CHT Gauge

[Goneflyin]

My A65 when backing off the throttle on down wind gets rough between 2000 and about 1600 rpm then smooths out at 1500 down. The cylinders are all 74 or better on pressure and I've changed the rubber on the intake tract. I thought maybe a gauge might give a clue on which one is going out, planes are tougth to pull a plug wire or to feel which header pipe is cool. I've tried to crack the primer to see if it's a lean condition but no change, rotating plugs(color is even on them) and L R both on the mags is normal and the cam looks good. Think a CHT might help in the hunt?

Bill

[jgerard]

Re: CHT Gauge

Only a 4 way gauge will help. Since your looking for roughness which is most likely related to mixture, I would go for an EGT gauge instead. May be a carb issue? Carb heat working properly? When you say the "Cam looks good" does that mean you have measured the lift and it is still in spec?

Jason
N43643

[Forrest Barber]

Re: CHT Gauge

Maybe don't run it from 1600 to 2000 rpm let us know what you find.

[Mark Julicher]

Re: CHT Gauge

- What is the condition of your engine mount rubber?
- Is the propeller in good condition or did someone file out a big nick recently and put it out of balance?
- Are the prop bolts torqued correctly?

[flyguy]

Re: CHT Gauge

What does it do on a ground runup at those RPM: you want to eliminate all the variables one at a time. There's a vertical feedpipe in the carb that works in that range and might do that if it was partially obstructed. The hole is VERY small and I know of it bringing down 2 aircraft, so be careful. I would keep it on the ground until I found the problem.

Also check it on one mag through that range and then the other. I suspect that mags just come off the couplers at that rpm, but aren't going fast enough without the couplers to give maximum spark. If one was weak it might not be sparking at all in that "flat" area.
Still I suspect it is a mixture problem.
D.

[Richard Boyer]

Re: CHT Gauge

You know.......At max RPM I get enough vibration that the panel shakes up and down. New prop! I drop it down a couple hundred RPM and the vibration smoothes out. I really don't want to send it back.......

irritating.

Richard Boyer

[Howard Wilson]

Re: CHT Gauge

When are you pulling on the carb heat?

[Robert Lees]

Re: CHT Gauge

irritating.

Aw bite the bullet, Richard, get a metal prop...I get no vibration on my A-65 & Sensenich (or the McCauley)

[Goneflyin]

Re: CHT Gauge

The roughness didn't just start, it's just the engine is pretty smooth above and below that range. When I bought the plane 7yrs and 400+ hours ago it had a fresh crank,bearings,cam,7443 Mccauley and a few other pieces, About 2 yrs ago we did a accessory case and I put new mount rubbers on at the time.
I thougt the cht gauge with 4 postion switch may help me narrow things down without drilling or cutting holes in things. Anyone know how quickly the gauge responds if a cylinder went out and the switch was in the right postion ?

Bill

[jgerard]

Re: CHT Gauge

takes about 30 seconds for the cht to stabilize-adjust to a new temp say 100 deg change. Is it a vibration, or a rough engine. Try putting the prop on 180 degrees from its current position.

Jason
N43643

[Forrest Barber]

Re: CHT Gauge

I would suspect harmonics, there are some prop , engine combinations that require that you do not operate in certain ranges. We have a ship here that is placarded not to run except while passing through 1800 to 2000 RPM. Suspect any recent changes, maybe rotate prop 180 degrees, I would hope that she is set to fire at the 7 oclock position now.
THEN we have the scary part , I flew a Luscombe home once that had a pronounced vibration between 1400 & 1900 rpm. We used a mechanics stethoscope to listen to a strange knocking noise while running at about any speed. Tore the engine down, split the case and the crank came out in two pieces broken at a center throw so she stayed together and still ran. Beat the crap out of the throw .
and no it was not me in the four fatality accident here in NE Ohio. I knew the one Instructor, mid-air between a Lancair 235 & a Cessna 172. Boy, did it tear both ships apart. My condolences to all the families involved.

[paulp]

Re: CHT Gauge

Howdy Tribe,

Before you do anything else, check the torque on the engine mounts and on the prop bolts!!!!!! Improper torque settings on either or both can cause similar harmonics.