engine paint prophecy

heres whats up , i bought a another project bike. frame allready sandblasted,looks good. engine looked really good,so good, i thought the guy had semi polished the heads and block. so i asked him how he made it look so good and he told me he degreased,sanded,blew everything down with airhose and then wiped it all down with acetone. here is the kicker, he says he then painted it with rustoleum metalic silver! I told him i didnt want it , and he said he has done it before on his hotrod engines and it works,so I bought it. now im afraid to start it and thinking of taking it back. what if it turns into a fireball,big gooy mess or some kind of nasty flaking,color changeing chamelion engine that i would have to strip. I REALLY DONT WANT TO DO THAT! it looks so good and it was a good price. anyone know what this thing is gonna do? anybody care to make an "engine paint prophecy"??????

im not a big fan of painted engines myself,especially not the pit stop performance prefered silver.
anyway might i suggest paint stripper and scuff pads on the motor? :laugh:

thanx wireman but thats what i dont want to do . i wondering whats gonna happen when i fire it up. i like the color . just worried about it turning into a effin nightmare. was hoping for a similar experience story from somebody.

id be willing to bet it will start changing colors very rapidly starting around exhuast port area of head and going down hill fast from there

what ya think like black or maybe a brownish gold?

Old school honda cb750f and CBX both had painted engines (silver) and they seem to last and not discolor more then the raw metals of Kaw engines oxidize. I am not a fan of the silver, but do have both the CBX and 750.

I would be careful not to paint on top of the the silver paint as you will reduce the cooling as you cake on the paint.

I have a prediction. I don't know that it qualifies as a prophecy. Your going to put the engine in the frame and run it. It's going to run strong. You're going to get it out on the road and really heat it up. It's going to start to change colors, maybe to a nice golden-brown color. The first time it gets fully hot, when you park it, it's gonna smell a little funny.This is the paint beginning to burn. As you heat it up and cool it down, eventually you will notice a little smoke coming off of the motor in the exhaust port area. Now if you bend in real close to see if your tach drive seal is weeping, you will notice the paint is starting to boil a little, and pull up off the metal, beginning at edges, right near the center of the front of the head. How do I know all this? It's what happened to the paint on my motor. One of the previous owners "touched it up" before he sold it.

I think Honda still uses that silver case paint. Supercharged is right, DO NOT REPAINT ON TOP OF IT! This will turn a bad situation worse: the original paint will ultimately peel, and now it will take the new topcoat with it. And it will adversely affect cooling until it does. The way I see it, you have three options: 1) Try to take it back. The downside here is the P.O. may not want it back! 2) Chemical strip it. Rinse it really well with water, repaint with a high-heat paint. 3) Soda blast it, rinse it and repaint.

thanx everyone , im not gonna paint over his paint . but his paint is over the factory paint . is this already gonna effect cooling . i called him to find out if sanded the factory paint off but he said he just scuffed it. he said it was silver from the factory because its an ltd. is this a silver paint engine from the factory? man i really don't want cooling issues.

plug up the holes and such...spray the whole thing with gel-spray-aircraft stripper....it will wipe off with a soft scrubber....imo...few times may be needed.....nothing sucks more than knowing you are not 100% okay with something and going ahead with it anyways...always seems to be the longest of shortcuts if i knew and ignored ahead of time to ...stop....re-group...and fix the issue.....

when i was younger i could get away with just about anything bike wise......now if i even think something is in question..(age-experience-hard knocks)and i go ahead anyways ...it usually costs me between 100 and 200 hundred dollars...:woohoo:

do i follow this rule of caution every time...no...i take short cuts ...lazy...or tIred...or in a hurry to go for a ride......by now.....i have about as much in re-do work as i do into the good work

separate subject in a way..."paint letting engine breath /cool itself correctly"...

i did my current project in auto store satin engine paint...and it may be running hotter now :whistle: ...hard to tell as i did not get to ride it before painting but once...


i have heard/read that some motorcycle engine paints are better at letting the motor breath...i do not know if this is true and i only used light coatings and a smooth thin finish....

i may be worrying too much...or misinformed....either way

it had been stripped of it's MKII factory scheme and i re-did it....

i will strip it again when i do the frame next season....

sorry for the hijack sort of...may tie in with others comments to your situation

before


after

On the issue of paint vs engine temperature I am going to chime in with some engineering speak.

First paint does affect all three modes of heat transfer. Conduction, radiation, and convection. This is true but the affect is very very small.

The paint forms a layer that must conduct heat, and paint may have a heat transfer coefficient that is differnt from aluminum though I doubt is much differnt. The issue is that the layer is so thin that the resistance to heat flux will be very, very small. Very thick layers of piant could present a problem, but the layer would need to be pretty excessive to do so.

Convection, here is where the bulk of the cooling occurs. The heat flux is dependant on the convective heat transfer coefficent. This is HIGHLY dependant on geometry ( the size and spacing of cooling fins) and fluid properties (the air). Paint isn't going to mess with the coeffiecnt very much at all. Clogged and broken fins will chnge this coeffient, but even then it wouldn't be as much as you would think. Dirty fins, broken fins, and very highly polished surfaces will reduce the heat transfer by convection. This is by far the most important factor in cooling these engines.

Radiation at these temperatures is a small part of the overall heat transfer. That being said a bright shiiny object radiates better than one painted black. The emissivity, or ability of an object to radiate, will be affected by paint. The heat loss from radiation is small compared ot the convective heat loss, so again paint will have little affect.

Long story short. Even a few layers of paint are not going to greatly affect an engine's temperature. The change will be there, but it will be small. Maybe a few degrees or so.

Paint is an issue personal preference, not one of performance.