SOHC.co.uk Forums > CB750
CB750/4 water damage to pistons
K2-K6:
What do you think then Julie?
I bet you can guess my view :D
Nurse Julie:
--- Quote from: K2-K6 on December 17, 2018, 03:44:59 PM ---What do you think then Julie?
I bet you can guess my view :D
--- End quote ---
Nope, can't guess your view Nigel.
K2-K6:
The taper shape of wear on the top ring lands shows its been running with the ring getting progressively more movement.
If it had been corroded to the bore and snapped when it was tapped down the cylinder to get it free, then the piston material would just snap off without any wear pattern. The wear is there without the top surface of the piston being displaced above the taper region, so material missing next to the ring with piston crown still in place.
Detonation craters visible with molten edges on the piston crown.
Nurse Julie:
That's interesting Nigel as i know this engine has been out of the frame sitting on the floor somewhere for 49 years. Graham has suggested the pattern of damage is consistent with water getting in and the resulting chain of events that causes rust to eat away at metal, which in turn lets more water down and so on and so forth. The worse piston was the one seized but actually freed off quite easily compared to some we have in. Also, on the other piston where the top ring has been eaten away by rust, there is no evidence on the piston crown of detonation.
Whatever has caused it, my point with these photos is that so many times, i read or hear of people that say 'the engine was a bit seized but it freed off easily' and they do not know what damage has been caused until it is too late and major damage has been done.
SumpMagnet:
Sweet baby Jesus .... I don't see the problem.
Stick it on E-Bay as a good runner in need of slight attention. Has compression and will fire on Easy-start .... might need carbs cleaning. Make good Cafe racer. Barn Find...and stick a price tag of around £5K on it.
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?
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