Valve to Piston Clearance Webinar

I'm sorry, was bit late in asking my question

When we start to aim to extract every last hp from the build. At some point there is always a possibility that piston and valve may have contact. It may happen during wide open throttle or at high rpm. Is there any means of knowing if we have valve and piston contact so that we can abort the run. Once we have contact at those conditions its difficult to notice and most times it will have bad ending. Any tips to know contact??

OK, what you seem to be describing is uncontrolled valve operation - bounce or float. This usually due to over-reving and/or incorrect valve spring selection for the application and/or some other valvetrain weakness. You NEED to address this, urgently, if it's even suspected! It shouldn't be a result of 'power' as such, unless an exhaust fails from excessive EGT.

If you're lucky, very lucky, the contact will be very light, with maybe a slight shiny contact area on the piston and valve.

If you're a bit less lucky, you may notice a slight noise and lack of power with the engine running rough at idle. Low compressions and pulling the head will confirm this.

If you're slightly lucky, you'll just have spat out a clearance shim.

If you're really unlucky, there will be a lot of noise and the engine will stop. This is usually down to one of two things - the piston has broken the head off the valve and it's been getting smashed around inside the chamber, or it's popped the retainers/collets/lockes and the whole valve has dropped into the cylinder with similar results.

What you MUST do, when making camshaft changes, is establish exactly what the static valve to piston clearance is, and take corrective actions as required to ensure that clearance is there - the nearest contact points may be a little before, or after TDC, so be sure to check around TDC, not just at TDC. Some companies offer 'mild', or 'fast road', camshafts that are supposed to be straight swaps, but they should still be chaecked, if possible, as if the timing is a little out, or the head and/or block has been significantly machined, the clearances will be reduced.

You MUST also use the valve springs, and other components, needed for the camshaft and rpm range you're using. Don't forget to check the actual installed spring lengths, too - if the seats have been machined it will increase the installed height and so reduce the forces holding the valve closed (a problem with high boost), and holding the valve train components in contact with the camshaft lobes which will increase the chances of valve bounce or float in marginal cases.

Oh, some idiots - I'm sure you're a better driver than that - will over-rev' engines on downshifts, for engine braking, which is just as bad as over-reving under power and, worse, there's no way a limiter can prevent it.

So, check clearances on initial build, select the correct components, make sure they're correctly installed, don't over-rev' the engine.

I might have missed something, but if so I expect others will pick up on it and advise you.

Very well explained thank you.

Downshift for engine breaking was epic. I have seen a few of them doing that. Lmao.

Appreciated