The International Cessna 170 Association

Recently I lost a cylinder due to mechanical damage by a bolt - where the bolt originated from is still unknown.

Cylinders have been replaced over the years (and various owners), which may have provided an opportunity for something to fall into the engine. All the obvious suspect spots to look for a bolt to perhaps fall into the intake, or, even more unlikely, back through the exhaust have yielded nothing. Any ideas?

The peened up part shown above next to the penny looks like a battered castelated nut rather than a bolt, I would think it is small enough to have been sucked in from almost anyplace in the induction system.

What is that in the lower picture?

Can you show us a picture of the spark plugs from this cylinder?

The lower picture looks like a shot peened piston?

Or a nut-peened piston. At least there is no lead or carbon build-up.

What did the valves look like and what indication did you have the cylinder was bad?

Attached are images of the plugs. Bottom plug lost part of the insulator. I'm replacing the cylinder.

hilltop170 wrote:Or a nut-peened piston. At least there is no lead or carbon build-up.

What did the valves look like and what indication did you have the cylinder was bad?

Valves looked fairly good.

I was doing touch and goes; landed, and in applying full power noticed a hesitation, and lack of full power (1900 rpm).
Aborted take off, and taxied back for run-up.
Could not 'clear' the engine - at this point I was ensuring that all the carbon would be 'cleaned' from the piston!
I found that the #2 cylinder was cold to touch, pulled the plugs, and saw the damage.

blueldr wrote:The peened up part shown above next to the penny looks like a battered castelated nut rather than a bolt, I would think it is small enough to have been sucked in from almost anyplace in the induction system.

What is that in the lower picture?

I'm with you BL, from the picture, looks like a AN3 castellated nut

At one time intake could have been open and someone dropped a nut and rolled into bottom of intake and couldn't find so figured it went on the floor. It can happen but I look till I find to confirm just as a surgeon has to confirm all instruments used in an operation.

John

In my opinion, a part as small as a #3 nut could be dropped in anywhere in the induction system, after the filter element, and could work its way into a cylinder.

It's amazing to me that there would be enough suction to lift a nut with that little surface area up past the carb and into a cylinder. You haven't been practicing inverted ribbon-cutting have you? The only place AN310-3 castle nuts were used originally on the 170b was to attach the rudder cables to the rudder bars. The thinner AN320-3 is used to attach the cable to the early style cabin heater control valve but the battered nut in the picture looks like a AN310-3 to me. I would guess someone planned on using the nut to attach an engine control cable -- mixture or carb heat-- and had the scat ducting removed from the air box when the nut dropped in.

n3833v wrote:At one time intake could have been open and someone dropped a nut and rolled into bottom of intake and couldn't find so figured it went on the floor. It can happen but I look till I find to confirm just as a surgeon has to confirm all instruments used in an operation.

Not long ago I heard that the medical profession was learning from aviation by doing such things as using checklists. It seems they have more to learn.

On 81D, AN3 steel lock nuts are used on the exhaust clamps. Dropping one there could get it down carb heat.
From the picture, it could be an AN363.
But I'd also be surprised if it could be sucked up like that...and I'm not volunteering to find out.

it's always nice to have problems like that on the ground.

A moment while I grab my napkin and pencil...

300 cubic inches is 0.17 cubic feet and would be moved each full cycle of the motor. (suck, squeeze, bang, blow)
A 4 cycle engine means 1/4th the RPM is blow or in this case, suck.
(2700RPM/4)*0.17CFM = 114 cubic feet per minute

A 5 horse ShopVac pulls about 175CFM
https://www.shopvac.com/specifications/quiet_series.asp


So, plausible.
Somebody call Mythbusters to try it out.

Once it passes the carb and into one of the two intakes, that number would be cut in half.
57CFM

Once it passes into a cylinder's intake, that number would be cut in thirds.
19CFM

If my math and assumptions are right, it seems less likely.