I have a 1980 CX500 which we are restoring. The engine ran a big end bearing and we had the crank rebuilt. Unfortunately this process has caused the crank to run out of true. The rebuilders got the main bearings aligned by welding them up and regrinding, but the ends are still not straight. The oil chain goes from tight to slack as the motor turns and I am scared the stator will touch the magnets in the flywheel casing. Any ideas where I can get a new crank, or does anyone have a spare good condition crank?? I am in Cape Town, South Africa. Thanks guys!!
Bent Crankshaft
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Sometimes worn chains have loose and tight spots.
Has this been checked with a runout dial to check that the issue is actually the crank?
You could also try removing the oil pump sprocket from the crank and checking that it is properly seated into the disc spring as this can cause misalignment if it is sitting on one side of the spring.
EDIT - thinking further on this I have also noted variations in the sprocket on the oil pump itself. It's just a stamping.
If it were me I'd remove the oil pump gear from the crank and check the crank runout without the gear fitted.
I don't have a dial caliper - which is the tool for the job - but would weld together a jig to bolt to the front cover holes in the case where runout could be checked with a feeler gauge as the motor is rotated.
If the crank is bent it would be a question for a good machine shop if it could be pressed straight. Another would likely be better.
At the back of the motor you should be able to remove the CDI advance cover and at the top of it you may be able to check the rotational clearance of the rotor to the stator at the top. A feeler gauge should reach through the opening above the advancer.
Has this been checked with a runout dial to check that the issue is actually the crank?
You could also try removing the oil pump sprocket from the crank and checking that it is properly seated into the disc spring as this can cause misalignment if it is sitting on one side of the spring.
EDIT - thinking further on this I have also noted variations in the sprocket on the oil pump itself. It's just a stamping.
If it were me I'd remove the oil pump gear from the crank and check the crank runout without the gear fitted.
I don't have a dial caliper - which is the tool for the job - but would weld together a jig to bolt to the front cover holes in the case where runout could be checked with a feeler gauge as the motor is rotated.
If the crank is bent it would be a question for a good machine shop if it could be pressed straight. Another would likely be better.
At the back of the motor you should be able to remove the CDI advance cover and at the top of it you may be able to check the rotational clearance of the rotor to the stator at the top. A feeler gauge should reach through the opening above the advancer.
Thank you!!! We have determined that the crank is bent. You can see the movement in the shaft as it turns. The motor is being re-assembled from scratch and I don't want to go any further as the crank is at the heart of the rebuild, which is why I am keen to source another crank... There will be issues with bearings I know but I have new Honda big end bearings and a new Honda oil pump chain which we have fitted, but not run yet so they can be carried over to the new crank as long as the bearings are in size..
Great - Thanks!! I have had a reply from someone in the USA that says he has a crank - waiting for as response from him. Goes under "Keith in Zulu In".
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Hopefully someone closer can help but I do have one but I won’t be home for a couple of days.
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I just got home and the crank I have is no good. I hope you can find something that works.
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