Piston Coatings: Any benefits?

[Greg_E]

This seems to be a common thing in the automotive world , but I haven't read anything on the subject regarding outboard engines other than Wiseco offers coated pistons.

There are two basic types of coatings and there are probably varients of each type.

The first type is a thermal coating that is applied to the top of the piston. The purpose is to prevent heat transfer through the piston thereby raising engine oil temps. My thinking is that this would only be advantageous in a four stroke engine where that heat would be transferred to the oil. Would this be of any benefit in a two stroke engine?

The second type is a Teflon coating that is applied to the circumference of the piston. This would provide a little extra protection should the piston contact the cylinder wall. Anyone tried this?

The Teflon coating is fairly inexpensive, while the thermal coating is more expensive.

 

[Faztbullet]

Re: Piston Coatings: Any benefits?

The first type is a thermal coating that is applied to the top of the piston.

Not good in a 2 stroke as increased possibility of pre-ignition. It ok in a drag motor as you your dumping a lot more fuel and can catch it as only running 1/4 mile.

he second type is a Teflon coating that is applied to the circumference of the piston. This would provide a little extra protection should the piston contact the cylinder wall. Anyone tried this?

Just about the the aftermarket pistons have gone to a molly coating for break-in.It is gone after several hours of regular use and the piston skirts do contact the walls, The powerhead I sent ya has the coated WSM pistons installed

 

[Greg_E]

Re: Piston Coatings: Any benefits?

Thanks for the reply. I posted this just to have a technical discussion. I'm already past that point in my rebuild.

I really didn't see any benefit in the thermal coating in a 2 stroke engine, and I can see where holding more heat in the combustion chamber could lead to pre-ignition. I hadn't thought about that, but it makes sense.

I would guess that the molly coating adds a little extra lubrication during the break in process. Once the cylinders are polished to a smooth finish it probably isn't needed.

I had no doubts that the power head was done right. That's why I bought it. BTW, I found a much cheaper alternative for the 1/4 -20 stainless steel 2001 BRP crankcase bearing assembly head screws. $9 cheaper and exceed grade 8 spec. Made by ARP. I started a thread on the subject. Give it a read when you have a minute.

 

[multimech]

Re: Piston Coatings: Any benefits?

Coatings on the walls of the cylinders and coatings on the pistons is why you can take an Etec out of the box and thrash it. Good frigging tolerances also help.

With any rebuilt engine, including an Etec I would do the proper break in. They are not built to the same standards as computerized machining at the factory.

 

[Faztbullet]

Re: Piston Coatings: Any benefits?

The Etech also uses a special alloy piston like the Merc 25hp Mercosil motors not a standard silica based piston....

 

[multimech]

Re: Piston Coatings: Any benefits?

Your right Fazt, just read an article on Nasa's site. I am just a dumb grease monkey , always looking for new information. Thanks. Seems the cylinder walls are machined with a more exacting honing process as well. So I guess the only thing that I said that was accurate is that if it has been rebuilt without the BRP honing process and pistons that are the NASA alloy type, don't thrash it out the box (as it were).

Question Fatz, do you do marine rebuilding as a business? I used to work for a company that did as an assembler in the shop and I currently work at one of the top BRP shops in this area. Have worked on OMC for 25 years and didn't know or to be honest took the time to read up on all of the technical features of the new engines, or simply forgot because I have a sieve for a brain. Or are you a motorhead who knows a bunch of facts and does rebuilding as a hobby? This is the reason I like this board, because I pick up all sorts of information that is really useful and interesting.

I know guys in this industry and I hope my question is not offensive (some have tender egos) , it sure wasn't meant to be. I am truly interested and appreciate the information.

 

[Faztbullet]

Re: Piston Coatings: Any benefits?

Question Fatz, do you do marine rebuilding as a business?

Yes you could say as I sublet a lot work for dealers, I get the old stuff and time consuming jobs(rebuilds) as they want techs to get more out the door.....

Or are you a motorhead who knows a bunch of facts and does rebuilding as a hobby?

If you enjoy it I guess you could call it a hobby but I make $$$ also . I could be called a motorhead as I did drag race boats at KDBA several years ago, like to go fast (118mph in 16fter) and been in marine industry since 1978..

 

[Greg_E]

Re: Piston Coatings: Any benefits?

Thanks for the discussion guys. . I have the time now to learn and work on my own engines. I've always done my own repairs, but I just like to learn as much as I can about how things work, rather than someone telling me "do this and it will fix the problem".

I would guess that Mercosil is mercury Marine's version of a Nikasil plated cylinder. I have read that the Nikasil plating can be affected by sulfer in low quality fuels. I would imagine that if this is used in a racing application a better quality fuel would usually be used and be less of a problem. Are the new engines using Nikasil plated cylinders or are they still cast iron sleeved? I probably know that answer based on the quality of the pump gas we get these days. If so are the cylinders coated with some other type coating as well as the pistons, or just the pistons.

 

[Greg_E]

Re: Piston Coatings: Any benefits?

Here is the article on the alloy developed by NASA and used in the Etec pistons if anyone cares to read it.

Outboard Motor Maximizes Power and Dependability

Here's an article on piston coating.
http://swaintech.com/swain-tech-coating-make-car-1-second-per-lap-faster/