1982 CB750F...Better Devil
- Thread starter Jimbonaut
- Start date
I sand fin edges back first to the level of polish that is desired. then paint the whole thing without any masking. once he paint has dried take a rag with acetone and carefully wipe the fin edges off. Since they are already polished its comes off very easy and gives a nice crisp line with zero chipping. it lets you do the internal fins if you want without risk of damaging the fresh paint.
Cheers Doc - think your method would also work if I don t heat cycle the engine first before acetoning the fins? I’ll be painting the engine soon but it’ll be a while before rebuilding the bike and reinstalling the engine. I don’t have an oven and the engine is gonna be painted assembled.
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Had a go at filing down the fins. Turns out it's a really satisfying little job. Here's a during -
and here's job done -
Feeling it. Definitely feeling it. They still need a finer sand and then a polish - undecided if I'll go the Maritime tape-and-paint route or the Doc Rot polish-and-acetone plan but both sound groovy 8)
and here's job done -
Feeling it. Definitely feeling it. They still need a finer sand and then a polish - undecided if I'll go the Maritime tape-and-paint route or the Doc Rot polish-and-acetone plan but both sound groovy 8)
CarbsAndCylinders
Careful With That Axe Eugene
That looks nice. Did you file parallel to the fins, I think that would be less likely to cause chipping?
I haven't painted the engine yet (it was painted black by the PO) but when I filed yeah it was pretty much at right angles to the fin. Not so much on the front and back of the engine (where the fins are tapered), but - on this old paint at least - no chipping.CrabsAndCylinders said:
Either I'll tape and paint or polish, paint and acetone.
Hopefully later this week my man Kieran's gonna help me bend up a hoop, weld the thing up and then I can get the frame painted. Saturday was de-shit the frame and swing-arm day so it's pretty much ready for its close up. Also doing a welding course this weekend, so, yeah - fabricating.
If it's messy, than you may not be doing it right. You just fold a rag (I use and old t-shirt) into a 4" x 4" square, then soak one side in acetone and clean the paint off. You have to flip to clean sides of the rag when one side gets full of paint. It's not messy at all. Using the folded rag allows you to span several fins at once..
It wipes right off the polished fin edges? Without wiping off any of the paint on the fins themselves? What if the engine/paint hasn’t been heat cycled - will the paint have cured enough not to get wiped off by the acetone (apart from the polished edges of course)?
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TBH, I have no idea about heat cycled paint, since I've never done it with cured engine enamel. As far as what it gets off, it depends on what you use. I use tightly folded cotton cloth, so it's kind of stiff. I soak one side, but I don't go nuts. Basically, you want it damp with acetone. Then just rub the paint off. If the cloth is folded tight enough, it won't touch the sides. I've also done this on my BMW's Lesters. I just painted the entire rim, then rubbed the outer lip clean with the rag and acetone.
The test looks great, Jim. I'm planning to do the same so a lot of good info here.
A bike mechanic friend of mine came round the garage yesterday and we go to talking about my plans for the engine. Truth be told I'm a bit polarized about what do to, what with the engine having such good compression (165psi across all four). Common sense would suggest leaving well enough alone - if it ain't broke don't fix it kind of thing. However there are a couple of motivating situations that would make pulling the head make sense. I'm totally 50/50 on what to do, but figure there's no wrong decision really. Here's the skinny -
Vote for pulling the head -
- have a stripped spark plug thread, helicoiling that mofo would be much easier plus no danger of shit falling into the cylinder
- I could change the valve seals. As far as I could tell before the tear-down the bike's not smoking, and I can't see any oil on the valve stems when I look into the exhaust ports. But if they haven't been changed in 35 years then now could be a good time to do it
- would make painting the engine easier
- I'm in no huge hurry to get the bike finished
- need a gasket kit anyway ($90) which has the seals included
- learn new skills. Because, skills
Vote against -
- compression's excellent, why go looking for problems
- see above
- see above
Maybe this isn't the engine to learn on - but if it starts smoking a few months down the line because the valve seals are cracked then maybe it was.
Pondering with intent.
Vote for pulling the head -
- have a stripped spark plug thread, helicoiling that mofo would be much easier plus no danger of shit falling into the cylinder
- I could change the valve seals. As far as I could tell before the tear-down the bike's not smoking, and I can't see any oil on the valve stems when I look into the exhaust ports. But if they haven't been changed in 35 years then now could be a good time to do it
- would make painting the engine easier
- I'm in no huge hurry to get the bike finished
- need a gasket kit anyway ($90) which has the seals included
- learn new skills. Because, skills
Vote against -
- compression's excellent, why go looking for problems
- see above
- see above
Maybe this isn't the engine to learn on - but if it starts smoking a few months down the line because the valve seals are cracked then maybe it was.
Pondering with intent.
