carburator nuts

[Chris Coios]

Tom,

I am reasonably certain that the original nuts securing the carbs to the manifolds are a special size, 12 mm across the flats, not 13 mm or 14 mm. I believe this is due to the tight space from the stud to the carb body for a wrench. The 12 mm wrench size is not a standard, and one would have to find some or have them made. The finish is black oxide. Typical for 250, 275 and I would I expect 330 also. Question on the caps you installed on the valve tips - are you not concerned about the caps becoming dislodged and bouncing off the stem? This type of shim cap is like that of an Alfa, but in that case, the shim cap is contained by the much larger tappet cup on top.

Chris

[Jimmyr]

Chris, yes the carb M8 nuts are 12MM on the flats, this is as you said becauce of the tight clearance. The 8MM wrench is a standard wrench size, Sears sells them. On the early 275 4 cam the "caps" that are used to set the lash are held down by the large cup that the cam pushes on, and do not come loose under normal conditions. In the later 4 cam engines this has been changed to the shim on top of the cup, and they too are well captivated, and easier to set the lash. Jim

[tyang]

Tom,

I am reasonably certain that the original nuts securing the carbs to the manifolds are a special size, 12 mm across the flats, not 13 mm or 14 mm. I believe this is due to the tight space from the stud to the carb body for a wrench. The 12 mm wrench size is not a standard, and one would have to find some or have them made. The finish is black oxide. Typical for 250, 275 and I would I expect 330 also. Question on the caps you installed on the valve tips - are you not concerned about the caps becoming dislodged and bouncing off the stem? This type of shim cap is like that of an Alfa, but in that case, the shim cap is contained by the much larger tappet cup on top.

Chris

Hi Chris,

You are right. I meant 12 mm and I installed 13s.

Tom

[Chris Coios]

Thanks Jim, Tom, Sorry I was not clear in that I meant the M8 x 1.0 nut itself is not readily available in the special size (12 mm across), not the wrench. I can see how the lash arrangement on an early 4-cam is similar to an Alfa and the cap will stay put. In Tom's 2-cam rocker arm application, there is nothing holding the cap on the valve stem other than perhaps friction or interference fit. Would not the action of the valve adjusting screw striking the cap perhaps cause it to bounce off the stem, especially at some phase of RPM that might be conducive? Chris

[Art S.]

Tom S. & Chris,

I agree that this a patch but, I'm not sure why it would come apart. Are you both suggesting that valve float is so bad on these motors that the caps would have a chance to come off? Unless you spin the motor up to 10K, I doubt there will be a problem (assuming the caps were properly installed).

I think it is far more interesting that this motor and my motor were previously done by the same shop!

Regards,

Art S.

[tyang]

Chris I fully agree, not the proper way 100% Absolutely

Another bandaid
I certainly would never advertise I was doing is type of repair.
(Customer would be asked to go somewhere else for this style of work)

But you are missing th point Chris:

The owner SAVED money

At least until the engine

a) falls apart or
b) implodes from this and other short cuts taken during it's life

Oh well, on the bright side:

1) permanent employment for the A list engine builders or
2) another parts car someday!

Tom,

I'm working with a gentleman that has built hundreds of engines, and has never seen a failure from this type of repair. Provided the proper precautions were used, have you seen a failure? We found the same modification on a PF coupe that had them installed back in the 60s without any signs of a problem. Band aid repair? Perhaps. But a pragmatic approach towards keeping a car on the road without immediately telling the owner he needs an engine rebuild. If that's the way you get guys to sell you their cars, to each it's own.

Tom

[tyang]

Hi Tom,

I agree if given the choice, we would not modify anything. Here's this particular situation:
1. a previous repair shows that someone removed the surface hardening of the adjuster tip, causing excessive wear on the top of the valve.
2. Wear on the top of the valve may have already begun before the adjusters were modified.
3. Valve lash cannot be set without proper surface to adjust.
4. Installing lash caps is a cheaper temporary alternative than rebuilding the heads with new valves, seats, and possibly guides.
5. Keeping an eye on the components with regular valve adjustments will hopefully let us know when the inevitable valve job is needed.

This set up is not better than stock, and we certainly are not claiming as such. My recently completed heads are of stock design because I'm starting with all new components. We have offered an alternative to belay a problem that will be addressed when necessary. It's not always black and white.

Tom

[tyang]

Please present a mechanical engineer's or alternatively an internal combustion engine design engineer's approach, to discuss why this is a correct and/or acceptable method. I will listen.

Oh, I'm sorry, I didn't read your last line. Never mind then.

Tom

[Art S.]

I'm an ME, what do you need to know...

Oh, by the way, if the cap is secured well to the valve and of low mass, there should be reletively low forces between the cap and valve (only point I can think of where any force may be present is when the valve head contacts the seat). While having no joint would be better, this solution is reasonable provided that there isn't significant valve float.

Regards,

Art S.

[Art S.]

To clarify: any force that may act in a manner to cause cap separation from the valve.

[Admiral Goodwrench]

Dear Art,

The valve lash caps with which I am familiar are hardened caps which fit fairly snugly over the end of the valve stem. There is no rigid attachment means. I would expect that the inertia of the cap would cause a slight separation (up to the amount of the tappet clearance) right after the instant that the valve closes. The lash cap is then restrained by the adjuster tip. All that said, I think that it still should be viewed as an interim fix.

Best regards,

Robert

[airsanford]

Your nearest Toyota is chock full of M8x1.25 nuts that are 12mm. Most other Japan origin cars as well.

Some of the misspent days of my youth were spent working on and racing sohc BMWs, which are quite similar in valve train configuration to the sohc Ferraris. Some of the reground cams we were using required lash caps in order to get a valve adjustment. The BMWs used an eccentric held by a pinch bolt in the end of the rocker arm that rode directly on the valve stem. We blew plenty of stuff up, but I don't recall ever seeing a cap jump off.

Lee, GTE 2811

[Art S.]

Dear Robert,

I agree completely with both the possibility of cap motion, the limit of the extent of movement and that it is an interim fix. If the fit is sufficiently snug and the caps are well designed (sufficiently deep pocket) they should be good for regular use without any problems. That said I suspect that if sufficiently snug, the caps do not move at all (maybe Tom Y can clarify this).

I chose the total rebuild route on my engine because of the numerous issues that Tom Y. described in his diary but, if all that was wrong with my motor was worn valve tops, I think I would have considered using caps to tide me over until a top end overhaul was needed for other reasons.

Regards,

Art S.

[PSk]

If you valve bounce and Alfa Romeo Nord engine (105 series twin cam) these caps have been known to dislodge ... but then if you valve bounce any engine expensive things happen.

In this case the gap between the rocker face and the top of the cap would be thousands of an inch ... but the skirt of the cap much longer, thus again unless the driver is an idiot and wants to valve bounce his 60's Ferrari engine I cannot see why this would be a problem.
Pete

[Yale]

What is valve bounce?