Pistons and coatings
 

I need to rebuild the bottom end of my 555 and considering the Mahle Powerpak set. I do like the smaller ring pack.

https://www.us.mahle.com/en/motorspo...iston-kits.jsp

These have a Phosphate Coating on the whole piston and Grafal Anti-friction coating on the skirts.

I am pulling out a set of Icon forged with their skirt coating and want to try something else.

Thoughts on hard anodizing or other coatings on a marine piston.

I may order custom pistons for a 4.580 bore to save the block a little so I can get any coating done. Diamond are the only ones with a catalog 4.580 set that I can find, but they are blower pistons. I have used Ross and BME in the past for custom pistons in my drag motors, any recommendations?

Glad to see you back in the hood! Hope all is well out west. Maybe icdedpeeps will jump in with some feedback! If I recall he did or had something similar done.

These guys are the real deal. Just recently had them put a thermal barrier and skirt coating on my 11.1 side by side piston. Real nice work that stays put.

https://swaintech.com/

There might be some power in the metric ring package some of these mahle pistons use over the std rings BUT i'm not in love with there tiny profiled, lightweight skirts etc in a marine endurance engine. I have taken several engines apart with them in past year and they looked like ****. As far as factory skirt coatings, the in house stuff done on pistons you buy doesnt seem nearly as good as stuff that gets done by a 3rd party. Ive used swqaintech, line to line and component coatings on different pistons and stuff all looked pretty intact at freshen up time. I bought diamond pistons with off the shelf coatings and looked pretty beat up at 35 hrs (I was under the impression they SENT THEM TO LINE TO LINE but evidently not), the stuff mahle uses looked like crap in no time.
Id personally just order a set of 4.560 JE, pay the upcharge to have them bumped to 4.580, its like 80 or 100$ extra.

My first question would be why do you want to change ? If you got good service from the Icons why mess with something that is working ?

That being said I like the Mahle pistons a lot. I just finished a late model 5.7 Dodge Hemi engine with them and I am putting together an Oldsmobile and also using them. Like AF said they have very short skirts and I am not sure if I would want to use them in a marine deal. And for me the jury is out on the real thin rings. The Hemi had 1mm top rings and 2mm oil. I know they say they seal better but I dont know about the long term. A lot of modern automotive engines are having oil consumption issues and I don't know if the thin rings is a factor.

One more thing to keep in mind is the Mahles are almost certainly going to be a lot lighter so you will definitely have to rebalance the crankshaft.

Call Mahle and talk to them. The few times I have called them they have been very helpful.

This is a pontiac 455 I just tore apart with Mahle pistons that had 200 miles on it, now I wouldnt blame the piston design or manufacturing process completely on how bad this looks BUT the skirt is really small (picture makes it look much bigger then it is) AND previous builder put them in too loose. There minimum clearance on these is .0025 and maximum is .0033, these were in at .005 to .0055, there NOT going back in! I freshened my 1000+ hp blower engine around the 100 hr mark and the JE's with swaintech coating looked almost new fwiw.https://cimg4.ibsrv.net/gimg/www.off...a38da0ce73.jpg

The hard anodizing from Diamond is awesome. Any other coating jobs send to Swain Tech because I've never seen it come off. They're also very easy to deal with and have quick turnaround.

Looks like there were some other issues too. The second ring looks torn up ? It amazes me how many guys try to out think the engineers that design these parts. I had a friend at another shop call me a few days ago and ask about clearances the other day because they didnt want to believe that they could be that tight.

Proven help for the metric ring pack.

https://products.totalseal.com/gas_ported_rings

How did your ICON pistons make out? Where they forged? What was their run time?

I was looking at an ICON option.

Thanks for sharing your experiences. I will be trying swain or line to line on this next set of pistons.

I have used Icon's a few times and have no issues with the piston itself, and they are forged. Like other's have said the coating that comes on the pistons from the manufacturer comes off really fast. These probably have no more than 20-25 hours? I had pulled these before because of a bad block after a few hours and the coating was basically the same as you see here. Some of the coating looks like it chipped off and not wore off.
https://cimg7.ibsrv.net/gimg/www.off...62a146aeac.jpg

Yep, seems to be my experience too , when the manufacturer coats them and it comes as part of piston price, never last like when you pay swaintech, line to line, etc.

I had the tops done by SwainTech.. I should have done the exhaust valves too.

https://cimg8.ibsrv.net/gimg/www.off...22f8653001.jpg

Skirt coatings looking like that after 25hrs are totally useless and just a liability. Putting the coating into the oil, and messing up the piston clearances.

Thanks for the sitrep.

I have noticed the very short skirts lately too.

Mostly in car drag apps, and when I see them in the Offshore market I always wonder.

In the photo above, of the one w/the worn skirts, there is near no skirt bellow the bottom of the wrist pin!

All the skirt support is above the pin and that is where there is already increased clearance designed in for thermal expansion.

Add to this the variable of combust chamber design, piston dome design and plug location.

As in, how much of the combustion process is actually side loading the piston from the start?

And w/little to no skirt support bellow the pin to counter the above…….

The short skirts would make me nervous, especially in highly loaded, high torque scenarios.

I bet there is an Engine Masters episode on this????

If not, should be.

I completely agree with you. I got into boats after drag racing and piston design I have found to be an important part of the differences. I do not like the short skirt in my marine motors for the reasons you mentioned. High load and high torque over a long period of run time is tough on parts. This is what most of my cylinders look like. No crosshatch left on the loaded side.

I love Engine Masters, I have not seen this on one of their episodes and I think I have seen all of them.

https://cimg6.ibsrv.net/gimg/www.off...5bc637b3e2.jpg

I rebuilt a 454 EFI about a 2 years ago that had Icon pistons in it. It had over 500 hours on it and except for the one piston that got torched from a bad injector they all looked pretty darn good. I ended up going to the next oversize and put it back together. I have used them in several automotive engines and they seem to hold up just fine. They are not my first choice but they have some oddball combinations available that nobody else does.

What alot of guys forget on these marine builds is RPMS and usage etc, there not drag engines, there not sp[inning 7400 so using a ultra lightweight piston with virtually no skirt, profiled to nothing is ridiculous . Every time I see lightweight Mahle pistons or similar come out of a marine endurance engine I roll my eyes, I have BOXES of them and they always looks the same, lost ring seal, cylinders skuffed, skirts tore up.

I have seen every episode Engine Masters as well.

Started as magazine articles which I read every one off too.

I love the out of the box thinking by some of the teams.

Sometimes when you follow one sport/hobby long enough, you see status quo take effect as everyone accepts the long term narrative.

Then someone gets involved who was top of the food chain of their previous sport/hobby.

Normally, that’s when we learn.

Remember the PB and HB tech series where there was always someone writing in about the miracle motor in their boat that was slower than stock!

Their next door neighbor was a drag racer and helped them build the motor!
Etc.

Ports, valves, cam so big you could walk through them w/a wire brush to clean the carbon off the piston domes!

On the piston side loading, the auto OEMS used to (maybe still do) offset the wrist pins in the pistons to side load the pistons so they didn’t slap when cold.

A trick from Direct Connection back in the day was to swap the pistons from side to side to eliminate this.

I did this in my home brewed 7k 440 Chrysler in my Super Bee.

There are many, many, VERY smart, go fast boat motor builders on here that know what works and what doesn’t.

One of the fast guys around me, educated me 30 yrs ago about the difference between HP’s and torque.

He had 25’ Checkmates running 120’s back then w/motors w/less HO’s than the others but WAY more torque!

And they never broke!

Word!

https://cimg8.ibsrv.net/gimg/www.off...3b8089d2df.jpg
https://cimg9.ibsrv.net/gimg/www.off...930da68a85.jpg
here's 16 pistons I took out of recent 540 rebuilds, they were slapping ike a screen door in a hurricane im.sure! I never did identify wtf they are but tiny skirts, short pins, super lighweight.

Crazy!

a little black rustoleum paint and those pistons are as good as new.lol

Whats interesting on those is that the bottom of the skirt looks fine ? I would think that if they were loose and rocking that the bottom of the skirt would take the most beating ? Strange.

This was a more convoluted story, these had the coating from factory stripped off and were RECOATED very poorly by a engine shop in Virginia. They were also then put in a block at about .008 to .010 along with bad machine work and assembly. The coating came off of them and went thru the oil system nearest I could tell as both cranks were torched too.

Short skirts often make men nervous.

Having the skirt terminate so high to the wrist pin means less leverage and more force on the bore rock at the clearance.

Back to those pics of the pistons with middle coating missing, before the engines came to me they were rebuilt poorly several times. from what I read from his rebuild paperwork he had, they had to much bore clearance from scuffing/rocking 2 rebuilds ago in under a 100 hrs and were stripped and recoated at the machine shop in a attempt to tighten them back up vs buy new and rebore over. When I took them apart that coat was peeling off, they clearly did NOT properly do it as I have had coating done that worked fine

That makes more sense. Personally I am not a fan of having pistons coated to tighten up clearances. I know quite a few shops swear by it but I feel it is just a bandaid. If the pistons are that loose you either need new pistons or the block needs boring or both.

I ended up getting a custom set of Ross pistons, to get me 10.5:1. Went with a 4.600 bore because lack of ring pack choices at 4.580.

The pin is below the oil ring groove and has a .043 .043 3mm total seal ring pack (file fit). Now just have to wait 8 weeks LOL

I have a local guy doing coating now (component coatings) . I have had pistons coated to fix bore clearance issues BUT not on street or marine applications, typically drag race and mud boggers. I call those rebuilds "10 hour rebuilds", a hill billys going to go out , smoke a bunch of weed, get drunk AF then hold his "mudder" acrossed the pit at wot for 30 seconds 2 or 4 times then park it. When it gets wet he'll go ahead and hold it on rev limiter in anger trying to "clear it out". So heavy coating a 4.623 dia piston thats going back in a bore that measures 4.634/ 4.635 after cleanup honing will get these guys thru 10 more weekends of "bogging" vs a new block or custom pistons but NOT a good long term fix!

I always thought coatings were only .001 - .002”!

Also that they were for friction reduction and or heat control.

Never realized people used it for clearance issues.

On ring packages….., another Engine Masters episode??

My theory is, the more the meat, the better the seal and I’ll give up some friction to get that and the better expected longevity.

Also prefer tighter end gaps and will file to fit.

I spend way more time in 2 stroke OBs where our options are scarce.

I do know that some of the Merc drag motors run a SINGLE skinny ass ring!

It’s funny that so much of this is “theory” and near impossible to prove.

You could write a book on the differing theories on break in procedures!
Also a huge fan of.

I used line 2 line coating to take up excessive clearance. My pistons were 007 to small. The coating filled in the gap in my "street" engine. 2200+ miles since done last year with no issues. Engine sees 7000rpm and seen over 30lbs of boost with a very short skirt piston that sticks out of the bore 1/4" or 3/8" (would have to check my build notes) Hopefully it keeps going for a longgggg time.

Is this the best way to go? Of course not.

If my memory is correct, line 2 line will do up to 015 thick coating There comes a time where the rings are sticking out in the line of fire/heat.

Yep, Ive used line to line and component coatings for same thing, usually to save from buying a block where its at its limit or high dollar race pistons that are too loose