33 mm shims · Mechanical valve clearance
Valve clearance adjustment for classic Fiat SOHC and Lampredi twin-cam engines, with selected Ferrari applications.
Correct valve clearance starts with accurate measurement and the right shim. Explore 33 mm valve adjustment shims for classic Fiat and Lancia engines, learn how to calculate the required thickness, and find the correct size for your next adjustment.
Understand the mechanism
The cam lobe acts on a hardened adjustment shim seated in the top of the bucket tappet. When the lobe turns onto its base circle and the valve is closed, the gap between cam and shim is the valve clearance.
A thicker shim reduces this gap. A thinner shim increases it. Diameter determines which shim family fits; thickness is selected from the measured clearance.
A closer look
Diameter identifies the shim family. Thickness is selected for each valve. These photographs show a 3.20 mm example from our catalogue.
Identify the engine first
These are relevant engine families, not a blanket fitment list for every version of each car. Confirm the engine, existing shim diameter and tappet arrangement before choosing a thickness.
| Engine family | Typical applications | Selection notes |
|---|---|---|
| Fiat Lampredi DOHC 8V | 124 Sport Spider 1.4/1.6/1.8/2.0; 124 Sport Coupé; 125 twin cam; 131 twin-cam versions; 132; Argenta; Ritmo 105/125/130 TC. | Mechanical bucket tappets with a 33 mm shim above the bucket. Match the actual engine specification. |
| Fiat 128-family SOHC | 128; X1/9 1.3/1.5; Ritmo 1.1/1.3/1.5; corresponding SOHC versions of Regata and Uno. | Model names cover different engines. Identify the correct SOHC version and confirm diameter. |
| Lancia twin cam | Beta Berlina, Coupé, Spider, HPE and Trevi; Montecarlo/Scorpion. | Use the specification for the engine and market version; the same shim family does not imply the same clearance. |
| Lancia 1.3/1.5 SOHC | Corresponding Delta and Prisma SOHC versions. | Do not apply this listing to every Delta or Prisma engine. |
Application overview based on the existing Oldtimer Shop shim listings. Final fitment depends on the engine and installed valve train.
Measure · calculate · recheck
Use metric feeler gauges between the cam base circle and shim, with the valve fully closed and the engine at the temperature specified by its workshop manual. Record every inlet and exhaust valve separately.
Use a micrometer to establish its actual thickness. A stamped size is useful for identification, but should not replace measurement of a used shim.
The selection formula
New shim thickness = old shim thickness + measured clearance − specified clearance
Use millimetres throughout. Choose a thickness that puts the resulting clearance within the specified tolerance.
Example 1 · gap too large
Old shim: 4.00 mm
Measured gap: 0.60 mm
Specified gap: 0.45 mm
4.00 + 0.60 − 0.45
= 4.15 mm
Example 2 · gap too small
Old shim: 4.00 mm
Measured gap: 0.30 mm
Specified gap: 0.45 mm
4.00 + 0.30 − 0.45
= 3.85 mm
Illustrative calculations only. The 0.45 mm target is not a universal setting for Fiat, Lancia or Ferrari engines.
Do not turn a cam lobe onto an empty bucket. With a bucket held down, only rotate the engine as required by the correct service procedure and with piston-to-valve clearance accounted for.
Specifications belong to an engine
These documented examples show why the engine specification matters. They are not settings for all vehicles carrying the same model name.
| Documented application | Inlet | Exhaust | Reference |
|---|---|---|---|
| Fiat 128 · version covered by the cited factory manual | 0.30 mm | 0.40 mm | Fiat 128 workshop manual. Do not extrapolate to all 128 variants. |
| Lancia Beta Coupé / Zagato MY1981 · 828 B4.040.1 | 0.42 ± 0.03 mm | 0.48 ± 0.03 mm | MY1981 service manual |
| Ferrari Dino 308 GT4 · cited workshop manual | 0.20–0.25 mm | 0.30–0.35 mm | Workshop manual, B28 |
Running clearance is not timing-check clearance. The Fiat 128 manual separately lists 0.50 mm for checking valve timing. Do not use that figure in place of its specified running clearances.
The Ferrari connection
Selected classic Ferrari and Dino engines share adjustment-shim references with Fiat and Lancia. The connection goes beyond a similar shape: some original part numbers appear in both parts catalogues.
Metelli identifies this Fiat/Lancia reference as a 33 × 3.40 mm shim. Maranello Classic Parts also lists 4204144 for Dino 206 GT, specified Dino 246 GT/GTS chassis ranges and Ferrari 400 GT/Automatic.
Manufacturer dimensions · Ferrari fitment reference
The original Ferrari 365 GTC/4 catalogue lists this familiar adjustment-shim reference. It also lists 4152460 at 4.10 mm, another Fiat/Lancia reference.
Original 365 GTC/4 parts catalogue
The two-valve V8 uses one adjustment shim above each bucket. Its parts catalogue includes 4204144 at 3.40 mm, linking this application to the 33 mm Fiat/Lancia family.
Check with the engine cold: inlet 0.20–0.25 mm; exhaust 0.30–0.35 mm. Measure between the cam base circle and shim using feeler gauges. These are running clearances; the separate 0.50 mm timing-check clearance is not the adjustment target.
Workshop manual B28 specifies shims from 3.25 to 4.60 mm in 0.05 mm steps. A 3.20 mm shim is outside that documented range. Select each valve’s thickness from measurements; do not transfer these limits to other Ferrari engines.
The manual specifies tool 706-AS-9560 and a retaining spacer to depress and hold the bucket for shim removal. Confirm the correct Ferrari tool; a Fiat SOHC/DOHC tool is not automatically suitable. Measure the removed shim with a micrometer, install the calculated replacement and recheck clearance. Do not grind the hardened shim faces.
These are specific catalogue examples, not approval of every stocked thickness for every Ferrari. The 308 GT4 workshop manual specifies a 3.25–4.60 mm range; thinner or thicker aftermarket sizes require separate verification. Ferrari 308 Quattrovalvole and 328 use a different 29 mm shim family.
Choose by measured thickness
Browse all 38 listed sizes in this 33 mm shim series, from 3.05 to 4.90 mm in 0.05 mm steps. Each button opens the matching product page, where you can check current price and availability and purchase that size.
Thin-shim check: Sizes below 3.25 mm are below the lower limit in the cited 308 GT4 manual. Verify the permitted range and cam-to-bucket-rim clearance for your engine before using a thin shim.
| Thickness | Product code | Fiat OE references | Shop this size |
|---|---|---|---|
 3.05 mm | P615-1 | Not verified | View product → |
 3.10 mm | P615-2 | Not verified | View product → |
 3.15 mm | P615-3 | Not verified | View product → |
 3.20 mm | P1333 | Not verified | View product → |
 3.25 mm | P615-4 | 4204141 4358374 | View product → |
| 3.30 mm | P615-5 | 4204142 4358375 | View product → |
| 3.35 mm | P616 | 4204143 4358376 | View product → |
| 3.40 mm | P615-6 | 4204144 4358377 | View product → |
| 3.45 mm | P618 | 4204145 4358378 | View product → |
| 3.50 mm | P619 | 4152449 4358379 | View product → |
| 3.55 mm | P620 | 4152450 4358380 | View product → |
| 3.60 mm | P621 | 4152451 4358381 | View product → |
| 3.65 mm | P622 | 4152452 4358382 | View product → |
| 3.70 mm | P623 | 4152453 4358383 | View product → |
| 3.75 mm | P624 | 4152454 4358384 | View product → |
| 3.80 mm | P625 | 4152455 4358385 | View product → |
| 3.85 mm | P626 | 4152456 4358386 | View product → |
| 3.90 mm | P615-7 | 4152457 4358387 | View product → |
| 3.95 mm | P628 | 4152458 4358388 | View product → |
| 4.00 mm | P629 | 4152448 4358373 | View product → |
| 4.05 mm | P630 | 4152459 4358389 | View product → |
| 4.10 mm | P631 | 4152460 4358390 | View product → |
| 4.15 mm | P632 | 4152461 4358391 | View product → |
| 4.20 mm | P633 | 4152462 4358392 | View product → |
| 4.25 mm | P634 | 4152463 4358393 | View product → |
| 4.30 mm | P635 | 4152464 4358394 | View product → |
| 4.35 mm | P636 | 4152465 4358395 | View product → |
| 4.40 mm | P637 | 4152466 4358396 | View product → |
| 4.45 mm | P638 | 4152467 4358397 | View product → |
| 4.50 mm | P639 | 4152468 4358398 | View product → |
| 4.55 mm | P640 | 4162888 4358399 | View product → |
| 4.60 mm | P641 | 4162889 4358400 | View product → |
| 4.65 mm | P642 | 4162890 4358401 | View product → |
| 4.70 mm | P643 | 4162891 4358402 | View product → |
| 4.75 mm | P644 | 4181812 4294418 | View product → |
| 4.80 mm | P645 | 4181814 4294419 | View product → |
 4.85 mm | P615-8 | 4181816 4294420 | View product → |
 4.90 mm | P615-9 | 4181818 4294421 | View product → |
OE references are for identification; these are replacement shims, not a claim of Fiat manufacture. Photos come from the corresponding product listings; some sizes share a representative catalogue photo. Choose by the stated thickness and product code. Open the product page for current price and availability.
Workshop questions
No. Check the actual engine and tappet design. SOHC and DOHC describe the camshaft arrangement, not a universal shim dimension.
No. Use feeler gauges for the gap between the cam base circle and shim. Use a micrometer for the thickness of the removed shim.
Follow the workshop manual. For the shim-above-bucket arrangement described here, the marked face normally sits down against the bucket, leaving the working surface towards the cam.
Use the correct manufactured thickness. The Ferrari 308 GT4 manual explicitly prohibits grinding because the disc surfaces have a special hardening treatment.
Only after verifying the permitted thickness and installed geometry. A thin shim can let the cam contact the bucket rim. Availability of a thin size is not proof that it is suitable for a particular engine.
Not necessarily. Use the tool designed for the engine and follow its workshop procedure. The tool must retain the bucket while leaving the shim accessible.
Measure each valve independently. Different valves in the same engine may need different shim thicknesses. Record the fitted shim, measured gap and calculated replacement for each position.
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