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Author Topic: 1979 CB750L. My first cafe/brat project. Denver Area  (Read 13540 times)

Offline V10Pilot

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Re: 1979 CB750L. My first cafe/brat project. Denver Area
« Reply #30 on: Dec 05, 2018, 00:20:21 »
:o Looks like you are putting in the good work!  That engine looks phenomenal.  Why did you decide not to paint the head? Also, can you tell me what paint you used its gorgeous!!

Can't wait to see more.  Bookmarked.
Thanks. A few reasons I didnít paint the head. I like to be different and everyone seems to be polishing or painting them black. I like the natural look and secondly the point of the fins is to aid cooling and coating them with paint will impede that. I would have had them vapor blasted also but I didnít have access to one back when I had the head apart. Oh well.
The paint is by VHT and called Cast Iron. Itís not a 2K paint so Iíll have to accept the durability isnít going to be great but I do plan on coating it with a high temp clear coat made by Eastwood called Exo Armor and that should help. Iíll report back after I get the bike on the road early next year.


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1979 Honda CB750L
2001 Kawasaki ZR-7S

Offline Jimbonaut

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Re: 1979 CB750L. My first cafe/brat project. Denver Area
« Reply #31 on: Dec 05, 2018, 11:21:05 »
Thanks. A few reasons I didnít paint the head. I like to be different and everyone seems to be polishing or painting them black. I like the natural look and secondly the point of the fins is to aid cooling and coating them with paint will impede that. I would have had them vapor blasted also but I didnít have access to one back when I had the head apart. Oh well.
The paint is by VHT and called Cast Iron. Itís not a 2K paint so Iíll have to accept the durability isnít going to be great but I do plan on coating it with a high temp clear coat made by Eastwood called Exo Armor and that should help. Iíll report back after I get the bike on the road early next year.

Good point.  I'm about to start tearing down my next 750, and although the engine has excellent compression (not much need to tear the engine apart) the casings themselves are looking a little ratty.  I'd love to paint it but right now just weighing up my options.  Interesting take on why not to paint the head.  I wonder how much effect painting would have on the cooling - with all the air rushing through the fins and between the cylinders I genuinely do wonder whether the paint (or lack thereof) would affect the cooling much. 

I've used Eastwood paint before - they make some excellent 2K clear which I've used on a couple of tanks with great results.  I'll be interested to hear how their Exo Armor holds up.  Well no doubt.
"I'm telling you Donnie, nuthin' but nuthin' but right"

Offline Kunipshun Fit

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Re: 1979 CB750L. My first cafe/brat project. Denver Area
« Reply #32 on: Dec 05, 2018, 11:42:15 »
Interesting indeed about the paint affecting cooling of the head.  I cant imagine it would do much considering paint isnt much of an insulator, but who knows for sure?!!
Lurker and dreamer.  Maybe one day Ill start on my bike.

Offline V10Pilot

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Re: 1979 CB750L. My first cafe/brat project. Denver Area
« Reply #33 on: Dec 05, 2018, 15:17:11 »
Iím not using exact scientific number to prove the cooling or lack of cooling but if you put a layer of paint on a surface itís going to hinder it slightly. Even if it does it would be just a few degrees and that wouldnít matter on an old Honda motor. I just wanted to keep it bare because everyone seems to be painting their heads and I like my stuff to stand out.


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1979 Honda CB750L
2001 Kawasaki ZR-7S

Offline wozza

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Re: 1979 CB750L. My first cafe/brat project. Denver Area
« Reply #34 on: Dec 05, 2018, 19:09:30 »

Black absorbs heat pulling it away from the internal parts and then the air passing over fins remove the heat.....Not a lot of temp difference between polish/light colors and black ...but a measurable difference all the same.Plenty of discussions on the subject around the net....and difference of opinions :)   

Offline V10Pilot

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Re: 1979 CB750L. My first cafe/brat project. Denver Area
« Reply #35 on: Dec 05, 2018, 23:17:21 »
An interesting article from an aeronautical thermodynamicist regarding the subject. Some parts donít apply because the engine isnít in an enclosed cowling:

Some overhaul shops claim beneficial cooling effects of black paint on their engine. The theory is that black is a better emitter of infrared (heat) energy. A hot engine in a cold surrounding, radiates energy from the hot object to the cold. The amount of radiant cooling (thermal emissions) is generally dependent upon the temperature of the emitter (engine) and how efficient the engine is at radiating energy ó its emissivity. This derives from Kirchoff's Law where good absorbers are also good emitters. Since black is a good absorber of energy (that's why it's black), it's also a good emitter. A black object emits more radiant energy (cools faster) than a white or gold object that emits less radiant energy per unit of time. Painting an engine black increases the amount of radiant energy emitted by the hot engine to its colder surroundings and it will be cooler than a non-black engine.

There are fallacies to the above argument. Most heat energy emitted by the engine is in the invisible infrared portion of the spectrum. What appears to us as black, white, red, or green in the visible spectrum is not what we would see in the infrared spectrum. Any color of paint that uses organic (non-metallic) pigments is black in the infrared spectrum. For example, white paint emits 90-95% depending upon pigment type. Black emits 96%, blue 94%, green 92% and red 91%. The best emissivity surface coating is acetylene soot at 97%. Painting an engine increases radiant cooling but the color of the paint doesn't.

The second fallacy is that you also have to ask what happens to the radiant energy being emitted by the engine. Engine cowlings with bare aluminum on the inside reflect about 95% of the radiant energy back to the engine where the black paint of the engine absorbs at the same high efficiency as it emitted. Black paint has high absorbency and high emittance. Better would be white paint that has low absorbency and high emittance. An engine contained within a bare aluminum cowling should be painted white not black to reflect the radiant energy back to the cowling. Another technique would be to paint the inside of the cowling black to eliminate reflection of heat energy. If the aircraft had a plastic cowling then the engine need not be painted white because of the low reflectance of plastic.

Most heat from the engine is transferred to the atmosphere by convection rather than by radiation. Radiant cooling of an engine is negligible. Engines run quite nicely no matter what color they're painted. Now when you're at that trade show and the engine shop salesman is talking performance and how his paint scheme helps cool the engine just tell him that his black engine is the same color as a red, white or blue engine ó in the infrared spectrum.

Although engines get all the attention, the engine compartment can be engineered to better manage temperature. The engine compartment is one of the most heat damaging environments there is. Packed in the same compartment are glowing exhaust components, rubber products, electronics, wiring, pumps and magnetos. Little effort has been made at controlling heat exchange by changing the infrared emissivity and reflectivity of components. Small changes, such as the addition of reflective heat shields, can be very effective.

Engine mounts are often corroded where they pass next to an exhaust pipe. Mounts painted with dark shades of organic pigmented paint efficiently absorb radiant energy causing the mount to get hot, burn the paint, and cause corrosion. Black or white paint is all the same as far as emissivity or cooling a hot object. However, when keeping an object colder than its surroundings, such as a mount section next to an exhaust stack, we need to reflect the radiant energy and not absorb it. In this case white paint reflects more radiant energy than black paint. A metallic pigmented paint, such as aluminum, is even better yet.

Another method of keeping objects cool in a hot environment is by using heat shields that reflect radiant energy. Small shields made out of aluminum or stainless steel are highly reflective not only at visible wavelengths but well down into the infrared. Your mechanic may be able to fabricate these small heat shields or contact me for pre-fabricated shields.

Aircraft, such as some Aerostar's, use heat shields to keep the magneto cool. We may be able to forgo the shield and add the reflective properties of the shield to the surface of the magneto. For this we want the magneto surface to have high reflectivity to bounce radiant heat off and we want high emissivity to radiate heat out of the magneto.

Bare aluminum or a metallic pigmented paint would not be desirable because it has high reflectance but low emissivity. Black paint, as most magnetos are painted, also is not desirable because it has high emissivity but poor reflectance. A white organic pigmented paint is best because it has both high emissivity and high reflectance.

Painting engines black is more effective as a sales tool than it is at cooling an engine. However, the concept of regulating temperature within an engine compartment by controlling radiant energy can be both effective and easily and inexpensively applied.


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1979 Honda CB750L
2001 Kawasaki ZR-7S

Offline V10Pilot

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Re: 1979 CB750L. My first cafe/brat project. Denver Area
« Reply #36 on: Dec 09, 2018, 12:56:56 »
Fresh gaskets and cleaned up oil pump.


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1979 Honda CB750L
2001 Kawasaki ZR-7S

Offline esmoojee

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Re: 1979 CB750L. My first cafe/brat project. Denver Area
« Reply #37 on: Dec 09, 2018, 18:50:16 »
Or find an r6 starter clutch and do swap that will outlast the motor.    I did it on my 750 and never had another problem.

Offline V10Pilot

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Re: 1979 CB750L. My first cafe/brat project. Denver Area
« Reply #38 on: Dec 19, 2018, 11:05:55 »
A little more progress. Just need to weld her up and paint the frame with fresh 2K primer and gloss black. Then the motor can go back in.


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1979 Honda CB750L
2001 Kawasaki ZR-7S

Offline Jimbonaut

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Re: 1979 CB750L. My first cafe/brat project. Denver Area
« Reply #39 on: Dec 19, 2018, 11:34:12 »
Looking good fella, feels great getting the hoop on!  Glad you found someone to make it for you, looks perfect.

And damn I'm jealous of your weather.
"I'm telling you Donnie, nuthin' but nuthin' but right"