| Author | Message | ||
| Bill Sebestyen (Bill308)
Junior Member Username: Bill308 Post Number: 107 Registered: 5-2001 |
Thanks for the discussion guys. I personally think the reuse of shims, with a fresh cam side surface, is ok, provided the contact edge mates well with the bucket ledge. I always use assembly lube on a new surface and break in the shims at a fast idle for 20-30 minutes, when first starting the engine. This procedure ensures lubrication during the first critical minutes and allows the wear surfaces to seat. Thinning of the shim because of wear does not significantly decrease the cross sectional area of the shim. The worst case will occur with a thin shim. The thinnest shim in my collection measures 0.1420 inches (3.60 mm). In a severe case, cupping could be imagined to reach a depth of 0.005 inches, a reduction in thickness of about 3.5%. This is equivalent to about 2.5 shim sizes smaller, at about 3.45 mm. Any reduction in stiffness of the shim, attributed to wear, is probably small. The biggest problem when fitting new shims is getting one with the correct thickness. I find measuring the gap with a feeler gauge imprecise and the available 0.05 mm graduations rather coarse. Remember that a shim marked 4.00 mm, should fall somewhere within a range of 3.975 to 4.025 inches. I ordered about 45 shims, over a 2-month period, to get my clearances close. In the end, I wound up surface grinding the bucket side of 3 shims to get the clearances just right, +/- 0.001 inches. This may be a little anal, but at least I know the clearances started out right, plus the exercise established a baseline to track future wear. Bill | ||
| David Prall (Davidpra)
Junior Member Username: Davidpra Post Number: 75 Registered: 2-2001 |
The relief in the top of the tappet makes the condition worse... But, a new shim is stiff enough to resist deforming despite spanning the gap created by the relief. Cheers | ||
| David Prall (Davidpra)
Junior Member Username: Davidpra Post Number: 74 Registered: 2-2001 |
Hey Bill (et al): I believe Peter and Craig elaborated very nicely to my post --- I assume your questions were answered? True, mine is primarily a theoretical explanation. However, I have directly observed and measured the ?clearance opening? phenomenon. The mechanism is that thinning of the shim from the wear combined with micro-cracks from the fatigue cause a substantial reduction in effective shim cross section (by as much as .020?). This weakens the shim to a point where cam forces can permanently bend the shim. That said, I would also add that this occurred in higher performance applications, and may or may not be indicative of normal / street usage. But, remember shims are designed and intended to be consumable, wear parts ----- in other words, to be used only once. | ||
| Craig Dewey (Craigfl)
Member Username: Craigfl Post Number: 313 Registered: 1-2001 |
Steve, Thanks for letting me know the center is relieved... I haven't had mine off yet, but soon. I realize that new isn't guaranteed because of unknown manufacturing defects. Knowing what I know now, I would feel comfortable with reusing old shims by turning them over(as long as they look "good". | ||
| Steve Magnusson (91tr)
Member Username: 91tr Post Number: 534 Registered: 1-2001 |
Craig -- the bucket (at least on the 2-valves) is relieved in the middle so whether or not the shim is slightly concave there is no support in the middle of the shim. But we are arguing about the subtle differences -- sure, if the used side of a shim was badly worn/scuffed/non-parallel I wouldn't flip it over and reuse it either, but I had no problems over 60K miles of use flipping a few good condition ones over at the 15K mile intervals. I would even argue that not all new shims (from different manufacturers) are necessarily of the same quality so always going new isn't a 100% gaurentee either. JMHO -- we all can make our own decisions. | ||
| Craig Dewey (Craigfl)
Member Username: Craigfl Post Number: 311 Registered: 1-2001 |
Bill, --explained in a different way... When the valve shim wears, it can actually make a concave "dish" in the material. If you flip the shim over, the center of the worn part of the shim will no longer contact the bucket evenly. Now the shim, instead of just carrying the cam load forces thru the shim as a compressive force actually cause the material to deflect in this gap. Since these are extremely hard shims and best for compressive forces only, there is a risk of fatigue and cracking which may cause failure. Of course this depends on how much the shim is actually worn. Note that this is only the theoretical/ engineering explanation and not observed. My personal feeling is that shims are reasonably inexpensive so they should just be replaced every time. | ||
| '75 308 GT4 (Peter)
Intermediate Member Username: Peter Post Number: 1558 Registered: 12-2000 |
Bill, from what I understood from that passage, that used surface, which now faces the bucket, is an uneven one and will not sit completely on the surface of the bucket, resulting in higher stresses and the chance of failure (two poor conditions: worked surface of the used side, plus less contact). Mike, if for whatever reason you need shims thinner than 3mm, try Bayless Fiat in Georgia. They have their own shims made in sizes under 3mm thick (everyone else seems to go no lower than 3.05mm). Just check that the 308 bucket lip is not higher than the shim. It may use Fiat shims, but the buckets are Ferrari and are different than the Fiat's. http://www.baylessfiat.com/ | ||
| Mike Dawson (Miked)
New member Username: Miked Post Number: 13 Registered: 2-2001 |
After following this post for the last few days and looking forward to the 60K mile service on my GT4 due all too soon, I did a quick Google search for the availability of Fiat and Volvo shims. In just a few minutes I found several sources with prices from $1.80 to $2.00 per shim. At that rate I can replace EVERY shim for about $30 total. It's hardly worth re-using them especially if I need only a few which is usually the case. Here is a link to an interesting "how to adjust valves" for those that are lacking experience in that area. Bear in mind that some of the information is Fiat motor specific. http://we.got.net/~fiatplus/valveadj.htm | ||
| Bill Sebestyen (Bill308)
Junior Member Username: Bill308 Post Number: 105 Registered: 5-2001 |
David, I'm not sure I understand the your fourth paragraph: When flipped over to contact the "fresh side", the "concavity" promotes deformation which opens the clearance and the "polish" promotes fatigue cracking which leads to breakage. This makes using even the "fresh side" undesirable. Could you please elaborate? Thanks, Bill | ||
| '75 308 GT4 (Peter)
Intermediate Member Username: Peter Post Number: 1551 Registered: 12-2000 |
Poker chips... never thought of that one. Good idea too, as the numbering can represent chip value (if your shims still have numbers on them!)  | ||
| David Prall (Davidpra)
Junior Member Username: Davidpra Post Number: 73 Registered: 2-2001 |
Actually, re-using valve shims (on either side) is a poor idea. If you want the Engineering explanation, read on... When a shim is "beaten in" (worn from cam lobe contact stresses and friction), a couple of things happen within the contact area. A shallow concavity is formed, an uneven surface is developed, a polished surface finish is created, and residual compressive stresses are introduced. The "uneven surface" makes accurate measurement impractical to achieve and re-registration (clocking) errors will result in unstable clearance values. This disqualifies the "used side". When flipped over to contact the "fresh side", the "concavity" promotes deformation which opens the clearance and the "polish" promotes fatigue cracking which leads to breakage. This makes using even the "fresh side" undesirable. The "residual compressive stresses" are benign in this application. The moral is that if you want accurate and long-wearing clearance settings, use new shims every time one has to be changed. They are trivially cheap compared to the costs of the work -- even if you DIY, they are cheap! Do it right with new shims -- you'll be glad you did. Plus, the old ones make good poker chips and vending machine slugs! | ||
| Jeff 77 GTB (Jbk)
New member Username: Jbk Post Number: 40 Registered: 4-2001 |
Thanks everyone for the advice. I think I'm going to go by Steve's rule and replace any that I can't find with the correct thickness and a fresh surface. | ||
| Thomas Pirie (Desmo)
New member Username: Desmo Post Number: 9 Registered: 8-2001 |
So,of all you guys that have done valve adjustments,how often has the clearence been out of spec.? I'm closing in on 45K miles and am wondering if I need to react promtly. Do these cars tend to need adj. frequently, or once set up correctly after break-in,tend to last a long time? By the way I'm talking about a QV. | ||
| '75 308 GT4 (Peter)
Intermediate Member Username: Peter Post Number: 1545 Registered: 12-2000 |
Yes, Steve, I forgot to mention that. 4-Valve's use 25mm dia. shims and unfortunately are unique to themselves (no other common engine uses this size). | ||
| Steve Magnusson (91tr)
Member Username: 91tr Post Number: 522 Registered: 1-2001 |
Kurt -- the 308 2-valve valve shim is 33 mm OD, but I believe the 308/328 4-valve valve shims are smaller in size (anyone know the size?) | ||
| '75 308 GT4 (Peter)
Intermediate Member Username: Peter Post Number: 1543 Registered: 12-2000 |
Volvo 240. Also any Lampredi-designed Twin Cam Fiat (124, 131, Lancia Beta, etc...) valve shims work as well. They are all 33mm diameter. When doing the shims on my engine, alot of the old ones were used twice, but even the ones that weren't, I replaced. My logic was, if I'm changing a whole bunch of shims, change them all. | ||
| Kurt Kjelgaard (Kurtk328)
Junior Member Username: Kurtk328 Post Number: 105 Registered: 3-2001 |
Rivee: What model Volvo/engine are you talking about? | ||
| 78308gts4re (Rivee)
New member Username: Rivee Post Number: 10 Registered: 1-2002 |
Jeff, I just did a valve adj. on my 308 and I talked to my Ferrari mech. and he said it is perfectly acceptable to flip them over and use them as long as they haven't been used before (as Steve pointed out) I went to my local Volvo dealer and bought a few random sizes of shims (they use the same as Ferrari and they're cheaper) to have on hand. As Steve pointed out if they have a circular pattern to them they have been used before. | ||
| Steve Magnusson (91tr)
Member Username: 91tr Post Number: 520 Registered: 1-2001 |
Jeff -- The best way I've found to state the confusing "F valve shim reusability rule" is: Each surface of any shim can be used only 1 time in contact with a cam lobe. It's not hard to distinguish a used side (highly polished in a circular way) from an unused side (dull non-directional mat finish) -- which is necessary on older cars like yours where many shims may have already been flipped over once. I know others have disagreed on this (i.e., they'd say reusing even a used side is OK), but IMHO there is benefit to presenting only a "fresh" (i.e., non-work hardened) shim surface to the cam lobe after shim replacement. | ||
| BretM (Bretm)
Intermediate Member Username: Bretm Post Number: 1638 Registered: 2-2001 |
I don't see why not. Providing they aren't bent or anything, they're still the same width and material. | ||
| Jeff 77 GTB (Jbk)
New member Username: Jbk Post Number: 39 Registered: 4-2001 |
Does anyone have any experience or advice about the reuse of valve shims? Is it OK to reuse ones that are removed, but are the right thickness for a different valve? |