Plug Thread

[Jimmy]

Enroute home this evening my bike ejected a spark plug, the breakdown/recovery mechanic reckons the thread must have been crossed and it just needs replacing. Is this a big job? If it is more than £400/500 then it's probably not worth it. I replaced the plugs about 7 months ago so it it strange that it has only just happened

[chromedome]

It's a bit of a tight fit in the tunnel in which the plug fits in the head to be honest, so it's quite easy to cross-thread.

Probably the easiest and cheapest solution is to get a helicoil insert fitted.

Another way is to get the damaged threaded hole "built up" with an alloy welder, and to drill/tap a new thread in it.

Problem is that the head will have to be removed in both cases to get this done (I think...)

You may be able to get a good condition cylinder head on evilbay if you're lucky.

Good luck on the job.

[hayden]

As chromedome has said, Helicoil is the answer.

Daft as it sounds just for a plug thread but, a replacement cylinder head off ebay or whatever may be the best way to go, there not expensive, and you will have to strip the head off what ever you do. by the time you have either paid the labour or farted about yourself you might be glad of just bolting another head on for what they cost.

If you do go the replacement head route, try to buy one complete, ie with cams and cam retainers. The retainers or covers are machine matched to the head and cams at the factory so work best together, mix and match of these components is not always a good thing.

[Guest]

Don't forget a new head gasket!

[hayden]

Jimmy

something like this..?

http://cgi.ebay.co.uk/HONDA-CB-500-PC23-99-CYLINDER-HEAD-C224-/380343955226?pt=UK_Motorcycle_Parts&hash=item588e442f1a

they have a returns policy, always better to pay by paypal too, better protected, just in case..

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