Honda-SOHC
SOHC.co.uk Forums => Project Board => Topic started by: Theoldboycarter on February 24, 2026, 02:00:16 PM
-
Has anyone had experience of using Simoniz VHT aerosol paint on engine casings? I used it on the clutch cover, final drive sprocket/starter motor cover and alternator cover on my CB400F. The instructions on the tin say to cure the paint by baking in an oven for up to 1 1/2 hours and up to 220 degrees c. I was a bit wary of getting the aluminium too hot and it distorting so I only heated it to about 150 degrees. I was quite pleased with the finish and colour, but the paint still seems quite soft and had no resistance to petrol at all when some dripped on it from a dodgy petrol tap connection. Is it ok to heat aluminium castings to 220 degrees, or would baking for longer compensate for the lower temperature, or should I find some other way of refinishing the casing?. Some people have suggested having them polished, but I don't really fancy that. Any thoughts greatly appreciated. With thanks, Roger.
-
Best let the paint sit a few days so the solvents migrate out of it, then bake slowly at 100-150 to help it even more. One day you'll fire up the engine and that will be the final bake so to speak.
-
We have painted and cured so many engines with Simoniz SIMVHT31D that I've lost count now but it's over 100. Do exactly as it says a on the tin, letting air cure as well as oven cure and it turns out perfectly. If you skip any part of the process, including skimping on the prep, you won't get a good outcome. The paint shouldn't be soft at all.
-
Has anyone put a laser temp gun on these engines after a good thrashing? I’d be interested in what temp they are at.
Oddly the web says any temp above 150 risks distortion especially with alloy with magnesium in it. Melting point of aluminium is around 660c so you’d think 220 would be safe but it appears not.
-
Just beware I used usautomotive VHT paint on my barrels and head, but got it wrong, used 2 hours at 200oc instead of 1 hour and it came out a lovely metallic gold colour. Repeated at the correct time and it was perfect.
Cheers
Dennis
-
Google says air cooled motorbike engines typically run at 100 deg C to 180 deg C with 200deg C + being too hot 🥵
I would worry about aluminium cylinder heads becoming warped if heated to 200C when not bolted down and cylinder liners getting lose in their bores and moving a bit.
-
Thanks everyone for your replies. Nurse Julie, when you say do exactly as it says on the tin, do you mean including heating to 220 degrees c? As Oddjob mentioned, I've seen on the internet that aluminium can distort at relatively low temperatures, but then I am aware you can't believe everything you read on the net.
-
I was watching a How it's Made TV program the other night and oddly they referenced alloy distortion in it, it was 150c so that's confirmed. There was also a program on the SR71 Blackbird plane, it also mentioned that they couldn't make it out of alloy like the U2 again mentioning the distortion problem above 150c. They made it out of titanium instead.
-
Thanks everyone for your replies. Nurse Julie, when you say do exactly as it says on the tin, do you mean including heating to 220 degrees c? As Oddjob mentioned, I've seen on the internet that aluminium can distort at relatively low temperatures, but then I am aware you can't believe everything you read on the net.
Alloy sheet may distort at 150° but alloy engine cases don't.
The only time we prepare to prevent distortion, is on bottom engine cases that need major TIG welding for major chain damage repairs on Sandcasts/ K0's, which is 660°. We bolt the case to a jig to prevent distortion during welding.
As far as the painting is concerned, the most important thing is to make sure all old paint/ oil etc is removed prior to painting. The parts must be thoroughly clean, we had all our engine chemically dipped to ensure no contaminates were left on or in the metal. If there is any left, it will just leach out under the new paint. Wipe parts down with clutch and brake cleaner.
So......
1. Prep the cases fully.
2. Heat cases in oven to 50°c.
3. Heat can of paint in hot water.
4. Spray 1 mist coat.
5. Leave for 10 mins and spray another light coat.
6. Repeat No.5.
7. Air cure somewhere warm and dry for up to 24 hours.
8. Put oven on at 50° and and gradually increase in 50° increments over 1½ to a maximum of 220°c.
9. Turn oven off, leave parts in oven to cool until cool enough to handle.
10. Remove parts from oven and air cure for 24 hours somewhere warm and dry.
Doing it this way, we have never had any distortion ( the parts are only at 220° for about 10 minutes), nor have we had any discolouration.
As far as fuel damage is concerned, paints like this are 'fuel resistant'. If painted and cured correctly, wipe any fuel spillage off, ie at the petrol pump, as soon as you can and it will cause no damage. Leave the fuel on without wiping it off, it would cause some damage. The easiest thing to do is not have leaky carbs or tap, then you won't have a problem.
-
I was watching a How it's Made TV program the other night and oddly they referenced alloy distortion in it, it was 150c so that's confirmed. There was also a program on the SR71 Blackbird plane, it also mentioned that they couldn't make it out of alloy like the U2 again mentioning the distortion problem above 150c. They made it out of titanium instead.
At Mach 3 the airframe got very hot and titanium had to be used to withstand the high temperatures. Nearly every photo of the Blackbird in the hangar will have large drip trays under the aircraft because it used to leak fuel badly on the ground, possibly because of the expansion and contraction.
Concorde only flew at Mach 2 and used to expand about 12 inches in length at that speed.