95 F355 Valve Guides.....Fact vs. Fiction !!!

You couldn't do it without at least taking some of it apart. Not sure if you can see the guides through the exhaust ports well enough to tell the material they're made of, but you'd at least have to take the muffler or bypass pipe off as well as have an articulating boroscope. If you don't have an articulating scope, you'd have to take a header off. You may be able to pop the valve covers off and see them from the top side, not sure. Does your car have an issue you're trying to diagnose? If not, I don't know why you'd want to open that pandora's box...

 

I did an early 98 355 a few years ago.

 

It is great to get information from the guys that have intimate knowledge on these cars. Thanks Brian, Rocco, and Tom, and Dave H. It helps set the record straight, fact from fiction.

 

Cant really see from the valve cover area but if I remembrer correctly with just a plenum off the intakes can be seen. Thats easier than an exhaust manifold. If dirt or discoloration prevents a good look at the color of the guide a magnet works quite well to differentiate.

 

The way Ferrari operates I would not be surprised. They don't throw things away. If they found another box of bronze guides laying around they were going to get used. But officially the change was mid 98.

 

Brian,

Let's go back to my original question. 95 355, 27k miles, good compression and leakdown. No excessive oil consumption. Is it unreasonable to expect the guides to be in acceptable shape? That they aren't going bad in another 1 or 2k miles? That there is no point in tearing down the engine to replace "good guides" regardless of what they are made of, just because?

 

If it was my car and I was planning on keeping it a long time and I was taking the motor out for a major service and it had original guides I would change them. But it costs me a lot less money than someone paying for the work to be done. If the car is not symptomatic that is a choice only you can decide the worth of.


I have done a lot of 355 valve jobs and have yet to sell one on a non symptomatic car but it seems a lot of shops and owners are not catching the symptoms. I also almost never attend an event with more than just a few 355's present that I don't hear at least one that has issues that evidently the owner and his mechanic seem oblivious to.

 

You missed my point

 

I'm going to change my suspenders when I change my belt

 

You could take your old belts and have suspenders made from them.

 

That could be a big problem if they break.

 

I avoided the whole issue and just bought a '99...I wanted the F1 anyway

I'm a materials engineer in the auto industry, I deal with component failures, warranty and recall almost daily. I'll just add that it's the nature of fatigue in a complex system like this that not every one will fail. There's many inputs that contribute to guides failing as already mentioned, rpm, heat, carbon build up, maybe variations in the fit between the guide and valve stem, etc. It's totally normal that seemingly identical guides would have a 20% failure rate. Changing to ferrous guides improved wear and brought the failure rate to 0.

 

The bronze guides have been found in 99 model years as well, although not as prevelant.

 

They can be seen through the exhaust ports.

 

I was suggesting a less invasite way such as thru the spark plug ports and using a bore scope.

 

No way you could see them through the spark plug port unless you had a borescope that could do a 180 turn in less than an inch and is able to fit past an open valve...Sounds like removing intake is the least invasive way to have a look at them.

 

Great post!!!

 

So here's one for all those who know more than I do:

Would removing the headers and cats relatively early in its mileage life perhaps be a way to "save" the so-called bad valves?

Assuming one switches to a non-shielded header which lets out more heat instead of trapping it in that sensitive area of the engine as well as removing the cats which can be an obstacle to heat flowing out.

toughts???

 

I suspect the guide wear is 100% related to the number of cycles and the guide material - I don't think the headers have anything to do with this issue Fab.

 

But just applying the physics, if a valve is cycling in very hot temperature, wouldn't it be weaker and more prone to fail than a valve cycling in a cooler temp?

 

In my engineering experience I've not dealt with wear based on temperature. My applications have been based on material under normal temperatures but I would suspect that if the material was getting so hot to make it soft than it could be an issue.

I'm not the best one to answer this question Fab.

 

The exhaust temp of the gassses leaving the motor are around 1500F. Probably a little higher in some circumstances. The cats are not causing that. The headers are insulated to try and maintain that heat to the cats. The gas heat in the header is already cooler than the heat at the valve.

It is called horsepower production. HP=heat.

 

Remember it's the guide, not the valve. Heat absolutely contributes to wear, especially a copper base alloy! That's why changing to ferrous which is more heat resistant helped. Another reason the wear was so bad in the 355 was the ultra narrow valve stems, with 5 tiny little valves per cylinder. The extreme analogy is like a wire cutting through clay.

 

All true.

The guide is actually used as a method to transfer heat from the valve to keep it below failure temp. One of the reasons for the high copper bronze. It's a very good heat transfer agent. It's also soft and the hotter it gets, the softer it is.

 

So, in your opinions, changing out the headers and removing the cats has no bearing at all on the lifespan of the valve guides and the chances of failure?