Permanent Fix For Grubee 1 Piece Wide Crank Problem

Discussion in 'Frame Mounted Engines' started by Irish John, Apr 4, 2011.

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  1. Irish John

    Irish John Guest

    Those of you 4-strokers who prefer the look of the one piece wide crank to the 3 piece cranks with the short crank arms and pedal holes that won't take cruiser pedals, will probably have noticed that, after prolonged use, the chainring will start to slip on crank. It feels like the chain is slipping on the cogs. This happens because the chainring is only held in place by the right side bearing cone being screwed on tightly against the chainring and the hexagonal hole in the middle of the chainring is never a good fit over the forged crank. In time the chainring will turn and the hexagonal hole will become rounded because the metal of the chainring is very soft (see pictures).
    This has happened to me a lot even though I use red threadloc on the bearing cones and adjuster nut. Eventually the immense forces generated by the extra wide crank will loosen the chainring fastening and the chainring will start to turn independently of the crank- at first just an occasional slip but eventually you will lose all pedal power on hills. Ordinary 1 piece cranks have a lug on the crank arm that goes into a hole on the chainring to stop it from turning but this is not feasible on the extra wide crank.
    After about 8 crank removals and fixes by replacing the worn chainring I have eventually chosen to spot weld the chainring to the crank itself. The drawback is that when the chainring needs replacing I will have to cut the spot-welds off to remove it but I reckon the chainring is good for a long time on a motorised bike because you don't really need to pedal very hard so it doesn’t wear the teeth out quickly.
    In the event of dropping the bike on a corner and bending the crank arm then it would be a real pain to take the chainring off to get the crank straightened.
    If the 3 piece cranks had pedal holes for cruiser pedals (15mm) and not for MTB pedals (14mm) I would consider changing but a good adaptor kit to fit a cruiser bottom bracket is $65 and the $15 Grubee ones are so inferior they are really not worth installing. I'm stuck with the one piece cranks for the time being.
    One piece cranks don't really suit heavy steel cruisers - the weight of the bike puts more force on the crank bearings and if you have a coaster brake the pedal chain needs to be very tight which adds to the strain on the bearings. I reckon alloy cruisers and derailleur gears are kinder to one piece cranks.





    Last edited by a moderator: Apr 4, 2011