You were able to drive the car when it was having some serious issues and you drove it for some distance. Since you are planning on re-using the damaged pistons, go ahead and use the parts you have which are in a usable condition. When you get it running again, you can monitor for any damage to the crankshaft. No point sinking a lot of money on this engine until you know the crank is good.
Before you reassemble the engine, make a list of the parts you would like to replace. Make measurements on the pistons, piston pins, piston rings, and cylinder so you will know what parts to watch for.
You need to figure out what bore size you have and whether the piston pins are an oversize.
Check out the oil pump to ensure it is working properly and in decent shape and check the condition of the clutch to determine if you will be needing a replacement in the future. If the head gasket is not damaged (especially the metal ring for each cylinder), you can reuse it
Put it back together, get it running, and then start shopping for the parts you need. You may even come across a good used engine for less than buying a bunch of parts.
You question about what happens when the cam chain breaks ........either you are (a) lucky because the valve closes and remains closed before the piston arrives or (b) the valve is still open when the piston arrives and you bend a pair of valves and possibly damage the piston.
When scenario happens depends on several factors....the engine rpms, whether the engine is coupled to the transmission, which of the 4 strokes it was on, the direction the piston was moving (toward the head or away from the head). The camshaft does not have very much mass and is working against a lot of load since it has the valve springs it must compress and the valves may be working against the pressure in the cylinder. The camshaft needs the engine hp to operate and if the chain breaks, I don't think it has enough inertia to take it past the point when a set of valves close.
When the cam chain breaks, I think it starts to slow down and stops when either the intake or exhaust valves close. If it was just starting to open a set of valves, I think it could stop before the valves are fully open since the springs would be exerting a maximum force.
The crankshaft, on the other hand, has a lot of mass in the counterweights and would have a lot of inertia. The roller bearings in the journals offer very low resistance. The pistons would present the majority of the friction but if you turn the engine over by hand, you will see it is very minimal. When the cam chain breaks, the crank could speed up because it is no longer driving the camshaft. So, you have a camshaft which is slowing down and a crankshaft which still contains a lot of rotational energy. If the engine was on an exhaust stroke, the piston is seeing very little impedance. If the engine is on a compression stroke, the piston needs to compress the gases in the cylinder (this removes energy from the crank) and if the spark plug has just fired, this imparts a little more energy to the crank and this cylinder pressure is trying to force the valves to stay closed which removes rotational energy from the camshaft and slows it down.
So, what happens when the cam chain breaks? Flip a coin since your luck can go either way.
That is my take on the subject. Others may have a different viewpoint and I would be interested in reading about them.
good luck,
Dale
> Dale,
> I have now bought a lot of cam chain parts on Ebay. Most of > them look a lot better than the parts I had. The Cam Chain tension roller was > the only part I could not get off ebay. I am considering re-using the old one > as you suggested. I think it will probably work to, but if I find a > replacement in time, then I will use the replacement one.
> My tension
> plunger was "modified" in some way. I got a new one of those on Ebay > to.
> I still have not located new pistons, but I'm not too terribly > worried about them. My shop professer has looked at them very closely. He does > of course recommend changing them, but also is confident they will be ok if I > insist on re-using them > As far as demise of my engine goes, I'm curious > what would happen if my cam chain did dislocate? Is this an interferance > engine?? Would the piston smack the valves and destroy > itself?
> thanks,
> Mike.
> --- In
> anzhonda600owners@yahoogroups.com
> ,
> goinhm@... wrote:
> > Mike,
> > In an earlier
> message, you indicated you were going to reuse as many
> > old parts as
> possible and only needed it to last 25,000 miles. Also, this > > is the > engine which may have a marginal crank because you had all the metal
> show up in the engine and its oil. For what you are intending to do,
> your cam chain tensioner roller will work fine. The aluminum rubbing block on
> > the bottom appears to be in good shape and the pad which the > tensioner > > presses against looks ok. If the roller part is not > crumbling every time you > > roll it along the cam chain, it will be ok.
> You might want to use a fine
> > wire brush or some fine sandpaper and
> remove any of the loose pieces of the
> > roller. If you find that it
> keeps crumbling, then you don't want to use
> > it.
> > I
> don't see your worn roller as being the item which leads to the
> demise of your engine. If you decide to start putting lots of new parts into
> > your engine, then I would consider replacing the roller.
> > Did you check out the cam chain tensioner? Is it ok? I thought you
> > said it had a bolt stuck at the end of it? It should have plunger at > the > > end of it.
> > Also, did you find a new set of
> pistons? If you are going to use
> > the old pistons then you definitely
> do not need to worry about changing the
> > roller.
> > good
> luck,
> > Dale
> > good luck,
> > Dale
> I'm just curious - what would most experienced Honda 600 engine rebuilders
> > do if they really needed a new cam chain tensioning roller like I > do.