Can't say I've ever seen a engine primer. I've never used a primer, nor have I ever been able to detect one ever being used when taking the paint off a motor.
Now that don't mean there ain't one out there, but I don't see the need for one and I've painted a bunch of motors.
The high points are what is hard to get coverage on so when you spray it don't try to get coverage all at once. Give it the first coat, wait till it almost dries and hit it again. A third might be necessary but stay away from build up, thickness, as heat has a habit of cracking the paint if it's thick.
Dan
