Bearings: What type to use

Forums Technical Two Stroke: Help needed Bearings: What type to use

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    • #5345
      John Gray

      My supa5 handbook recommends Plastic caged C3 bearings for the mains, and metal caged C4 bearings for the gearbox. However, the earlier 4-speed manual specifies plastic cages throughout, and the later ETZ ones use C4 bearings throughout. Does anyone know the reasons for these changes? I would prefer to use plastic cages for my Supa5 rebuild if possible.

    • #5346

      Hi there is plenty of information on the internet, and you could do a lot worse than speaking to your local bearing stockists.

      plastic cage bearings are cheaper to make, however they are very good at tasks they are designed for – including running quieter- however some materials can be degraded by heat and contamination (oil and combustion products),

      C3 and C4 are bearings with larger operating tolerance than normal or “CN” bearing.
      in the main bearings for example they allow for expansion due to heat – C3 having more clearance than CN and C4’s have more tolerance than C3 – and again the operating requirements for the bearing may demand the more clearance that a C4 provides –
      I always tend to use recommended bearing types (C3 C4 etc.) however I am old fashioned and I view metal caged bearings as of being better quality.

      some eastern block bikes used to have less balls or rollers in than western made bearings ( because they were cheaper to make) and this is what lead to a lot of bearing failures
      so in short do some research on the internet and ask someone who knows about bearings and don’t forget YOU GET WHAT YOU PAY FOR

      sorry I cannot provide a definitive answer however if it was my bike and I could not get advice from someone who knows what they are talking about – I would use what the manufacturer recommends

    • #5347
      John Gray

      Thanks, Ian for taking the trouble to reply, but I am seeking info specific to MZs and the Supa5 in particular.

      My local bearings trader says C4 mains are Ok for modern Jap motorbikes and would *probably* be OK for an MZ.

      The internet has a lot of information about bearings in general, but nothing about what to use in an MZ.

      I agree it is wise to follow the manufacturers recommendations, but these have changed for what are essentially very similar engines. Why?

      • This reply was modified 8 years, 10 months ago by John Gray.
    • #5349

      hi again, the difference in the main bearings may be due to the different methods of lubrication, eg pre-mix and oil injection

      and in regards to the gearbox, this differs from the main bearings in the way it is lubricated eg. by thicker gear oil.

      and the different cage materials may be due to the fact that as the models developed mz had to adapt to a increasing market in western Europe that demanded better quality ?. and as oil technology improved this may have effected the choice of bearings.

      One final factor to consider is the power characteristics of the engine – the etz seems to be a more “revvy” engine than the Super 5 which has more torque lower down. It may be worth asking the same question on one of the MZ racing web sites or post it on the German MZ site which has an English speaking forum

      keep us posted of your findings…..ian

    • #5353
      John Gray

      Thanks again for taking the trouble to consider the question, but I am still hopeful somebody on this website will know the answer before looking further afield.

    • #5370
      Peter Fielding

      Hi John,

      Intrigued by your query so I had a look at my spares books and they seem to differ from your source. My TS250 book specifies C4 fit bearings for mains and gearbox for the 5 spd motor. The only C3 fit is for the clutch outrigger bearing which is mounted in a steel drum whereas the others are mounted directly in the alloy. The ETZ motors are the same which is predictable as they are very similar in construction – indeed many of the bits are interchangeable. The 4 speed TS motor is specified as C3 for the main bearings C4 for gearbox so I wonder if your reference book has got them mixed up. I suspect the slightly tighter fitting for the 4spd engine is because its mains are lubricated by gearbox oil (rather than petroil as in the 5spd motors) so probably run a bit coooler.

      Let us know if you get any better answers.



    • #5372
      John Gray

      Hello Peter,
      You are clearly correct. It is some years since I actually read the Supa5 spec, and obviously my memory must have been playing tricks about the mains. Your explanation for the difference seems extremely likely, so thanks a lot for clearing it up.

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