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High temp cylinder paint

Submitted by david_henshaw on Sat, 06/02/2010
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Commando

Can anybody recommend a good high temp paint for painting the cylinders on my 750. I have heard that many so called 'high temp'gloss paints are not high temp enough and bubble.

What was the factory finish - were the barrels stove enamelled?

Also originally, was it a gloss or satin finish?

Many thanks again

Jamie

Submitted by Anonymous (not verified) on Sat, 06/02/2010

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Deep down in the Technical pages of this site there is an answer, but you have to know where to look. As a general point to everyone there is a search facility sitting top right of this and every other web page. A few key words such as 'barrel' and 'paint' take you close to this reference.I use PJ1 Fast Black which says it is good to 260?C (that's 500?F for those who still use those units). The instructions say it cures overnight but I find it is still a bit soft and can be easily marked by rough handling or spanner dings. Ido the following:-

  • Spray up the barrel
  • Apply further coatings as necessary at 2 - 4 hour intervals
  • Allow to dry overnight in a warmish atmosphere to let all the solvent evaporate
  • Sendmy wife out for a few hours
  • Cure the barrel in the oven on a rising temperature ramp. I start at 50?C then increase in 50?C increments athourly intervals up to say 200?C or whatever the oven will go to. The final cure is when you run the engine
  • Open the windows to let out the smell before the other half returns

PJ1 Fast Black is a gloss black but it is not so glossy it looks silly. Impact by road dirt soon makes it a satin finish anyway. From the look of some barrels I have seen, I would suspect they were originally powder coated, but that's just a guess on my part.The trouble is that according to my notes, the correct barrel colour for a 1971 750 is silver; they did not go to black until 1972. Can anyone confirm that? Anyway, I think there is a silver version of the PJ1, but I have never tried it.

Submitted by wayne_tolson on Sun, 07/02/2010

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Hi

My barrels were coated silver, over 25 years ago via RGM they still look good even now, donât know if they can still do this service, I think the firm that under took the work were from Gateshead, were RGM started.

Regards Wayne

Submitted by david_evans on Sun, 07/02/2010

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The first 750s had silver barrels until the combat engine from then on all were black, The original coating will probably need grit blasting to remove prior to powder coating, or whatever finish you choose. Grit blasting is an extreme process and care must be taken to ensure the machined surfaces are protected with a thick aluminium tape. (I know from recent experience on the rotor housings of My IP2) Despite this protection you will have to spend considerable time cleaning the grit from threaded holes, pushrod tunnels and oilways. If you can, leave bolts in the theaded holes to protect them. Again wait until the Mrs is out and put the barrels in the dish washer, and that's just for starters. The threaded holes need to be clean enough to allow the screws to go in fully without galling or you won't get an accurate torque setting.

Yours Gripper

Submitted by gino_rondelli on Wed, 24/02/2010

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Pj1 is good but if you can't find that locally B&Q do a range of high temp enamels called Magicote (or something like that) they even do it in pink if you want to be different!

Its as good as PJ1 but needs to be cured for a while before handling

Submitted by phil_hannam on Sun, 28/02/2010

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Words of Caution

Several years ago I received a phone call from a very distressed fellow member regarding hisAtlas which had just seized it's pistons for the third time in a row since being rebuilt. In between the sobshe swore blind that the ignition and carburration were spot on.

Being curious as to the cause and knowing that cheap 750 pistons were on the market, at the time,I droveoff to his placeto see the damage.

Examination of the engine with just the head removedconfimed several key points. The ignition was spot on despite the use of Hepolite Commando 8.9 to 1 pistons in this motor. The Twin Carb set up had the correct jets and no obvious leaks in the manifolds. The plug colours were the right shade. Everything looked good................

..............then I noticed the paint on thebarrels. It was so thick on each fin that you could not squeeze a pencil between them. A mate had done him an Expoxy 2 Packfavour which included the Engine Plates, Fork yokes and Barrels. Despite being Black, the paint was actually acting as an insulation barrier and once the engine got hot it thencaused big grief to the pistons.

Always make sure that you use the correct paint for the job in hand.

 


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