Flex Plate Specifications for Procurement Teams
Buyers reviewing flex plate specifications need more than a part number match. A flex plate is a thin, stamped steel drive member that connects the engine crankshaft to the torque converter and carries the starter ring gear. It has to transmit cyclic torque while holding the crankshaft pilot location, converter bolt pattern, starter mesh position, and engine balance condition in the right relationship. A complete specification controls the crank bolt circle, converter bolt circle, pilot bore, ring gear tooth count and position, plate thickness, offset, flatness, runout, tooth form, material condition, surface protection, and traceability.
Small dimensional errors can quickly turn into assembly delays or warranty claims. The wrong offset can push the torque converter out of its designed axial position. Excessive ring gear runout can create starter noise or abnormal tooth wear. Poor hole position or burrs can reduce fastener clamp load, and uncontrolled balance features can lead to idle vibration or added main bearing load. For procurement teams, the useful data are the controlled drawing dimensions, material grade or equivalent standard, heat-treatment condition, hardness window, flatness and runout limits, coating specification, packaging method, inspection plan, and lot traceability records.
A quote that lists only an application name or interchange number is not enough for repeat supply. Two parts that look nearly identical can still differ in offset, ring gear plane, balance holes, converter mounting geometry, or chamfer direction on the starter teeth. Driventus is an independent aftermarket manufacturer; brand names are referenced for fitment only. We manufacture engine and powertrain parts in Taizhou, Zhejiang, and supply distributors, repair networks, and OEM-oriented buyers that need repeatable inspection data, documented quality controls, and stable production lots. The sections below explain which values belong on a proper spec sheet, how to compare supplier offers, and which checks matter at receiving inspection.
What belongs on a flex plate spec sheet
A useful spec sheet gives a buyer enough information to verify fitment, durability, and repeatability before a purchase order is issued. At minimum, ask for the controlled drawing revision, application family, engine and transmission reference, and the dimensional features that affect assembly. These include outside diameter, center bore or crank pilot diameter, crankshaft bolt-circle diameter, crank bolt-hole diameter and quantity, converter bolt-circle diameter, converter hole size or slot profile, ring gear tooth count, tooth pitch or module/DP reference, ring gear plane, plate thickness, overall offset, converter pad height, pilot location, and any local relief, window, drain, dimple, weld, rivet, or balancing feature.
Strong flex plate specifications also define datums and measurement conditions. For example, offset should state whether it is measured from the crank mounting face to the converter pad face, the ring gear centerline, or another datum plane. Runout needs a location and inspection diameter, such as ring gear face runout, ring gear radial runout, converter pad face runout, or OD runout. Hole position should be controlled by true position to a defined datum structure, not by a loose description such as “fits model year range.” If the part has welded, riveted, or press-fitted features, the sheet should describe the joint type, weld location or press fit, and the inspection method used to confirm it.
For supplier qualification, request these documents with the quote package:
- Controlled drawing or specification sheet with revision level and datum scheme
- Material declaration with grade, equivalent standard, and thickness before forming
- Heat-treatment or stress-relief record where applicable, including hardness method and range
- Dimensional inspection report for the quoted sample batch or production lot
- Balance requirement, including neutral balance or external balance details and correction method
- Ring gear details, including tooth count, tooth form, chamfer direction, hardness, and joining method
- Traceability identifier tied to batch, heat number, work order, or date code
- IATF 16949:2016 and ISO 9001:2015 certificates where applicable to the manufacturing site
- REACH (EC) No 1907/2006 declaration where required for EU supply
- Packaging specification showing rust prevention, separators, carton strength, and label information
If the supplier cannot show how a feature is measured, that feature is not truly controlled. The gap usually becomes expensive later, during incoming inspection, installation troubleshooting, or warranty analysis. Procurement should treat the spec sheet as the commercial baseline: the same revision, material, inspection method, and acceptance criteria should appear on the quote, sample approval file, purchase order, and production inspection report.
Core dimensions and material controls
The table below highlights the fields that matter most when comparing quotations. Exact values should always follow the programme drawing, but these are the controls procurement teams should expect to see in a serious offer. A low unit price does not mean much if the quotation leaves thickness, offset, ring gear position, material condition, or inspection method undefined.
| Spec item | What to verify | Buyer note |
|---|---|---|
| Outside diameter | Bellhousing clearance and starter path | Must match the approved drawing revision and ring gear OD |
| Center bore / pilot diameter | Locates the plate on the crankshaft pilot | Confirm datum, roundness, and allowable clearance |
| Plate thickness | Maintains stack-up, stiffness, and clamp geometry | Common sheet thickness is application-specific; control is often within ±0.10–0.20 mm where the drawing allows |
| Overall offset | Aligns converter pads and ring gear plane | Measure from the defined crank mounting face or drawing datum |
| Converter pad height | Controls torque converter axial position | Verify after forming, not only on flat blank stock |
| Flatness / face runout | Prevents wobble, starter noise, and fatigue | Typical aftermarket receiving targets may be ≤0.25–0.50 mm TIR, but the drawing requirement governs |
| Crankshaft bolt-circle diameter | Keeps crank mounting concentric | Control true position relative to center bore datum |
| Converter bolt-circle diameter | Supports torque converter installation | Slots, holes, pad embossments, and thread-clearance features must match the application drawing |
| Bolt-hole size and burr control | Protects fastener seating and clamp load | Edges should be deburred; burr height limits should be defined, commonly ≤0.10 mm where specified |
| Ring gear tooth count | Determines starter compatibility | Check against approved application data; visually similar plates may use different counts |
| Tooth pitch and tooth form | Controls starter mesh and noise | Inspect involute/profile, chamfer direction, lead-in, and tooth damage |
| Ring gear position | Sets starter pinion engagement depth | Measure axial plane and radial runout after joining |
| Material and hardness | Supports fatigue life under torsional and thermal cycling | Commonly low-carbon or medium-carbon steel for the plate with separately hardened ring gear; grade and hardness range must be stated |
| Balance features | Controls vibration and engine smoothness | Identify neutral balance, external balance weight/hole pattern, and allowable residual imbalance if specified |
| Coating / surface protection | Limits corrosion during storage and shipment | Define oil, phosphate, e-coat, zinc-rich, or other finish and any salt-spray or storage expectation |
