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[Firen81]

Hey guys, names Greg, and I have a 1984 CB650sc. have had the thing for a while, ended up getting it for free off a bike shop that had it abandoned broken there. its sat for a couple years at my house, and I'm now to the point that I am reaching out to the online community for help. It has a thrown conn rod in cylinder 3 (the shop had it apart, but never fixed it) and I have come to an impassible point, which has had me stuck for 3 years now. All that needs to be done is fix the conn rod, balance the carbs, and throw a battery in.

I have found a part on BikeBandit.com listing 2 different conn rods. Everyone I have talked to does not know the difference between the two listings, "rod C", and "rod D". It has come to the point that I wish to be enlightened! Seriously, I want this on the road, its been agony.

Thanks in advance, and I hope to become a functioning member of the community!

Greg

[Laminar]

Check out this thread for a thorough rebuild of a 650 and a lot of useful info.

[fortyhourdays]

That thread should tell you just about everything you need to know.  Interesting that yours was the #3 cylinder as well.  There have been several of these #3 connecting rod bearing problems in the last year.  As far as the connecting rod C and D, I ended up just getting some used connecting rods off eBay which obviously doesn't list whether they are C or D.  There is a number code on the connecting rod to help in identifying which bearings to use.  I assume the letter code C or D is referring to this since several of the parts warehouses have switched around the codes between letters, colors, and numbers.  In the end it really came down to trial and error with plastigage to make sure I had the right oil clearance for my bearings.  If I were you I would order connecting rods and crankshaft off ebay since the prices for NOS (New Old Stock) are ridiculous.  I did measure all the connecting rods I had, and could not find any difference between them other than the bearing number codes.  I think as long as you get 83-85 connecting rods you should be good.  Mine has a mix of 83 and 85 connecting rods in it right now, and it's been running great for about 4000 miles since the rebuild. 

[Bumblebee]

That is the weight code on the connecting rod.

There is, or should be, a number and letter on the connecting rod.
The number determines the bearing size.
The weight determines balance.

The shop manual tells you how to determine which is needed.

The irritating part is that it's impossible to know what connecting rod bearing to get since you don't know what the number is until you have it in your hand.

[fortyhourdays]

That is the weight code on the connecting rod.

There is, or should be, a number and letter on the connecting rod.
The number determines the bearing size.
The weight determines balance.

The shop manual tells you how to determine which is needed.

The irritating part is that it's impossible to know what connecting rod bearing to get since you don't know what the number is until you have it in your hand.

Interesting.  The shop manual for the 83-85 550/650 doesn't list anything as far as a weight codes for the connecting rods.  Only the codes for selecting new bearings.  Here's an example of what you need to know (Stolen from my rebuild thread)  You can see there are letter codes for the crankcase, number codes for the crankshaft main bearing journals, letter codes for the crankshaft connecting rod journals, and number codes for the connecting rods.  Once you have all this info, you cross reference it with the table in the back of the engine section of your shop manual and it tells you what bearings you need.  (Many of them are no longer produced)

I went through and cross referenced all the numbers and letters to find out what bearings I need to order.


Main bearings I need:
2 green
6 black
2 blue

Connecting rod bearings I need:
2 green
6 brown

Most of the parts places have them listed by a letter code as opposed to a color code but I finally found someone who could tell me what each color's letter equivalent was which I'll post here in case anyone else is wondering.

A=Blue
B=Black
C=Brown
D=Green
E=Yellow
F=Pink

[ariwhiteboy]

You already have three of the best mechanical minds on the forum pointing you in the right direction, so I'll just say  !