The International Cessna^® 170 Association

In the last 2 times I have been flying I have notice a power reduction. The first time I noticed that we cleared the trees at a lower altitude than normal. A friend checked the tach on a static runup and we had 2100 rpms. This should translate to 2150 rpm because the tach reads 50 low. I am going to clean and reoil the airscreen. I will also check the throttle to stop and have checked the carb heat and it hits the stop (I can hear it.)

What else can I check before taking it to my A&P?

Thanks

Tom Arsenault
taa@winternet.com

Recheck with an electronic tach to make sure it is still "only" 50 RPM low.

Mike Smith
1950 C-170A

Tom
I know this may sound way out, but if you have just one (1) hyd lifter unit that is not holding long enough to open the valve properly then you will have a power loss of from 100 rpm under load like climb or 50 rpm or so in lever flight. This problem can come and go it may take weeks for it to happen again. It is very very very hard tell this is what the problem is unless you have seen it happen. The engine won't have a dead miss but you can feel it bogg down and hear the rpm change. Unless you are very used to your engine you would not notice it. I hope I am wrong that this is your problem but keep it in your thoughts just in case. The lifter units are about $25.00 each. I would change them at least one side at a time. If you try just one cylinder at a time you are taking a lot of the same parts on and off for each one. I have been there done that I know of what I am speaking. Not fun at all.

I am thinking along the lines that it is a lifter problem or a sticky valve. Another thing to check is the nylon drive gear in the Bendix Mags, it could have lost a tooth or two and is skipping, changing the timing randomly.

Hyd. lifter units and nylon drive gears are a pretty special "leap" of logic to make over the internet regarding a problem description like this.
There's way too many other, more conservative, methods to use in diagnosing this perceived problem,...starting with instrumentation accuracy.

I agree with George, look for the simple basic stuff first. If one mag isn't working you have that kind of power loss. Sticking valves show up more as a rough running engine at idle.

Been mentioned before I think. But along the rule out the simple first. Take the cowling off at night, (does get dark down there doesn't it this time of year) and look for spark leaks from any of the plug wires or anywhere else. Don't forget the prop.

Tom, it sounds as if you are not complaining of a rough engine. Am I correct? You didn't say anything about rough running, so that would rule out virtually all the responses rec'd so far.
It's summertime. The density altitude is higher compared to earlier in the year, and your engine/airplane performance will be less than winter. Simple as that.
If you believe it's more than that, it's an easy matter to have the mags timing checked and clean your airfilter, check plugs and compressions.
But I'll bet the reason you're seeing 50 rpm less and getting slightly less perceived climb is density altitude (which can be helped by leaning prior to brake release. Just don't lean too aggresively fo a takeoff. Lean only enough to make up for the rpm loss. Remember that full throttle runs slightly rich on purpose for cooling.)

Those items discussed sticky valves (rough running), lifters (noise), timing gear (check through hole by removing the plastic cap on top of Mag, air filter, carb heat valve, all can be done by an owner visual/sound inspection. The other stuff (carb, etc) is going to require an A&P to look at.

Density altitude might be an issue, but I sure would check it over good if there are any indications of a power loss.

Back when I was in college, working at an airport to pay tuition and stuff, we had this guy come in with an erocoupe. He said he had an unexplained power loss when he took off and then it would go away then come back whenever. We checked everything, and everything checked fine, it turned out to be a problem with the float in the carb, when new it worked fine, but after several hundred hrs of some wear and tear the float's safety wire interferred with the float movement only when it was at a certain angle of attack. Ran fine on the ground, take off/climb sometimes a minor power loss needless to say it took for ever to find it.

This is a follow up to a post I made July 1, 2003 about my 170 not developing enough power to climb out as expected. Here is what I did:

Had the prop repitched. It was a cruise prop (53) even though the logs said it was a climb (51) Cost $275 because they had to recondition it. Now have a black prop with white stripes instead of a aluminum one.

Replaced the harness with a new one from Chief. ($304 + $200 for labor). The logs said the harness was 30 or 36 years old. It was causing lots of noise in the radio.


All problems fix now. Flies great.
Now to work on getting my medical back. See my web site for info on that. http://www.winternet.com/~taa

Tom Arsenault
N4163V

Tom,
Are you using AUTO fuel? If so how old is it?

I am not using auto gas since I can not fly as much as before. Now I want 100 LL for the storage protection.

Tom A.