Join Date: Dec 2007
Location: Coon Rapids, MN
Car Year: 2008
Car Model: Forester X Premium
In all honesty, Subaru has a history of playing mix and match from their lego bin of parts when these cars are being assembled. Which may or may not explain why your heads are short compared to the book spec. Would I assume the heads are original however, hell no. ALWAYS, ALWAYS error on the side of caution. A lot can happen in that 50K before you bought it, a lot that may not be in the service history.
For the side of caution I would assume that the previous owner had issues at some time and go with the assumption that the heads have already been milled before, maybe a lot OR maybe the heads were even replaced. In either case you can either do the math to see if the valves will hit the pistons witch may not be possible with out the proper measuring equipment.
Factory valve to piston clearance
- amount removed from head
+ amount cut from valve seats and valves
+/- any change in HG thickness
= you new theoretical valve to piston clearance(should be checked with clay(see below)
(you need a degree wheel and test indicator + transfer clay)
The other way is to set the head/s up with a set of "checker springs", basically substitute valve springs with a real light tension that will allow the valve to get pushed back into the head if needed. In doing this method you assemble the engine as normal using a old (crushed) HG along with a piece of transfer clay(witness clay) in the valve reliefs in the pistons and no rocker arms/cams... Put a dial/depth indicator on the valve stems. Slowly and gently turn the engine over to the point where the valves would be closest to the pistons(not always max valve lift(degree wheel and cam specs will tell you this location)) once at that spot manually open the valve to the max valve lift by referencing the indicator. This will make a witness mark in the clay that can then be used to tell you how much piston to valve clearance you have at that point in the cycle or you can just move the valve from max valve lift until it contacts the piston, referencing the indicator will then tell you the clearance you have. Add to the HG thickness as needed to get your desired valve/piston clearance.
If there is no clearance, again do some math, max valve lift minus the lift you had at the point of interference + the amount you want/require for valve to piston clearance + your crushed HG thickness = your new CRUSHED HG thickness.
I would not consider the above to be a step by step of how to do it. It is only an example of how to get the answer, there may be spots left out. For a OEM street engine with OEM cams/valve springs I would want no less then .020" valve to piston clearance.
The simple thing to do would be just get a set of thicker HG to make up for the amount that was milled off. You know the heads ran on the engine before being milled so they should have no issues if that material is added back into the equation.
.010" removed from milling
.005" extra removed to create the taper
.024" OEM HG
= .039"(.040") replacement HG
That would put you right back where you started.
Again as long as the surface is flat there should not be any issues, only possible one I see is if the timing belt wants to severely track back towards the engine.
Regardless of what happened at the machine shop(their mistakes) you are in the end responsible for the fit and function of the engine as it was your hands that put it together and as such falls on you to verify the clearances.
His - 08 X Prem 5mt
Hers - 08 X 4EAT