Hi everybody.... This is NOT my normal type of car-I'm principally an Italian racing car guy...that said, my level of normal precision is to a ten thousandth, or better, as might be required... I have been "drafted" into doing a cylinder head overhaul on a 2010 Prius... Interesting wear profiles, these cars have, and extremely consistent throughout the model range for 1800 CC engines. The faults/causes are pretty clear to me, but that's another story for another day... What I require, and can fine NO WHERE in either print, or the internet(Toyota dealers have laughed as they say they just don't do this sort of work, as the cost to "do it properly" is so high that: most people have it done by independents, DIY-ers, or they just trade it in or sell the car.. I fix blocks with holes in them , so that's not going to cut it here.... What I REQUIRE/am seeking is: the specification for: valve stem installed tip height. Once you replace valves, or bump grind them and or the seats, the valve stem "rises", and must be machined to this spec, in order that the hydraulic compensating element does NOT hold the valve open and burn the valve, or its seat... A specification, or a link to a spec sheet-I'd like to know where the number comes from....would also be requested as verification is rather important in my world(measure five times, and cut ONCE). Nobody wants to do a job like this again due to an error in measurement/set-up... thanks for your help in advance!!! JCK
Here's all I've pulled out of the Repair Manual so far, regarding the cylinder head. The document "...Inspection and Repair" specifies max and min height for the valves, but says nothing about checking installed height. I wonder about the validity of: Is that right, that hydraulic adjuster require the valve stem installed height to be so precise?? That seems contradictory to the concept of the hydraulic adjustment, which I would think means it can accommodate a range of heights. I'm completely winging it btw, so feel free to correct me, lol.
Hi John, Somewhere in here a member rebuilt a 2010 from scratch due to a blown head gasket. If I remember correctly, he pretty much did the same thing you are doing. I don't think he had the details of what you need, but, his rebuilt was a success. Perhaps if you found his thread it would help. It should be under "blown head gasket repair"
Are you thinking second gen? Third Gen is hydraulic self-adjusting. The details are over my head; I should read up on it.
Thank you for these links FWIW: none of them has the specification I seek, which is odd, since they are so specific about valve face seating width, margin width etc The hydraulic elements DO use lash caps in valve tips but the thickness according to Toyota is a SINGLE size which means that they have a very limited range of distance by which they can compensate. The specs available are extremely specific and precise-within the areas I typically deal with(an order of magnitude smaller than what appears to the layman.... What this indicates to me is that they don’t intend for seats and valves to be ground to any degree greater than what’s called-in racing “overhauls” as: “bumping the seats and kissing the valve faces” This does not bode well as far as I am concerned. Thank you for your links and references Machineshop
There's a procedure for testing the lash adjusters. A person could probably use that procedure to measure how far the lash adjuster plungers are able to move. Some of that range of motion would need to be available to compensate for thermal expansion as the engine warms up. Somebody could probably do a back-of-the-envelope estimate of that by looking at some references for valve temperature in operation and coefficients of expansion. The range of motion that's left over could give an idea how much variation in installed height can be accommodated.
I would just setup a fixture to measure the height before and after machining and then skim off the difference. Or if you are using a modern seat cutter record the measurement when the cutter starts to touch the seat, then record the final depth and the difference is the amount I'd take off the valve stem. Just curious - How bad are the valves in the head and how many miles on it?
