Hello, at idle my 455 '70 runs real smooth but with throtlle there's a mechanic rattle near the valves. I removed the tumblers and found out that I can push the valves by hand. Are the valvesprings old and tired???

 

Wow! If you can depress your valves without any mechanical leverage that is not good. The sound could easily be valve float. The valves are unable to close before the cam lobe comes back around and slaps everything in the valve train. I'm not doubting you, just amazed, you can really depress the valve by hand? How by hand? Yes, your springs are more than tired. They are almost non-existent. Fix that and then see if you still have a rattle. Good luck. You may already have flattened spots on the lobes of the cam, mushroomed pushrods and valves and some ugly lifters.

 

As I wrote I removed the tumblers so there is no futher pressure on the springs, then with my 2 tumbs I push hard on the spring and depress the valve. However I also have a head of a chevy engine and I checked the springs with the same procedure, I can depress them too.
The problem is valve float and it only drove with it for 1 or 2 miles.
I checked pushrods and they are like new. I bought this engine a month ago.
The previous owner had had it rebuilded and almost everything is new in the engine. But for some reason his crankshaft bearings brokedown. I renewed the crankshaft and installed new bearings. I also cleaned all oil passages and checked the working of the oilpump.
So now I am thinking maybe a little dirt came between the lifters and they are stucked?????

 

I checked the lifters and they are clean and in good shape.
So it must be the springs that are worn.
Does anyone know which valve springs I need to buy and what they costs?

Merry Christmas and Happy New Year from the Netherlands.