Hi folks, I thought I'd share this little gem on info with you guys

I've been stripping down a cylinder head today from a polo, it's the same roller rocker type as used on the 1.4 16v engines in the fabia, I noticed something quite odd with a couple of the valve seats which is worth a look

a few of the valve seats on the exhaust side appear to have been formed wrongly or have been incorrectly machined.. ( sorry the pic is dark I will fix this later, looked ok on the laptop but looks cack on the iPad) one side of the valve seat is much wider than the other where the valve face makes contact with it, this makes the inner throat of the seat too wide which prevents the valve from fully sealing properly. it's kind of like it has been ground incorrectly.. Oddly enough in the back of my mind i do recall seeing this exact same thing happen on another cylinder head of the same type years ago when I worked for a engine reconditioning specialist.. It is of my learned opinion that this example has been like this since it left the factory, also it could potentially be a contributory factor in the early piston ring failures that these engine suffer from..

Exhaust valve with burnt out edge, this is the effect of the improperly seated valve, a small portion of the exhaust gas is constantly passing the valve which leads to it getting very hot, if the valve gets this hot then the piston rings on the affected cylinders would also see some heat as well which would accelerate their wear rates

At first I thought it would be related to the valve guide being inserted into the head casting slightly off true, the machine that cuts the valve seats uses a mandrel in the valve guide to centre the cutting head, but I've discounted this theory because the top cut ( the 30 degree angle on top) is dead true to the valve guide and is completely concentric and even all the way round.. Very strange indeed. It looks as if they were just poorly machined at the factory, I'm surprised it passed quality control like this, I bet this engine has had low compression since day one!

Word out folks

Interesting.

The only cylinder head issue I have come across before is when the valve guides were made incorrectly so there is to much lateral movement in the valve stem causing the seat to wear oval and drop compression and/or burn the valve out.