• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Weak engine....strong engine

fobjob

MEMBER
Salt Lake City, Utah
Having flown only two 150hp cubs so far, I have discovered that some have strong engines, and some weak. (Mine, unfortunately)...does anyone have suggestions and/or stories about whysome engines are strong or weak. ???? :crazyeyes:
 
It's very simple.

1. Compression all above 70
2. Fresh spark plugs set correclty and mags and points set on the money( inspect the points and replace if not perfect)
3. Mag Timing dead nuts (Do a hard check the old fashion way,to make
sure you have the correct flywheel)
4. No intake leaks
5. When doing all this try to find something out of adjustment.
6. Mag drop minimal. Timing is everything.

Now a 1800 hour sure isn't going to pull like a 150 hour engine. But the things above I think are important- will help. These are things you already know but revisit this area and she will run better. But also be darn sure your comparing apples to apples when the prop is concerned. Wash the windsheild too that sometimes helps.
 
Found one problem on a annual last year while changing the #4 cylinder.....the intake manifold tube sticking out of the oil pan was bent inwards by the hose clamp so that about 25% of it's area was blocked, and a small air leak was happening under the coupling hose. Which is why we were changing the cylinder......this helped quite a bit, but it still doesn't leap off the ground like a 'younger' cub of the same year manufacture, probably the extra 6000 hrs of mouse droppings......
 
fobjob,
Maybe it isn't the engine. Mark Englerth (Thrustline) has identified that the thrustline mod doesn't work on every Cub because there are Cubs in the fleet that have incorrect tail geometry. These aren't necessarily old bent-up beaters, either. You aren't the first pilot to notice that two Cubs, side-by-side and practically identical, can be very different in performance. How many years have passed since your airframe was in a jig?
SB
 
fobjob said:
Having flown only two 150hp cubs so far, I have discovered that some have strong engines, and some weak. (Mine, unfortunately)...does anyone have suggestions and/or stories about whysome engines are strong or weak. ???? :crazyeyes:

A prop that has had a "Borer Prop Expert" fine tune it will make a Cub come to life. Just because it's an "82/ forty something" dosn't mean it will perform. I found this out after a rock ding made me take the prop off and get it looked at. It was all screwed up. After a total paint strip, blade balance, correct pitched at all stations and re paint, it was like adding 15 hp to the plane. That was one great prop., I sold it when going to the 180 hp. Crash
 
Now I'm feeling warm and fuzzy all over. (I bought Crash's prop!)
I take back what I said about the load-hauling.

No I don't.
SB
 
High CHT

The picture of why my cub was running hot and weak has now clarified.
The intake riser adaptor has given me more horsepower, and redistributed the CHT's around the engine so now the remaining problem is practically identified....but not quite yet.
The #4 EGT is right at 1420F, and the CHT is 460F. Not good. But, the front #1 is at 375F, and the rear #3 is at 390F. So, clearly, #4 has a problem that is still there after changing out the cylinder. The only other thing I can think of is a bad lifter or cam lobe on the exhaust side. I'll measure the valve lift tomorrow. Can anyone think of anything else I can look at????
 
O-320

Anyone know if you can put an optimized cam in a stock O-320 and keep it legal? What about an O-360 sump with the equal length larger O-360 risers? I've heard of guys doing this along with 10:1 pistons and getting some pretty good results. Crash
 
Fobjob,
Once I had a bad intake tube on one of my engines. It was cracked at the sealing flange. I would study the fit with this tube,gasket and flange. Is the plenum flange secure. Try to shake the whole ass. before you take it apart, shaking it together will give you more leverage. Go slow back and forth and see if any part of the #4 intake pipe is loose. How do you have such accurate temp readings? Engine analyzer I would guess. Have you tried swapping probs for the cylinder temp.
 
Crash, could you define "optimized"?
4612, last year the previous #4 cylinder had a compressed intake tube with an air leak under the hose splice clamp; the EGT was high and the curve sharp. The present EGT is broad and right where it should be for peak rpm: 1420F....so I don't suspect an air leak at this point, but I will look. My chief suspect other than an air leak and bad cam would be the dreaded one-piece venturi causing mixture distribution problems, but it's just not acting like that (this time)....I'm a retired electronic- computer tech and I've designed many gizmos in the instrumentation and telemetry area...so I interfaced my crappy westach meter with the same chip used in the electronic meters to front-end with J and K type thermocouples.. After a few painstaking calibrations, my readings are probably within 10-15 degrees F (for CHT)...and that's as good as can be done, period. The subject of exactly how crappy the old meters coupled directly to the thermocouples are would fill a book. That's where you get variation between individual thermocouples...their ability to handle the large currents required to directly drive a 20 ohm meter movement. The voltages they put out (into the high impedance interface chip) are standardized. In other words, no. I haven't moved my thermocouples around! But should. :-?
 
Re: O-320

Crash said:
Anyone know if you can put an optimized cam in a stock O-320 and keep it legal? What about an O-360 sump with the equal length larger O-360 risers? I've heard of guys doing this along with 10:1 pistons and getting some pretty good results. Crash
I am putting on the O-360 sump which moves the carb. further forward and gets the CHT closer and can get a field approval. There has been as much as 125 degrees differance of CHT on the stock O-320.
 
What carb do you use? Is the diameter of the intake the same as the -32 carb?
 
fobjob said:
What carb do you use? Is the diameter of the intake the same as the -32 carb?
Lycon is making my engine and I asked about the carb and explained that I wanted all the HP possible and they are putting on a carb that has better atomization. Sorry, cant remember the type.
 
fobjob said:
What carb do you use? Is the diameter of the intake the same as the -32 carb?
Lycon is making my engine and I asked about the carb and explained that I wanted all the HP possible and they are putting on a carb that has better atomization. Sorry, cant remember the type.
 
Last time I checked on a factory engine Lycon beat Van Bortel on price by quite a bit. I bought 6 O-470 cylinders from Van Bortel and they charged me $40 each cylinder for shipping. I live 75 miles from them and they are on an airport. If I had known they jacked up the shipping I would have flown over and picked them up or even driven.
 
valve lift measurements

I measured the valve lifts today. Numbers represent the lift after a 30 second bleed down. All were about .03 in higher for a few seconds.

---------- exhaust----- intake---CHT----EGT

#1--------- .423--------.402-----375------ ?

#2--------- .409--------.431-----375------ ?

#3--------- .385--------.300-----395-------?

#4----------.404--------.431-----460----1420

* #4 EGT at peak RPM

I can't make much sense outta this... any observations, opinions?
 
I updated the table above with the CHT from #2....I also performed the power test in the link below...a terrific trouble shooting guide for engine problems...


http://www.buy-ei.com/The_Pilots_Manual_by_EI.htm

The power test indicated 120 HP at 5000 ft and 79F outside air temp.
I conclude from all this , unless someone corrects me, that I've pretty much eliminated the sources of excess heat generation ; just hot, thin air and poor cowling design is left. Any opinions? Anyone out there? I can hear you breathing!
 
Heat

How is your baffling? The RV guys did some testing on the front baffles and found that an angled ramp type baffle at the front of the engine gave much better cooling. I guy I met said he did this on his cronically hot running Cub and it fixed the problem. Look at how the air comes throught the front nose bowl openings and hits the front cylinder straight on. The ramp would cover up half of the font cylinder and direct air up into the cowling and down through the cylinders. Also if you have a rear oil cooler, it will also rob some of the cooling air from the left rear cylinder. Take care! Crash
 
I have ramps in front of my cylinders installed already. It worked well, but it might be time to enlarge them a little. About one inch of fins are still showing.
No rear oil cooler. I wonder if the oil drain tube might be partially blocked?
What kind of angle on the front ramps are we talking about? I have about 60 degrees.....
 
Back
Top