I just got my heads back from the machine shop................had a valve job done, and am now adjusting them. The manual calls for: Intakes= 0.20-0.25mm Exhaust= 0.30-0.35mm I'm planning on going for the larger limit number in both, if I can. Does this make sense? The reason is that, as the valve wears, it will decrease the gap, thus I have room for that, and still be within limits. The other minor reason is that the valves are open a little longer for better breathing. Agree? Can someone tell me about how many miles one can drive, where the gap will shorten by 0.05mm? The reason is that it seems that I am approaching the thin limit of shims available to adjust the valves.........some I used are the 3.35mm shims.........the lowest available shim is 2.50mm. My guess, is that the new valves, especially exhaust, could have been a few thousanths shorter. Thanks for your opinions. Hank
Ideally you would like to have the valves on the shorter side to allow for the thicker shims. I would think they followed the factory spec on valve heights when setting them up to prevent this from happening. If not then do it again now rather than later. I would also go with the larger gap as well but not for breathing, just to reduce valve adjustment frequency. I would double check the valve heights.
I have heard from various sources, and many have written here as well, that the valve clearances on these cars dont change appreciably once the motor has 25K or so miles on it. The cams get harder and polished the more it runs as long as it remains well lubricated. Between initial wear at the lobe/shim that would add clearance, you have valve seat erosion/recession that would diminish clearance, and its balanced fairly equal. As far as clearance, you have it reversed. Tighter clearance will keep the valves open longer, better performance. Looser clearances allow better valve cooling as the valve is on the seat longer to transfer heat, as well as the stem being receeded into the guide longer to do the same. But its negligible at the clearance differences we are talking about. I would set for the minimum limit. Myself, I would prefer a bit longer valve stem with thinner shims, say .020" inch shorter than maximum for example, as they would be lighter and would have less reciprocating mass. Might not seem like much, but at 6500 engine rpm those little shims are bouncing up and down 54 times per second. Thats why a lot of racing engines have gun drilled stems, and why several have converted Ferrari's to use an Alfa bucket with the under bucket stem shims, it all reduces wieght.
Shorter valve with a thicker shim or a longer heavier valve with a lighter thinner shim is getting silly. This isnt a race car. Me, I want durability and plenty of adjustment to buy time if needed so I guess its personal preference. I would however think that sticking to stock specs isnt a mistake. Look at it this way, 4 rings per piston with 80Kg rotating mass in the crank case and we are worried about riffle drilled light weight valves? Stick with stainless, go with the thicker shims if possible and enjoy the symphony behind you.
After some thought, I realize that Artvonne is correct and that I have the clearance understanding in reverse.......thanks. I agree with Newman........I DON"T want a race car. If I wanted one, I would buy one........a real race car from IMSA or NASCAR.. I have NO intentions of turning a beautiful cruiser into a racing machine! While some like to do this sort of thing.........that is fine for them, but not for me. My concern was that the valves where almost at the minimum shim adjustment, and that I would not have much more adjustment available should the valve seats wear. But as Artvonne pointed out, valve wear is minimal. I assume that by the time they need major adjustment........such that I would have to shorten the valves themselves, I would be doing a major engine rebuild anyway. Would you agree?
Whats the riff? Did I suggest rifle drilling the stems? No, I gave the simple reason why people do it. If your spending the money to have the valves ground and the stems set to one length or another, why not keep them as long as possible and run thinner shims? Its not like you can add it back on later. Why does Ferrari have any specs on shim thickness from thin to thick, is it some joke? As far as it being a race car, it already is. You cant hardly drive one of these cars without hitting 6K RPM, and any excess wieght from excessive material is just more crap that has to bang into each other. There is a little over .050" span from thin to thick. If you just picked the middle ground youll be about where I was saying. Like I said, you can always take more off the stem, you cant put it back on.
The cams won't wear, that will just not be an offsetting happening for the valve/seat wear. The amount the valves and seats allow or cause diminishment of valve clearance has many factors and there is no rule of thumb but one thing is known, you need to start off with some adjustability. If you are at or near minimum shims now you are headed for trouble. Your machine shop dropped the ball if they allowed that to happen. The heads should be fixed now. Another consideration to support that course of action. If the installed stem height is high enough to cause your current problem it is high enough to lower the seat pressure due to the reduced preload of the spring. Lower seat pressures than designed for is the root cause for several other problems including but not limited to, higher valve temps, lower engine speed before valve float. Specifications like installed stem height are arrived at for a multitude of reasons and should not be ignored. When we do valve jobs it is one of the specs we go to great lenghths to maintain.
Sorry I quoted you as saying riffle drilled not gun drilled on the valve stems. My point was that he should be more anal about the valve heights rather than the valve weights. These cars are supposedly race cars for the street, I disagree. They possess the poor qualities of a race car on the street but lack the ability of a race car. They're very cool cars no doubt, I disagree on the requirement that you need to hit 6K to drive a boxer, I sure dont have to, perhaps you should drive one you might like it.
Hank, I've been down this path and the above advise is spot on. If the spring pressures are set correctly, with the corresponding (correct) valve heights, you're nominal valve shims during set-up will fall between 3.95 and 4.05. If the spring pressures are indeed correct, then likely the seats are quite worn, hence the valve are recessed into the head more than "normal". If this is the case, the valve stems need to be cut to utilize the more "middle of the range" shim. There a great picture in the WSM that show the "dummy" camshaft used to check valve "installed" height. Regards, David
Thanks, This is sort of what I was thinking. I will talk to the guy who did the valve job. He does all the machining work for one of the Chicago Ferrari dealers. When I dropped mine off, he showed me a head off an F-40..........I couldn't believe how small the 4-cylinder head was!!!!!!!!!! I may have to send the heads back........more time without the car! Now, THAT is why I have two Ferraris. My 328 comes in about a week or two, hence I won't be in such a hurry with the Boxer, thus I will do what is necessary.
As a newbie I'd like to know I did it right. I measured them twice. None were out of spec with too much clearance. I measured 5 that were clearly too little clearance. These were the ones I replaced as it was my understanding there is where the danger is for damage. As I recall everyone I ordered from the Volvo dealer was in the 3.90 or 3.95 range. I assume there are a lot of 308s with valve clearance adjustment neglect. What's the eventual damage? Seamus
Having just recently done this job on my '84 Boxer, thought I'd add my 2c worth: Firstly, I used new stainless Ferrea vlaves, and found the seats were not as concentric with the shafts as I'd have liked. With the valve inserted it was possible to see light between the valve and seat. All the seats had been freshly 3 angle cut. When I put the valves up in a grinder you could see the heads were not concentric, so I ground every valve until they were perfect. I then lapped everyone into its seat. All my shims were bang in the middle of the range, but didn't fit, so ground the tops so clearances were top of the range (ie large) then installed and rechecked. This is a frustrating job! Even with everything spotless, they never measure exactly the same twice!..but we're talking 1/10 thou here, so still within spec. The difference between before and after in terms of engine response etc was worth the trouble Robert
When a guy presents like this you think wow I can have confidence in his work but obviously he dropped the ball. Sometimes the biggest swing di*k is not the best guy for your job. It is so sad to hear. I hope it all gets straightened out. I wonder if your springs were even tested or just reinstalled?
Robert, What is the current theory on lapping valves? There is controversy on lapping at room temp getting perfect valves as some claim they will not seat at operating temp. I have read in the past that valve/seats should be cut at the angles specified and installed as is because at operating temp everything will seal. I'm confused on taht issue and likely out of date on what's current.
I'm not sure how you would compensate for the increased temperature effects on valves or seats....not even sure it makes too much sense...I'd expect the seats and valves to expand / shrink 'concentically', if you see what I mean? I've always lapped my valves: just a few turns on each and you can see the difference, it also allows you to check the valve/seat inteface for uniformitty. The seats were cut with the triple angle, as this gives the best air low and valve seating (and it's recommended in my manual I seem to recall). A number of people made the comment "don't worry about being able to see the flashlight past the valve/seats....it'll close up when you put the springs in" I feel this attitude is poor engineering, and can only lead to guide, valve and seat wear over time. My problem turned out to be the new valves; the seat surface was not concentric to the stem. a few seconds on a valve grinder set to the correct angle, made all the difference. I guess my engineering tolerances are somewhat finer than the average valve manufacturer? Must admit to being finicky...it's either right or it's not! With new guides, and seats cut as above, the valve and seat should fit perfectly with little or no pressure behind it, and this is confirmed once a little light lapping is performed (I'm talking 2 or 3 seconds a time here...any longer and you should cut the seat surface...). All my springs were tested for poundage whilst out, and were all easily within spec, as I would hope on a 20,000 mile engine! At the end of the day it boils down to common sense and good engineering. Robert
To pay top dollar for supposedly top shelf stuff, you should expect top shelf quality. No way you should have to take brand new valves and regrind them to get them squared up. Anyone know anything about Superformance valves and springs, or other parts? Quality? I am seriously thinking of sending for some.
Just a couple of points: I agree the valves should be perfect, but sticking them in a grinder before instalation isn't such a bad idea anyway...just to check they havn't had a knock in transit. The guys at Ferrea were excelent....in every instance that I had a problem they sent new parts same day, even when they had to get them made. Ferrea was also the only manufacturer that could supply the valves....A few others listed them, but none had any available, nor would they make them. Lastly, the Ferrea valves were excellent value for money! I would go back to them again, despite the problems.
