Topic: Frozen Engine

[cb750f-2010656]

I got a 750F0 that is locked up tighter than a nun's downstairs.  Would splitting the cases and LIGHTLY tapping the bottoms of the pistons help to get it apart?  This is the idea:  Two pistons are gonna be heading up, and two down.  I should be able to remove the con rod caps of the two closer to TDC and lightly tap the ones closer to BDC just enough for the crank to clear the others, then be able to remove the last two con rod caps and be able to spin the crank.  I would have it apart already but the engine froze while the cam sprocket bolts are at 12 o'clock and at 6 o'clock (down in the cam chain tunnel).  A bit too snug to get a 10mm wrench on it while it is down there!

[Stev-o]

If it is stuck and not seized,try the acetone/ATF trick.

Pull plugs and pour the cocktail in each cyl and let it set three days and then rock it.

Worked for me!

[Spanner 1]

'Prolly seized... likely a big-end bearing seized. Won't release with any amount of lube  and 'rocking-in-gear'..... have to take 'er apart to release the seize IMO.

[cb750f-2010656]

Well, I don't have a frame to put it in to rock it, and it has been sitting for about a week with penetrant.  Some $#!T called "Kano".  If it is a bearing seize then I would be pi$$ing in the wind try to free up stuck pistons.....  Anyway, I am getting impatient.  Tearing down and selling this engine is all that is keeping me from riding mine.  I need some tires, chain/sprocket set, tailight, front brake parts, etc.....  Fall is coming and I can feel a major depression coming on.  I may need this bike going to stay sane and not eat a piece of lead candy.   

[bryanj]

Bearings rarely sieze from standing, more likely rings to bores. remove head and use a block of wood plus hammer on the top of the pistons, skirts are too fragile to hit upwards plus rust is usually above pistons not below

[KingCustomCycles.com]

I just took one apart with seized piston and a stuck rod bearing.  I ended up lifting the cylinder block with wood shims as I pounded the piston tops with another chunk of wood and a 3 1/2 pound sledge hammer.  That got the block clear and undamaged.  I then removed the rod bolts of the seized rod, and used a steel punch to remove the rod and cap.  The rod and cap were replaced, the bearings replaced, a new sleeve inserted into the cylinder block and it was ready for honing and cleaning. I would not have done all that except it was a correct 69 engine for my frame.

[cb750f-2010656]

I had planned to hammer the pistons out through the bottom, but you can't unload the top end with out removing the cam, which must be separated from the sprocket first.  There just isn't enough slack on the chain to simply pull it off of the cam sprocket, unless I'm doing it wrong.  The tensioner is out and there is a little slack in it, but not enough to even work it off the crank sprocket.  Yes, I wen't ahead and split it today.  I removed the con rod caps and placeed a peice of wood against the rods and hammered with a hammer.  Only ONE moved, and only a short distance, nowhere near TDC.  The valves in that cylinder are closed, so it didn't hit them.  I found a few bad bearings, though.  I'll post some pics and see what y'all say but it looks like an oil issue  so I doubt I'll make any money off of it.....  If it was an oil issue then I doubt those pistons will EVER come out.