C70 Crank Bearings - Is this normal?!? Need serious help!

1

1981Honda

Member
I have a 1981 Honda C70 passport engine that I rebuilt over the winter, did a top end job on it. Put it all back together and now there’s some ticking noise coming from the clutch side of the bike. When putting the right side engine cover back on, I kinda crushed some of the clutch components in there since I did not install it right, and I’ll be getting new parts for it soon. I’ve been trying to diagnose the ticking/knocking noise. Definitely is nothing related to the valves or piston slap, and it’s definitely not rod knock. I’ve been able to diagnose it to something with what I did with the clutch.

While inspecting everything, I had the right side cover off again, and when I spun the crankshaft, the outer race of the crank bearing was spinning slightly when I moved the crank. And when you pull on the clutch and push on it, it moves in and out slightly. I also have a 1981 C70 parts engine and it does the same, with the outer race spinning and the crank moving in and out the same amount. I’m assuming this is normal and this bearing is not a tight fit to that case? Hopefully it’s not a spun bearing? Seems to be normal since I have two of these engines and it does the same thing on both of them. Maybe when the motor gets hot, the bearing will expand and hold itself in place? Really hoping it’s not a spun bearing.
 
1

1981Honda

Member
1981Honda said:
I have a 1981 Honda C70 passport engine that I rebuilt over the winter, did a top end job on it. Put it all back together and now there’s some ticking noise coming from the clutch side of the bike. When putting the right side engine cover back on, I kinda crushed some of the clutch components in there since I did not install it right, and I’ll be getting new parts for it soon. I’ve been trying to diagnose the ticking/knocking noise. Definitely is nothing related to the valves or piston slap, and it’s definitely not rod knock. I’ve been able to diagnose it to something with what I did with the clutch.

While inspecting everything, I had the right side cover off again, and when I spun the crankshaft, the outer race of the crank bearing was spinning slightly when I moved the crank. And when you pull on the clutch and push on it, it moves in and out slightly. I also have a 1981 C70 parts engine and it does the same, with the outer race spinning and the crank moving in and out the same amount. I’m assuming this is normal and this bearing is not a tight fit to that case? Hopefully it’s not a spun bearing? Seems to be normal since I have two of these engines and it does the same thing on both of them. Maybe when the motor gets hot, the bearing will expand and hold itself in place? Really hoping it’s not a spun bearing.
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OLD CT

OLD CT

Well-Known Member
The part is called a clutch center guide inside the gear and it is supposed to spin a little when you install it, not stay tight. Oil it up good.
 
1

1981Honda

Member
OLD CT said:
The part is called a clutch center guide inside the gear and it is supposed to spin a little when you install it, not stay tight. Oil it up good.
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I guess I wasn’t clear on what I was asking… I’m talking about the actual crankshaft bearings, I will provide a picture of them, but it seems the outer raceway is able to slide back-and-forth and rotate a little bit when crank is moving. Is this normal? Seems to be, it looks that way on both of my engines. Checked it on my parts engine and it does the same on both sides of the engine.

From my experience on rebuilding chainsaw motors that outside raceway should be tight and not able to move. Maybe it’s different on these?
 

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1

1981Honda

Member
OLD CT said:
Your crank bearings aren't the healthiest looking in the world. They seem worn and pitted to me.
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Sorry, should’ve mentioned that these are pics of the parts engine that I have. That engine is dirty and hasn’t ran for years, it’s solely for parts. The bearings in my running bike engine are fine, they look like they are clean. They’re not pitted. They roll smoothly and there’s zero up and down our side to side play with them. They are in pristine shape. I’m just curious if the outer raceway of the two crankshaft bearings need to be tight in the cases and not able to move or rotate at all, or if they are supposed to be loose. Both of the bearings on my parts engine and running engine are able to move (the outer raceways) I’m assuming this is normal? Just need a yes or no answer. Seems like it is cause I doubt both of those engines would have two rolled bearings.
 
OLD CT

OLD CT

Well-Known Member
I am not well versed in c70's. My ct70 engine with the flywheel installed and grab it with my hand, it will not move in and out, up or down. It's tight. If yours is the same installed, you are good.
 
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