Rough Engine, please help

The IO-520 in my Cessna 210 is running rough. It seems to run smooth
at 1000 rpm but the roughness appears above about 1400. One cylinder
is “cold” and apparently not producing any power. I
pulled the rocker cover and found that the intake valve spring was
broken. My mechanic and I replaced it yesterday. But the cylinder is
still not producing. The compression is good (74/80). The spark
plugs are good. He’s going to check the flow through the fuel
injector later today.

Any more ideas? What should we do next?

Thanks!
John Clonts
Temple, Texas
N7NZ

At the very least, borescope that cylinder, and especially its valves.
Compression may be terrific if a valve never opens!

Rip

John Clonts wrote:
The IO-520 in my Cessna 210 is running rough. It seems to run smooth
at 1000 rpm but the roughness appears above about 1400. One cylinder
is “cold” and apparently not producing any power. I
pulled the rocker cover and found that the intake valve spring was
broken. My mechanic and I replaced it yesterday. But the cylinder is
still not producing. The compression is good (74/80). The spark
plugs are good. He’s going to check the flow through the fuel
injector later today.

Any more ideas? What should we do next?

Thanks!
John Clonts
Temple, Texas
N7NZ

If anything has happened in the valve train, you should verify that the cam
lobe and lifter face are still good. The broken valve spring might be the
result of cam wear or something entirely unrelated could have happened and
the improper function of the valve train could have damaged the lifter.

The valve train is very delicate and has some of the highest stresses in the
engine. Any difficulty should result in a complete check from the cam
through to the valve seat.

I know of one case where a broken valve stem was simple replaced. The
engine later lost power on take off and three people died.
--
Roger Long


John Clonts wrote in message
om...
The IO-520 in my Cessna 210 is running rough. It seems to run smooth
at 1000 rpm but the roughness appears above about 1400. One cylinder
is “cold” and apparently not producing any power. I
pulled the rocker cover and found that the intake valve spring was
broken. My mechanic and I replaced it yesterday. But the cylinder is
still not producing. The compression is good (74/80). The spark
plugs are good. He’s going to check the flow through the fuel
injector later today.

Any more ideas? What should we do next?

Thanks!
John Clonts
Temple, Texas
N7NZ

I'd have that whole cylinder removed and sent off to be
checked/rebuilt by a good qualified repair station. Our 172 is in the
shop right now due to one cylinder intermittantly running cold and not
making power. We had the jug pulled and upon first examination, the
intake valve had lead deposits on the face/seat and was only sealing
sometimes, yielding zero compression during one check, and 74/80 the
next time around. My A&P suspects the guide and or stem may have some
slop too, so we're just going to have the valves in that one jug
rebuilt since the other 3 are fine and the engine is only mid-time.

"John Clonts" wrote in message
om...
The IO-520 in my Cessna 210 is running rough. It seems to run smooth
at 1000 rpm but the roughness appears above about 1400. One cylinder
is “cold” and apparently not producing any power. I
pulled the rocker cover and found that the intake valve spring was
broken. My mechanic and I replaced it yesterday. But the cylinder is
still not producing. The compression is good (74/80). The spark
plugs are good. He’s going to check the flow through the fuel
injector later today.

Any more ideas? What should we do next?


Thanks for the replies. It WAS the fuel injector, which was blocked.

Cheers,
John Clonts
Temple, Texas
N7NZ

A broken spring and a clogged injector... Murphy does not like you, does
he...
denny
"John Clonts" wrote in

"Jay Honeck" wrote in message news:pygZb.224397$U%5.1418539@attbi_s03...
Thanks for the replies. It WAS the fuel injector, which was blocked.

Good deal, John.

Any idea what caused the clogged injector? Bad gas?

Good question!

My mechanic posited that the broken valve spring somehow facilitated
the clogging of the injector. I'm not sure I can see that...

Also, it's kinda hard to resolve the "intermittent" nature of the
problem from flight to flight beginning a month or so ago, i.e. "When
did the valve spring break?", and "When did the injector clog-- and
was it suddenly, or gradually?".

I will be pondering these things during my next few flights!

Cheers,
John Clonts
Temple, Texas
N7NZ

I repeat. Make that next flight after the entire valve train has been
checked. Just the broken spring could have caused other damage that will
come back to bite you. I've been talking to another guy who had the lifters
in his 210 go bad just under 700 hours even without any broken valve
springs.

The cam shaft is driven directly by the engine and, when things go wrong in
the rather delicate valve train, all that power can really screw things up.
--
Roger Long

John Clonts wrote in message
m...
"Jay Honeck" wrote in message
news:pygZb.224397$U%5.1418539@attbi_s03...
Thanks for the replies. It WAS the fuel injector, which was blocked.

Good deal, John.

Any idea what caused the clogged injector? Bad gas?

Good question!

My mechanic posited that the broken valve spring somehow facilitated
the clogging of the injector. I'm not sure I can see that...

Also, it's kinda hard to resolve the "intermittent" nature of the
problem from flight to flight beginning a month or so ago, i.e. "When
did the valve spring break?", and "When did the injector clog-- and
was it suddenly, or gradually?".

I will be pondering these things during my next few flights!

Cheers,
John Clonts
Temple, Texas
N7NZ

Jay Honeck wrote:
: Thanks for the replies. It WAS the fuel injector, which was blocked.

: Good deal, John.

: Any idea what caused the clogged injector? Bad gas?
: --
: Jay Honeck
: Iowa City, IA
: Pathfinder N56993
: www.AlexisParkInn.com
: "Your Aviation Destination"

Speaking of which, Jay... did you ever swap your Grape's fuel filter and cut
open the old one? I ended up rigging a funky plumbing concoction with water-absorbing
spin-on filter for refueling from 6 gallon cans.

-Cory

--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

(John Clonts) wrote
My mechanic posited that the broken valve spring somehow facilitated
the clogging of the injector. I'm not sure I can see that...

That's because it makes no sense whatsoever. Your mechanic is
grasping at straws because he doesn't know what's going on either.

First off, while it was certainly necessary to replace your broken
spring, the truth is that the spring can be broken and still work for
a long time. The ONLY function of the spring is to keep the valve
closed and seated when the lifter isn't pushing on it, to keep gases
from leaking through and eroding the valve/seat. If your compression
is really 74/80, then the spring was doing the job. Otherwise, you
would see leakage past the intake valve.

The fuel injector is actually a nozzle - it sprays fuel onto the
intake valve. The spring never gets near it. Even if some flakes
came off the spring when it cracked, there's no way for them to get
into the fuel. What you're positing here is that a metal flake, small
enough to get into the injector, but big enough to clog it, somehow
came off the spring and bounced around and got in. Pretty far
fetched, IMO.

In all likelihood, the problems (clogged injector and broken spring)
are unrelated. I know how that sounds, but bear with me. The art of
troubleshooting is really all about Occam's Razor. We look for the
least hypothesis - what ONE point failure will explain all the
symptoms. A good troubleshooter who knows the system well will find
the problem quickly, because the list is usually pretty short. When
you stump a good troubleshooter, it's usually because there is no one
point failure. It's two or more. The planes we fly are so old and so
poorly designed, and the parts are so poorly made, that unfortunately
multiple failures are not too rare. Every time a problem stumped me,
that's what it turned out to be.

Also, it's kinda hard to resolve the "intermittent" nature of the
problem from flight to flight beginning a month or so ago, i.e. "When
did the valve spring break?", and "When did the injector clog-- and
was it suddenly, or gradually?".

I will be pondering these things during my next few flights!

Intermittent fuel injector clogging is the result of one of two things
- bad fuel or rust. Did you save the material that clogged it? You
should put it under the microscope and look at it. Metal is shiny,
rust is reddish, both are magnetic. Shiny metal would suggest that
the one in a million happened, and a piece of spring did get in there.
If this really happened, lunch is on me next time you make it to
Weiser.

Non-magnetic crud implicates fuel. Flush and clean the tanks, and
hope for the best.

Rust implicates the fuel servo. Check everything past the fuel filter
carefully. I had this problem before (and it lead to an inflight
failure) and tracked the problem to a corroding fuel filter plug. Be
careful - next time you may lose more than one cylinder.

Michael