carburator nuts

[Chris Coios]

Hi Yale,

As I understand it, valve bounce or float is when engine speed is such that the valve spring can no longer keep up with the rate at which the cam is opening and closing the valve. The valve opening/closing becomes out of phase with the cam and the valve is floating off its seat - not healthy as the valve timing goes away and the valve can bounce off the pistons, depending on clearances. At the same time, the valve tappet clearance is also lost as the valve could remain open when the tappet relationship says valve closed. An extreme case could dislodge the cap as Pete describes, and I agree by this time the damage is likely done anyway.

I have just a few remarks to add to this. While the skirt length will keep the cap on the valve stem, Art's comment about the low mass of the cap is my point. The Admiral described it well - the cap, if it moves off the stem - which is likely due to its low mass- is going to float in the territory of the valve clearance. Sounds innocent enough, but that floating cap is going to repeatedly get hammered back down onto the valve stem on impact of the tappet screw and bounce off the stem again within the range of the tappet clearance. These caps were intended to sit on the stem under the relatively higher mass of a tappet cup which recieves the cam action. The tappet cup is held square to the valve, guided by it's bore, and the cap receives the load uniformly (across its top face) from the cup, which also keeps the cap from leaving the stem (unless you float the valves). In the case of the tappet screw acting directly on the cap, the cap receives a point load (and some side load) from the tappet and as Tom S. rightfully points out, hardness matters. Having said all this, the solution may in the end work fine, but sorry, I would not do take such an approach as "interim solution" to failure could be a short time - hope I'm proven wrong. Thanks Lee for the suggestion of the Toyota nuts, this would be great except that the Ferrari application is fine thread, 1.00 mm pitch not 1.25.

Chris

[tyang]

I have just a few remarks to add to this. While the skirt length will keep the cap on the valve stem, Art's comment about the low mass of the cap is my point. The Admiral described it well - the cap, if it moves off the stem - which is likely due to its low mass- is going to float in the territory of the valve clearance. Sounds innocent enough, but that floating cap is going to repeatedly get hammered back down onto the valve stem on impact of the tappet screw and bounce off the stem again within the range of the tappet clearance. These caps were intended to sit on the stem under the relatively higher mass of a tappet cup which recieves the cam action. The tappet cup is held square to the valve, guided by it's bore, and the cap receives the load uniformly (across its top face) from the cup, which also keeps the cap from leaving the stem (unless you float the valves). In the case of the tappet screw acting directly on the cap, the cap receives a point load (and some side load) from the tappet and as Tom S. rightfully points out, hardness matters. Having said all this, the solution may in the end work fine, but sorry, I would not do take such an approach as "interim solution" to failure could be a short time - hope I'm proven wrong. Thanks Lee for the suggestion of the Toyota nuts, this would be great except that the Ferrari application is fine thread, 1.00 mm pitch not 1.25.

Hi Chris,

Thanks for your description. I know what will happen when I ask Francois this question. He'll say he's never seen this happen but will agree it's an interim fix. Did he ever do this with the race cars he's work on when he was a team mechanic with NART? Absolutely not, but this is something he's done to get a car to work until the owner can decide what to do. I certainly wouldn't recommend reving this engine to 7K at every shift. Again, a close eye on the wear will let us know when the heads have to come off.

I appreciate this discussion, and the education. I can only distill this information and apply it to what works.

Tom

[Yale]

Damn, between me and Tom S it's getting very Ferrarichat in here.

Thanks Chris for the explanation. I was wondering how this was something that one could do after this comment "If you valve bounce and Alfa Romeo Nord engine..." which seemed to say one would have a choice in the matter.

[tyang]

Being the investigate reporter is very very harmful to others,
in addition showing how inexperienced you really are. (Opinion)
Please realize the reason I chose not to host the party this year is an association thing.
I can not be painted with that brush. Reservation of the room is as easy as phone call for me. ANd NO you can not have the breakfast room (already been discussed with management), you pay no dues to the club, and DO NOT STAY AT THAT HOTEL.
( What does the club or hotel have to gain except liability for more guest drinking wine and beer.)


You may be helping entertain, but are doing very little for
- the clients cars you are working on,
- mechanics you are working FOR, and
- yourself

Sit back and reflect, I do not requie or want a response.

This is meant to be constructive.

Wow, Tom. Something must be up with you!

The website began 10 years ago with the idea that I knew very little about Vintage Ferraris, and was willing to roll up my sleeves and learn something. During that time, I hope we have all learned something. I certainly do not claim to know everything today, and am always open to constructive criticism and advice.

That said, Tom S. I'm sorry you feel differently. I, along with the most of this crowd, have always enjoyed your banter, but if you don't want to associate with us, I'm at a loss. I hope we can remain friends despite your professional feelings.


Sincerely,

Tom Yang

[330Jim]

Wow a lot of fuss about this topic. Tom Yang is using the lash caps for the purpose they were designed for. Lash caps are sometimes used in racing on titanium valves to provide a hardened surface for the rocker arms to actuate against. This is done because the titanium is too soft to run the rocker arm on directly. For mass produced Ti valves they can put hardened inserts in them, but in custom applications it is common to use lash caps. In Tom’s case where the hardened valve tip is no longer functional the lash cap is an acceptable repair. These caps are regularly used in racing so I would not limit the operating range of the engine just because these caps were on the valves. A couple of notes of caution though, I would make sure the lash caps fit the valve stem correctly. I would also check to insure the caps are not contacting the keepers or retainers.

David Vizard is an author and an engineer that has written many books on engine performance. He discusses using lash caps on page 125 of his book “How to Build and Modify Chevrolet Small Block Cams and Valvetrains”. This discussion is primarily about using them on Ti valves but he also suggests using them if longer valve is required to get the correct rocker arm geometry.

Cheers Jim

[Art S.]

Wow this got rather ugly.

Jim,

I think this is the reference you were talking about:

http://books.google.com/books?id=mm8oM7 ... #PPA109,M1

Regards,

Art S.

[Rudy van Daalen Wetters]

My own two cents...I just could not handle an interim fix
on any of my cars. With my luck, the interim fix will cost
me much more later after the interim honeymoon period
is over. Besides, it isn't correct to begin with!

Rudy van Daalen Wetters
1963 GTE s/n 4001
1966 330 GT s/n 8705

[PSk]

Peace it seems is impossible on this planet ... Beam me up Scotty.

One must also remember that he valve and the rocker follow each other. The only time there is actually a gap is when the valve is closed and for a very short period of time the rocker no longer pushes on the valve stem.
Pete

[330Jim]

Hi Art,

That is actually a different book, but it is part of the same series and the text in it is virtually identical to what I was quoting. In my opinion they are some of the best books available for understanding engines.

Rudy,

I can understand your reluctance. When a valve manufacture first recommended them to me for use on a custom valve I was considering, I was skeptical. After looking into them, I now consider them a viable alternative to the more traditional hardened valve tip. Personally I think either route is acceptable.

Cheers Jim

[PSk]

I think we have gone the full circle and using lash caps may actually be superior to the original Ferrari design.
[quote=http://store.summitracing.com/egnsearch ... toview=sku]COMP Cams Valve Lash Caps
Protect your valves' stems.

In today's higher rpm engines, the tip of the valve stem is subjected to a tremendous pounding. The best solution to this problem is COMP Cams' lash caps. These hardened lash caps are precision-machined and ground perfectly flat, to maintain accurate valvetrain adjustment.[/quote]

I must admit that I find all this stuff on the internet fantastically interesting, and I do share my cars restoration on the AlfaBB site, but for businesses there is always going to be people who question this and that ... in the end I think we have proven that this modification in no way harms the car or anybodies reputation, etc.
Pete

[250GT]

Hello,
The most importend things about the carb nuts has not been discussed
I am not interested in the colours or orther trivial things
You can do a lot wrong by simply putting the carbs back on the manifolds
First, always place a ring/washer under the nut ,to spread the force more over the basis
I cannot see this on the fisrt foto with the yellow nut( red arrows)
Second NEVER overthighten these nuts !
When you first start the engine The spacer will turn his colour from lightbrown to dark braun.
This comes because it sucks it self full of fuel it will feel wet this is OK.
This procedure DRY/WET will always repeat it self ,when the car dont run often.
Most owner always start there engines with open hoods to check if everything is OK
Then they see a drop of fuel commimg out between manfold and carb basis.
So the do REthighten the nuts again. this sound logic but this is a big MISTAKE
Simpy wait .it will stop from it self, after some time.
by rethightning the pressure is mostly only on the corners , not in the midleof the car basis.
The 36 and 40 DCL-6 are made of very soft material.
By overthightning you will bent the flat basis.( hollow)
Than is later on the synchronising a lotto game.
You adjustingscrews dont react correct.
Because it sucks wrong air.
Inside plug boys must have these three dip trays. important: some little fuel comes always out

P.S A non dripping Ferrari is a not driving Ferrari.

Its only a hobby here
ciao
Cornelis

[tyang]

Hello,
The most importend things about the carb nuts has not been discussed
I am not interested in the colours or orther trivial things
You can do a lot wrong by simply putting the carbs back on the manifolds
First, always place a ring/washer under the nut ,to spread the force more over the basis
I cannot see this on the fisrt foto with the yellow nut( red arrows)
Second NEVER overthighten these nuts !
When you first start the engine The spacer will turn his colour from lightbrown to dark braun.
This comes because it sucks it self full of fuel it will feel wet this is OK.
This procedure DRY/WET will always repeat it self ,when the car dont run often.
Most owner always start there engines with open hoods to check if everything is OK
Then they see a drop of fuel commimg out between manfold and carb basis.
So the do REthighten the nuts again. this sound logic but this is a big MISTAKE
Simpy wait .it will stop from it self, after some time.
by rethightning the pressure is mostly only on the corners , not in the midleof the car basis.
The 36 and 40 DCL-6 are made of very soft material.
By overthightning you will bent the flat basis.( hollow)
Than is later on the synchronising a lotto game.
You adjustingscrews dont react correct.
Because it sucks wrong air.
Inside plug boys must have these three dip trays. important: some little fuel comes always out

P.S A non dripping Ferrari is a not driving Ferrari.

Its only a hobby here
ciao
Cornelis

Hi Cornelis,

Yes, flat wave washer under the carb nuts.

Almost every carb I've taken off show some kind of warping. Some shops heat the carbs bodies up and straighten, while others sand the bases flat. The two bad designs on webers are due to the soft material used for the carb bodies; Warping base plates, and worn throttle shafts. Both of these issues suck air into the engine causing a lean mixture which makes precise carb tuning impossible.

Tom

[afwrench]

Note to Yale. Rudy posted with 3 sentences on Tuesday the 26th. Mike