the intake valve may fail to open. If you've observed the valves opening/closing while turning the engine over with the rocker-cover removed ...that would eliminate the cam and lifters.

There's a baffle above the carburetor that in some engines is rivetted and has been known to shake loose and block one of the "spiders" ...or intake pathways. You'll have to remove the carburetor to check for that. I recommend you first do the compression test, then the rocker-cover removal observation, then the carb removal to check the intake baffle.

[W.J.Langholz]

Just a side note. Double check to make sure they put a new intake gasket on,I did not , and after run up (20 mins) I shut it down and double checked the spark plugs that I had just cleaned the day b/4 and both were not burning as clean as should be. After alot of head scratching and some of the stuff George had mentioned, I pulled out the cylinder and put a new intake gasket on and it corrected the issue.

I guess that's why they send one along with the kit.........Life Lesson's #101

W.

[gliderman]

I have done a compression check and it was about 78/80 so I expect the valves are closing correctly. I also did have the valve cover off after the cylinder installation and post run-up, and the valve function seems about normal. There did not seem to be any clearance on the rockers to valve stem, but as the compresion was OK that would (should?) rule out the valves being open.

The hint on the carb baffle will be my next investigation. Once the carb is removed will this baffle be attached to the carb or on the "spider" itself. If it is loose what will be cure for that?

Thanks for now.

Mike

[gwillford]

Been through this also. After chasing my tail for several months, it was the first thing I checked, intake leak. Take the elbow off and true up the surface with oiled sandpaper on a flat steel plate. New gassket and don't over tighten and bend again. My leak was on the back side where it could not be seen. George

[cessna170bdriver]

deleted by the author

[sloPoke]

I second the leaking intake elbow gasket. We had that on an O200 and thought it was sticking valve. Doesn't run on that cylinder at low rpms because the mixture is too lean but if you push the throttle up it runs okay because the relative added air is no longer big enough to keep it from firing. We had a 4 point EGT on it and could watch it happen. Try new gasket and maybe a little permatex, hylomar or similar.
Good luck.
Charlie

[Bruce Fenstermacher]

I have a friend who recently had very similar symptoms. No power, ruff running and his would not idle under 1000 rpm. He had a cold cylinder and wanted in the worst way to pull it and almost did.

I convinced him it was a carb issue by running his engine at 600 rpm with judicious use of the primer. He pulled the carb and disassembled it to clean it. His report was he only found a little bit of dirt in it and couldn't imagine that was the cause.

With the carb reinstalled after the cleaning the engine runs great. Lucky guess on my part.

[sumpthiscom]

NTSB Identification: LAX72FUQ52
14 CFR Part 91 General Aviation
Event occurred Saturday, January 01, 1972 in S.FERNANDO, CA
Aircraft: CESSNA 170, registration: N2631V

Notice further below in remarks section about the location of sump drains

Of 47 NTSB Probable Causes for engine failure Cessna 170:
1- Questionable
17- Undetermined Reason
16- Water found (poor pilot preflight)
13- Carburetor Ice
REMARKS- DRAINS LCTD APRX 1-1/2IN FWD AFT END OF TANKS.
---------------------------------------------------------------------------------------------------------------------------- FILE DATE LOCATION AIRCRAFT DATA INJURIES FLIGHT PILOT DATA F S M/N PURPOSE----------------------------------------------------------------------------------------------------------------------------3-0211 72/1/1 S.FERNANDO,CALIF CESSNA 170 CR- 0 0 1 NONCOMMERCIAL PRIVATE, AGE 29, 385 TIME - 1130 N2631V PX- 0 0 1 PLEASURE/PERSONAL TRANSP TOTAL HOURS, 265 IN TYPE, DAMAGE-DESTROYED OT- 0 0 0 NOT INSTRUMENT RATED. NAME OF AIRPORT - SAN FERNANDO DEPARTURE POINT INTENDED DESTINATION S.FERNANDO,CALIF LOCAL TYPE OF ACCIDENT PHASE OF OPERATION ENGINE FAILURE OR MALFUNCTION LANDING: GO-AROUND NOSE OVER/DOWN LANDING: LEVEL OFF/TOUCHDOWN PROBABLE CAUSE(S) PERSONNEL - PRODUCTION-DESIGN-PERSONNEL: POOR/INADEQUATE DESIGN POWERPLANT - FUEL SYSTEM: VENTS,DRAINS,TANK CAPS MISCELLANEOUS ACTS,CONDITIONS - WATER IN FUEL TERRAIN - ROUGH/UNEVEN FACTOR(S) MISCELLANEOUS - EVASIVE MANEUVER TO AVOID COLLISION TERRAIN - HIGH OBSTRUCTIONS MISCELLANEOUS ACTS,CONDITIONS - DOWNWIND COMPLETE POWER LOSS - COMPLETE ENGINE FAILURE/FLAMEOUT-1 ENGINE EMERGENCY CIRCUMSTANCES - FORCED LANDING ON AIRPORT/SEAPLANE BASE/HELIPT. REMARKS- DRAINS LCTD APRX 1-1/2IN FWD AFT END OF TANKS.DEFECTIVE CAP O-RING SEALS.AVOIDING PWR LINES.