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

John Clonts wrote:

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



Man, did you dodge a bullet. Congrats.

Last week, I finally got my Comanche back from maintenance, and what
started out as an annual last July, with the engine seeming to run fine.

It turned into a major overhaul, when it was discovered that my #5
cylinder had problems, and it turned out the cam lobes were worn past
airworthiness. Labor to correct that was equal to labor to major. I
majored.

It's a crapshoot.