® How Not to Build an Engine


I was contracted early this year to fix a problem of 0 cylinder compression -- yes, zero -- on a Honda CBX.


Here is what I found as the cause. All 12 exhaust valves were bent.


The witness marks on the pistons.


It seems after the engine had been worked on (I refuse to call it "rebuilt") it sat out of the frame for a while in a warehouse near the ocean. This resulted in severe corrosion.


The cast iron valve guides rusted heavily and virtually seized up the valves to the guides. So the valves were trashed.


The guides fortunately escaped damage -- not always the case with bent valves -- and cleaning out their rust was all that was needed. Here I am honing the rust out, more polishing really. Special tool with abrasive paste on it.


The cylinders were rusty too, and the piston-to-cylinder clearance excessive. Sigh.


But that's only the beginning. There was actually a lot more wrong with this engine. Even if the exhaust valves had not been bent, the valves -- all of them -- would still have needed to have been replaced, and this on a just-"rebuilt" engine. Note the significant recession on this cleaned-up valve. This valve should have been replaced a great many miles ago.


The engine got stainless steel valves this time around. Not because of the corrosion issue, but because the stock and pattern valves wear out quickly. Only better material valves should ever be put in a CBX for this reason. In addition, this being a shim valve train engine, this makes stainless valves even more of a necessity.


As I say, there was a lot more wrong with this engine. Many assembly mistakes were made. Here is one. This intake valve has so much of a burr on its stem that heavy sanding had to be done just to get it out of its guide. This is more or less normal for a high mileage engine. But remember, this engine had just been assembled. Just one of many oversights by the engine builder.


Here's another. No assembly lube on the valves. If the correct moly grease had been used, the exhaust valves probably would have survived. Almost any grease would have given them at least a chance. But as you'll see, the builder did a lot more wrong than this.


Two different brands of intake valves were found in this engine, stock and Japanese pattern. Nothing wrong with using pattern valves, but mixing the two is something you would do as part of a repair, an economy job, a make-do. It is poor showing for a project that included a big bore, porting, and clutch mods.


But there's more. This is an aftermarket cam chain. So what? Well, its link pins are smaller than stock, by a half millimeter.


K&L repackages these from a part originally marketed for the -- you ready? -- Honda XR500 single-cylinder dirt bike. Both bike's cam chains are 120-link.


Here's the stock Honda CBX cam chain. You can see the difference plainly.


And note the 3mm pins as opposed to the XR500's 2.5mm. I guess the engine assembler didn't know about this issue of the different qualities of cam chains,


Here's the head gasket. See anything wrong? No sealer. Anyone familiar with Hondas of this era would know their head gaskets have to be sealed. This is really basic and a significant oversight.


Note the oil on the gasket. I'll show you why it's there next.


Here's why. The builder used a roloc pad on the gasket surfaces! Unbelievable! When I was a dealer tech so many years ago, using a roloc abrasive disk on a gasket surface would have got you thrown out of the shop onto your ear. And rightly so. It's hideous practice.


Another shot of the cylinder's gasket surface, All chopped up by that abrasive pad.


Speaking of gasket surfaces, what do you think of the valve cover gasket surface on the cylinder head? Whether it happened at the beginning of the rebuild or long before, an engine builder, first, should not use the awful, juvenile technique that would cause this, and second, has an obligation to repair it as part of the build. I don't think much of the ability, conscience or ethic of a person who would assemble an engine like this.




And more.


This is pretty significant. It is very common for aftermarket piston kits to not as accurately as stock line up with the top of the cylinder. This is called the "deck". In this case, there is a negative deck of half a millimeter. The cylinder should have been machined, "decked", if you will, to correct this.


This is one of the engine's two "oldham" couplers, the parts that join the two intake cam halves to each other and also the two exhaust cam halves. The 1979 model CBX has extra loose couplers that result in quite a lot of noise, many mistake for valve noise. But it's actually these couplers rattling. So an enterprising European has made these oversize couplers available for many years. They work well. The thing is though, they are way oversize to accomodate differing fits in different engines, and the assembler must hand-fit them, filing a bit, trying, etc., until they can just snugly fit. This was not done with these parts. It took me a couple of hours to get the cams out of this engine. Really a challenge. Just to get the coupler in this picture out of the cam took clamping the part in a vise. Incredible. This is one of many evidences that the builder of this engine did not know the Honda CBX.


This is controversial, and I allow that others have a different opinion. But the CBX should almost never be "ported". The ports are already too big, and most folks haven't a clue what real porting is about. This example proves it. Really. Get the basic things right before you try to improve on the factory. Many basic things were ignored on this job.


The starter motor is pinching the oil cooler hose. This usually means the engine mount is installed incorrectly.


The very common "spanking" issue of Honda steel clutch discs of the era has not been corrected. More evidence this assembler does not know Hondas.


This sets my teeth on edge. I hate this stuff. In my book, silicone sealer is the trademark of the hack. No other way to put it. It has its uses I suppose. But folks should think long and hard about it. This just makes me sick.


The airbox support bolts were missing. Not sure what was up with that.


So the repair begins. Here the head and cylinders have just been resurfaced, the gasket surfaces repaired.


Another shot.


And the seats properly attended to.


Being methodical. I guess some people just don't take this kind of work seriously. To me, I don't know. Why bother if you're not going to do it right?

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