Valve guides fail more than once?

You might be able to remove your valve covers and determine which material was installed? You would hope that the updated guides were installed but you never know. If the old style guides were installed, then they could absolutely fail again.

 

So the next key question to ask is - who perfomed the replacement - a dealer or an independent or an owner?
The dealer would have installed the updated ones - it is safe to assume.
as for the other options, who knows.

 

Very interesting...if you have the old guides that failed, would you be interested in sending me one for analysis? I've done some work on the brass guides but haven't seen a steel one yet. Send me a PM -

 

How is this a known fact? Source?

I have not seen a mid 98 through 99 to ever have a OE brass guide installed.

MTM,

One would assume the dealers would use the steel but that too is not always the case. Some have used the aftermarket brass guides that are offered around.

 

Lots of hearsay Dave. Owners on here should take things with a grain of salt.

 

A while back I came across a thread here where someone claimed to have replaced valve guides in a Fiorano 355. I'll see if I can find the thread.

 

Just because they replaced the guides does not mean they were brass.

 

I'm currently having my heads upgraded with cast iron valve guides, 360 valve seats and new exhaust valves at Ferrari of Fort Lauderdale. I hope I never have to remove the heads again! Good documentation is key for resale as well (although my 355 will never be for sale )

 

It was owned by Steve from DC. User SGMDCFD.

I believe the guides were bronze, from the factory.

 

First of all the correct word is Bronze not Brass.

There are at least a dozen Bronze materials suitable for vavle guide activities and some are more appropriate for 348 RPM levels while others are more appropriate for 355 RPM levels. You are not going to be able to tell from seeing a Bronze guide in the heads what metalurgy it has--and it is the metalurgy that is improtant in the "worry quotient".

Yes, the Ferrari Bronze metalurgy is (as has been shown) to be completley unworthy of the F355 RPM range capability.

Yes, Ferrari changed to sintered steel.

No, sintered steel is not always better than the appropriate Bronze material.

Yes, you can find Bronze guides made of appropriate metalurgy when doing a head rebuild. (And for a lot (LLLOOOTTT) less than the Ferrari sintered steel guides.)

{I just can't remember what the proper metalurgy to look for is.}

 

The (W)right formula used in a PM guide is so far superior to ANY bronze guide it is not even in the same universe.

 

Both contain copper. In terms of the metallurgical composition of the guides, it is telling that page B40 of the F355 Workshop Manual 1 refer to the guides as "copper alloy."

Is it possible they are closer to brass than bronze after all? We may never know.

 

UConn Jay did tests on various sample guides from a range of Ferrari engines I sent him years ago and did an excellent write up on the results.... we know what they are. What we dont know is the composition of the new steel guides and at the time they were hard enough to get my hands on that sending Jay one of those to cut up would have assured an owner not getting his heads back on.

Bruce stated it correctly, the new PM, sintered steel is incredible. For decades I machined my own guides out of 642 bronze both for the street and race engines, and never had a problem. I would no more consider doing that for a 355 than I would consider using playdo. A Cernobyl hot running engine with agressive cam lobes pushing a stem just over 5mm in diameter using rabbit pee fuel and turning near 5 digit RPM's..... that is a whole new game and using results from 20 years ago has little bearing on the conversation.

The risk to cost ratio of using the aftermarket bronze guides is too great for my personal tastes when labor is factored in. Simply stated, we think they will work fine over the long run but only time will tell. Ferrari engineers thought the original bronze guides would work but were proven wrong. They choose the sintered steel guides as a replacement and even changed the design of the guides. Little happens by accident at the factory, especially when there is egg on their faces.

Upside to all of this is folks have an option these days and can make their own choices as to what they use.... something that rarely happens in this market.

 

As Dave said we did some work on this a few years back, the topic is well addressed in an older thread. I've attached the summary of the results from the guides Dave sent me.

They are all copper alloys, the terms 'bronze' and 'brass' don't always strictly refer to certain alloys. The nice thing with copper alloys is they are relatively 'slippery' which is why they're often used as static or sliding bearings (which is what guides really are). The problem is they soften quickly with temperature. I reject the criticism that Ferrari used 'junk' guides in the 355 based on this analysis; rather, the material has the highest hardness of any I looked at (HV column on the far right). But the heat, small stem diameter (and thus less bearing surface) and high rpm's were simply too much.

Somebody will point out that it must have been a 'bad batch' because not every car fails guides. That's the normal failure mode of ANY component; not every one will fail, it's a statistical distribution.

The fix of moving to sintered steel gave them (I suspect) a significantly higher hardness and much better heat resistance. If anybody has a spare I'd like to add it to the list!
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