I am a bit stuck at the moment with my G10 head job. I have had a few problems with this as I broke a worn guide inside the head while taking it out but managed to replace it after cutting a thread all the way through the remaining part and screwing in a SS bolt, providing me with something to safely bang on. Installed 3 new exhaust guides OK.
Right now my exhaust valves seem sunk by 1.1 mm after the grind, as compared to the intake valves. I measured from the valve cover gasket surface to stem tips. I never noticed such a thing before. It is not the first time I have done a grind on this head so it could be that the seats are now sitting lower than when the head was new. Intakes seem ok. The seat area on the exhaust valves is 1.7 mm but the stem is closer to the cam now. Seat seals good with the cam off but the valves stick open if I install the cam and remain so even after waiting an hour to let the lifters bleed.
I disassembled the lifters, drained the oil, cleaned and reassembled. Measured the distance to the lifter tops again and the exhaust ones are still sitting higher in their bores than the intake ones (without the cam installed). However, they depress easily and the valves don't stick open now after cam install. It is all about what happens when they are pumped with oil during running. Someone mentioned a similar thing in this post (valves sticking open after lifter install) http://www.teamswift.net/viewtopic.php?f=5&t=21819&hilit=stem+height
Going thru this post, it still isn't very clear to me as superf1y mentions a 2-3mm preload (?!) in context of a smaller base and higher lift cam. That translates to a "greater" distance between base circle and stem tip which the lifter can then "fill
". Please correct me if I am wrong.
I am facing the reverse situation as the stem is closer to the cam by 1.1 mm so don't know if the mentioned post applies. I don't have a G10 manual but I do have a GTi shop manual which says something about grinding off the valve stem tip
provided that the distance between stem tip and throat (the cotter locking groove on the stem) doesn't get smaller than 3.6 mm. I don't know what that does to the hardened stem tip and I don't want to do that as I would be sacrificing lift even further. I also searched the G13 manual (I am assuming that valve heights are similar between the G10 & G13), but I was unable to find a valve stem height spec when installed.
So, does the 2-3mm preload mean that we have a window that the lifter's piston MUST be in with the valve(s) fully closed and the lifter can then make positive length adjustments for 0 lash.
In my case we have to add 1.1 mm to the original preload figure. If that was 1 mm or so then I should still be ok. But if it was 2 or 3 mm then the final preload would go well over the spec as given by superf1y. I have tried measuring the preload with the intake lifters which seems to be around 2mm. (uncertain here) How does one "accurately" measure lifter preload with a cam installed?
The big question is that, "Will the exhaust lifters be able to adjust and operate normally with this "shortened" distance?" or am I sure to see valve float? I am tempted to give it a try to see if it turns out ok but if it doesn't then it will cost me another head gasket and I will also have to lug the head to the machine shop for a valve seat replacement. Also, even if lifters are able to "adjust", will I be looking at hotter valves/higher exhaust back-pressure? I'd love to think that it won't be anything catastrophic. It is supposed to be a street car and won't be driven hard (regularly
A bit confused at the moment on unfamiliar grounds. Hydraulic lifters have always been a bit of a mystery for me. Would like to have your valuable input.