Long story short: I bought a '77 CB750F, mostly original albeit some UNI pod filters. Typical blemishes given the age, condition and backstory of previous ownership. Factory original cracked tires and rusty drive chain and a few shade tree mechanical band-aids. When the gent I bought it from said it ran "pretty rough" I wasn't too concerned given the rough looking state of the carbs, gas leaking from the pinch welds in the tank and oil dripping from the pan. I'm building it into a café so tearing the bike down to the frame is pretty much step one for me anyway. Half the bikes I've built I didn't hear run beforehand.
Before I pulled the engine I drained the oil and oh boy was it sparkly. Metal dust and metal shavings (image 1)
The cam chain is the culprit. Looks like it was doing some self-clearing.
You can see in the images where the chain was making contact with the engine case/cylinder/cylinder heads.
The tensioner and guide wheels are badly worn and chipped. The cam guide is also badly worn, with the metal of one of the guide pins exposed, causing damage to its seat in the cylinder. The seat on the top engine case is also damaged. It's imprinted and cracked.
My guess is improper adjustment of the cam chain tensioner. (The tension didn't seem out of ordinary when I was pulling the camshaft and top end off). The engine still had all the original Philips head bolts and they looked new, so safe to assume I'm the first person since assembly to be inside this engine.
Anyone else seen something like this before?
I'm now wondering if the engine isn't worth saving. I doubt replacing the guide, chain, tensioner /guide wheel will be enough. The gouges in the guide pin seats on the engine case and cylinder looks like it'll cause the chain to wonder, slip or otherwise lead to accelerated wear, or worse, cam chain lockup/snapping.
I have a '76 CB750K in the shed that's waiting to be built so it's not a total loss if I have to put this on the back burner.
Before I pulled the engine I drained the oil and oh boy was it sparkly. Metal dust and metal shavings (image 1)
The cam chain is the culprit. Looks like it was doing some self-clearing.
You can see in the images where the chain was making contact with the engine case/cylinder/cylinder heads.
The tensioner and guide wheels are badly worn and chipped. The cam guide is also badly worn, with the metal of one of the guide pins exposed, causing damage to its seat in the cylinder. The seat on the top engine case is also damaged. It's imprinted and cracked.
My guess is improper adjustment of the cam chain tensioner. (The tension didn't seem out of ordinary when I was pulling the camshaft and top end off). The engine still had all the original Philips head bolts and they looked new, so safe to assume I'm the first person since assembly to be inside this engine.
Anyone else seen something like this before?
I'm now wondering if the engine isn't worth saving. I doubt replacing the guide, chain, tensioner /guide wheel will be enough. The gouges in the guide pin seats on the engine case and cylinder looks like it'll cause the chain to wonder, slip or otherwise lead to accelerated wear, or worse, cam chain lockup/snapping.
I have a '76 CB750K in the shed that's waiting to be built so it's not a total loss if I have to put this on the back burner.
