Coating Al Cylinder for Small Model Aircraft Engine

I have no experience in this, but I would be curious about the intent.

One thus, or ten thousand?

The anodized surface will have a lower thermal conductivity which may cause heat build up in the cylinder. All so it have a different thermal expansion rate then the under lying aluminum which may cause it to crack due to the heat. So if you are talking about anodizing a part that is stock wouldn't recommend it. If designing it you will need to provide a surface area to take care of the needs of both.

Somebody's doing it.

Team Associated Cylinder Head: MGT 8.0

SKU# ASC25441

Be the first to review this product

Availability: In Stock

This item ships in 2 to 3 business days.

Price: $41.39 Qty:Add to Cart

• Add to Wishlist

Hi there,

Press a s/s or steel sleeve into the Al cylinder and re machine/hone the bore.

All the model plane engines I have dismantled had an aluminium crankcase, head and piston, but a steel bore, crankshaft and con-rod.

Admittedly I have not dismantled one for a good few years .......

Is the cylinder cast? If it is, the aluminium will have silicon in to help it flow during casting. The silicon will make the anodising uneven & patchy.

Thank you all for your answers.

It is one-of for now. Just trying to build an engine with least effort. It is a test unit of 33 cc. Granted, a steel sleeve would be best. However the unit I am building is a bit different where there is no contact between pistons and cylinder walls, only the seals will have seal contact, making the load condition a bit less severe, also needing less oil, presumably. Piston seizure, as in the old days, is very unlikely even at higher wall temperatures.

Regarding a lower heat transfer coefficient, I trust that the 1.5 thou (or ~ 0.04 mm) would not have a great insulating impact. Differential expansion and possible separation is of course a concern. However, wall temperature should not exceed 250 deg. C? The unit is air cooled. During flying cooling should be adequate.

It is not a stock piece. The material is simply 6061-T6. Silicon is low. Per Mat. spec. Si is 0.4 to 0.8%. I trust hard anodizing would be ok.

Lyn, that picture and statement that somebody is already doing it seems to me it is a cylinder head, not the cylinder itself? I am looking for a wear coat I can run seals against.

It looks that anodizing as a wear coat has not been done, as far as I can tell. But then, my case is a bit different.

Greetings

i would advise against coating the cylinder walls. compression rings are designed to seal with different types of metals, depending on the hardness of the cylinder walls. the rings need to be softer than the cylinder so the rings wear [creating a constant seal] rather that the cylinder wearing in an oval shape.

contant a ring manufacturer.

silicone is added to aluminum cylinders to enable the rings to seal and prevent premature wear.

Firstly, I understood that you wanted to coat the cylinder bore, is this correct? Not the fins.....

If you want to coat bores then think chrome or similar.....many engine manufacturers use coated cylinders.

There were some 2 stroke engines starting in the 60's and 70' with an alumium bore that was chrome plated and then honed to the exact diameter needed. They appeared to be relatively long lived to the best of my memory....in a small motorbike/scooter of the time.....or chainsaws and other small motors (also adaptable for model aircraft and the like.

This is interesting:-

http://www.sunnen.com/graphics/assets/documents/2b6bcac2b33a.pdf

Andy, thank you for your comment.

Yes, the cylinder bore as a working surface.

A local chrome plating firm said that Al needs first a copper coat before chrome can be applied. For a small inside diameter copper is difficult, he said. Well, it is being done on chainsaws, so it can be done.! Need to look for another firm, I guess.

On inquiring for anodizing I was told it would produce 63 HRC on 6061-T6 and would work well together with seals in a sliding engagement that are also hard anodized. Best to add a coat of PTFE on the housings, was suggested. It that is so it may be the easiest for a one of.

The honing article is very informative, thanks. I agree with that. However, finding a firm might be not easy. For mass production it is certaiy the way to go.

As per the article Nikasil is also available. For a first unit, only one of, it is hardly possible. Anodizing seems the simplest.

The "chrome" in most of the 2 stroke motor cylinder bores was/is not plated on, actual deposition was done placing a pin of a specified hard chrome type metal at the axis/centreline of the bore and discharging a massive charge through the pin causing it to vapourise and bond to the aluminium bore (this is done in a vacuum). One branded chainsaw, Danarm, actually had a second pin of a different metal and this left a pock marked surface for oil to reside in the bore.