BD16's and machining
 

Do you need to get the head machined to stop the spring coil binding due to the high lift of a BD16?

Thanks

You can not fit BD16's if you have standard valve springs as the springs will coil bind. You need to fit up-graded valve springs and these normally require that the base (where the spring seats) be machined further down into the head to allow for the increased length of the up-graded valve springs :D

what he said :D

I just did some research on this, cause I got a bit nervous about mine. I fitted BD16+ inlet and a BD14 exhaust this summer (from new profiles). Since it has a wider basecircle and higher lift i decided to lower my springseats 2mm:s. I also installed pipers doublesprings. Now I never checked initial spring pressure and that was what was worrying me.

However did some research this night.
The springs I installed is supposed to have a 34mm install height.
Carefully reading thru the Cosworth manual I found that the original springs is supposed to have a 32mm height.

So for some unexplainable reason my 2mm:s was spot on, and I'm very glad.


Another thing I think you should pay attention to is the valvesteams on the exhaustvalves. The exh. valves is thicker than the inlet valves. but not for the full lenght of the valve (the retainers and colliers(?) is the same, and therefore the tip/dick of the exh. valve has the same dia. as the inlet valves.
Well so........when installing my BD14 exhaust camshaft I had concerns that the valve opening would push the valve so far down, that the valvesteam would be mating with the valves thinner part.

With the BD14 cam I had ca 1mm clearance, but BD16 has over 1mm more lift and would mean that the valvesteam no longer is tight on the valve, hence a lot of exhaust would be getting into the valvetrainarea and causing high "crankpressures".

I dont know how to get around this. Maybe by machining the valveguides?




Sorry for my dizzy explaination, english isnt my native language.
And I should probably add, that i am no Pro, it's just my thoughts.

Kind regards Andreas