the lvferraripilot engine rebuild thread

Yes, that's the WSM spec for the outer spring's length with valve closed (aka installed spring height).

Is that what yours measure, or were you just providing the WSM spec?

You're probably well ahead of me on this, but I can only come up with a few causes:

- NEW VALVES ARE OFF: The new valves are different dimensionally. Measure against the OEM ones. A 2mm difference should be pretty obvious to the eyeball.

- SEATS ARE OFF:
1) Seats were off to begin with:
.Possibly they were badly worn & while a light cut cleaned them up, excessive wear accounts for the difference. If the seats had been previously worn & re-cut, then they wouldn't have looked very worn this time.

.The seats may have not been fully seated in the head at the factory, then subsequent valve operation drove them deeper into the head. When shim-cam clearance was measured, this would be indestinguishable from valve & seat wear. I've heard this from a couple of professionals. They ended up having to replace & re-machine the valve seats on engines where the valve & seat sealing surfaces didn't show enough wear to account for the shim-cam clearance reduction.

3) Seats were cut too deep in spite of what your guy believes.

- BOTH VALVES & SEATS ARE OFF:
If both are off in the wrong direction, the combined error is the sum of the individual part errors.

Hmm, what were the original shim-cam clearances, and what were the original shim thicknesses?

 

I'm sure you'll hear something quickly....they want to sort this out.

 

That 0.190[4.826 mm!!!] intake shim is also a problem. The factory shim sizes are: 3.25mm[0.126"] up to 4.60 mm[0.181"]. I wouldn't go outside that range without someone(preferably at least 2 someones) with a LOT of experience building up modified 3x8 engines saying it's OK. Risk is if the shim is too thick, at high engine revs, the cam lobe can whip it out of the cup & launch it!!! Even then there's going to be the problem of getting custom shims made & hardened. The shim hardness must be matched to the cam hardness or either the cam or the shim will undergo rapid excessive wear!!

Definitely time for some careful measurements of both the intake & exhaust valves. Especially the stem lengths & valve keeper groove locations relative to the valve seating surfaces.

 

I'm now very concerned. It is absolutely impossible to grind a seat and have it come out bigger than is was to begin with so there is NO WAY the intake valves are seated to high. what you want to do is pick up the heads and either bring them home to measure or take them to a shop that knows what they are doing.

You most likely have the wrong valve part numbers....they are probalby for another ferrari model but they are not 308 valves. Pop the valves out and compare to your old ones and you will see your problem.

 

I'm no pro here , but surely you don't want to sink/drop the inlet valve ? The short side radius in the port it so short already sinking the valve only makes it worse !
With a new seat and the valve as high as possible ( original spec ) you minimise the combustion chamber volume and maximise the short side radius of the port ?

 

Here's something you might find interesting.

When I do heads I'm still doing them caveman style with grinding stones vs. a form cutter with all the angles or radii on it.

There is not a lot of room on the 308 seats for the angles that define the top and lower edge of the seat ... a person learning on 308 heads will be in the surrounding aluminum of the combustion chamber in no time using the standard 30 deg top angle. Now I have a set of stones all cut and sized specifically for the 308 heads.

I also lap the valves so you can really see the exact conctact patch.
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They should be working against a copy of the WSM, it's very explicit as to the dimensions in this area, INCLUDING valve stem height relative to the cam centerline. In which case they have no come back as their work doesn't comply with the WSM.

I'm having trouble fullowing what you're saying about the back cut angle, could you post a sketch of the seat profile & valve profile with angle dimensions? Did Ferrarea provide a seat profile drawing? If so, could you also post it?

I share mk e's concerns about these valves.

I know that thicker FIAT & VOLVO shims are available, BUT the largest that the FERRARI FPC lists is 4.60 mm[0.181"].

I wouldn't exceed Ferrari's specs without some strong reassurance from someone with a LOT of experience that a thicker shim would stay in the cup at redline. For example, the FIAT cups might have a higher side wall around the shims, & I doubt that the FIAT engine revs to 7500+ RPM.

 

I see that Sean & I were posting at the same time. Yes, I meant a dwg of your valves & seats like he posted.

 

They are morons. The back cut is for air flow and doesn't touch anything in the head...it sit below the seat surface on the valve and that's way they call it a cut not an add.

YOU NEED A NEW SHOP!!!

I called my localish Ferrari dealer for a shop recommendation the other day and they gave me a couple names. I called both places and they both knew what they were doing…and you know I wasn’t asking for easy stuff. This might be a good way for you to find a decent shop.

Looking at the pics of your heads I don’t see anything wrong so you probably don’t need a shop at all, what you need are the correct valves.

 

+1

Like Verell, I'd be real cautious of the larger shims too.

Rick

 

Suspect they won't make that mistake again any time soon. Their faces have to be pretty red.

 

No one with any experience with these engines would ever suggest going to such thick shims. A QV or 2-valve engine with the installed heights done correctly will always fall into the 3.80-4.35mm range. Going with a super thick shim almost guarantees that the shim will be knocked out of the bucket at high RPM. And, why would you want the excess mass of a heavy shim sitting "that much" above the bucket edge.

We're doing two QV motors now. Everyone involved knows the importance of the installed heights...and the proof is in the pudding when the baseline valve clearnaces are set.

David
Ferrari Service of Bedford

 

John,

Sorry, but this is not possible. If the installed height (of the valve) is correct, then you'd have adequate bucket to cam base circle clearances. If they had measured all of the installed heights prior to disassembly, they would find that, on average, it would be very close to what Ferrari specifies. The thickness of the cam buckets (which does vary slightly) must also be taken into consideration.

Personally, your heads are at the wrong shop...

David

 

I'm confused & having trouble parsing the preceding statement:

1) Are we talking about the same installed height? It commonly means the valve closed spring height, which is what I (& I'm pretty sure mk e) were referring to earlier. We're concerned that it's probably off. I don't know of a WSM procedure for directly measuring it as it's the distance between the valve spring seat & the valve retainer's bottom with the valve in the head & closed.

I believe David is referring to the valve stem clearance (ie; valve end - cam lobe bottom) measurement shown in the WSM figure from the 308-328 WSM pg. B26 below. Which has got to be way off or we wouldn't be having this discussion.

2) What dimension are you saying the shop measured as 'installed height'?

3)When was the measurement done? ie: when installing the valves, or shortly before you posted the above statement?

4)What was 'done correctly' setting the 'installed height', or the measurement procedure?
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John,

I am really enjoying the photography.
My heads are in the shop now, new guides and exh. valves.
Your shims are way too thick. This is not good.
:-/
I sent an exhaust valve from my 1981 Euro 2V 308 motore'
to Si Valves.
And, they made me correct valves, the first time.


Edwardo

 

The valve are of course wrong, but it has nothing to do with the back cut being high or low. The back cut is a basically cosmetic feature and does not and cannot contact the head or affect the way the seat contacts the head. Your machinist is an idiot, is feeding you a line of cr*p, and clearly has no idea how to measure a valve. I really would not trust him to continue the project......