Ferrari makes engine head with non-aligned bore holes

First of all, welcome to FChat.

Secondly, sorry about your belt breakage. I and a few others here have been trying to get a real world sense of when and why the belts break. Could you provide more info about your incident: age and mileage of belt, circumstances under which it broke, how the car has been driven and maintained over the life of this belt, etc?

As to the issue with the guides, that’s a very strange indeed. They seem to be saying that the bores in the head that hold the guides were not machined perfectly perpendicularly to the valve seats. I’ve seen seats that were not concentric with the guides but I don’t recall seeing what they’re describing. Are they certain that the head was not distorted when the valves bent?

If the problem is indeed that the bores in the head for the valve guides were drilled at the wrong angle, and assuming that the seats seem to be installed correctly, I can think of a couple of potential solutions. One would be to have “blank”, unbored guides made to the correct spec (SBI in CA ought to be able to help you there), install those (which may prove to be a bit of a trick since guide drivers have mandrels that fit inside the bore of the guide), and then bore them in situ by indexing off of the valve seats. The downside there is that this time consuming boring process would have to be repeated any time the guides need changing (which should not be often). The upside is that you get as many chances as you want/need to do the job correctly and the original guide thickness is maintained, so you don’t have to worry about cutting into cooling jackets and heat transfer should be roughly the same as the original design. That’s likely what the factory did, based on the quoted description of the problem. Note that sourcing guides with holes already offset or angled would not be an option because there would be no way to index them properly during installation.

Another option would be to remove the guides and correct their bores by indexing off of the valve seats and then drilling the guide bores in the head oversized. You’d then have custom guides made to fit the new, larger bores. The upside there is that the guides would be easier to install and if they ever needed replacement it’d be simple enough to have new custom guides made. The downside is that you screw up the head if you goof the cut badly and there may be space considerations, although presumably the angle is not so far off that it would require that much bigger of a bore to get the guides aligned properly.

A more expedient solution would be to install new valve seats and cut them based on the existing valve guide angles, but that strikes me as a poor choice because it would not correct the relationship of the valve tip to the lifter bucket.

Considering the expense and risks involved in correcting this problem it may well be better to just source a used head or heads (check eBay and negotiate, negotiate, negotiate!). Incidentally, are all of the guides on both heads the same or is it only one row of guides on one head?

Best of luck and please follow up as you learn more. This is a new one on me… at least as far as my poor memory can recall.

 

Welcome to the forum mate.

A Ferrari engine with the bores not machined correctly from the factory??? I find this very hard to believe.

I have never heard of this before and why didn't this problem happen 20 years ago??

After all, this engine is 20+ years old now so this would have happened in the past.

A little more information in regards to the car would be much appreciated thanks mate.

I will take a little guess here and say your 348 just had a major service from this dealer, they messed it up and now the cam belt has broken causing major damage to the engine.

And now the mechanic has made a ridiculous claim like this to try and cover his ass!

This claim from the mechanic reminds a little of this mechanic's claims in another thread with a 348 cam belt failure.

 

Sounds to me like the valve seats have not been installed correctly. Maybe some swarf under one side.
Pete

 

I'd bet the original guide bores where concentric with the seat bores (within part print specifications) You need a machine shop that knows what they are doing. The guides need to come out and then they can inspect the guide bore with relationship to the seat. If stuff is screwed up, you might need new seats and full machining. I'm Pretty certain Ferrari used Comau machines and they are amazing for doing this work. We had a Comau line when I was at GM and it was some great equipment.

 

P M sent

 

It's not that uncommon to find machining oddities in the pre-1970 engines. I have a 60's Ferrari engine here with similar issues as well as slightly different valve angles, head to head. With that said, it is uncommon to see issues, as described, in more modern engines without external (self-induced) forces being involved.

With that said, ///Mike offers some viable solutions to the problem.

 

Seems like we're on the same page, David. How are you addressing the issue in the '60's engine you mentioned?

 

Tech installed the valve guides improperly.

 

Let me be direct. BS! Seats are ground with a tool/machine that is aligned with the axis of the guide bore so that the seat is perpendicular to the axis of guide bore and the valves seals correctly. I agree with Dave Rocks. Someone didn't know what they were doing.

 

Like this:
Image Unavailable, Please Login

 

According to his similar post in the 355 section, the guides have not been replaced.

 

Correct, John. Even before the guides or seats are pressed in the head, the guide and seat bores are done from the same side and typically with the same stepped (combination) tool that cuts both at the same time.
Image Unavailable, Please Login

 

Agreed^^. Something strange going on here.

 

Agreed. An authorized dealer skipped the timing belt service because the belt looked fine? Doesn't make sense.

 

Dont believe it, how on earth could you fit off centre guides in the original head, you would never get them in the right place so the valve sat correctly on the seat. Assuming you suspect the guides you need to take 1 out and turn a bar on a lathe which just fits, then clock the outer diameter to see if it runs off centre. These guides would have been chilled and pressed in. Why not fit a new set of guides that run true, then replace the valve seats and cut in situ to suit the new valves- you will get in right trouble trying to adjust the guides to the valves.
When the head was originally made they would have used the same centre to machine the head for the valve guides and the seats so this idea of off set does not ring true with me.

 

I'm smelling some dealer-generated, unadulterated Bull**** here.

Mike

 

Also, after market parts? Not at a Ferrari dealer that I have dealt with. They only use OEM parts.

 

Anybody getting the idea of waffle from the workshop here. It will be interesting to see how they fix this one, tubes of silicon next !!!

 

And Duct tape!

 

So, he can show you the original "factory offset guides" he removed so that you can see for yourself?

If they know what they are doing....the sequence is to install the guides and then machine/replace the seats.

I have seen improperly machined replacement guides. I'm curious if all the valves have the seating problem or only a few.

 

The only way you would have off set in the guides would be if they were oval with wear. I think i would be going for a set of new guides, then see how true the guides were to the seats. You can get those air driven seat cutters which use a centering pin fitted in the valve guide. We used them in big marine diesels but we used to cut the seat with 0.7 degree extra angle so the valve only touched at the top- you run the engine on light load for a short time and the valve makes it own seal.

 

That tooling is beautiful!!!