Rotax crankshaft: when to rebuild it and which measurements to check
In short The Rotax crankshaft is checked at every engine rebuild, which on the 125 MAX evo and the DD2 is due every 50 running hours. You measure the bearing seats, the con rod clearances, the run-out and the distance between the two crank halves, which must be 49.0 mm with a 0.05 mm tolerance. If the seats are worn you replace the complete crankshaft, if the con rod clearances are out you fit the overhaul kit with con rod. Watch out for 2027: under the RMC Global regulations the copper coloured con rods numbered 213, 365 and 367 will no longer be allowed.
What the Rotax crankshaft does and why it must be checked
The crankshaft turns the up and down movement of the piston into rotation. On the Rotax 125 MAX evo engines, from Micro to Senior, and on the 125 MAX DD2 evo it is made of two crank halves pressed onto the crank pin, with the con rod in the middle running on a needle cage.
It is one of the parts you see least and check least, because it sits closed inside the crankcase and under the engine seal. But it is also the one that does the most damage when it fails: a con rod that breaks at full revs rarely takes only itself with it.
That is why the crankshaft is not only looked at when the engine makes a noise. It is measured at every rebuild, with precise numbers, and those numbers decide what gets replaced.
How often the Rotax crankshaft is rebuilt
In the maintenance schedule of the Rotax 125 MAX evo and DD2 engines, the full engine inspection by an authorised service centre is due every 50 running hours. That is the rebuild where the crankcase is opened and the crankshaft is measured.
Fifty hours sound like a lot, but in a season of races and testing they come quickly: a test day with 5 or 6 sessions easily adds up to more than one running hour. To know where you are you need an hour meter or a track logbook where you write down the hours every time you go out.
Before 50 hours there are signs that tell you not to wait: new vibrations, noise from the crankcase, leaking oil seals, an engine that has taken in water or has seized. In these cases have the crankshaft checked straight away.
The measurements to check on the Rotax crankshaft
Before measuring, the crankshaft is cleaned with a degreaser and inspected visually: bearing seats, running surfaces, oil seal areas, taper and keyway must show no wear marks or overheating colours.
Then you measure. These are the values for the 125 MAX evo family and for the DD2:
CS01, main bearing seats: new 29.980 - 29.995 mm, limit 29.94 mm.
CS02, clutch bearing seat: new 14.98 - 15.003 mm, limit 14.95 mm.
CS03, piston pin bearing seat: new 18.99 - 19.005 mm, limit 19.015 mm.
CS04, con rod axial clearance: new 0.52 - 0.87 mm, limit 0.90 mm. Measured with a feeler gauge.
CS05, con rod big end radial clearance: new 0.020 - 0.026 mm, limit 0.03 mm.
CS06, crankshaft run-out: maximum 0.03 mm, measured with a dial gauge.
CS07, distance between the two crank halves: 48.95 - 49.05 mm.
CS08, thrust washer thickness: 1.00 - 1.07 mm.
Why the distance between the crank halves is the most delicate measurement
CS07 is the measurement most often got wrong when a crankshaft is re-pressed. It must be 49.0 mm with a tolerance of 0.05 mm either way: half a tenth.
If the crank halves are too wide, the con rod has too much side play: it moves left and right on every revolution and in the long run it can break.
If they are too narrow, the con rod does not have enough play: friction goes up, the big end temperature rises and the needle cage ends up failing.
That is why after every re-pressing all the dimensions from CS01 to CS07 are measured again before the engine is reassembled.
Crankshaft out of spec: what gets replaced
The measurements also tell you what to replace. The rule is simple:
Worn seats (CS01 or CS02 at the limit): you replace the complete crankshaft. For the MAX engines it is the Rotax MAX complete crankshaft, part number 685098, for the DD2 the Rotax DD2 complete crankshaft, part number 685099.
Con rod and clearances out (CS03, CS04 or CS05 at the limit): you fit the Rotax crankshaft overhaul kit with con rod, part number 685011. The price list also has the version with copper con rod, part number 295871.
Bent crankshaft or crank halves out of dimension (CS06 or CS07): the crankshaft is realigned and re-pressed with the dedicated tool, the Rotax crankshaft repair kit, part number 276052, then everything is measured again.
The overhaul kit is always fitted complete. The parts are matched to each other: you do not replace only the big end needle cage and leave the rest.
Con rod: what changes from 2027
Under the RMC Global Technical Regulations 2026 the con rod must have one of these numbers stamped on the shaft: 213, 365, 367 or 362. The 213, 365 and 367 con rods have a copper coloured shaft, the 362 is grey. The shaft cannot be ground or polished.
The same regulations warn that from 1 January 2027 the con rods numbered 213, 365 and 367 will no longer be allowed. The Italian RMC Italia 2026 regulations still allow all four for now.
If you are about to rebuild the crankshaft and in 2027 you want to race under RMC Global regulations, check the number stamped on the con rod and choose the right kit. If you are not sure which kit carries which con rod, message us before you order.
Main bearings: only the approved ones
Together with the crankshaft you also check the main bearings. Under the 2026 regulations only the original 6206 FAG bearings supplied by Rotax are allowed, marked FAG Z-579165.11.KL or Z-579165.21.KL. The fitting direction is free.
The Rotax 6206 bearing is in the shop together with the other crankcase spare parts.
Our advice
The crankshaft is the heart of the engine. Do the 50 hour rebuild even if the engine seems to run fine, keep track of the hours in a track logbook and, if a measurement is at the limit, replace the part instead of doing another season. An overhaul kit costs less than a broken crankcase.
If you do not have the tools to re-press the crankshaft, rely on a Rotax service centre: without the tool and a dial gauge the CS06 and CS07 dimensions cannot be held.
Frequently asked questions about the Rotax crankshaft
How often should the Rotax crankshaft be rebuilt?
The full engine inspection, with the crankshaft check, is due every 50 running hours on the 125 MAX evo and on the DD2. It is done earlier if vibrations or crankcase noise appear, or after a seizure.
What should the distance between the crank halves be?
CS07 must be 49.0 mm with a tolerance of 0.05 mm, so between 48.95 and 49.05 mm. If it is wider the con rod moves sideways and can break, if it is narrower the big end overheats.
Can I replace only the big end needle cage?
No. The crankshaft overhaul kit with con rod has parts matched to each other and must be fitted complete.
When do you replace the complete crankshaft instead of fitting the overhaul kit?
When the main bearing seats (CS01) or the clutch bearing seat (CS02) reach the wear limit. If instead the con rod clearances (CS03, CS04, CS05) are out, the overhaul kit with con rod is enough.
Can I use the copper coloured con rod in 2027?
Under the RMC Global regulations, from 1 January 2027 the con rods numbered 213, 365 and 367, the copper coloured ones, will no longer be allowed. The grey 362 con rod remains allowed.
Is the Rotax crankshaft the same for MAX and DD2?
No. For the MAX engines there is the complete crankshaft 685098, for the DD2 the complete crankshaft 685099. The overhaul kit with con rod 685011 is in the price list for both.
Sources: BRP-Rotax, Repair Manual 125 MAX evo and 125 MAX DD2 evo, edition 1 April 2024; Rotax Tech Tip 04; Global RMC Technical Regulation 2026, article 5.7; Rotax Max Challenge Italia 2026 Technical Regulations V2.1; Rotax 2026 spare parts price list.
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Read also: Rotax engine maintenance → · How to measure squish on Rotax engines → · Rotax MAX torque settings → · Rotax engine running in → · Rotax technical scrutineering → · Kart track logbook →
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Author: Sergio, TKS RaceLab | Published: 22 October 2026
TKS RaceLab is the Italian online store dedicated to karting: spare parts, accessories and everything you need to get on track. With Arrive & Drive you arrive at South Garda Karting (Lonato), Franciacorta, Cremona or Ala and find your kart ready to go. No hassle, just driving.
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