valve guide replacement


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LamarX
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Location: Winnipeg Manitoba

valve guide replacement

Post by LamarX »

Hello, Upon inspection I noticed a large amounts of carbon in the intake and exhaust runners and combustion chamber, which made me suspect bad guides. Most are well within specs except one exhaust guide. The question goes like this, how far in the guide using a ball type tool does it go in, the tool has 1 inch stem and that is close to where the valve stem is measured according to the manual. The one guide has out of limit near the bottom, shaped like a bell sort of speak, there is a noticeable amount of wobble just off the seat from the valve but the seat looks fine, I even took the time to lap the original valve and it formed a nice even seat, the plan is to use all new exhaust valves. Now to replace the guide, the head is heated to 200 degrees for expansion, then the new guide in the freezer for an hour, everything has been cleaned then heat the head again at 200 f after and hammer it in gently with a proper size tool, . Does this sound like a correct procedure. I don't quite know the reason for so much carbon build up, the crown of the pistons were covered as well. Ring gap sits at about .012 in the cylinder. I appreciate all coming up with suggestions, thanks working on a 79

Marc

daves79x
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Location: Knox, PA
Location: Knox, PA

Re: valve guide replacement

Post by daves79x »

Could be that the bike was run a lot of miles with too-rich jetting in the carbs.

Dave

LamarX
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Re: valve guide replacement

Post by LamarX »

Thanks Dave, yes that's possible, bad ignition as well. What about the procedure of replacing the guide, any advice ?
Thanks,
Marc

daves79x
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Re: valve guide replacement

Post by daves79x »

Never replaced a guide. Guys tell me it's just by the book though. Preston Marks in Florida does it all the time, but has all the correct tools for the job. JR here I'm sure does as well. I'd farm that job out.

Dave

CBX-tras
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Re: valve guide replacement

Post by CBX-tras »

It's rare that I come across a heads that require guides but, usually from damage not wear. If one's worn, others will be too. I scrap heads that need more than 4 guides as cost prohibitive as opposed to replacement.
However, I tag out to one of 2 local shops that do this type of work every day when I need this done. It's not only the guide, it's cutting the seat after honing the guide to size with a 5.5mm ball hone. You probably don't have these type of machine shops in Winnipeg.
Carbon buildup is from leaking valve stem seals and/or lugging the motor and/or too rich.
CBX's have race inspired motors, drive it like one.

LamarX
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Re: valve guide replacement

Post by LamarX »

Thanks Dave and CBX-tras I spoke with Preston about the procedure of replacing guides, its as described above by CBX-Tras with the addition of heating up the head in an oven at 350 f. I did find a machine shop that says they do it, yet to see on that later.
Thanks for the input, much appreciated.

Marc

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