What should be min RPM @ take off be ?

[jatkins]

I was flying to-day and I see I am only getting 2250 RPM at take off at 50 mph .
It does not get above that, until I start to level off after climbing out at 80.
In cruise at full throttle i get 2625 Rpm at 2500ft .
Static full throttle not moving I get 2200 RPM.
I have a C172/EM7655 prop. Prop overhauled 15 hrs ago.
The tach was calibrated in April/08.
Mags check ok ??
Mixture seems OK,.. I get a very slight rise in RPM, when I pull the mixture out to shut down.
Engine has 15 hrs since major overhaul.
I do seem to be getting a little blow-by, or something as I get a very small bit of oil on the windshield every 2-3 hours.
I am running 7 qts of mineral 100 oil.

Any suggestions ??

John

[mit]

buy a tach checker.

[buzzlatka]

That RPM is normal for a stock motor.

As gahorn says, this is a 145 hp motor but only gives us about 110hp at takeoff.

[jatkins]

So , that RPM (2250 ) is about normal for a "normal" O=300 motor.
Ok so i guess she is abit weak on 1600 ft strip 3/4 tanks and 2 guys !

[Green Bean]

Would be okay if it isn't to high or to warm, and maybe a little breeze. If you were looking for a little more rpm and a little less speed you could twist the prop back to 53, but it just depends on your desires.

[hilltop170]

John-
Did you replace your crankshaft with a factory new crankshaft at overhaul?

If you did, that oil on the windshield might be coming from a loose plug inside the end of the crankshaft. The new cranks are sold for fixed pitch prop installations (O-300) as well as constant speed prop installations (IO-360). That plug is installed on fixed pitch prop cranks to stop the oil flow that normally goes to a constant speed prop.

The plug on my factory new crank has come loose two times in the first 80 hours since overhaul. Both times Continental said just Locktite it and screw it back in. Not an acceptable solution to the problem but all Continental will commit to. It did not have ANY Locktite from the factory and came loose in 15 hours.

Your rpm numbers are about the same as I get with the same prop and a digital tach.

[jatkins]

Thank-you for the information Richard.

It is good news, that the RPM is normal, so I will not chase anything on the engine / carb. to try to get more RPM.
So it is fair to say then that with a 55 pitch prop 2200/2250 RPM on the takeoff roll is what to expect.
I have a "53" prop , I will try it and see how it does.

As far as this crank plug goes, my crankshft was changed at overhaul, due to corrision.
My new ( purchased used ) crank is part number 628124. Which according to my Continental Parts Book,
dated November 1981, is the corrrect crank for O-300C and D, engines.

Any ideas / suggestions , on this blow by ?, I am guessing it is coming out of the crank seal ?
I can not see any leaks leaks fron the engine.
But why is crankcask pressurizing ? I am getting a very very fine mist of oil on the windshield, mainly on the right side,
I seems to only happen after take-off if the engine is hot.( 19 hrs SMOH on the engine )
I am keeping the oil level at 7 qts.
My oil pressure is running at 40 psi.


Thanks again, John

[ron74887]

John, Be sure to check your crankcase vent line. The elbow coming out of the engine should point up about 45 degrees and the flew hose connects to the alumimun tube exiting the engine comparrtment. I had a dirt daubber plug mine up one time even with all the oil and fumes in it. got qiute a bit of engine crankcase pressure--lucked out. Ron

[GAHorn]

John, your EM7655 prop is "roughly" equivilent to the DM/MDM7653 standard prop which, according to the TCDS, should indicate 2230-2330 static rpm. (Sea level, standard day)
Your 2200 static is therefore about 30 rpm low... if you're measuring with a micrometer.

Although your tach was "calibrated" in April, it's possible that the calibration didn't account for the atmospheric conditions that day. (You also don't state what atmospheric conditions exist at the moment you said you achieved 2200 static. And it can only be assumed that you leaned over to the right and rid yourself of parallax when you supposedly saw 2200.

In other words.... there are some variables involved here.... and I'd venture you don't have a problem. But you might check your mag timing just to be certain it's set correctly.

Meanwhile, as for the oil leak, you might wash your engine, run it around the patch once, and look for evidence of a leak with dye-penetrant developer or baby powder, or ordinary flour. Chances are it's a pushrod tube rubber or crankshaft seal.

[jatkins]

Thanks Ron / George,

I guess I am Ok on the RPM, I will get my 76/53 prop , overhauled/certified, and installed.

The oil issue is a very very fine mist ( drops about the size of the pointy end of a pin ) ,
I only ever see it on the R/H side of the windshield, ??
I think I can see evidence of a bit of oil on the back side if the prop.
There-fore I a guessing I am building crankcase pressue and it is coming out of the seal ???
Could this have any thing to do with the high oil temp ? ( to-day oil temp was 220, at 3500ft
and the OAT was 20c.

John

[GAHorn]

220 is not "high" , but even so it's unlikely the cause of oil misting. Is there any oil mist on the lower front cowl below the spinner?

[hilltop170]

John-
Your crank might still be one of the ones that is drilled for a constant speed prop. If the oil is coming out of the spinner or between the prop and crank flange, look down inside the prop/crank and see if there is a hex head plug in there.

If there is a hex plug in there and there is oil inside the crank, that's your problem and it will only get worse until the plug falls out. Then you will lose all your oil as fast as the oil pump can pump it thru a 3/8" diameter hole.

If there is no hex plug in the end of the crank, it's probably your prop seal leaking which makes a mess but won't kill you.

[jatkins]

Thanks Richard,
I am going to pull the prop off this weekend to check it.
IF there is a hex plug there what is the fix so that the plug will not fall out ??

John

[hilltop170]

John-
There is no available fix that will make the problem go away permanently. Once it happens once, it is likely to happen again. Luckily as I have found out it takes some time to back out and there is plenty of warning with oil spraying on the windshield before the plug comes out completely. Continental refuses to address it. They say there is no problem. I say if the plug falls out twice in 80 hours since a new crank there is not only a problem but a life safety problem. I have given them a very inexpensive solution but they still refuse there is a problem.

In the meantime, the way to get the leak stopped temporarily is to unscrew the plug and clean out the threads VERY well with a spray solvent such as brake parts cleaner that will completely remove all traces of oil. It will take several tries but keep spraying and swabbing out with long Q-Tips or some other absorbent until NO traces of oil are left.

When you unscrew the plug, there will (or should be) a standard AN crush washer under it. Replace the crush washer with a new one and get the strongest Loctite (which I can't remember) and load up the threads and screw it back in to the proper torque for that size crush washer (which I can't remember either). The torque is standard for AN crush washers or you can call Continental customer service and talk to Scott at 888-826-5465 option 1 and tell him you have another crank plug that came loose like that guy from Alaska.

There is no mechanical lock of any kind on the plug other than the integrity of the Loctite. You can't torque the crush washer enough to lock it in place or the crush washer would be smashed flat and would not seal properly. NO WHERE ELSE on a Continental engine is there a crush washer installed that is NOT mechanically locked in place by some method except in the crank where there is cyclical rotational, vibration, heat, and pressure stress factors to help loosen the plug. It's a recipe for disaster that Continental refuses to address.

IMG_3140_4_1.JPG

IMG_3137_2_1.JPG

IMG_3116_4_1.JPG

[jatkins]

Thanks for the super explaination !

I do not have a hex plug ! Lucky for me.

Looks like I am going to change the Crank nose seal pn 530917.

John