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Discussion and questions related to the course How to Degree a Cam
Hi, so just want to clarify whe measuring piston to valve clearance do you do this with out the head gasket then add the thickness so your not torquing down a new head gasket and then taking the head off again to check and remove the plado?
My opinions - might be wrong, as it's been a while, so bear that in mind.
You use a head gasket*, the same installed thickness as the one to be used. Because there's a slight 'set' in most gaskets after some heat cycles, some like to use an old, good condition, gasket for accuracy if running tight clearances. Otherwise you will need to use a new one - the better suppliers will give a nominal installed thickness, which you should be able to get close enough for 99.9% of builds - and if all the surfaces are clean and wire/fire rings, etc aren't used, and fasteners are only lightly torqued, you should be able to use them later for the full build. If there's any doubt, use a new one for checking clearances, then put it aside for further checks and use a new one for the final build.
Something to note, though, is that if your engine uses TTY (torque to yield), AKA 'stretch', bolts where you fully tighten them with an angle or two after initial torque, you will need to discard them as even though they haven't actually been used in a running engine they've been stretched. For almost all instances, using the old ones and taking them down to the initial torque figure (no angle) will suffice for checking.
*without the gasket you can have problems with piston to head interference if running a zero or negative deck height, you're removing some of the initial clearance you need to check and so increasing the chance of contact, and due to the geometry the change in clearance isn't at the same rate as the difference in head height without the gasket.