I was just on another forum reading about the valve guide issues with 355s (been there done that) and was surprised to read that it's common to the 456 as well. i wonder why i've never heard that before (even though it sort of makes sense)
i was also surprised to read that the problem with the 355 headers also applies to the 456 AND 550!!
thank god i never have to worry about either of those two issues with my car again and i can sleep at nights.
"Ah the valve guide discussion...I just can't resist offering my theory. I've personally analyzed valve guides from many Ferrari models, checking actual chemistry as well as hardness. The guides used in early model 355's were as good as anything used by Ferrari up to that date (all various copper base alloys / bronzes). However the 355 proved a unique challenge - the tiny valve stem (6mm I believe) has much less bearing surface and can 'cut' through guides easier than a larger valve stem. This is combined with the 355 heat issue...i.e. it likes to create lots of heat! So the higher temp makes the guide a bit softer than engineers hoped and the narrow guide is more aggressive.
It's not surprising that this issue hasn't affected all cars. That's how pretty much all mechanical / material issues progress. For example from a batch of poorly shot peened valve springs, not every one will fail. Same here...maybe some cars don't get as hot (due to driving style or other variable), or maybe you need many cycles above 8k rpm to really induce a guide failure.
Unfortunately the issue wasn't caught in development (again not uncommon), it took many cars accumulating miles to really reveal the problem. So they upgraded the guide materials to a still higher hardness iron based composition (I still haven't gotten my hands on one of these to analyze yet...send me a PM if anyone has a spare!).
Feel free to disagree, this is a hotly debated issue with many opinions. This is just the conclusion I've reached. "
I believe it was the outsourced suppliers which is ALWAYS Ferrari's problem. Luigi is the cousin of so and so and there it goes.
Ferrari does great engine design and such, but seem at times to either fill their quality product with 2nd hand sourced products from the local shops or just don't go the extra mile.
Look at the 'problem' of the 348 transmission getting trashed on some models. Best that can be determined was not a bad design, but a change in the manner in which they were put together.
The VALVE guide issue is also found on the 456 GT, and like the OP< I am just waiting for the day to rebuild the entire engine
The replacement guides are better than OEM and should not be an issue.
ON THE 355: Remember to include a paragraph on the exhaust manifolds!!!!
and -- that same manifold problem exists on the 456 and now the 550 series as we are finding: Ask me how I know "
I love my car. Buy your own