1970s Japanese valves
One of the scandals of powersports is that Honda and Kawasaki from the mid 70s through the mid 80s employed soft, very fast-wearing valves in their engines. On those engines having correspondingly hard seats, the valves last less than 15,000 miles, and cylinder compression quickly becomes a fleeting hope. The GL1000 and GL1100 at least have softer seats so valve recession is slower in them. But it still happens, just as with every engine. And since the OEM valve is plated (actually plasma-coated), refacing the valve as was commonly done on old cars is out of the question. Saving the odd NOS appearance on eBay or the expensive of sourcing from CMS -- when they have them -- factory valves for the four-cylinder Wings are all gone. Two Japanese companies have stepped up and are providing aftermarket replacements, and this keeps head work on these engines possible as time marches on. However, the quality of the replacement valves is not consistent. Out of four I recently ordered, half were out-of-round and had to be sent back. Of the two sources for these valves, the ones coming in green boxes appear to be better quality than the ones shipped in brown paper.
Valve seats
A cylinder head's valve seats are a mystery to many, with the usual hype and unfortunate misinformation obscuring the plain facts. No one for example needs five angles on their valve seats. In fact, without even trying, a good three-angle valve job becomes five-angle in practice. So it's just hype. Tooling for valve seat work takes a dizzying array of forms. There are too many choices for the initiate to make sense of it all. However, very good work can be done with tools that don't cost as much as your house, if you are careful, knowledgable and proficient. And even the valve seat machines that are as big as pickup trucks have their drawbacks. The real proof of whether a valve seat is sealing in partnership with its valve is the vacuum test, and this is the test pro engine rebuilders use. It's eye-opening. See my video.
Cylinder compression and related (cam musings, pt 5)
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Re: Cylinder compression and related (cam musings, pt 5)
Extraordinary Mike. Extraordinary. Once again, thank you for sharing. Your contributions here are invaluable and should be broadcast far and wide. I can't think of any other author who's offered up (or is capable of doing so) such a broad swath of insight into the inner workings of these vintage machines. I know, personally, I am compiling it offline. All of it. Thanks again.
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Re: Cylinder compression and related (cam musings, pt 5)
Another wonderful series, Mike. Thanks. I'm curious, are the 'middle if the road' aftermarket valves offered coated like the originals, or of better (longer lasting) materials? I'm just pondering the cost/ benefits of actually doing a 'proper' head rebuild, such as getting the cams and rockers hardened, valves, seats, guides, etc. I know it would probably cost more than what I've invested in the bike already, lol!
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Re: Cylinder compression and related (cam musings, pt 5)
I have assumed for some time that coming from Japan they like Honda's original suppliers are coating them. But they might not be, and some think they are not. But they know no more than I do from what I can tell. So I say, hmm, treat 'em like stock. At their inexpensive price, you can afford to replace them when they recede. Should have 15,000-20,000 miles of good use though.
Mike Nixon
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