Surface Finishes Inside an Engine

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Surface Finishes Inside an Engine

Postby david brooks » Wed Jun 07, 2006 4:18 pm

What is the best type of surface finish inside the motor to help it run better, such as the head finish, carb finish, maybe even inside the crankcase, ect. Sandblasted, Polished or Coated, Hard Anodized...
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Postby gossie » Wed Jun 07, 2006 5:27 pm

Good question, but seems there are two schools of thought on that.

Highly polished or rough so there is always wet mixture in the rough stuff that the mixture slides over.

Will be interested to hear views on this one. :?
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Postby aaronnovak1999 » Mon Oct 16, 2006 1:34 pm

Good Afternoon,
You have asked the most debated question in the airflow world. There is a lot of folklore, misunderstanding, and flat out wrong ideas floating around. Here is what we have learned in the "big" engine world, and how it scales.








To sum it up, spend your time on getting rid of sharp edges, radius all your inlets, and in general smooth out the airflow path with disturbing its direction ( especially in the bybass region ). Keep everything as smooth as possible but dont waste your time polishing anything, fine scotchbrite finish is about right. Anybody else have any imput?
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Postby gossie » Mon Oct 16, 2006 9:50 pm

aaronnovak1999 wrote:Good Afternoon,
You have asked the most debated question in the airflow world. There is a lot of folklore, misunderstanding, and flat out wrong ideas floating around. Here is what we have learned in the "big" engine world, and how it scales.








To sum it up, spend your time on getting rid of sharp edges, radius all your inlets, and in general smooth out the airflow path with disturbing its direction ( especially in the bybass region ). Keep everything as smooth as possible but dont waste your time polishing anything, fine scotchbrite finish is about right. Anybody else have any imput?


Fully agree with all of this. Most of my model engines have been pulled appart and simply 'cleaned up' inside----rough edges etc.
I would not say they are much 'faster' than other, but it's I feel a nice thing to do to them.

I am also in to 2 stroke PWC (Jetski's) and I did have the top end done by a Japanese mechanic, and I made sure he smoothed out the various passages inside the engine. The ski's that have never been appart, same brand as mine are slower at top end speed by about 3 to 4 MPH.
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Postby jydracing » Sun Nov 05, 2006 6:13 pm

aaronnovak1999 wrote:Good Afternoon,
You have asked the most debated question in the airflow world. There is a lot of folklore, misunderstanding, and flat out wrong ideas floating around. Here is what we have learned in the "big" engine world, and how it scales.








To sum it up, spend your time on getting rid of sharp edges, radius all your inlets, and in general smooth out the airflow path with disturbing its direction ( especially in the bybass region ). Keep everything as smooth as possible but dont waste your time polishing anything, fine scotchbrite finish is about right. Anybody else have any imput?


The only other thing is polish the head to a mirror finish than ceramic coat the top of piston and head and exaust port
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Surface Finishes Inside an Engine

Postby Ken McClenahan » Mon Nov 06, 2006 9:39 pm

Once upon a time 50 years ago I polished the inside of a head. This was one of the worst mistakes I ever made. The connecting rod broke after running about one minute at a four cycle.
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Postby gossie » Tue Nov 07, 2006 4:38 pm

Polishing the inside of your head would have had nothing to do with a con. rod breaking. There would have been another reason.

Further to polishing a head on an I/C engine, may I suggest you all go out and do it, give it one or two runs and see what's there on the part of the head that you polished.

CARBON build up straight off. Negates all the polishing in the world.

Cleaning up the intake passages is the way to get more performance.
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surface finishes and ceramics

Postby aaronnovak1999 » Tue Nov 14, 2006 12:21 pm

Good Afternoon,
Polishing your combustion chamber looks pretty and sells well in biker magazines, thats about it. As far as ceramics, what are you trying to manipulate? You may reduce transient heat absorbtion on a cold engine accelerating to WOT, but as soon as the engine parts stabalize at their opperating temp ( which will be the same coated or not ), there will be no affect. This is not myth or something written in the car comics ( hot rod, street rodder, circle track etc ) but this is REAL data from an engine designer. If your engine could stand some more combustion pressure, you will be better off modifying the mechanicals of the engine rather then a magic coating (ceramics). As another side note, the ceramics wreak havoc when they flake off of the surfaces, and they will eventually. Its just not worth the effort, and is not an "easy" fix. The people in the know, will know when and how to use ceramics in an engine, other then that my advice would be to leave them alone.
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Postby jydracing » Tue Nov 14, 2006 7:26 pm

in presant time there is synthetic lubercants that do not leve a resadue in the engines. I polish the head buttons and they do not dirty up. as far as the ceramic coating been doing it a long time and have had no problems. done this to a drag car and shaved a full secand off of the time. i am not a engine designer but been building and racing for 26 years and know what works and what does not.
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surface finishes and ceramics

Postby aaronnovak1999 » Wed Nov 15, 2006 7:33 am

JDY,
You hit on my point exactly. In drag racing ceramics can help, but thats a transient condition, not steady state running. As your engine reaches opperating temp you will see the HP gains fall off to normal. Model avaition engines tend to run with high duty cycles in steady state conditions, and therefore will not see much if any improvement from ceramics. Why does polishing your head buttons help do you think? Do you see gains over a CLEAN unpolished button? If so how much? How do you measure performance?
Thanks!
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Postby jydracing » Wed Nov 15, 2006 7:11 pm

I am racing RC boats and we were having problems with getting enough heat in the combustion chambers. i even run a nova rossi 21 outboard with no cooling not even a heatsink head. i run the ceramic coating to hold the heat in the combustion chamber. I also relised that by doing this the block stayes cooler so the bearings are running cooler I was changing them three to four times a year now only once a year. coating the exaust port and inside the headder and tuned pipe inside and out will speed up the exaust gasses. you only have a certion amount of time to get the used gasses out and the new ones in. as far as polishing the head button when the piston moves to make compression this is the last place that you want any restance or bad air movement. you want the gasses to move to the glow plug as fast as it can. also polishing the head button has for me elemated the preignition and detonation in my engines.

Think of it this way every inperfection in the head button acts as a hot spot and can ignight the fuel before it is needed. even where the sguash band ends and the combustion chamber starts that little corner is bad a rounded one will not get hotter than the rest. I test my engines in race conditions using a gps and the other competion. Also i use a eagletree onboard datalogger that i record the rpm, head temp, and exaust temp.

Please excuse my spelling it has been a hard 12 hours today till later jimmy
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surface finish and ceramics

Postby aaronnovak1999 » Thu Nov 16, 2006 7:44 am

Good Morning,
How do you know your not " getting enough heat" into the combustion chamber? I would tend to believe an engine thats prone to pre-ignition would not have a problem with heat. And by heat I assume you are referring to the mean combustion chamber temperatue that plays a vital role in ignition timing on a glow engine. Would you not get the same effect by raising the compression ratio and or/ altering the nitro content? My experience has shown charge motion in the combustion chamber has little to do with minute surface finish changes, but can be greatly affected by how much say a transfer port is deburred. If you increase the exhaust temperature in the header and tuned pipe, you are not changing the mass gas flow, but you are decreasing the gas density, this will affect tuning more then a mean exhaust gas backpressure. If your exhaust system wants to run hotter, it will also respond to having its primary resonance length shortened. This will allow the pipe to dissipate heat away from the exhaust port rather then insulate it. Just some ideas to throw around. I would be curious as to the actual temperature difference in your bearings, and what other conditions might affect their life.
-Aaron
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Postby jydracing » Thu Nov 16, 2006 7:20 pm

Hi I found out about the heat by accident. I was running a boat and it all of the sudden hit the secand stage on the pipe then the third the speed was ausom when i brought it back in the cooling line was off. i repaired it and ran it again and it ran as always. so i restriced the cooling line and the speed came back. then i did a little resurch at the local rc car track and found out that they were running the engines at 225 deg head temp. so i ran again with the data logger and the cooling. i was running at 180 deg head temp. that is when i started playing with the cooling.

I run 10.1 to 11.1 compression with 70 percent nitro fuel and was getting pitting on the top of the piston and on the head and polishing the head stopted it. I also work on the ports on the sleeve and block and leave a saton finish on them then i work on the port timming on all of the ports. i need to add that i machine my own head buttons and run a flat squash band with a certon width and a certon volume. i added the ceramic coating because the blocks were getting really hot I was loosing the top bearring under the flywheel all the time before i did the coating.

I also need to add that i build my own tuned pipes and carburators. I can not explane all the reasons that my mods work but they do for me. some of what i do may not work for everyone. well until later jimmy
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Postby david brooks » Tue Apr 10, 2007 6:22 am

I'm going to have to agree to the polished head button. Hot spots aren't the thing to have in a combustion chamber, and with the synthetics these days, carbon isn't an issue. Even running 5% castor with the synthetic really shouldn't leave anything behind. The only time there's carbon is when things are too hot to start with.

I've seen head buttons grit blasted before, with the theory of keeping the mix shook up and slowed down to keep it in the cylinder as it was being inducted, but I don't think the benifit would be there without experimenting that way. If you think about it, it would help keep the charge from whistling through, but I could see it adding to a pre-ignition problem if one exists.

Another thought on polishing the chamber - when you mention it stopping pre-ignition, it is hard to polish a button without loosing that sharp edge going into the bubble, and that most likely what helped that problem. That corner going from the squish band into the bubble, the more it is radiused, the less pre-ignition you'll have, but loose rapid expansion on the downstroke (?)
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Postby jydracing » Tue Apr 10, 2007 4:54 pm

Well if you think about it, it will not. Our engines do not have rings so it does not have the full down swing to hold the pressure. It is let go when the exaust opens. In fact as soon as the piston goes below the fit at top it will start loosing compression. I feel that a small Radious where the combustion chamber meets the squash band is helpfull in letting the flame to go the full distance quicker. Think of it this way witch is quicker going around a sharp corner or going around a corner that is round.
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