Should I have my CB360 crankshaft rebuilt and balanced?

[thrillseeker]

Hi all. I have this CB360 that I'm rebuilding and converting to the infamous PJ378. I got my head and cylinder work done by a really good local machinist who has specialized in motorcycle head/cylinder work for about 30 years and works on a LOT of old bikes. Since we just did all this work on the top end, when I went to pick up the head and cylinders, I brought my crankshaft so he could look it over quick to make sure it is in good working order. While taking measurements, he noticed that the rod-pin clearance was a little too high. 0.003in to be exact. He recommended that I not use it in that condition and suggested I call Falicon to see if they could repair it. After talking to a rep at Falicon, they can repair it but it would be a full crankshaft rebuild. They would take the crank apart, inspect everything, machine the pin openings to be larger, and press in bushings to fit the pins. I really like the idea of having this done because then I have the piece of mind knowing my crankshaft is in good shape and is going to last. The cost for that service is about $500 though. But I'd rather spend $500 to have that done than buy a crankshaft on ebay and risk a problem down the road, potentially ruining all the work I just had done on the top end. The other thing I'm considering is having it balanced. If they're already rebuilding the crank, its an extra $200 for the dynamic balance. They balance for the pistons I'm using so I'd send the crank, pistons, and pins. Since I'm using the lighter GS850 pistons I'm thinking maybe this would also be a worth while investment.

I understand the basic benefits of balancing the crank but, for this motor, is it worth while to spend the extra $ to get the crankshaft balanced while it's already being worked on? Does anyone here have experience with having their 360 or similar crank balanced? What should I expect if I do or do not balance? This is my first rebuild so I'm open to any suggestions. Thanks everyone.

 

[Sonreir]

What are your expectations for the balancing? What is it that you're hoping to gain?

 

[thrillseeker]

I'm hoping to make the engine run smoother and more efficient as well as maximize it's reliability. If I get performance gains from it that will be a plus too. I also want to know if it is generally a good thing to do when changing pistons since the weight is now different than what it was stock.

 

[Sonreir]

The rebuild will definitely get you the reliability you're after, but the balancing isn't likely to have a big effect in this area.

The balancing will make things smoother, but only at a given RPM. Any shop worth their salt should ask you at which RPM you want the crank balanced. There is no such thing as a perfectly balanced crankshaft and a lot of it is going to come down to your desires for your engine.

Engine balancing is not a simple concept. Changing the weight of the pistons will definitely have an effect on the balance, but what you've lost in one are you may not gain in another. Talk to the pros and see what their recommendations are, but also ask them to give the reasons for what they're saying.

Here's some basic info on the topic:
https://en.wikipedia.org/wiki/Engine_balance

 

[DohcBikes]

There are some cranks that are particularly receptive to balancing. Have your crank balanced at whatever RPM your bike is comfortable cruising at, or at high RPM to realize the most gains.

Balancing the crank can be a worthwhile performance mod, especially on a crank that has been deemed questionable. The question is how much expendable income you have.

 

[mydlyfkryzis]

A vertical twin, 180 degree crank, even perfectly balanced, will still vibrate a bit. The left and right forces cause a rocking couple that cannot be balanced away unless the motor has a separate balancing shaft. Don't waste time balancing the crank...the difference would not even be noticeable.

 

[DohcBikes]

Don't waste time balancing the crank...the difference would not even be noticeable.

Have you ever actually had a crank balanced or are you just speculating?

 

[mydlyfkryzis]

Have you ever actually had a crank balanced or are you just speculating?

No, I know nothing and make up stories. I don't even know what a CB360 is.

 

[thrillseeker]

So it sounds like the main reason the engine has so much vibration is because of the 180 twin configuration. I could get it balanced but the amount of difference that a balance would make would not be enough to really smooth out the vibration caused by the 180/540 ratio that the cylinders fire at. If it wouldn't do a ton for vibration, is there a performance or efficiency benefit that I would gain by balancing? Especially since I'm using pistons that have a different weight than the pistons that the crank was originally designed to work with? Also, if anyone has some experience with balancing a CB360 or similar crank, I, and I'm sure anyone reading this in the future, would love to hear about your experience.


Sent from my iPhone using Tapatalk

 

[thrillseeker]

Another thought, since the engine is a 180 degree twin, and there is always one cylinder moving upwards to counteract the force of the opposing cylinder's power stroke, maybe changing the pistons equally wouldn't have any effect at all on the balance of the crankshaft?


Sent from my iPhone using Tapatalk

 

[Sonreir]

Yes, there will be performance benefits, but you're venturing into territory most folks only enter if they're ready to drop several grand on just their engine.

If it's performance you're after, there are much better things to address first.

 

[mydlyfkryzis]

If you are racing, or running at full RPM a lot, then larger pistons and existing crank being rebalanced will benefit....The cost/benefit is not really very good....

If you have no worries for $$$, you can throw lots of money at it. But most people don't have bottomless wallets. It is a 360, so it's value is not exactly diamond like. I would spend my time improving oil flow (See CrazyPJ post's). Good oil flow to the head will be more bang for the buck. A perfectly balanced engine with scored cam journals and scored cam is somewhat of a waste.

These engines are good enough for the bike, adding reliability is a good thing, trying to get a HP or 2 extra is expensive in relation to the bike.

When I first thought about restoring my 360, I estimated about $3500 without major engine work. For $2000, I bought a "no work needed" 91 Nighthawk 750. It is far smoother and faster than the 360. Later, I spent the money to get the 360 roafdworthy and my cost estimates were pretty close. At this point, I have about $4 K in the 360. From a performance point of view, the 750 was a better investment to go faster. If IO had $10K to invest on performance upgrades to the CB360, I'd get a Ducati 1000 GT, better performance for the dollar.

Some people will spend quite a bit on a bike to increase their performance even a little bit. The CB360 is not particularly rare, the chassis sucks for handling at speed, but it is a nice reliable, fun bike stock or close to stock.

So my view is a little jaded with age and experience.

I would make sure your new pistons are equally weighted. If you go for crank balancing, make sure it is after the pistons are balanced.

180 Twins are in primary balance, unlike 360 deg. Twins, but the firing order still creates rocking couples. Like a see-saw vibration.... You cannot balance out the rocking couple as the smoothness of a good balance is disrupted by the fact the motor is having 2 explosions on one pair of revolutions then another revolution with no explosions. Excited vibration cannot be balanced out. So you can make the engine smoother, but you can't make it smooth.

 

[DohcBikes]

No, I know nothing and make up stories. I don't even know what a CB360 is.

That isn't what I asked. My question is whether or not you have ever had a 360 crank balanced, or if you are speculating as to the level of benefit. Your sarcastic response leads me to believe that you have not had one balanced, but yet you are here telling us how much it will or wont reduce vibration or help performance. Just making sure about that.

This isn't a thread about oiling, or the most cost effective mods. It is a thread about having a crank balanced while it is already at the shop being worked on. He clearly stated in his first post that he would send the rest of the rotating assembly to have the crank dynamically balanced in respect to the weight of his new pistons. I would do it.

As I said in my first post, it will undoubtedly show several benefits. Whether the level of benefit in your model is worth it or not is subjective until someone comes along and says they had it done. You already know the cost. Decide for yourself.

 

[thrillseeker]

Thanks a lot guys. I know the 360 isn't the best performing bike. If I was just going for performance I never would have bought it. My performance twitch is mostly satisfied by weekend track events on 4 wheels. I have loved the vintage honda twins for a while because of their history and I just think they're really cool. I'm already down the rabbit hole I was expecting to go down and was planning on having a couple speed bumps along the way. The crank needing rebuilt happens to be one. I've somewhat already made up my mind about pulling the trigger on that. I guess now it comes down to the question of if it is a good idea "best practice" if you will, to get the crank balanced with my modifications. Especially since it is already being rebuilt. The extra $200 isn't going to break my budget but if it's not a "best practice" kind of thing to do in my situation then i may spend the money elsewhere. I have plenty other parts of the project that need money thrown at them.

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!


Sent from my iPhone using Tapatalk

 

[thrillseeker]

Maybe I'll be the guinea pig though since it seems like I have an opportunity to do so and share some experience with everyone here who has helped me out so much along my venture.


Sent from my iPhone using Tapatalk

 

[mydlyfkryzis]

Have you balanced a CB360 Engine and have measurements before and after to show the improvement? Are you speculating?

If the OP thinks I am full of it, he can ignore me......I would never presume to give you any suggestions. Your experience and knowledge are far superior to mine.

So specifically, how much smoother will his CB360 be and how much horsepower will he gain with balancing? Do you know? You question my background, but I am not seeing specifics from you.

Will balancing and engine give improvements? Sure ! is it free? Is it worth the time and $$ to do this to a street bike?

I was not questioning the results of balancing, rather the value for a street bike..... You have not addressed the value, only that it will make improvements. Will the improvements be measurable? Cost efffective

Since he is not building a racer or LSR bike, I doubt the cost is really a good investment.

By the way, are you a certified Vibration Analyst? Just wondering......

Have you ever balanced a 6,000 HP compressor? Do you know to do fast fourier transforms on vibration signatures? Can you do 2 plane balancing? 4 plane Balancing? 26 Plane balancing? What do you really know?

If you have driven a Buick, does that mean you are unqualified to drive a Ford?

Do you think a reciprocating compressor and reciprocating engine have entirely different forces acting on them?

You don't need to answer any of this....why? Cause I wouldn't believe anything you have to say. You don't need to believe anything I say.

I may have no credibility with you, nor you with me, but that's life on the internet.

 

[thrillseeker]

First of all let me say I value EVERYONE's input. I apologize if I started anything here. I'd like to stop it here as well. Nobody needs to get heated over this little question I've raised. If anybody has relevant information based on experience, please feel free to chime in. Otherwise, I'd like to keep the trash talking to a minimum.


Sent from my iPhone using Tapatalk

 

[DohcBikes]

Have you balanced a CB360 Engine and have measurements before and after to show the improvement? Are you speculating?

If the OP thinks I am full of it, he can ignore me......I would never presume to give you any suggestions. Your experience and knowledge are far superior to mine.

So specifically, how much smoother will his CB360 be and how much horsepower will he gain with balancing? Do you know? You question my background, but I am not seeing specifics from you.

Will balancing and engine give improvements? Sure ! is it free? Is it worth the time and $$ to do this to a street bike?

I was not questioning the results of balancing, rather the value for a street bike..... You have not addressed the value, only that it will make improvements. Will the improvements be measurable? Cost efffective

Since he is not building a racer or LSR bike, I doubt the cost is really a good investment.

By the way, are you a certified Vibration Analyst? Just wondering......

Have you ever balanced a 6,000 HP compressor? Do you know to do fast fourier transforms on vibration signatures? Can you do 2 plane balancing? 4 plane Balancing? 26 Plane balancing? What do you really know?

If you have driven a Buick, does that mean you are unqualified to drive a Ford?

Do you think a reciprocating compressor and reciprocating engine have entirely different forces acting on them?

You don't need to answer any of this....why? Cause I wouldn't believe anything you have to say. You don't need to believe anything I say.

I may have no credibility with you, nor you with me, but that's life on the internet.

I never claimed to know the specific level of improvement on his engine. That's why I told him that it will undoubtedly improve it, but we would need someone with model specific experience to relate their feedback. You are just telling him it wont make a noticeable difference, and you simply do not know.

Yes, I have had many cranks balanced, and fortunately have been graciously allowed to balance a few myself. Depending on the model, there are very noticeable gains to be had. This part is my opinion: If I were already having the crank worked on, and was already spending $500 on that particular part, I would spend the $200 to have it balanced.

I can't speak for anyone else, but this doesn't get me heated.

 

[barnett468]

.

By the way, are you a certified Vibration Analyst? Just wondering......

.........................................I am

 

[barnett468]

.
using lighter pistons will create an overbalance which can reduce vibrations at higher rpm but increase them at lower rpm . . using heavier ones will do the opposite.

as DOHC mentioned, engines should always be balanced for the rpm the operate most often.

You seem very concerned about the balancing and dont seem to be worried at the price so definitely get it done and you will never ever wonder if it would have been better/smoother if you you had had it balanced when you had the chance.

the stator flywheel should also be balanced if one goes thru the time and expense to balance the crank . . these are always neutral balanced.