cylinder question

[robbie]

I found a standard cylinder that I want to have rebuilt.
The question is "My other cylinders are +.015 can I keep this one
at standard."
Does a + .015 piston weight that much more that a standard piston.
Ok everyone give me their comments before I talk to my AP.
I hate to bore a good standard jug out .015 if I don't have to.

[LostnSpace]

Re: cylinder question

Ok everyone give me their comments before I talk to my AP.

Does this mean you don't trust your A&P???

[robbie]

Re: cylinder question

can't i get some comments before I ask a question to my AP/IA.
Lostinspace need not comment

[Pearson]

Re: cylinder question

Robbie,

I put together several high performance engines when I was more into hot rodding. Every time I took an engine to the machine shop and told them I wanted it balanced, they asked me if I was going to use it for racing. When I told them, "no I just want it for high performance on the street", they always told me I was wasting my money. They always told me that I would never turn up enough rpms to make balancing worthwhile.

So............... with that admonishment in mind. And considering the fact that our little engines turn about 1/3 the rpm of my high performance street engines, I would suspect that the slight difference in weight between a standard piston and one .015" over would be unnoticable. I am sure that there are pistons in the air "as we speak" that have more weight in carbon buildup on them that what little extra the oversize piston would add.

[flyguy]

Re: cylinder question

I'll go with Richard on this one. Engines are never really balanced, as the effective weight on the throw varies as the engine rotates and the balance weight is pretty much an average. That means it is out of balance more often than in balance. Reciprocating engines are crude, frankly; but very tough.
Darryl

[3Dreaming]

Re: cylinder question

I installed a used engine in a T-Craft once and it had a mix of STD. and .015 cylinders. It ran just fine.

[NY86]

Re: cylinder question

Balancing issues aside, the standard cylinder will have a less displacement and lower compression. Significant? Maybe not, but it just sounds chinsy!

[Forrest Barber]

Re: cylinder question

Probably will work, unfortunately you will only know till after start up and if you feel any more vibration. IT might be smoother! I had a Harley with .080 over on one cylinder and it was smoother.

[NY86]

Re: cylinder question

I had a Harley with .080 over on one cylinder and it was smoother.

I'm not surprised!

[fearofpavement]

Re: cylinder question

I don't think an oversize cylinder will be noticeable. I am sure there are plenty of planes flying that have that configuration. As previously mentioned, there is not really that much weight difference between a standard and oversize piston. Even pistons of the same diameter have differing weights. I think these variances are less nowadays with higher tech production techniques but I agree that at the relatively low rpm it will probably be unnoticeable. And the difference in power is going to be miniscule...

[Ragwing nut]

Re: cylinder question

It is bad practice to run a mixture of cylinders on an engine. Running unbalanced (out of factory tolerences) on an undampended crankshaft will create a harmonics issue even if you do not feel it. The harmonics issue when coupled with a metal prop could cause the crankshaft to fail at some undetermined point in the future.

I can think of all kinds of reasons not to do it, and none for it.

[Ragwing nut]

Re: cylinder question

I'll go with Richard on this one. Engines are never really balanced, as the effective weight on the throw varies as the engine rotates and the balance weight is pretty much an average. That means it is out of balance more often than in balance. Reciprocating engines are crude, frankly; but very tough.
Darryl

that would be true of a 6 cylinder where the throws are 60* apart. On the continental 4 cylinder they are 180* apart so the thows are at equal points of the rotation

[flyguy]

Re: cylinder question

This is something I worked on when balancing a small block for racing so I haven't thought about it for a long time, but----

I refer only to the effective mass of the piston assembly where it is attached to the throw, versus the counterbalance weight that is supposed to balance it. One varies throughout the stroke, the other doesn't. Soooo-- whatever weight you choose, it will be wrong most of the time. Angularity of throws doesn't change that, it is just piston assembly mass vs balance mass.
DC

[NY86]

Re: cylinder question

I disagree. In a flat 4 the balance "weight" is the opposing piston, which moves the in concert with the piston in question.

[mohawktipi]

Re: cylinder question

Just a thought> Since you are going to be pulling one cylinder, pull them all and weight the pistons and rods. Reassemble the engine by balancing the rods and pistons. At the very least, pull the opposing cylinder and weigh that piston and rod. If you get significant difference, then proceed as needed.