CB750/4 water damage to pistons

[Nurse Julie]

One thing I am not sure about, though, is which model of Submarine was fitted with these engines....I mean..it did come out of a subamrine? yes?

No, no, you really must brush up on your product knowledge. This is the model fitted to the submarines (a totally different CB750/4 engine than the one above  )
We get some cracking examples through here 

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[ka-ja]

You all expect miracles, after all, it is complete apart from the odd piston ring.

[Trigger]

Julie got this a little wrong it was number 2. Here is a picture before the barrels were removed and it was the only piston with a pond  [ Guests cannot view attachments ]

[Trigger]

Oxidation to any alloy causes pitting and not only on pistons.
Here are some pictures of a piston from a engine that had been rebored and then left for about 40 years, without been started. The oxidation had started and the rings had seized to the piston. If this engine had been started, the corrosion would of burnt off and the detonation would of caused a chain reaction 
As you can see from the underneath of the piston it is untouched.


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[MarkCR750]

Probably blend it out with some wet & dry and a bit of autosol eh Graham?

[Rob62]

A lot of damage on that piston crown.... probably why it was separated from the frame in the first place.

[matthewmosse]

Wow, that is some severe damage. I think endoscope inspection before any startup attempts on unknown motors from now on in my shed. Admittedly it won't show the rings but piston crown and bore inspection will give a good insight as to if sutch horrors lurk beneath the crown. My own far more limited experience is that once engines contain that much damage and corrosion they often won't turn over well enough to run, still it's a worthy warning of what can be amiss in an engine that seems reasonable. I had a cb500 engine that kept eating tensioners but otherwise seemed extremely clean and low mileage. One day I'll tear that down and see what similar horror lives down in the crank end. Top end was mint, hardly even carbon on the head. The flip side of the coin is that for us less experienced engine dabbles can do more damage looking inside a motor that was fine before we set to with spanners.

[Bryanj]

Matt most common reason for 500 damaging tensioners is if the holder gets a bit bent and does not locate in the correct place in crankcase.

[Nurse Julie]

A lot of damage on that piston crown.... probably why it was separated from the frame in the first place.

If you are talking about the piston pics i put on, nope. The drive chain made a hole in the crank cases the size of a football which is very common on these early engines. The engine was removed from the bike having covered less than 1000 miles (approx).
If you are referring to the ones Trig put on, i have no idea.