Engine full of fuel and seized up

[Trigger]

That is one clean engine inside 

[PJM47]

Probably that petrol wash it had!

[K2-K6]

Probably that petrol wash it had!

 

[Trigger]

Well, it did not wash the coating off the inside of the engine. Are you sure that this is a K1 engine ?

[SteveW]

This is one of the best threads ever.

Almost as good as when I was a kid eagerly waiting to find out who shot JR in Dallas.

[Nurse Julie]

This is one of the best threads ever.

Almost as good as when I was a kid eagerly waiting to find out who shot JR in Dallas.

🤣 🤣 🤣 🤣 🤣
It's sort of like a murder mystery, I'm really enjoying it as well.

[Laverda Dave]

I don't know anything about the 750 engine but looking closely at the sump off photo and zooming in on what I think is the kickstart gear can I see a chip on one tooth or is it the light playing tricks? It's the tooth closest to the back of the crankcase casting. If the tooth is damaged could the chip be stuck somewhere in the engine causing the partial lock-up?

[philward]

That's a good spot Dave! Looking on my phone screen, I can see what you mean

Sent from my moto g(7) power using Tapatalk

[PJM47]

I didn't spot any chipped teeth but will have a closer look when the engine is out. The bike is a K2 BTW, engine number is CB750E-2060793 which I think is consistent.
I have everything stripped now ready for engine removal so hopefully won't be too long before the next instalment..

[Trigger]

I don't know why i had K1 in my head and yes it is a K2. I can tell from the pictures that it has not been apart since the factory put it together 

[Lobo]

I’m no engine builder, but if the guts have been washed of oil in the petrol soak (a few weeks ago now) would it be worth spraying some kind of rust inhibitor asap about the internals?

[PJM47]

Engine out, it was actually quite easy, did it as per this https://youtu.be/Ezl3B5Jv6B8 suggested by 71 V12 below. I also added a motorcycle jack underneath to position the engine in about the right spot to come through the frame before attempting it. But it worked fine.

I have split the cases and everything looks ok. There wasn't a drop of oil anywhere though, everything had been washed clean by the petrol, so I oiled everything up I could and the engine started to turn over much easier on the crank, the more I turned it the better it got. I am now able to turn it a bit on on the kick starter, there is no way I could do this before. I'm not sure there was ever anything much wrong with the bottom end, could it be it was all just a bit seized up?

Do we think the issue was just that the pistons had seized up a bit after sitting in petrol for weeks and no oil and were reluctant to move, this might be consistent with the start of this thread where a few weeks ago I'm sure I couldn't turn it on the crank at all. Then when I tried again the crank would turn but it was still too stiff for the kick starter.  Then finally after taking apart and oiling it is now free enough to move on the kickstart (a bit). It does seems to be gradually freeing up which would explain why the symptoms are changing and not making sense.

So what next? how easy should it be to turn the engine over (no plugs and lower case removed) on the crank, it's still seems a bit stiff and has tight and loose spots? But after a lot of turns I can now turn it a bit on the alternator just by hand, not all the way round though that steel needs a wrench. Is that normal?

What can I check to get a good feeling it is safe to put back together and try to start it?

And finally anything I should replace/check whilst its apart?

[Nurse Julie]

What's this circled in red? (It could be something or nothing, difficult to tell on my phone)

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[K2-K6]

That description still sounds wrong to me "tight and loose spots" have you any pictures looking up the bores of the top half?

I've still a suspicion it's tweaked a rod from hydraulic compression,  can you equate the tight spot to a regular positioning of one pair of con rods?

It should rotate with very similar friction for whole rotations just by hand on the alternator.

Pretty simple to work on though,  aren't they?

[Trigger]

I would pull the pistons out as it many be a broken ring. I had a engine in once that one part of a three part oil ring had got out of the ring groove in the piston and had folded up the side of the piston.

Can't see anything in the bottom end. Are all the cog teeth OK, no chips ?