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Can extended high RPM damage flywheel magnets?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by jeremystones, May 9, 2016.

  1. Hi Guys,

    New Member here.. Got myself a 1980 KZ250 C which i'm in the process of getting on the road.
    I'm learning more about bike mechanics but don't have a space of my own yet, so took it to a local Mechanic.

    Having bought it (from interstate) without test riding, i was ready for a few surprises, but had a heap of unexpected issues.
    Turns out that the whole top end needed rebuilding (bad oil leaks), including overbored cylinder, OS piston & rings, valves, valve seals & springs, rockers, camshaft, cam chain, new points & timing advancer... Basically the entire top end is now new.

    SO.... I thought i'd be on my way with this done, but heading into the workshop to check it out I noticed that my (chrome) muffler had all this new heat damage on it. When questioned, the mechanic explained that he'd run the thing consistently at really high RPM to "Wear in the rings". To my understanding, this is the opposite of what you should be doing anyways. After this process, the mechanic took it for a test ride wher he discovered that it was also starting to have timing issues, despite the new points and advancer.

    He's then apparently spent 10 hours, unsuccessfully trying to get the timing right, finding out that it's now got a really weak spark. Finally after all this time looking at the timing marks on the rotor, he's noticed 2 significant cracks in the flywheel rotor magnets, which look even more severe when we removed the stator coil.

    Ok. now i've set the scene (thanks for bearing with me so far), my QUESTION is: Can this process of extended high RPM / redlining the bike (to wear in rings) have potentially caused the rotor magnets to crack? I've had a few people say yes and have found anecdotal evidence online about it, but need more proof before I go in there & challenge him on it.

    To me, that would explain why this issue of low spark (as alternator stops working & battery begins being drained) has only just appeared after the rebuild & gotten progressively worse. Does that sound plausible?

    Unfortunately, this would reflect a pattern of behaviour for this mechanic - they snapped my Fuel Tap / Petcock without telling me (using pliers) and hoped that i wouldn't pick up on it (i did).

    Any help would be really appreciated. I've ordered a replacement flywheel (which was US$350) All i want is to get the bike out of this garage ASAP, without having to pay these guys the labour they've wasted on my bike, let alone the damage they've caused to it over th last 6 MONTHS they've had it!

    Thanks everyone.


  2. hello
    • Like Like x 1
  3. ?????????????????????????
  4. It takes 2 minutes of reasonably high,NOT REDLINE revving to seat rings on a first start. That's 3500 rpm and then 3 or 4 heat cycles with plenty of cool down time between. You can expect wear on old bikes,some things need fixing. Sounds to me like your getting everything fixed and maybe not to well done at that.How much money are you expecting to spend on this $1000 bike.
  5. slightly more?
  6. Speak of the devil, I purchased a 250ltd yesterday and have engine issues.

    Running a aircooled bike at high rpm with no airflow and with no load on the engine is the most idiotic thing I could think of.
    If the engine has been overheated to red hot without cooling then yes its very possible things would have cracked, warped or thrown things out of wack.

    If it was a few cycles of warmup, slow advance to full rpm and hold for 30 seconds, then back down a few times it would be fine.
    You do not 'wear in' the rings by bouncing off the limiter with no load.

    Honestly I doubt you will have any luck with them unless you have proof of the condition before the overhaul. The bikes 35 years old, its expected for it to have gremlins.
  7. Thanks for the feedback guys. Appreciate that it's an old bike and things will let go.

    I have contacted the guy I bought it from and he's confirmed that there was no damage to the flywheel when he sold it to me.. It did have fuel issues (which he disclosed) so It was shipped directly from QLD to this mechanic, so I've never ridden it.

    Had planned on spending around 2k on getting this thing running really nicely. Thing is I've been the one doing all the research on issues / sourcing and purchasing all the parts myself and constantly having to chase the mechanic for updates over the last 6 months since I bought it.

    I've made some other enquiries to bike mechanics that my mates reccomended, and most importantly they've all given pretty damning reviews of the workshop my bike is at..

    If anyone has any more info about the specific issue though, of cracking flywheel magnets due to negligent high rpm (with no load), that would be super helpful

  8. Good luck finding evidence of any damage done to the flywheel by this mechanic.

    If your not happy, before he does any more work on the bike, ask for the bill pay him up and take the bike to someone you have confidence in.
    • Agree Agree x 1