Piston to valve clearance

Hello,

Is not possible to make it somehow you don't need to fit and remove the cylinder head?

Thank you so much.

If you're using off the shelf relatively low compression pistons, cams are stock or mild, and cam phasing is not present or is very limited, then piston to valve contact is unlikely as long as mechanical timing is maintained, but if you really want to confirm clearance, fitting and removing the head as shown is the way.

Been a while, and might miss some points, so please correct it where needed - thanks, folks.

It depends on the engine, and what you're doing with it. Some engines are "non-interference", which means the valves are far enough away from the pistons that they can't ever hit, some are designed with very little clearance between the valves and the pistons at one, or more, points, and some have a reasonable amount of clearance that allows longer duration and/or higher lift camshafts to be fitted safely - with some clearance for timing swings.

From the question I surmise you're either looking at fitting an after-market performance camshaft (or more), re-timing the one you've got, or both.

With OEM camshafts you're 99.9% safe a degree or two either way - provided the bloack and/or head haven't been substantially skimmed. With aftermarket camshafts they will usually have a guide, or comment, if P2V clearances need to be checked - most mild upgrades are fine, but...

The usual recommendation is to check during pre-assembly (AKA dummy build), when all the clearances are being checked, as it's easier and part of ANY build. However, there are sometimes good reasons for checking an assembled engine and there are ways of getting around stripping it down.

With some engines, you can fit the camshaft and use a DTI, or for an extremely budget build your fingers, to check you have clearance between the valve and piston. Before installing the camshaft and rest of the required valve train, turn the crankshaft BACK 45 degrees (not 100% sure about V10 or V12, but you should figure it out) from TDC on #1, this will ensure you should have clearance regardless of how the camshaft is oriented. Fit the camshaft(s), etc, and turn them gently to their timing marks (there are holding tools available for many engines, it makes it easier and prevents them turning later). Gently bring the crankshaft round until it's at TDC, STOP if any sudden tightness or contact is felt, because that means interference and the pistons will need to be machined. If you're lucky, aftermarket cam's usually have a "clearance at TDC" minimum value and, if so, you can use a DTI on the valve spring retainer and, by pushing down on the valve until contact is felt against the piston, you can directly read off the clearance. The minimum value specified is important and IS NOT the actual minimum recommended clearance, as due to the geometry of the piston't travel, and the valve lift profile, there may be less clearance a little before, or after TDC.

If you are considering adjusting the timing a little one way or the other, or there isn't a "TDC" clearance given, check by depressing the valves up to 10-15 degrees BTDC to same ATDC. Repeat with the timing adjustment ranges you're considering.

With OEM valve springs, especially with multi-valve engines, it's usually not to difficult to depress the valves by hand(or with a SOFT push-stick made out of something like nylon, that CANNOT mark the spring retainer or follower. However, with a higher performance engine the seat pressure (spring force) can be substantial, and by swapping over to special light springs (or just the inners on a dual/triple setup), it's much easier to depress the valves.