What is the thinnest valve shim that can be used on a 2Vi motor? I'd expect that as long as the shim is thick enough that the cam lobe doesn't touch the edge of the bucket it's OK, and that's somewhere south of 3.00 mm. The smallest shim Rutlands and Ricambi list is 3.25 mm, but Fiat DOHC and SOHC engines use the exact same shims and buckets, and the shims are available in sizes well below 3.00. One of the shims in my motor now is a 3.00 that had been ground down to 2.97: grinding marks on the underside, someone wrote .117 on the underside (.117 inches is 2.97mm), and the micrometer says that the grinding was done pretty well, with only a few ten-thousands of an inch variance across the entire shim.
That is an interesting question, and I do not know the precise answer. But, if anyone is measuring a clearance that indicates a need for a shim < 3.00mm, I would recommend they check the valve seat to ensure that it has not exceeded its wear limit (per the spec in the WSM) ---- too thin a shim means the valve stem is too high (i.e., valve seat is worn too much).
Would you pull a cylinder head to perform this check if you found that a valve wanted a 2.95 shim? BTW the Fiat crowd, using the same shims and buckets and generally comparably aggressive lobe profiles, have been known to grind a few thousands of an inch off of the top of the valve stem.... That's one way of keeping the valve stem from getting too high.
If you think you need to remove the head in order to perform the seat / stem measurement, then I would say you are fine doing whatever you want with regard to shims.
The depth of the shim cup holder is something like 2.85mm, and it's perfectly ok to go to that depth. I would guess the mechanic who ground that shim had no other choice, otherwise it's a bad idea to grind those shims as it removes any hardening. My concern is that the valve seat is getting a bit to worn or never installed correctly to begin with as you shouldn't ever need to shim that thin. Might be time to pull the heads....
I would prefer to grind the tip of the valve stem. When regrinding valves you should cut the tip to compensate for the valve depth anyway.
Time to take the heads off. Your problem is almost invariably caused by a butcher doing a valve job. Either grinding the valves, the seats or both into never never land. My 328 needed all new valves and all new seats for just that reason. You should have seen what he did to the alloy cylinders with a hone. Some people should not be allowed to posess tools. All started when one of the timing belts that never break, broke.
One vendor advised that I should change out all the shims when checking valve clearances for the 30K service. I haven't seen that recommendation here before, but I am relatively new - would any of the experienced techs care to comment? Should shims be replaced at 30K intervals, or can they be re-used? This might seem like a stupid question, with an obvious answer - but I'm asking only because of that vendor's comments. I believe the recommendation was made on the basis that the hardened surface of the shim would be worn somewhat, and that it could cause accelerated cam lobe wear if the old shim was left in place. I would have thought that a shim could be turned over and re-used, since both sides would be hardened and the underside would not have any wear; and that even if a shim had worn through the heat treated surface, then it would be the shim that would wear quicker, not the cam lobe.
Eric --- Do the measurement check first to confirm before you pull the heads, unless you need to pull them anyway for some other reason. While it may be the case that the heads are getting "tired", and will eventually need a full rebuild, you may not quite be there just yet . Of course, that is always a matter of preference and weighed against other considerations. I do not mind taking some machinery all the way down to its wear limit (plus a bit of margin) before rebuilding ---- but some folks like to rebuild a bit more proactively, I suppose. Do whatever makes the best sense to you ---- and trust your own judgment. The seat wear limit check is certainly easier to do with the head off and sitting on a bench. But, it can be done without removal and even with the engine in the car, too. Image Unavailable, Please Login
don't know if the shims are case hardened or heat treated but if you only grind the non contact side of the shim it will have no effect on the cam lobe side and if they are hardened by heat treating and you grind them so they stay reasonably cool no effect on that either. jon s
Eric, You confirm for yourself. I have been told by a very experienced Ferrari mechanic and machinist that you must use a spacer (.030" ??) that is placed between the tip of the valve stem and the depth gage when measuring the height of the stem. From what I've been told most shops make this rather than buy from Ferrari. Failure to do so will give low readings. Not wanting to put out bad information so Fchatters feel free to comment. Thanks, Brewman
Yep - that's what I'm trying. It would be nice if were the rear bank, but of course then it would be easy, and when does that ever happen?
246, Daytona and 365GTC4 all had a reputation of eating up cams and shims. There was a school of thought at the time that if all the shims were changed at every valve adjustment it would prolong cam life. Without taking a side in that old argument there has not been a Ferrari built since that was known for cam or shim wear problems. Changing them all is a waste of time on any Ferrari built 308 and newer.
Guys, this is very basic. If you need a shim THINNER then the factory minimum, the valve is "sunk" too much. ANYTIME you grind a valve or a seat- you are sinking it, PERIOD.Look at the shim thickness range- If you have sunk the valve .030 inch,on a stock American 308 you have effectively eliminated 10% of the valve lift. For the record- the FACTORY says ON ANY FERRARI- to replace seats- do not do a valve job. Dont shot the messenger!
Thank you, Brian! That's what I'd have expected. I'll be checking my valve clearances next weekend, and will only change out of range shims.
I just spent some time playing with a few random buckets: measure height of bucket without a shim in it; measure height of bucket with a shim in it; subtract one from the other to find how much of the shim is not in the bucket; subtract this from shim thickness to see how much of the shim is in the bucket. There's a surprising amount of (repeatable) bucket to bucket variance, but I'm seeing values in the range of 3.15 to 3.25 mm on my 2V (and Fiat) buckets. Any possibility that the QV is a bit shallower and that's what you're thinking of? BTW, I'm not doing this because I think that it's important. It's just a nerd thing (Also, it's something to do instead of the stem/seat measurement, which I expect is just going to depress me.)
Hi Eric, I'm just doing clearances on my QV Mondial 1983 it has 50,000miles and my shims vary between 3.85 - 4.10mm. Hope this helps all the best, Bell
