Should I have my CB360 crankshaft rebuilt and balanced?

thrillseeker said:

By the way, I am planning on doing the oil flow mods, (clutch basket complete so far) but none of them seem to require any money at all! So how could they possibly be beneficial? Just kidding. There's not much I like more than easy and free improvements! Thanks PJ!

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ok, if you have an option of doing the oil mod or using better oil, using better oil would likely be the better choice.

doing the oil mod AND using the best oil you can is the best choice and valvoline wouldn't be it.

in general the best oils are pao or mpao based because they are basically shear free. . both typically have some ester, although i have found a good use for a warm bottle of wesson on occasion.
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Thanks for the input, everyone. At this point I'm going to go forward with the balance. I'd like to be able to share as much info as possible from my experience so please let me know of anything I should pay attention to and be able to share


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180 degree cranks are very different to 360 degree cranks or singles in terms of balancing. They can be balanced to match rotating masses side to side on a dynamic balancer, but the question the Mid life asked is valid - is it worthwhile? And the answer is for a performance and reliability modification no it is not, IMHO. Will the bike be smoother - maybe. Will it make more power - unlikely to be much at all, but potentially it could be a more pleasant ride.

Smoothness on that crank is all about rocking couples and resonance in the chassis. If it resonates at revs at which you ride, it could be very annoying and tiring. Chaning the balance factor will change that but not as much as on a 360 twin or single. We never balance our Yamaha race cranks. Rick Schell will do it for you for a fee and the guys I know that had those cranks could not tell the difference.

On Honda twin street or race bikes we never have cranks dynamically balanced and when they wear out we get another off ebay and run that till it expires in a decade or so. I have stripped a couple of CB72 cranks and had 350, 160, 175 and 360 cranks rebuilt by Bill Bune but not balanced.

I used to balance Triumph twin cranks and change balance factor on those to shift resonance to different revs. Our old style TZs vibrate like mad so maybe they would be smoother with a balance job, but there are not a lot of people I would trust to do it. And the only dynamic shafts I have balanced are gas turbines for planes and that was a very long time ago.

If you have the cash to get Falicon to do a crank and balance it, I think we would all be very interested to hear the results. Do they have new rods and bearings for that crank? Rods will need to be balanced top and bottom. Pistons and pins will also have to be matched. They balance the crank first assembles without rods and after it is balanced they strip rebuild and true it again.

Here's one of a number of articles on the subject. https://en.wikipedia.org/wiki/Engine_balance

Or for more detail there's http://orbi.ulg.ac.be/bitstream/2268/10643/1/DEA.pdf

http://wikicars.org/en/Engine_balance

Thanks for chiming in, Teazer. I'll give Bill Bune a call to pick their brain and compare prices. I'm also going to give my machinist a call to discuss with him since he has a lot of experience with race engines as well. I talked to Falicon again yesterday to get more details about their balancing process. If I send them the pistons, they balance them before balancing the crankshaft. Also, they will balance to any rpm I want and said to let them know what rpm range to balance for as well as if the bike is for street or race use. The rep I talked to said he does have experience balancing cb360 cranks and that they are fairly out of balance from the factory, so a balance (especially with new pistons) would create a noticeable difference in engine vibration. I'm not sure if he was just saying that to get the sale or what because I don't know this company that well. Though, he did make sure to point out that there will still be vibration from the full cycle without any power strokes.

thrillseeker said:

what rpm range to balance for as well as if the bike is for street or race use. The rep I talked to said he does have experience balancing cb360 cranks and that they are fairly out of balance from the factory, so a balance (especially with new pistons) would create a noticeable difference in engine vibration.

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Ya don't say?

By george thats interesting.

Do let us know. Thanks for the update.

Buy a used crankshaft. I have beaten a CB 350 to the point when the big end bearing failed and the piston skirt slammed into the crank. I doubt that you will abuse your weekend ride to this level. Don't waste your money, ,build a good top end in that motor and it should last you for years

I have always done these few things to a 180 degree twin .
cc the combustion chambers . Make them and the quench distance identical .
if possible or feasible weigh and equalize the big and small ends . A note on this , if I'm not going to strip the crank I'll at least weigh the small end level with the crank journal . Sometimes it just doesn't make sense to strip the crank .
Weigh the pistons , rings , clips , pins or buttons and make them the same left and right .
Just accept the rocking couple . It is what it is .

Teazer , I figured our TZ's vibrated like crazy because crap was always buzzing loose because they vibrated like crazy because ...

~kop

I talked to Bill Bune. They take a different approach than Falicon. They also seem to be more helpful and not just in it for the bill. They recommended not worrying about balancing it because the pistons balance each other out. In fact, they don't even do balancing. As far as repairing the rods, they recommended 2 approaches. 1. find replacement rods and have them pressed onto the crank. 2. find oversize pins and machine the rods and pistons to accept them.

I don't like the idea of machining the pistons and rods so I decided to buy a used crankshaft. I'm going to inspect it when it gets here and, if everything looks copacetic, I'll just install that one. if not, I'll ship both of them to Bill Bune to have them rebuild my crank and replace one of my rods with a good rod from the crankshaft that I purchase.

Bill Bune's prices were better than Falicon's and they seem friendlier and more helpful so, if I need the work done, I'm going with them.

thrillseeker said:

I talked to Bill Bune. They take a different approach than Falicon. They also seem to be more helpful and not just in it for the bill. They recommended not worrying about balancing it because the pistons balance each other out. In fact, they don't even do balancing. As far as repairing the rods, they recommended 2 approaches. 1. find replacement rods and have them pressed onto the crank. 2. find oversize pins and machine the rods and pistons to accept them.

I don't like the idea of machining the pistons and rods so I decided to buy a used crankshaft. I'm going to inspect it when it gets here and, if everything looks copacetic, I'll just install that one. if not, I'll ship both of them to Bill Bune to have them rebuild my crank and replace one of my rods with a good rod from the crankshaft that I purchase.

Bill Bune's prices were better than Falicon's and they seem friendlier and more helpful so, if I need the work done, I'm going with them.

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They dont do balancing. Of course they dont recommend it! Cheaper and friendlier. Two very important aspects.

Yeah I was thinking the same thing about the balancing recommendation. but that seems to be the consensus. it may do something but not much, especially since it's an inline twin and the pistons balance each other out. if I were going with falicon I might go for it for the sake of science but if it's not convenient I'll probably pass on it.

Friendly and cheap maybe not, but Falicon is the best crank builder in the U.S. If they recommend balancing for your application, there is no other person with better credentials that can dispute that.

interesting. I didnt know they had such a good reputation. They certainly were not rude by any means. they just seemed eager to get off the phone and back to doing something else.

thrillseeker said:

interesting. I didnt know they had such a good reputation. They certainly were not rude by any means. they just seemed eager to get off the phone and back to doing something else.

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Ya they probably wanted to get back to some small stuff like building cranks for NHRA drag bikes.

DohcBikes said:

Ya they probably wanted to get back to some small stuff like building cranks for NHRA drag bikes.

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ha yeah thats along the lines of what I was thinking as well.

be careful how much $$ you sink into a 360...they're fun bikes, and if you're doing all this for the love of learning and doing it go for it..that being said though its a 360

Yeah that's why I'm hoping I'll be able to do a straight swap and not have to rebuild


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swap the engine to just another one? honestly not a bad idea if you know the engine youre putting in is fine

No, swap the other crank into my engine


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A new (used) crankshaft came in the mail yesterday. I inspected all the bearings and they seem to be rolling smooth and tight. I then checked the wrist pin clearances and both seem good and tight as well. I think I may be in good shape to just throw this crank right into my motor without any modification! If it all goes well, that will be a $50 fix, compared to a possible $500 fix!