a balanced view

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Could it be that the part of the lobes sticking out from the base circle are so small and that they are at a smaller radius that the vibes from them are small compared to those that come from the decomp weight running its cg at a larger radius?, and that makes countering the decomp weight more important than countering the lobes? I have seen lobes holed on other cam shafts and that could have been intended to counter the lobes but I don't know for sure. Regards
 
Taffy said:
it's almost as though the decomp balances the sprocket but that the am lobes are unbalanced!
Click to expand...
Why ask the question when you can answer it yerself?

I reckon Sorgasboard nailed it above. The holes must've been put there to help balance the flyweight only. The plane that the lobes rotate on is so far away from the plane of the sprocket that trying to balance the lobes by putting weight on the sprocket ain't much help.

My only evidence of this is that my camshaft that has the solid alumin sprocket without any holes shakes like a bitch when spun in a drill. This was mentioned in one of your previous threads about decomp spring.
 
sorry brad if you couldn't guess...

i knew all the answers all along but how else do you introduce a subject that's over 90% of people's heads if you don't wrap a riddle in an enigma.

anyway, this is the only fun i get!

i'll add more later - now you know that i know!

regards

Taffy
 
Understand. There's one question I've been struggling with:

"Where do flies go at night?"

:)
 
I wonder if the decomp would still work properly if you lightened the weight a little

have you tried a balanced cam taffy ? drill a ole or added a weight ? was it good...

regards
Bushie
 
the cams are too tough to drill but if you drilled itfirst...

as for a balance weight well i dissagree with this thing about th balance of the sprocket being too far from the lobes... i belive you can balance the whole assembly.

maybe we should getour resident balance expert in on the job?

regards

Taffy
 
Send me the cam, and I can drill them to any bore, as you wish, taffy.I've got the tools, which can drill accurately any hardened steel.Just tell me what bore and exactly where you wish to drill the cam lobes.The cam with attached drawing (with dimensions) welcome.
 
Would balancing the cam on its own really be worth the exercise? What does it achieve?

When you take into account the mass of the followers and rest of the camgear & valves, the mass of the cam lobes is bugger all. Also, since the lobes are going through a circular motion but the camgear is going in an essentially linear motion, changing the mass hanging off the camshaft can change the direction of vibration from the valvegear, but not cancel it out.
 
what about:

1. temporarily balance the whole thing with the decomp inboard, take measurements of how much and at what point (use adhesive lead strips).
2. temporarily balance the whole thing with the decomp outboard, take measurements of how much and where again.
3. experiment with the dynamic balance of the whole thing, like 4/5 balanced in favour of the decomp inward, which means that is is more in balance at revs, but less out of balance al low revs when decomp is working.

feel free to point ot uf i am horribly off track - im sure you will anyway!

Azza.
 
No point considering balance at revs below which the flyweight flips out for two reasons:

1: By definition the engine is only spinning slowly with decomp active. Balance issues are much less important at slow speeds.

2: If the decomp comes or stays on (ie flyweight in) during any time other than inital start you've got bigger problems than balance, as the exhaust valve train will quickly destroy itself. The decomp is brutal on the follower etc when operating and gets very much worse the faster the engine revs if it keeps operating.
 
mines done

6 gm stainless weight tig welded and doweled, preheated gear first and peened the welds, stainless filler.

slight grind on the decomp weight and out of the 3 oclock ole

I see what you mean bundy with the lobes up one end and the linear stuff, sure feels smoother in the hand drill though.

me cameras bust might get some pics in a week or so

regards
Bushie
 
Bushmechanic has sort out the issue.You can get the thing balanced by adding an extra mass or by removing mass at opposite side.I would say that the second way is better, cause whole thing is geeting more lighter, what is generally better.But is more difficult to achieve.theory of balancing says that forces, which operates on bearings, and which are come from imbalanced masses, rise to SQUARED value , when rpm of shaft is increasing
Other aspect is that you got something like static and dynamic balancing.The first one is carried out using X axis (Across the shaft), the second is to carried out using Y axis (along the shaft) either one and second' if not done, generate vibrations in different directions.Bushmechanic done static balancing, what sorted out up and down vibrations.How about dynamic one, which is responsible for side-to-side vibrations?
 
it feels better in the hand drill at about 3000rpm with the static balancing done.

I figured that I use 4000 to 6000 crankshaft rpm on the bike mostly so I'm happy. its a bit surprising though since I added weight to the same side as the lobes........... hmmmm perhaps the decomp weight is more "massive" than I thought.

only thing might be that the factory had it right ina reasonable compromise when all things are considered with real world application actually in the bike with shock loading and how the cams interact with the rockers/valves etc but it sounds a bit complex for them to have that sorted with all the other shenanigans going on.

regards
Bushie
 
Looking at the way this cam is balanced it appears that it has been balanced "dynamically". Dynamic and static balance is different. If the cam is balanced by the factory, for a set rpm value, it will be smooth. The other thing with the balancing is the other spinning masses. Piston, crank, counter balance. A single cylinder engine produces different vibes from say a v8, so different balancing methods are used.

I am an aircraft tech by trade, working on gas turbine and piston engines with and without propellers . When you balance a 6 blade 4 blade, 3 blade or 2 blade prop or a turbine disk, they are all done dynamically. They all are balanced in a different manner, the weights are all in different spots, and when compared to static balance, they can vary significantly.

The cam you have showed has a moving weight, so this will change both the static and dynamic balance. So if this is how the cam has come from the factory, it is oprobably set right for the use it was designed.

This is my opinion, but it could also be wrong, but the idea is now here
 
its not at all out of the question, of course we have been both shocked and amazed at Berg ingienuity.

Azza.
 
my firsat task would be to rotate the cam sprocket and see if there is a better balance this simple way?

regards

Taffy
Click to expand...

I think that will make things worse for the static test.

maybe remove the decomp weight altogether and spin the sprocket 180 ?

while there are other vibrations i guess the cam is the only thing thats asymetrical and rotating at 1/2 engine rpm? so the cam being out of balance can perhaps only be of use if it interacts with other out of balance bit bits in the cam train like rockers or something.

regards
Bushie
 
="bushmechanicwhile there are other vibrations i guess the cam is the only thing thats asymetrical and rotating at 1/2 engine rpm? so the cam being out of balance can perhaps only be of use if it interacts with other out of balance bit bits in the cam train like rockers or something.
Click to expand...

regards
Bushie

That's called rezonance (rezonanse?)two "waves" come peak at a time, so the force from imbalance of the cam, comes onto imbalance of the crank with piston, or rockers and valves.It's happening at certain engine speed, and we can feel its frequence on handlebar.It can causing loosing the engine mountings bolts.
 

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