I would like to see some info on coatings and see what everyone thinks about them. What experience have you had with them?

Coatings as applied to snowmobile engines can be broken down into two categories, decorative and performance (thermal control, primary & secondary lubrication, and tolerance change).

To be successful many factors come into play. The correct coating must be selected, the substrate must be prepared properly (this accounts for over 90% of coating failures) and a knowledge of metallurgy must be had so important qualities of the part are not altered in a negative way (an example of this would be over heating a piston when curing a coating that would alter the heat treat placed in this part).

I have been in this industry for over 10 years and our coatings are used in virtually every form of racing as well as many industrial applications. We have trained many other companies and consult for the big three. I am also a avid snowmobiler and love the sport.

If any of you have questions I will attempt to educate so you can make an informed decision on your application.

Doug Byron
Process Coatings, Inc

Hi Doug...At this point I'm most interested in the different types coatings available for the top of the piston and the combustion chamber and what their effects are. Will any of these coatings help with any of the ring failure that we are seeing.

Thanks

Keith

Piston dome coatings can be very effective at increasing performance by reducing piston temperature and evening out piston/combustion temperatures thus reducing distortion and detonation if the coating being used has certain qualities. The older ceramics that were used years ago without success did not have the ability to "move heat" thus they developed hot spots and lead to many problems. Todays coatings (that are used by most) are incorrectly called ceramics (buzz word) they are if fact ceramic/metallics, the addition of various metallics enhance the properties by allowing the coating to move the heat thus evening out the temperatures in the combustion chamber and allowing the heat that would be wasted to be converted to power, this wasted heat has many effects on power output, one being heating of the intake charge and lowering the charge density resulting in lower power output.

Ring life should be increased by lowering the amount of heat that the ring has to get rid of.

Skirt coatings are also very effective at reducing friction/heat if you doubt the coatings have any positive effect ask yourself why do the manufactures use them? Skirt coatings can also be used to take up excess clearance and are very cost effective (cheaper than re-plating or using oversize pistons).

Thanks Doug Byron

Doug,

What type of clearances can a skirt coating make up? hundreds? thousandths? Most definately not tenths? Also with a skirt coated piston does the thermal characteristics change such that the sizing tolerances will be tighter? looser?

Are the coatings (top and skirt) good for the life of the piston? or do they have a certain life span? Would running any particular fuel additives negatively affect the coatings?

Also as a sales pitch to a trail riding snowmobiler that occasionally likes to grass drag his sled, what particular benefits would a coating process provide, and what would it cost (on average) to have the pistons coated for said benefits?

Thanks so much for your willingness to share info.....


Tony Biagiotti

Okay... if the coating is designed to move heat, just where is this heat going? Is it reflected or is the coating just evening out the heat. If it's evening out the heat in the piston, the rings still have to get rid of the same amount of heat don't they? I guess I'm really just trying to understand how these coatings really work. It sounds like the best part of coating the piston top would be the fact that the heat is spread around to avoid hot spots and curb distortion which could prevent some types of seizing. Is that about right or am I way off on this yet?

What about head coatings? You wouldn't want the heat reflected back into the cylinder. How do head coatings work?

Doing anything with rings?

We've all had experience with coated pistons, it's called carbon. It builds on the dome and provides an excellent insulating layer. Ever notice how many seizures are with with new pistons? 1 factor is the new piston is usually +.001 then what it will be after it has been heat cycled numerous times, the 2nd factor is that shiny new dome will pass the piston swelling heat real fast. Since the running piston has zero wall clearance and is just riding on a thin film of oil, the extra pressure of piston trying to swell that extra .001 can wipe out the oil film. A skirt coating may save the day, most the oems are using it a sacraficial lubricant coating to keep warrantee seizures at bay. The dome coating really helps also, expecially till there is some carbon build up. Look at some pistons that ran too hot and had the ring land close up and stick the ring or melt the edges, notice how it often lines up where the wash was? As clean oils seem to be a big selling point, more so with exhaust valves, carbon on the piston is being reduced. In my mind this makes the dome coating more attractive than ever.

Originally posted by TonyB@Sep 12 2003, 11:30 AM
Doug,

What type of clearances can a skirt coating make up? hundreds? thousandths? Most definately not tenths? Also with a skirt coated piston does the thermal characteristics change such that the sizing tolerances will be tighter? looser?


Tony,

Keep in mind, when your trying to make up lost piston clearance, you still have to respect correct ring end gap and reduce the amount of ring excusion from the piston's ring land (groove). It's fine to have a good skirt fit but it's only a thrust bearing. The real work is done by the piston's upper region where the ring(s) lie.

First off I consider the high build skirt coatings a good "bandade" and is not the proper way to solve a problem but it has worked much better than expected. We have build up pistons as high as .003 on the surface (dia change .006) with extremely good results. The benefits to skirt coatings are numerous, I consider them a very good insurace policy with some performance gains. All engines benefit from coatings, we have had customers more than quadruple their engine life. One Price motor that we coated was broke in very fast (30 min) followed by three passes on the lake, it was then brought in running rough, upon inspection it was determined that the oil pump was not working, teardown revealed that damage was so small that the pistons could have been re-used.

I believe that the heat is moved around the combustion chamber, evening out the temps and allowing for a more complete combustion process allowing the piston to run cooler. Heat reduction is observed by numerous observations, dark spots on the piston underside from oil burning no longer appear, on automotive engines a 25F temperature drop in the lubricating oil seems to be the norm.

The dome coating can be enhanced by polishing the surface with steel wool and polishing compound resulting in a mirror like appearance, this improves reflection capabilities and reduces the surface area for carbon to stick. I just tore down our 800 Rotax and after 800 miles you could still see your face in the dome, the piston did show some carbon build with the wash being very evident. I would also add that the engine had oil pump problems maybe pumping 2-3 times more oil than necessary and still slightly rich (stock jets were 380 and we are down to 340). I have talked to people that have a hard time jetting coated engines as the wash could not be read even after two years running.

I have been working with ring coatings some what and coat some of our test engines but more testing is necessary to determine if it is of value. We know that it sure doesn't hurt anything. We have just coated the land areas (.000025) and not the face of the ring , we are concerned about being to slippery and not getting ring seal.

If you coat your piston domes I would coat your heads, there is a lot of different opinions on this but to me this is where common sense applies, maybe I'm wrong and it wouldn't be the first time. Dome coatings are only $20.00 ea (piston/head) and can be removed so its not a major investment. Skirts vary from $15.00 to $25.00 ea.

I hope I am getting my points across as putting words on paper so to speak is not my best talent.

Can't wait for snow
Doug

PS: I can post some pictures if you like.

Yes Pictures please!


I find this very interesting!!!

Thanks!

Tony

Here is a picture of RKT head and domes coated and polished . About 800 miles on this w/rich mixture and about 2-3 times the oil needed (bad pump, it was sticking at half throttle when it was returned to a lower setting. I don,t know if this will work but I will try, if it dosen,t I will try later--off to the grass drags in Frankenmuth.


Doug

Doug,

How were the drags?

Also what are the coatings called? In your posts they are just called "coated" or "coating", but I presume that there are different coatings depending on the application. How would a person know what to put where, if one were talking to a friend that had coated pistons and you wanted to compare what was done?
Can used pistons be coated? I assumed so since they can be build up (evidently from wear- and not a bad hone/bore job)

Thanks,

Tony

Piston coatings can be applied in three areas,
1-Dome, Our dome coating is called "Nitro Coat" and is a ceramic/metallic coating that moves heat three times quicker across the surface than thru it. It helps even out the combustion temperatures as well as insulating the piston. Used on pistons and heads. $20.00ea.

2-Skirt, Skirt coatings are for lubrication.
Cermalube is ultra thin, burnishes to .0002 and becomes translucent with a glass like apperance, designed for applications where minimal clearance change is mandated. $15.00 ea

DFL-1 is a medium build, burnishes to about .0007, used where a slight clearance change is necessary (.001 to .0015), $17.50 ea

HI-Build is used to take up large clearances and has been used as thick as .003 (.006 total diameter ). $25.00 ea

3-Underside, TD is a thermal dispersant and oil shedder used to help pull heat out of the piston and shed oil/fuel. $10.00 ea

Thanks
Doug

I forgot used pistons add $3.00 ea and make sure to take out both clips and remove any oil. I have attached a picture of a piston coated with Nitro coat and Cermalube, 800 rotax w/RTK piston, 800 miles on this. The engine was still rich (340 main) and had a bad oil pump injecting way too much oil (the arm was sticking at half way and staying there when the throttle was closed).


Doug