Honda Twins banner

1 - 10 of 10 Posts

·
Registered
Joined
·
54 Posts
Discussion Starter #1
I've searched around but cant find specifics. How critical is side to side clearance (between big end of rod and crank) of the con rod big end?

I'm rebuilding a 71 cb350 and the crank is in great shape. There is not "up and down" or "back and forth" movement in the rod, the the left side rod has quite a bit of side to side clearance.

Is there a specific measurement tolerance, or is "up and down" and "back and forth" movement the most critical?
 

·
Registered
Joined
·
2,948 Posts
According to the CB350 FSM, the service limit for "up and down" is .002" and the service limit side clearance is .023".
 

·
Registered
Joined
·
54 Posts
Discussion Starter #3
According to the CB350 FSM, the service limit for "up and down" is .002" and the service limit side clearance is .023".
Thanks - for some reason that info isnt in the service manual im using.

I have a side-side clearance that is almost triple that. I wonder how that is possible as the entire engine was in great shape.

Would my best option be to find a good used crank?
 

·
Registered
Joined
·
2,948 Posts
Side clearance is measured, with a feeler gauge, between the side of the rod and the flywheel. The amount of movement from rocking the top end of the rod back and forth isn't really relevant.
 

·
Registered
Joined
·
54 Posts
Discussion Starter #5
Side clearance is measured, with a feeler gauge, between the side of the rod and the flywheel. The amount of movement from rocking the top end of the rod back and forth isn't really relevant.
Correct, that is how I measured it with a .023" feeler gauge
 

·
Registered
Joined
·
794 Posts
I was curious so went and checked the 4 crankshafts I have in my parts area. I just tried a go no go with a .023 gauge and all eight were definitely no go. I know at least one of those cranks is from late 68 and had a hard life.
Post up a photo as out of the 15 plus CB350 engines I've had not one crank had issues let alone something like that.
 

·
Registered
Joined
·
54 Posts
Discussion Starter #7
I was curious so went and checked the 4 crankshafts I have in my parts area. I just tried a go no go with a .023 gauge and all eight were definitely no go. I know at least one of those cranks is from late 68 and had a hard life.
Post up a photo as out of the 15 plus CB350 engines I've had not one crank had issues let alone something like that.

Picture attached. That is a 0.024" feeler for reference

Unfortunately, i just sealed the cases before i realized i didn't check the rods. Glad I didn't go further.
If you're willing to part with any of your spare good usable cranks please let me know!
 

Attachments

·
Registered
Joined
·
794 Posts
Picture attached. That is a 0.024" feeler for reference

Unfortunately, i just sealed the cases before i realized i didn't check the rods. Glad I didn't go further.
If you're willing to part with any of your spare good usable cranks please let me know!
Damn, I have never had to do more than a visual check on the cranks I've played with.
I am clearing out parts but shipping from Canada would be expensive ... best to find one local.
 

·
Registered
Joined
·
54 Posts
Discussion Starter #9
Damn, I have never had to do more than a visual check on the cranks I've played with.
I am clearing out parts but shipping from Canada would be expensive ... best to find one local.
So I got the new crank in the mail today. its in grate shape and the rod big ends look good and are within tolerance, but of course its never that easy!
The crank i had was from a K2 or K3, this is a K4 crank.

The outer bearing is different! #9 here: https://www.cmsnl.com/honda-cb350k3_model50720/partslist/0034.html#.YAIq2pNKgbl

instead of a cage type bearing, it is now a standard roller bearing with no dowel hole. At some point the outer bearing must have changed

Is this ok? Can I just install the crank and leave the dowel out? If so, how does that bering stay oiled?
 
1 - 10 of 10 Posts
Top