Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: Neilw on June 13, 2026, 08:38:30 PM
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I have prepped the top end of the engine, primed with etch primer and given three light coats of VHT Silver. So far everything looks great, have also done the bottom end.
Today I loaded the top end bits into the oven and baked for 60 mins at 200 degrees as per instructions on the can.
When i opened the door, smoke poured out. I assume now from oil from the head, as I left the tappets in.
This has resulted in all the silver bits coming out a golden colour! I've also got a small amount of blistering on some parts.
The bake seems to have worked as the paint is hard, but the colour is wrong!
How do I recover the situation? I plan to key the paint somehow ( ideas on how, please?) and apply a couple of fresh coats of paint? and then either bake again individually, but forget doing the head and let that cure on the bike when the engine gets hot.
Any other ideas or thoughts, please. It took a lot of work to get to this stage, and I'm gutted it hasn't come out as i had hoped.
I don't want to put the golden colour on the bike, as i have to touch up the blistered bit with silver, so it will look patchy!
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I thought VHT paint is applied directly, is the etch primer heat resistant?
Not sure what you mean by leaving the Tappets in?
Have you melted the valve guide rubbers?
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I thought VHT paint is applied directly, is the etch primer heat resistant?
Not sure what you mean by leaving the Tappets in?
Have you melted the valve guide rubbers?
I had removed the valves, rubbers, etc., and it can have primer and is heat-resistant.
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I thought VHT paint is applied directly, is the etch primer heat resistant?
Not sure what you mean by leaving the Tappets in?
Have you melted the valve guide rubbers?
I had removed the valves, rubbers, etc., and it can have primer and is heat-resistant.
Reads as though oil or solvent has discoloured your paint?
Not sure what you mean by leaving the Tappets in?
Before I used our oven to bake my engine parts I used the Pyrotechnic Cleaning Setting on our oven to ensure there was no residual fat in my oven. Could be the bubbling be etch primer solvent not being fully dry? I also followed the temperature step guide for gradual increase of the baking temperature.
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I think it's the oil in the rocker cover that has discoloured the paint. ( i meant rockers, not tappets)[attachimg=1]
I've given the breather cover a quick coat so you can see the difference between the two.
The only option I have is to give everything another coat and bake it separately. I guess a light rub with 400/88 grit should give a good key for the coat, unless anyone has a more informed idea of what I should do?
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I did a similar thing in that my silver VHT paint went golden, I set the oven in centigrade not Fahrenheit.
Cheers
Dennis
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The spots are caused by oil in the metal coming to the surface due to the heat. You need to start again I'm afraid. Use some sort of acid to get rid of the oil in the metal before repainting. And take the rockers out next time. That's just more oil vapour being released.
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I used vht engine enamel many years ago, it was branded sperex back the before holts bought them out. Just branded VHT now and not to be confused with simoniz.
It didn't need a primer and it's stayed on aside from where I have been careless with spanners.
You need to wash with paint thinners or acetone, bake it in the oven at 100C, then solvent wash again. This will bring out any oil from the pores in the casting or corrosion pits which is probably what is causing some paint to lift. When baking paint, dry overnight and then put it into a cold oven and slowly ramp up to 100C in stages then hold at that temp for half hour.
Regards
Dave
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Sprex black was the go to for exhaustd back in the 70's
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Thanks for all of your suggestions. I can't face stripping the paint off and starting again, it's a huge job to do manually for the whole of the top end.
As it's only cosmetic, I think I'll lightly sand all the components and give them another coat or two of VHT. As for baking, i'll try the incremental increases and do them separately so I don't get any cross-contamination, i'll try a small test piece first to see if that works.
I know it's not the perfect solution and may come back with issues in the future, but I'm not planning on riding more than a few 100 miles a yr. Trust me what i have now is 1000% better than what was there before.
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With my golden components I just gave them another coat and baked them again at lower temperatures, the crankcases were left to bake when the engine was running.
Cheers
Dennis
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With my golden components I just gave them another coat and baked them again at lower temperatures, the crankcases were left to bake when the engine was running.
Cheers
Dennis
Yep, that's what I intend to do. Nice to know someone else has experienced similar issues.
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I did a similar thing in that my silver VHT paint went golden, I set the oven in centigrade not Fahrenheit.
Cheers
Dennis
I've just discovered that's exactly what I did!
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Has anyone tried painting a small piece and baking it. Then soaking it in petrol to see how the paint reacts?
Neil, you have access to a Dremel or similar?
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Has anyone tried painting a small piece and baking it. Then soaking it in petrol to see how the paint reacts?
Neil, you have access to a Dremel or similar?
Many decades ago I did that with a car rocker cover using Silver Hanmmerite brush paint that was air dried for several weeks, finally oven baked at a low temperature.
It was oil, petrol & brake fluid resistant, it did go a tad yellowish after a couple of years. Not sure if they have improved the formula since then. It would crack on bulkheads if applied too thickly.
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Just remembered Ted. That satin black engine paint was called PJ1
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Just remembered Ted. That satin black engine paint was called PJ1
Wow ,they make quite a few products as well as paint,thanks Ken.
Ceramic Enamel - sounds good stuff, I'm still cleaning the engine unit up, preparation is time consuming, hopefully time well spent.
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Just remembered Ted. That satin black engine paint was called PJ1
Didn't they do various oils too? Fork and 2 Stroke etc.?
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Has anyone tried painting a small piece and baking it. Then soaking it in petrol to see how the paint reacts?
Neil, you have access to a Dremel or similar?
I have something similar to a Dremel.
I sprayed an additional 2 coats on the breather and will bake this at the correct temp and test.
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Bit late then if you’ve already sprayed it. I was going to suggest that you buy some plastic abrasive discs, search for them on the forum, you could then remove the paint only it those areas where the paint is blistered. I would remove a full section so you don’t leave marks left by the new paint sitting lower than the old paint. It’s something those discs excel at. They are also really good at removing casting marks and blemishes.
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Bit late then if you’ve already sprayed it. I was going to suggest that you buy some plastic abrasive discs, search for them on the forum, you could then remove the paint only it those areas where the paint is blistered. I would remove a full section so you don’t leave marks left by the new paint sitting lower than the old paint. It’s something those discs excel at. They are also really good at removing casting marks and blemishes.
I can agree with Ken, the plastic abrasive discs are a game changer for cleaning up alluminium based castings & other metals.
It took me a while to get the hang of using them.
These are the type of wheels Ken is talking about, they come in various grades. I use them in pairs, they last a long time as long as you don't use a high speed in your rotary tool. I use mainly 400,600 & 1000 grit.
www.ebay.co.uk/itm/397859407787
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Bit late then if you’ve already sprayed it. I was going to suggest that you buy some plastic abrasive discs, search for them on the forum, you could then remove the paint only it those areas where the paint is blistered. I would remove a full section so you don’t leave marks left by the new paint sitting lower than the old paint. It’s something those discs excel at. They are also really good at removing casting marks and blemishes.
I can agree with Ken, the plastic abrasive discs are a game changer for cleaning up alluminium based castings & other metals.
It took me a while to get the hang of using them.
These are the type of wheels Ken is talking about, they come in various grades. I use them in pairs, they last a long time as long as you don't use a high speed in your rotary tool. I use mainly 400,600 & 1000 grit.
www.ebay.co.uk/itm/397859407787
Good advice, i actually used some 400/800 grit and sanded them down. the areas are quite small and not really noticable onced painted. Thanks for the suggestion.
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Just a random thought, but, about 40 years ago I worked for a short time for a company that reconditioned car gearboxes. When it came to cleaning the earlier type mini boxes, which used the engine oil, once they had been gutted of all internals we used to have a large tank in a hidden(!) back room which contained a fluid made by Turko Chemicals. I remember it contained phenol(!!!!), and I used to gently lower 4 gearbox cases into the tank whilst holding my breath. After about 4 hours, they were carefully removed and hosed off with clear water. They looked like new casings, all oil varnish, old gaskets and 'O' rings had disappeared. I nused to get through two pairs of those red industrial rubber gloves per day. I guess modern day 'elf & safety have probably banned these types of cleaners now, but it was good stuff. Even used it to remove a black bin liner that had wrapped round my bike exhaust. Just wondered if you had any similar transmission companies near you that could use something similar on your engine casings.
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Just a random thought, but, about 40 years ago I worked for a short time for a company that reconditioned car gearboxes. When it came to cleaning the earlier type mini boxes, which used the engine oil, once they had been gutted of all internals we used to have a large tank in a hidden(!) back room which contained a fluid made by Turko Chemicals. I remember it contained phenol(!!!!), and I used to gently lower 4 gearbox cases into the tank whilst holding my breath. After about 4 hours, they were carefully removed and hosed off with clear water. They looked like new casings, all oil varnish, old gaskets and 'O' rings had disappeared. I nused to get through two pairs of those red industrial rubber gloves per day. I guess modern day 'elf & safety have probably banned these types of cleaners now, but it was good stuff. Even used it to remove a black bin liner that had wrapped round my bike exhaust. Just wondered if you had any similar transmission companies near you that could use something similar on your engine casings.
It's a good suggestion, but i'm too far down the road to want to start again. I'm in patch up mode now. I think for my needs a few coats of VHT over what is there and a bake at the correct temp should sort it, fingers crossed!
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Sounds like a Trichlorethylene Tank, lots of garages had them in the 1960s,
now illegal due to serious health risks.
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Sounds like a Trichlorethylene Tank, lots of garages had them in the 1960s,
now illegal due to serious health risks.
Carbon tetrachloride was even worse, even in the labs we had to stop using it and find alternative solvents. Good degreaser though. We kept a bottle for saving up the `slops` which came in handy for cleaning oily things at lunchtime. Chloroform was more enjoyable to use.
Dave
Dave.