SOHC.co.uk Forums > CB500/550
Cam shaft and rocker arm wear?
Oddjob:
Got the reply from them today, they have quoted £100-120 plus VAT plus P&P.
Good price.
Sesman:
I presume that’s just a regrind and surface heat treatment?
Oddjob:
That was a price to reprofile the cams, which is essentially the same as repairing the lobes.
I asked for an additional 5 degree overlap and 10 degree duration as per Mark Paris recommendations.
Additional information.
After emailing with Newmans the price for repairing the lobes is the same as reprofiling them, just wanted to confirm that. They are EXCELLENT at responding.
I also asked about journal wear, like scoring etc, these can also be repaired by hard chroming the journal and grinding it back down to size, cost is £40 a journal, even doing all 4 at £160 is cheaper than finding a NOS cam. Plus it would probably last longer so long as the oil problem that caused it in the first place is solved.
He did however say that the cam lobes must not be knackered, I presume by that not blued etc due to oil starvation where the lobe has virtually melted. I'm trying to get some clarity on what or how much damage is knackered.
Hope that helps those who want a cam repaired.
Laverda Dave:
Admittedly I am no metallurgist and therefore my knowledge of surface treatments is somewhat limited but, I remember asking a question to a camshaft engineer a few years ago about surface treatments applicable to my Honda 400/4 camshaft as in would they case harden the re-profiled lobes to bring it back to standard. The response I received was Honda camshafts are made from chilled iron and don’t have any surface treatments?
I always thought the lobe of a cam is case hardened to prevent rapid wear or does ‘chilling’ cast iron produce the hardened surface? When I was at school we case hardened metal by heating it and dipping it into a tin of powered carbon (I think, it was a long, long time ago). I also thought a worn cam lobe is built up by ‘welding’ new hard wearing metal (stallite?) to it using a metal spray technique but apparently this isn’t always the case, some lobes are just re-profiled but this is something I just don’t understand, surely re-profiling will make the lobe smaller so how can it therefore provide the specified lift to the valve? This would especially apply to something like a four cylinder ohc, if one lobe is worn and re-profiled I therefore assume the remaining lobes will have to be re-profiled to match even if they are not worn otherwise one lobe will be smaller than the others?
Also, if the cam is chilled iron and therefore has a certain depth of case hardened material on its surface, how deep is the case hardening and will re-profiling the lobe go below the hardened depth?
Is the above the reason why Honda recommend the frequent oil changes they specify, to protect the cams that are not case hardened?
My head hurts now ???
Sesman:
Ken.
Can you expand upon the 5 and 10 please.
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