The Saga of my First CBX

[erik]

Dave,
I will not run it again, I will pull some covers this coming weekend and report back. I've ordered the tool to tighten the clutch center nut. Should I plan on purchasing the spanner wrench designed to hold the clutch when tightening, or can I put it in 5th and hold the rear brake to keep it from spinning?

[EMS]

...and if you did trash a cam bearing, buying cams will not solve your problem. The cams in most cases are O.K. The softer cam supports in the head are the one that wear.

[daves79x]

The hub nut tool is all you'll need, as well as a shop manual. You can just hold the crank end (under the right crank cover) to loosen and tighten the clutch nut. But just tightening the nut is not that simple. The primary shaft gear the clutch basket gear engages is a double gear and you have to line up BOTH sets of teeth to seat the basket the whole way, as well as engaging the oil pump drive sprocket, as well as making sure the collar inside the hub is seated the whole way. If this all isn't done correctly, you'll break something expensive. You really need a shop manual.

Dave

[erik]

Update:
So I pulled the clutch cover off and found that while a previous "tech" took a screwdriver and hammer to the clutch nut, it still seemed to be tight. I pulled the sump and found quite a bit of trash in it. Some plastic and some metal. Until I get the clutch out and a chance to investigate further I dont want to make assumptions but at this point I feel I may need a new engine. Its not for sure yet but I want to put the word out in case anybody has a line on one for sale.

[daves79x]

A known, good-running engine ready to install will be quite pricey. You can do a lot of fixing on yours for that kind of money. Don't panic, something obvious will be found.

Dave

[erik]

At the suggestion of Jebbysan, I pulled the motor and benched it. The heads and cams looked great, nearly no wear, however when I removed the cylinders I found one scored piston. THE cylinder corresponding to the scored piston seems to need a good honing to return it to service, the piston may need replacement. The material I found in my oil pan turned out to be copper, suggesting I trashed some bottom end bearings. Sure enough the #4 and #5 connecting rods were spun. Hopefully a case splitting doesn't reveal more severe problems. In the event my mains spun, what are my options. Are oversize bearings available? What about 10 thousandths oversize pistons and rings? I'm not sure if I would go with "big bore kit" if I cannot reuse my stock cylinders, obviously with some machine work. Are there kits available that reuse machined cylinders?

[daves79x]

This all happened for a reason. Did you determine if this was a 'School Bike'. If so, that's probably the answer. It needs completely disassembled and you'll likely find the crank junk. Used ones are still plentiful. Be prepared for some bucks for all new bearings. Did you ever get a shop manual? If you didn't, STOP until you do.

Dave

[NobleHops]

Erik,

Forgive the digression but didn't you just buy this bike? It seems to me the seller is on the hook for at least some of this.

N.

[daves79x]

Yes, I agree. Turns out he basically sold you a nice rolling chassis at this point.

Dave

[erik]

Dave,
I do have a copy of the Factory Service Manual. I have had no luck in contacting the seller. I'm going to chalk this up to a hard learned lesson... I'm still unsure if it was in fact a school bike, the inside of the engine is CLEAN, with almost no wear on the cams, and very nice crosshatching on the cylinders, with the exception of the scored one. The internals definitely confirm the low mileage shown on the odometer.
Also yes, I did just buy it.

[erik]

At least it looks good sitting in my garage

[erik]

All,
I finally received my clutch hub nut tool in the mail and promptly pulled the clutch out. I saw no evidence of the clutch walking off the oil pump sprocket. The nut was tight, it took several hits from my 1/2 inch impact to remove it, so at this point I'm at a loss. It will be several more days before I will be able to touch it again, so I thought I'd let y'all know.

[daves79x]

Your spun rod bearings were causing all the racket. The engine will have to come completely apart and everything checked out. First thing to note is if the cases have been split before - you can usually tell by how much case sealant is hanging everywhere. There was some cause for the spun bearings. Certainly lack of oil is likely, but why? Loss of oil pressure maybe, but why there also? Oil pump may be junk and the crank certainly is. The rods are likely salvageable. Even the smallest detail has to be noted upon disassembly. Are the rods installed correctly? Were the bearing sizes correct. This assumes previous disassembly. Only one scored piston is very strange as well.

Any issues like this point to a school bike being taken apart by kids and no one really knowing how it went back together.

It can be fixed, with some money invested and a LOT of work.

Dave

[erik]

Dave,
Thanks for the reply, hopefully I will know more by Wednesday, was there a list of VINs that were donated? I didn't see any tool marks on the case bolts, or excess sealant squeezed out. I was very surprised of the fact only one piston was scored, I did find some plastic in the pan, Jebbysan suggested the primary tensioner failed and sent plastic through the oil pump. Hopefully I find something obvious, as not having a single clue why this happened is driving me nuts.

[RJ CB650]

hard plastics in these engines can only come from chain guides/slides as I am pretty sure there are not any roller tensioners on these. Think those were only the 450 DOHCs?

In the world of 750s, I have seen failures like yours due to improperly set chain tensioners. Result is chain chews through the tensioner, and then the engine aluminum itself. Scoring could be due to something getting into the cylinder during a plug change, or through the intake and bouncing around. Seen it sometimes in cars. Person pulls out plug, dirt falls in. Course, running badly out of tune can cause it to fail too, excess heat or carbon buildup.

From my honda experience, bottom end bearings seem to be tough to come by. However there are places that make bearings by order which are superior to most anything OEM for the time. I have not needed these services, but it could be worth looking into. Perhaps there are other CBXers who would like/need high end bearings and can arrange a group buy? The biggest risk with a spun bearing is if it was heat cycling the bearing mating surface potentially causing the crankshaft to warp. Only had it happen once to me with a VR6 engine, but a good machine shop should be able to tell you when you do the bottom end.

Pretty sure a rebuild is not what you wanted to ever do, but if it is, might as well take time, save money and make one bad-ass and smooth as silk CBX