Spring retainer to stem seal clearance

[Chipwizard]

Having read conflicting values for maximum valve lift with stock components that varied between .380" and .415" I thought I'd section a damaged head and measure myself. I also cut a window into a cam follower so I could see, and measure, what clearance there is.

This is a Gen-II head, damaged when an intake valve head fell off as they do, so it was donated to the cause of experimentation.

[Chipwizard]

The little gap you can see is, give or take .022", so it looks like the .380" lift maximum is correct, for the Gen-II head at least.

[MJ Williams]

 
Picture is worth a thousand words!!

[Jay]

You gain a little over .030" with our retainers.  http://www.hayabusazone.com/springs.html

[Ghost-Geezer]

I'am at .395/395.  Clearances are a helluva lot bigger than .020.  That is tighter than a gnat's arse.  Twice that would seem to be a bit more conservative.

I've heard some guys run .050.  I might even have Jay's stuff in my bike.........I dunno. 

[proutyc]

Is it the same on the exhaust side?

thanks

[Ghost-Geezer]

Nope, about .010 more if I am not mistaken.

[Competition CNC]

Here's a few quick tips on this topic.

You can run .020" retainer to seal clearance. You can even run tighter than that if need be and it will not cause any harm to the seal as long as you have good valve springs.

 There are 3 ways to gain seal to retainer clearance and we use all 3 methods in different combinations depending on the application, and the springs etc.

You can heat the head to 300 deg F and press the guides down with a tool .030" to gain more clearance or you can use the APE Titanium retainers and gain another .030" or you can also use different valve seals and gain another .025" or so. The seals are Viton and are way better than the junk OEM valve seals that harden up and smoke over time.  Viton can take much higher temps like on a turbo or nitrous motor.  Every racing engine for the last 20 years uses Viton valve seals, from NASCAR to Top Fuel and everything in between. They last forever if you don't damage them taking them on and off during freshen-ups. And they are half the price of OEM seals so many guys want us to replace them every time anyway.

One thing to note, if you lower the valve guides you have to do a valve job.  The guides will no longer be concentric to the valve seats.  And be careful lowering the guides they are made of iron and will crack if not done properly. Any questions just give us a call. We have the seals in stock.