New pistons -> new rings??

Hi guys,

Although I have plenty of experience in automotive engines (also in aircraft), I feel I am a bit out of my depth on these Lycoming things. So newbie question:

I plan to upgrade my narrow-deck, 150 hp O-320 in various ways:

1: Fabricate/ Install EFI (with electronic ignition)
2: Fabricate cold air induction
3: Up the compression ratio from the current 7:1 to 8.5:1 (unless someone can convince me that 9:1 and 93 octane fuel would be a happy combination)

I understand that I need to go to thick wall wrist pins. No problem

Question: Does one install new rings at the same time, or would it be a better idea to re-use the old rings (with the idea that they have been run-in on the cylinders already)?

(My current compression checks are between 71 and 75, by the way)

Thanks!

Use new rings. Not only have the rings to cylinder worn but the part of the ring that touches the piston has worn. If you are using new pistons, you want to use new rings.

IF you are using the same cylinders, I suggest also checking valve guide clearance and rocker shaft bushings.

While I have never done it, I do not believe that re-installing old rings on new pistons would provide optimum results. It is definately not a standard approach. Also, when you install new rings, the cylinders need to be honed first. You do not want to install new rings without honing, as they will not break in properly. I think Chrome cylinders are an exception to that rule, but have no experience with them.

As mentioned above, you are far better off starting with new rings/hone, as it resets the wear clock and you already have everything apart. If you choose to re-hone yourself, be sure that you have a dial bore indicator to measure for excessive wear. If you have excessive wear, you are better off boring them 10 over.

Larry

Thanks guys. Makes more sense to me too. It was just that I had read elsewhere about re-using rings.

I believe mine has chrome cylinders, so in that case no honing unfortunately.

Is there any way to see from the outside if cylinders are chrome ones? The logs that came with the engine are kind of unclear...

And Gary, indeed, this would also be a good time for checking the valves.

Thanks!

Lycoming - Understanding Engine Color Codes

You probably already know this, but did not indicate so in your post - so:

If you have a paint "color", in a short band on the tops of each cylinder, then your answer lies in a Google search (or other search engine) of the above title.


HFS

OBTW - I also am working and RV-3 (build - S/N 11226)

Typically chrome cylinders are denoted with orange paint on the fins between the pushrods or on the cylinder base.

That with the orange stripe is new to me. Thanks!!

And I believe mine doesn't have one. There is hope...

I don't know of any new chrome cylinders. Channel chrome is a process to restore used cylinders to serviceable dimensions. Once done the base is painted Orange or the fins on top by the plug holes are painted orange. The standard chrome moly rings are used in steel nitrated bores. Once chromed Plain cast iron-manganese phosphate coated rings are used. You can't run chrome in chrome. Any Idea as to how many hours are on your cylinders? How old are the valves? I learned a lot from the Sky Ranch Engineering manual. The cost of building your motor is not the assembly,it's getting the parts tagged,specked out and on the bench ready to build. IMHO
R.Hill

I've got 4 yellow tags for Chrome cylinders, dated 1992, and a log entry dated 1999 for a 0 SMOH on the engine, mentioning those same cylinders:

"...Rebuilt cylinders with silicone Chrome..."

My take on it is that these rebuilt cylinders have not been the original ones.

The yellow tags from 1992 show:
Mfr Name: Lycoming
Class: CL8
Model: Chrome
Work order: 2251
S/N: 56026 (and three other)

Then there are checkmarks for:
Welded
Silicone Chrome
Head parts
ACA HT2R884K (which seems to be an FAA code for Aircraft Cylinders of America Inc in Tulsa)

Engine has done 1479 hours between 1999 and 2004 (being the left engine of a 1956 PA-23). After 2005 no more log entries have been made.

This photo of 2008 of said PA-23 shows it parked on a ramp without its left engine (nor rudder, nor flaps): https://www.airport-data.com/aircraft/photo/000162372.html

Somehow the engine made its way from Florida to Europe in the mean time, and now it's on the nose of my RV3.

Gives "on condition" a whole new meaning...

I've done a compression check prior to taking the aircraft apart, after having run the engine for a bit over two hours a few days prior:

1: 72/80
2: 72/80
3: 75/80
4: 71/80

Which isn't all that bad actually.

So... now what? New pistons, with rings that are suitable for Chrome cylinders, thick wall wrist pins and go? Or would that be a stupid idea?