Topic: knocking crank? how check clearance externaly

[roysohc]

A few months ago I had a litlle accident with my bike (750 F2). The oilpressure gauge the I installed on the engine broke and the bike lay at its side with running engine and oil comming out.

After sealing the oil, and filling it up again, it started directly. When I ran the bike for some miles, the oil light camo on at low RPM.
At that point my quest began.
Changed plugs, timed bike, synced carbs, tried other oil,...
Now when I rev the bike it starts knocking. The knocking sound comes from the around the crank at the ignition side.
An inspection of the ignition showed oil in the housing off the ignition.
I pulled away the ignition and saw that oil (very little) was dripping from the oilseal at the crank.
I can move the crank a little sidewards. Is this normal? or should it move a little.

I think I'm in trouble, isn't it??? 

[mystic_1]

Sorry, you're in trouble.

You should not be able to move the crank AT ALL except to spin it.  Sounds to me like the crank took a hit when the bike went down, lateral force damaged one or more main bearings and now they're slowly dying.

mystic_1

[roysohc]

thanks I suppose mystic_1,

Is this an expensive replacement?

What should I replace also once the block is open?

Roy.

[scondon]

 I would think that in order to damage the crank the ignition shaft(threaded shaft that your ignition advancer bolts to) would have to take a serious hit. Your ignition cover would be damaged beyond repair and the shaft would be bent off axis making your ignition timing very off and difficult, if not impossible, to set properly.

   Certainly any side to side play in the crank is NOT good, but did you pull the advancer to check this?

    A little more info on the damage of your "little accident" could be helpful. Changing the crank bearings/engine seals and whatever else might be damaged can be a time consuming and somewhat costly repair.

[mystic_1]

I would think that in order to damage the crank the ignition shaft(threaded shaft that your ignition advancer bolts to) would have to take a serious hit. Your ignition cover would be damaged beyond repair and the shaft would be bent off axis making your ignition timing very off and difficult, if not impossible, to set properly.

   Certainly any side to side play in the crank is NOT good, but did you pull the advancer to check this?

    A little more info on the damage of your "little accident" could be helpful. Changing the crank bearings/engine seals and whatever else might be damaged can be a time consuming and somewhat costly repair.

You're right, I'm making assumptions about how the bike went down.  Just figured that with the bike on it's side and in order to break off the oil pressure gauge in an accident, the points cover is almost guaranteed to have touched down.  Point is assumption are bad, so do tell us more, Roy.

mystic_1

[FunJimmy]

Knocking sound emanating from the crank, lateral movement of the crank and seal leakage are all positive symptoms of bottom end bearing failure. Perhaps the drop in oil pressure when the gauge broke off was enough to finish old and worn bearings. Hard to say from here, but it sound like a bottom end rebuild is in order.

Sorry
FJ

[TwoTired]

Makes those awful ugly engine guards seem downright economical, doesn't it? 

[bryanj]

If its knocking you will need crank; rods; bearings; gaskets; seals; piston cirlips and probably primary and camchains with tensioners------or to put it another way loadsamoney!!

[bwaller]

How long did the bike run on its side and how much oil did it bleed out while it was? Was the throttle wfo on its side or was it idling?

With the ignition, mechanical advance and plugs removed do you still get the knocking when you turn it over. Could the knocking be from a bent advance shaft? Clean up the area around that right end seal and try to find the source of the leak first.

Point is I've seen ignitons torn off right side get-offs before without causing life threatening engine injury. If it was still running the igniton was at least still mostly intact.

Couldn't have taken too big a hit, but you need to keep checking.
 

[754]

Crank & rod bearings CAN be changed with engine upside  down & cases split WITHOUT toucking top end.

 The only check in the engine I can think of is if you mount a dial indicator to the crank and check for movement, , but it could still be damaged and not show.

 let any engine builder listen to it, they will know instantly.

[bryanj]

754 is right bearings can be changed without splitting the top BUT i have yet to find a Honda that when knocking has a salvegeable crank

[roysohc]

sorry for not responding.

I opened the engine, and found the bearings where worn.
Also the crank surfaces are worn also. It's not an equal surface or is this normal.
I think the engine had an oiling problem at this level.
The side off the ignition,is worn most.(having no main standard,bike is always on its side standard. maybe this effects the oiling at right side)

I have a K4 engine for spare parts. can i use the crank to fit in the F2 engine?
I don't know the state off the K4 crank but if it is bad also,  can the crank surfaces be machined and still be able to find the correct bearings?

Roy.

Why me

[bryanj]

I know there are some differences in the F2 but not sure what, Honda cranks CANNOT be re-machined as nobody makes undersize shells

[merc2dogs]

how well do the cranks hold up to weld/grind to stock specs?

Ken.

[bryanj]

With the number of used cranks out there is it worth the cost?

[MRieck]

With the number of used cranks out there is it worth the cost?

No. Get a used one.