A crankshaft is a multi-axis fatigue-critical component, not a conventional round shaft. Its main bearing journals should establish a common rotation axis, while each connecting-rod crankpin intentionally follows an offset orbit. Webs, counterweights, thrust faces, fillet radii, oliehuller, nose features and the flywheel flange all influence measurement and the safe load path.
A reliable crankshaft straightening solution must therefore answer five questions before machine selection:
- Is this a production crankshaft, a remanufacturing part or a small-engine repair?
- Which main-journal axis and support condition define the bend map?
- Is the deviation a correctable global bend, local journal form error, grinding-stock problem or crack/damage condition?
- Which pressure, roll-straightening or peening route is approved for the material and process stage?
- Hvordan vil frigivet geometri, fillet integrity, grinding allowance and final balance be verified?
*Engineering concept illustration: a multi-throw crankshaft supported and measured for a controlled correction study. It is not a customer-site photograph. Actual contact zones, force limits and machine architecture require drawings and representative sample tests.*
Crankshaft Straightening Is Not One Market
DataForSEO results for crankshaft straightening machine show several different search intents on the same results page: small-engine repair tools, workshop hydraulic presses, large crankshaft repair equipment and high-production deep-rolling/roll-straightening systems. These should not be combined into one generic machine offer.
| Crankshaft Family | Typical Context | Engineering Route |
|---|---|---|
| Forged automotive crankshaft | Controlled production between machining operations | Automated measurement plus validated pressure or roll-straightening process |
| Large diesel, marine or industrial crankshaft | New production or specialized repair | Heavy handling, multiple supports and project-specific pressure/rolling route |
| Remanufacturing crankshaft | Slid, varme, crash or bearing-failure history | Inspektion, grinding-stock and repair decision before straightening |
| Small vertical-shaft engine crank | Compact repair-tool market | Separate product, fixturing and safety envelope |
| Built-up or pressed crankshaft | Multiple assembled webs, pins and interference fits | Assembly alignment process; not a one-piece forged-crank recipe |
| Cast or nodular-iron crankshaft | Material-specific fatigue and crack behavior | Metallurgical approval and restricted correction study |
This page focuses on one-piece industrial and automotive crankshafts. A small lawn-equipment straightener or a built-up motorcycle crankshaft needs a different solution.
Define the Crankshaft Anatomy and Datum Chain
The technical proposal should identify every functional feature:
- all main bearing journals and their numbering;
- connecting-rod crankpins, stroke and angular phase;
- webs and counterweights;
- front nose, timing, nøglespor, spline or gear features;
- rear flange, pilot bore and flywheel interface;
- thrust faces and axial datum;
- main- and pin-journal fillet radii;
- oliehuller, cross-drillings and internal passages;
- hardened or deep-rolled regions;
- balance holes, milled pads or added balance features;
- centers or temporary process datums;
- grinding stock by journal and process stage.
The main-journal common axis normally controls the global bend decision. Crankpins are intentionally eccentric and must be evaluated relative to the main axis, stroke and phase. A crankpin’s raw radial motion is not direct evidence of a bent shaft.
Frys produktions- eller reparationsfasen
After Forging and Rough Machining
The part may contain scale, stock variation and unfinished datum features. Correction can support downstream machining, but the measurement system must distinguish stock variation from actual axis displacement.
After Main- and Pin-Journal Pre-Machining
Functional journal tracks and process datums are available while grinding allowance remains. Hegenscheidt describes deep rolling and roll straightening after pre-machining, with main-bearing TIR measured before the correction calculation. This confirms that the process stage and stock plan are inseparable.
After Heat Treatment or Surface Hardening
Residual stress, hardness and springback may change. A force/displacement recipe from a soft blank cannot automatically be transferred to a hardened crankshaft. Crack risk and post-process inspection become explicit acceptance gates.
After Fillet Deep Rolling
Deep rolling is used to induce compressive residual stress at highly loaded fillets. A subsequent correction operation must not destroy the intended fillet condition or impose an unvalidated strain path. Pressure contact on the fillet is prohibited unless the crankshaft designer approves a dedicated process.
Før endelig slibning
Straightening may reduce the stock required to generate a common main-journal axis. The outgoing map must prove that every journal still has adequate grinding allowance.
After Final Grinding
Journal diameter, rundhed, overfladefinish, fillet geometry and thrust faces are functional. Contact becomes more restrictive, and a regrind/repair/reject route may be safer than further pressure correction.
Service eller genfremstilling retur
Heat damage, bearing seizure, scoring, revner, previous grinding, svejsning, plating or prior straightening can alter the risk. A repair history and inspection record are required before force is applied.
| Scene | Main Opportunity | Hovedrisiko | Påkrævet bevis |
|---|---|---|---|
| Rough forging | Reduce machining imbalance | Stock variation masks geometry | Qualified process datums and stock map |
| Pre-machined | Multi-journal bend map is available | Wrong support reference | Main-journal TIR and grinding allowance |
| Heat-treated | Korrekt varmebehandlingsforvrængning | Springback and crack initiation | Material/hardness and force-displacement trials |
| Deep-rolled | Coordinate runout and fillet-strength process | Damage to compressive fillet condition | Process-owner approval and fillet protection |
| Finish-ground | Salvage within final geometry | Surface/form damage and lost stock | Full journal/fillet inspection and repair limit |
| Service return | Recover a repairable component | Hidden fatigue, heat or prior-repair damage | NDT, history, stock and disposition rules |
Separate Main Journals from Offset Crankpins
Marposs describes crankshaft gauging that measures both main-journal diameters rotating about the main geometric axis and pin-journal diameters following an orbital path around that axis. This is a fundamental signal-separation requirement.
*Engineering concept illustration: the main-journal bend map and offset crankpin geometry require separate measurement tracks. The actual probe locations, rotation model and feature masks follow the drawing and gauge-correlation plan.*
| Målespor | What It Establishes | Common Error if Misused |
|---|---|---|
| All main journals | Common-axis runout and bend map | Local lobing is interpreted as global bend |
| Front and rear main journals | Support/reference axis | End damage biases the full map |
| Crankpins | Diameter, orbit, stroke and phase relation | Intentional eccentricity is interpreted as runout |
| Thrust faces | Axial location and face runout | Burrs or local wear dominate the reading |
| Front nose and rear flange | Connected-component relationship | Feature error is treated as shaft bend |
| Journal roundness/cylindricity | Lokal form | A low TIR value hides local form error |
| Fillet and oil-hole regions | Structural and surface condition | A fatigue-critical defect is missed |
| Balance correction planes | Mass-axis condition | Balance is mistaken for geometric straightness |
Nidec’s crankshaft measuring system separately grades journal and pin outside diameters. Marposs also supports final or inter-operational dimensional, geometric and non-destructive measurement. The transferable lesson is not a competitor accuracy value; it is the need for a drawing-based multi-characteristic inspection plan.
Select the Correct Support Reference
Crankshaft runout may be measured:
- between qualified centers;
- on end main journals;
- on selected V-rollers;
- in bearing-equivalent supports;
- in a grinding-machine or dedicated gauge setup.
Hegenscheidt lists runout measurement referenced to centers or V-blocks. These setups do not automatically produce identical results. The solution should define:
- physical support journals and coordinates;
- center condition and qualification method;
- journal roundness compensation;
- axial restraint and permitted movement;
- crank angle and angular indexing;
- gravity sag for large crankshafts;
- sensor force and feature masks;
- released-state repeatability;
- correlation to the grinder and customer gauge.
The machine must not change datums midway through the correction loop without an established transformation and correlation study.
Pressure, Roll Straightening and Peening Are Different Processes
Controlled Pressure Straightening
A press applies a localized three-point or constrained load at an approved main-journal region. Gleason’s heavy-duty repair equipment demonstrates one market route in which supports, overhead hold-downs and a movable ram localize the work around a selected journal. The exact competitor layout and capacity are not a StraighteningTech specification.
Pressure straightening requires:
- a verified global-bend diagnosis;
- an approved load path through journals/webs;
- broad radiused contact tooling;
- force and displacement ceilings;
- springback characterization;
- full unloading before acceptance;
- post-correction crack and surface checks.
Rulleopretning
Hegenscheidt combines angle-dependent deep rolling, main-bearing TIR measurement and roll straightening. This is a production technology linked to fillet treatment and pre-grind geometry. It should not be described as a generic multi-roll bar straightener.
Peening
Repair-market SERPs also show peening methods. Peening changes local residual stress and requires a separately qualified work instruction, operator controls, surface rules and inspection. It is not an automatic substitute for pressure straightening, and this article does not claim a universal peening recipe.
| Metode | Potential Fit | Primary Control | Do Not Assume |
|---|---|---|---|
| Pressure straightening | Approved bare crankshaft with safe load path | Kraft, forskydning, support span and released TIR | Finished fillets/journals tolerate contact |
| Roll straightening | Production process integrated with journal/fillet operations | Angle-dependent rolling and main-journal map | Same tooling fits every crank family |
| Peening | Specialist repair method | Beliggenhed, intensity, residual stress and surface inspection | Hammering is inherently safe or repeatable |
| Slibning | Local form/diameter and limited eccentricity within stock | Journal geometry and stock removal | Grinding can remove every global bend |
| Replacement/rejection | Crack, burn, insufficient stock or unsafe load path | Engineering disposition | Every bent crankshaft is repairable |
Byg et beskyttet kontaktkort
Default No-Press and No-Support Zones
- main- and pin-journal fillet radii;
- oil holes and cross-drillings;
- offset crankpins unless a dedicated route approves them;
- thrust faces and finished flange faces;
- nøglebaner, splines, threads and timing features;
- balance holes and local mass-correction features;
- sharp web transitions and thin counterweight edges;
- deep-rolled, induction-hardened, nitreret, welded, plated or repaired regions;
- revnet, brændt, scored or heat-affected surfaces;
- finished journals without protected tooling approval.
Potentially Approved Zones
- rough or semi-finished main-journal lands with adequate stock;
- process collars or sacrificial extensions;
- designer-approved web/journal load paths;
- dedicated rolling contact locations defined by the manufacturing process.
*Engineering concept illustration: correction is confined to an approved main-journal load path while fillets, oliehuller, crankpins and thrust faces remain protected. The image does not authorize these locations for a real part.*
The safe contact map should be stored by part number and drawing revision. A journal that is safe before grinding may become a protected final surface later.
Styr tilbagespring og krydskobling
A correction at one main journal changes the elastic shape of adjacent webs and journals. The process should use a complete main-journal bend map rather than chasing one indicator peak.
For each correction step:
- rotate and measure all controlled main journals;
- separate local form from center displacement;
- identify the correction coordinate and crank angle;
- apply a validated incremental load;
- record force and displacement;
- fully unload;
- rotate and remeasure the complete map;
- check adjacent crankpins, thrust/flange and protected surfaces;
- stop on abnormal stiffness, non-repeatability or inspection indication.
Loaded displacement is not the finished result. Only the released and repeated map can determine whether springback has been compensated safely.
Straightening vs Grinding
Grinding can generate journal diameter, rundhed, cylindricity and surface finish. It can also remove limited eccentricity while stock remains. It cannot be assumed to restore a common main-journal axis if the required stock removal would violate size, fillet or hardness limits.
The decision needs a journal-by-journal stock map:
- incoming diameter and runout;
- minimum finished size;
- remaining hard layer or repair coating;
- permitted undersize/repair class;
- fillet and thrust-face geometry;
- grinder support and datum setup;
- expected stock after released straightening.
Marposs in-process grinding gauges show that main and pin journal diameters have distinct motion and measurement requirements. Straightening and grinding should therefore be planned as connected but separate operations.
Straightening vs Balancing
Crankshaft balancing corrects mass distribution relative to defined correction planes and, in engine applications, may be linked to bobweight and rotating/reciprocating mass assumptions. It does not correct main-journal coaxiality, pin-journal form or a bent global axis.
If straightening, slibning, boring, milling, svejsning, plating or material removal occurs after balancing, the final balance condition must be reverified. A crankshaft may pass geometric runout and still fail the balance requirement, or pass balance while a main journal is geometrically displaced.
Crack, Surface and Fatigue-Sensitive Inspection
Meeting a runout target is not sufficient if correction introduces a harmful indication or damages a fatigue-critical surface. Inspektionsplanen bør definere:
- pre-cleaning and visual inspection;
- magnetic-particle, eddy-current or other approved NDT route by material/process;
- fillet and oil-hole coverage;
- journal dent, bruise and surface-finish limits;
- grinding-burn or heat-damage inspection;
- hardness/depth checks when required;
- acceptance criteria for prior weld, plating or repair;
- inspection timing before and after correction/grinding;
- engineering disposition for borderline indications.
Hegenscheidt’s process claim regarding fatigue-strength preservation belongs to its validated rolling system. It cannot be transferred to a pressure-straightening proposal without our own samples, material approval and fatigue-sensitive validation.
Closed-Loop Crankshaft Straightening Process
1. Identify the Part
Load the correct recipe from crankshaft number, engine family, materiale, processtadiet, drawing revision and repair history.
2. Efterse og rengør
Clean journals and datum surfaces. Inspect oil holes, fillets, journal surfaces, webs, nose and flange. Complete required pre-process NDT.
3. Kvalificere datoopsætningen
Verify centers or support journals, axial location, rotation and seating repeatability.
4. Build the Multi-Journal Map
Measure every main journal through rotation. Record pin-journal, thrust, nose and flange characteristics separately where required.
5. Klassificer afvigelsen
Separate global bend from journal lobing, tilspidsning, grinding-stock error, crankpin phase/stroke error, flange damage, sprække, heat distortion or unbalance.
6. Select the Approved Method and Load Path
Choose pressure, rullende, peening, grinding or rejection according to the validated part route. Confirm all protected zones.
7. Anvend trinvis korrektion
Control force, forskydning, crank angle and tooling position. Stop on abnormal response.
8. Frigivelse og nymåling
Fully unload and rotate the crankshaft again. Update the complete main-journal map rather than checking only the corrected location.
9. Inspect and Route Downstream
Perform post-correction NDT/surface checks and confirm grinding stock. Route to grinding, final gauging, balancing and assembly inspection.
10. Optag resultatet
Store identity, opskrift revision, datum opsætning, før/efter kort, correction coordinates, force-displacement curves, alarmer, eftersyn og disponering.
Proposed Crankshaft Straightening Cell
A project-specific system may include:
- electromechanical or hydraulic correction unit sized by sample testing;
- adjustable main-journal rollers, centers or V-supports;
- servo rotation and crank-angle indexing;
- multiple runout sensors for the main-journal map;
- separate crankpin, thrust, nose and flange measurement modules;
- broad interchangeable press shoes and protected supports;
- automatic keep-out logic for fillets, oil holes and counterweights;
- force/displacement monitoring and springback compensation;
- heavy-part loading, lifting and anti-roll safety;
- recipe control, traceability and quality-data export;
- interfaces to grinding, NDT and balancing records.
The configuration for a small automotive crankshaft is not automatically suitable for a large marine crankshaft or repair-shop part.
Prøveprøve og acceptplan
Representative samples should cover:
- smallest and largest crankshaft length, swing, mass and journal diameter;
- different main-journal counts, crankpin strokes and counterweight layouts;
- forged, cast and approved repair conditions;
- rough, pre-machined, heat-treated, deep-rolled and finish-ground stages;
- material and hardness extremes;
- expected incoming bend shapes and crank angles;
- journal form-error samples that should not trigger correction;
- minimum grinding stock;
- godkendte og forbudte kontaktzoner;
- force/displacement and springback envelope;
- adjacent-journal cross-coupling;
- main-journal and crankpin gauge correlation;
- pre/post NDT and surface results;
- final grinding and balance verification;
- repeatability and NOK routing.
Brug Udretningsprøvetest og acceptvejledning to separate feasibility, FEDT, SAT and production capability.
Data påkrævet for et teknisk forslag
Angiv venligst:
- crankshaft drawing and revision;
- engine/application and crankshaft family;
- one-piece forged/cast or built-up construction;
- materiale, varmebehandling, hardness and fillet treatment;
- current manufacturing or repair stage;
- main-journal, crankpin, thrust, nose and flange dimensions;
- slagtilfælde, pin phase and counterweight layout;
- oil-hole and internal-passage map;
- incoming main-journal runout map by angle;
- journal roundness, cylindricity and taper results;
- drawing datums and customer measurement setup;
- approved support/correction zones and prohibited features;
- grinding stock by journal;
- sprække, burn, surface and repair acceptance criteria;
- downstream grinding, balancing and assembly sequence;
- report and traceability requirements;
- representative samples for trials.
Ofte stillede spørgsmål
Can a Crankshaft Be Straightened?
Some crankshafts can be corrected, but feasibility depends on material, konstruktion, processtadiet, bøje form, grinding stock, fillet condition and a safe load path. A crack, heat-damaged journal or insufficient stock may require repair or rejection instead.
How Can You Tell If a Crankshaft Is Bent?
Measure all main journals in a qualified support setup and separate local roundness from center displacement. Crankpin orbital motion, thrust-face runout and flange/nose features require separate tracks.
Can You Press on a Crankpin or Fillet?
Do not assume so. Crankpins are offset features and fillets are fatigue-critical. The default contact map protects crankpins, fillets, oil holes and finished thrust surfaces unless a dedicated process is approved.
Is Peening Better Than Press Straightening?
They are different residual-stress and correction processes. The correct route depends on crankshaft design, materiale, production/repair stage and validated work instructions. Neither should be selected from a generic internet procedure.
Can Grinding Remove Crankshaft Bend?
Grinding can remove limited eccentricity within the stock allowance and generate final journal form. It cannot safely solve every common-axis error. Use a journal-by-journal stock map.
Is Crankshaft Balancing Still Required?
Yes when specified. Straightening corrects geometry; balancing corrects mass distribution. Reverify balance after any operation that changes geometry or mass.
Should a Service Crankshaft Be Inspected for Cracks?
Ja, according to the material, repair standard and customer requirement. Straightening must not be used to hide a crack, burn, seizure or previous-repair condition.
Build the Solution Around the Main-Journal Axis
We develop crankshaft straightening solutions around the actual crank family, main-journal datum, offset crankpin geometry, processtadiet, beskyttede fileter, safe load path, released bend map, grinding stock and final inspection sequence. The machine architecture follows evidence from drawings and sample trials—not a generic shaft recipe or a competitor specification.
Send the crankshaft drawing, processtadiet, materielle tilstand, incoming journal map, grinding allowance, inspection standard and representative samples. We can then define the measurement strategy, pressure or rolling route, tooling map, correction envelope and traceable acceptance plan for your crankshaft application.