I'm rebuilding an M40 and would like to get the color as close to original as possible. I assume it's a red oxide primer, but I wanted to get some input from someone with more experience.

I just painted mine Volvo red when I rebuilt it.

I use easily available Ford engine red for the motors -- maybe a bit brighter than B18/20. The M40 is a more a muted red than the motor - but then I've never seen one brand new. - Dave

I'm thinking of using red oxide primer.

https://www.amazon.com/Rust-Oleum-7569838-Professional-Primer-Spray/dp/B000ZYUY5M/ref=sr_1_2?dchild=1&keywords=red+oxide+primer&qid=1593543022&sr=8-2

I went to the link. If you are looking for - close to original - that's not it, way too brown. The only M40 I have right now is deep on a shelf in a dark corner --and covered in black schmootz but it's color is visible in spots. The red is somewhat like the color of the Hi-Temp Silicone sealant (Permatex) I have--the silicone itself--not the tube color. The color on the M40 is pretty much the same red as the motor but not as bright and it's a flat. - Dave

I know this an old thread but if anyone still cares, look inside the gearbox for a colour match, certainly mine was cleaner and not much chance of colour fade or oxidation.

Primers are good, but they are just 'primers', made for paint to stick on to. I suggest a red enamel paint which will hold up to chipping, salt, oil, grease, etc.

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Keeping it running is better than buying new