Valvetrain Rejuvenation: Reviving A 4-Valve Modular Valvetrain
Rebuilding a set of 25-year-old 4-Valve Cobra heads is a lot easier than we thought, thanks to all-new valvetrain parts from Melling.
Here is a great article recently posted about reviving Lincoln B series modular heads. Lincolns were the 1st to get 4v modulars and their are still a plethora of 4v modular heads available in the junkyards.
The editor of article did a great job portraying most of the technical aspects needed when rebuilding the modular head, but one thing not mentioned that is 100% critical to anyone inspired to perform a rebuild with old lincoln heads.....is the valve guides are under cut a smaller diameter at the area for valve seals. Meaning specific lincoln valve seals are needed for this smaller diameter. I believe this was done due to available carry over parts already made from a different engine, meaning they made the heads work with available parts from a catalog. And Last time i checked felpro was discontinuing these particular seals and iirc that was a few years ago. When looking up the seals for pre97 lincoln heads i find a general seal issued for all 4v B series heads that are listed for cobra and lincoln all years. The cobra valve guides are like all other modular valve guides, 2v and all 4v after 97, the same overall diameter throughout the length. Shoving a seal ment for a bigger diameter over a small diameter will allow oil passage and the seal will not remain still it will rotate along with the spring.
Long story short, if you so feel inclined to rebuild a set of lincoln 4v heads, simply remove the valve components and the valve seal to get a good look at the valve guide. Youll notice the under cut. The solution is find a different set of heads or get the valve guides replaced.
