CBX Top End Mess

[haden2342]

Hello everyone,

I have 79 CBX with 19k miles that I bought some time ago that needed some work to get running. I was able to ride around the block a few times and it ran great other than it started puffing out some white smoke once it warmed up which I'm assuming is the valve guide seals. This and the fact that the spark plugs for cyl 2 and 4 are cross threaded made me decide to remove the head. I don't have the head off yet, but I got the cams out and I found a few concerning things that I'd like some extra opinions on.

First thing I noticed even before I got the valve cover off, the tachometer drive housing is broken in half, of course. When I rode the bike, I had noticed that the tach reading was slow and it never climbed above 3-4 grand. I don't know if this is related, the drive doesn't look chewed up at all. I'm not sure what to do about this yet. I know of a guy nearby that specializes in aluminum work so I might see what he thinks. Unless anyone knows of someone in the Portland OR area that has experience with this.

Next thing I noticed is one of the long valve cover bolts is broken off in the cam cap post, if anyone has a spare bolt I might be interested as the only thing I found was a entire new set for $100. I also might need one of those long cam cap bolts, mine for cap 13 is a little stripped.

Looking at all the cams and caps, it mostly looks good but there are a few things that concern me. For one, most of the cam lobes have wear marks on the sides just where the lobe begins. Not sure how normal that is or what would cause that. They look a little duller than the shiny wear marks on the lobes themselves. The worst of them are the cyl 6 intake and exhaust lobes which I provided pictures of. Most of the cam caps look good, but two are questionable. One is cap 14 which appears to have slight pitting. I read somewhere that this isn't uncommon and might just be part of the casting and not worth any concern. This makes sense to me as I can't see how it would wear that way. The other is cap 3 which has a wear line down the middle that I can feel with my finger nail. There doesn't appear to be any marks on the cam itself. Maybe I could find a replacement and run it if the clearances check out? Maybe I could do the same for cap 6 with the tach drive. A couple of the shims have circular wear marks on them, should I be concerned about those?

I plan to get the head off soon and check all the clearances and service limits that I can. Any input is appreciated, thank you.

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[daves79x]

You need a replacement #6 cam cap. They are getting pretty hard to find and $$$$. I wouldn't worry about the cams just yet. You can get a complete replacement set of cam cap bolts. Your tach is slow because it's slow. Send both gauges off to Mike G and he'll have them working good as new. Working on something that 10 other guys have been into over the years is a learning experience.

Dave

[broook]

I had two brand new tach drives and they were both pitted from the factory so I wouldn`t worry about that.

[Jeff Bennetts]

Just some insight to your existing problems. The tach drive is broken because someone didn’t unbolt it from the cam cover (two bolts) before removing the cam cover, the broken cam cover retaining bolt was done by over tightening the bolt, it has a limiting shoulder on it, you’re lucky the ham fisted PO didn’t break the cam cap which is normally the case.

Most likely you need to replace all the grommets on the cam cover bolts, they have aged out if they are original, also check all your cam caps for cracks at the bosses from over tightening the cam bolts.

You do have a FSM ? You’re going to need it!

Did you remove the oil pool plates? I don’t see any.

[Larry Zimmer]

A sidenote for down the road: Do not over-torque the cam cap bolts. Go for the nominal. Why: these castings have porosity. If it just happens to be in the thread area, the threads in the head will strip easily. Then, you're in for a timesert project. Ask me how I know. Mine went at max torque spec. That broken bolt was some gorilla who over-torqued and got lucky the head threads held. And, they will hold IF the casting is solid in that area. No need for any torque higher than spec nominal. P.S. -- don't oil the threads.

[haden2342]

Thanks everyone for the replies, some great information here. I do have the FSM and yes I did remove the oil pool plates. Any thoughts on the wear on the cap in the second picture? Should I try to replace this cap as well?

[haden2342]

Looking at the corresponding journal for cap 3 a little closer there is unfortunately a similar mark. I measured all the cam lobes and found all but one were in spec. I measured 37.18mm for the cyl 2 left intake lobe which is 0.02mm under the service limit. Most other lobes were 0.05-0.15mm over the service limit aside from a couple intake lobes that were around 0.02mm over the service limit. The intakes have some black discoloration on the low spots. Overall the exhaust cams look great aside from the one journal for cap 3.

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[daves79x]

If there's any doubt, Plastigauge the cam journals. Most cams with some miles do not measure over the minimum spec. Yours are more than fine.

Dave

[haden2342]

That's very reassuring. I just picked up some plastigage yesterday so I will give that a shot.

Recently I saw a video of a cbx with the tach plugged and I saw that they make tach plugs for CBs, I'm assuming they fit a cbx too. Is this an option for me at least until I find a replacement cap 6? I can't imagine the housing was an integral structure for anything other than the tach drive.

[haden2342]

I checked the cam journal clearances and they were all great, but I made a stupid mistake and accidentally dropped a bolt on the head in the absolute worst place possible. Just my luck. It's a fairly deep gouge, but I ran a plastic razor blade along the journal and I can feel it just barely. Should I take a bit of fine sandpaper to it just to try and deburr it?

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[haden2342]

I got all the valves out and visually everything looks great, just dirty. I still need to measure everything but at this point I'm fairly confident it'll all check out fine. Concerning the gouge I put in head, I put the cam in and torqued it down just to see if it would spin fine. It spins nice and smooth so I think I can get away with leaving that gouge alone. Would love to hear what you all think though.

[daves79x]

The score mark is fine. I assume you plan to at least lap all the valves and install new Viton seals?

Dave

[CBX-tras]

The cams ride in the caps due to the upward spring pressure. Just smooth out the gouge so it doesn't create more damage. It'll be fine.

If the clearances are too much, the cap can be put back in spec by sanding on a perfectly flat surface, a little at a time. Check with plastigage with the valves out.

[haden2342]

Nice, thanks for the input. Ya, I plan to lap the valves and replace the guide seals. I need to chase a couple spark plug threads as well. The cylinders look great aside from some weird rust in a few of them so I might be looking at least having them honed, maybe bored if necessary. I'll be taking them to a machine shop next week to see what they think.

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[daves79x]

Clean the cylinder and pistons as well as you can (remove all the pistons). Mark each piston. The have your shop check cylinder to piston clearance. Should not be over .0025. Honda allows .004 but that's way too much. Standard when new was close to .001. The bores will not be completely round, but if you keep the pistons straight, won't be a problem. Have them lightly honed to remove any glazing. Do not let them hone to remove material. This will remove some of the rust stains, perhaps not all. As long as the bores are not pitted very much, you'll be good with new rings. Bob at CBX Performance sells made in Japan standard rings. That will run you many thousands of miles quite fine. The head is the key to getting everything up to snuff.

Dave