The International Cessna^® 170 Association

As frustrating as it may be.... a "shudder" is not infrequently caused by valve-springs that do not meet specification. Many times cylinders are "rebuilt" and the old valve springs are re-used without any testing whatsoever. A weak, worn out valve spring will give exactly the symptoms described. Don't skimp on valve springs. If in doubt...install new ones whenever the cylinder is worked on.

gahorn wrote:As frustrating as it may be.... a "shudder" is not infrequently caused by valve-springs that do not meet specification. Many times cylinders are "rebuilt" and the old valve springs are re-used without any testing whatsoever. A weak, worn out valve spring will give exactly the symptoms described. Don't skimp on valve springs. If in doubt...install new ones whenever the cylinder is worked on.

I've got the same springs installed by Central Cylinder in 1999 at major, so I have no reason to suspect their quality, but that is good to know that they can be culprits when worn. Thanks.

KG, sorry for the thread hijack, I just thought that our issues might be similar.

1SeventyZ wrote:KG, sorry for the thread hijack, I just thought that our issues might be similar.

Not to worry.......

I've done a thorough run up with multiple mag checks and I haven't been able to duplicate my problem. I'll keep you posted if I find out anything.

KG, I once had a problem with a lead braking down. I flew to FL and landed at Crestview all was fine-- took off and got a shutter thought Ice or ??. Landed - nothing I could find took off again same thing pull carb heat settled down--Ha that was it. No problems after--On return trip at Crestview same thing again. Something wrong in Crestview. Got home told Mechanic --flew pull up in steep climb did it again. Got a lead tester and sure enough had a lead leaking thru and grounding out only when under a load. Change leads, steep climb all OK. might be this ?? Ron

ron74887 wrote:might be this ?? Ron

That's certainly a possibility. My buddy who helps me with maintenance is out of state getting his daughter started in college. When he returns, we are going to do some troubleshooting. I'll keep you posted......

Keith

Anyone ever suffered a broken ring in a O-300? A guy on the CPS site mentioned that it had happened to him with the same symptoms.

I have no idea. That sounds a little more rare.

I took notice my engine seemed lazy lately and I had reason to be checking everything and found a broken intake elbow on #1 cylinder. I figure it wasn't getting full mixture all the time and just along for the ride. I will find out the difference when I get back to flying.

John

1SeventyZ wrote:Anyone ever suffered a broken ring in a O-300? A guy on the CPS site mentioned that it had happened to him with the same symptoms.

I have no idea. That sounds a little more rare.

I had a compression ring break on my O-300-D right after start-up one time. I was still in the tiedown and had not taxied out yet. The engine had about 1200hr SMOH. As the engine was warming up at an idle, it shuddered fairly hard for just a moment then smoothed out. I pulled the mixture and the prop jerked to a stop. The engine had noticibly more drag while turning it over by hand using the prop. Compression test showed 20/80 psi. Removed the jug and found it scored where the ring broke. +.015" re-bore cleaned it up and it was good as new. The piston was ok. I think much more damage would have occurred if the plane was flying at the time the ring broke but I don't know if it would have been felt.

While at 200' AGL on pipeline patrol in a C-150 ...way out on the Mississippi Delta...(long ways from solid ground)... a ring broke and the damage to the piston, cylinder and valves was pretty extensive by the time I nursed it to Westwego airport just SW of New Orleans. I couldn't read any of the instruments due to vibration and the wingtips were a blur. Longest 20 minutes of my life looking at all the water, alligators, snakes, and mosquitos.

A follow-up on my issue:

Mag check showed the vibe/miss only on the right mag. Leads were good (check with high tension tester), plugs were good (cleaned all and checked resistance), so the only thing left was the mag internals. Points a little frosted, so we replaced points and condenser.

Vibe has gone away. Points wear, condensers degrade!

Back to making a smooth 2275 static, and 2475 at Vy.