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Discussion Starter · #1 · (Edited)
There are lots of threads asking about failed TL cam buckets and the most severe being ones with splits across the top of them.

It usually happens on the exhaust side and seems most prevalent on the front cylinder. More commonly it is happening in europe in places where there are unlimited speed restrictions.

Taking this into consideration and using some quite sophisticated measuring equipment and some clever software analysis I will endeavour to support my assertations that the problem lies in the cam / spring /rev relationship.

As I have mentioned in other places the role of the camshaft is to open the valve. The shape of the cam is designed to open it at a certain time to a certain height and for a certain time.

The role of the spring is to control the movement of the valve as it is acted upon by the cam. it holds the valve in contact with the cam as it opens, stops it overshooting the full open position and guides it back shut in sync with the cam.

the spring has a certain "spring rate" that is how springy it is and this is measured usually in pounds per inch.

The spring also has a natural frequency. If you pluck a guitar string it produces a sound, pluck a thinner string and the sound is higher. it has a higher natural frequency. spring frequency is a product of design and material. some materials have higher frequency some shapes have higher frequency. less coils per inch = higher too.

Cams are measured on duration , how long they are open. lift, how far the open the valve. and lift per degree (accelleration) how far they lift per degree of rotation.

Within each of these considerations are the subtleties of design..

A spring has to be the right dimension to fit in the space available and strong enough to do the job. it has to have a frequency which is suitable for the application too.

The camshaft has to open the valve gently and close it gently. we don't want the valve train subjected to the valve being banged open or the valve slammed shut.

banged open is known as 'jerk' . slammed shut is known as "seating velocity"

Cams have opening and closing ramps. (for the slow start / stop bit) flanks (these do the work ) and the "nose" ( where the valve slows down , stops and starts to close).

Good cam design takes these components and does them in harmony with the air demands of the engine and the cylinder head design.

Any overhead cam bucket cam profile will work in a TL, whether it accomplishes the desired outcome is a totally seperate consideration.
does it have the right lift, duration or area under the valve( the combination of area and time , it equates to how big the valve hole is and for how long).

Lift, duration and area all influence the characteristics of the power produced. but that is the realm of another thread

We assume that these things are done for us by the cam designer or the engine manufacturer.

It is all a compromise. and in some cases it is not proven in testing. As a former engine reconditioner and cylinder head specialist and now as a computer support techie for some clever engine developers and a cam designer I see many cases where cams are just "knocked out " with little or no thought to the interaction of components in the valve train and the consequential damage.

In the next post I will display a cam plot and explain the various events on the graph..
 

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Thank you for the tech info, not sure if I will ever be able to utilize your post but I am glad you are sharing this info.
Hopefully you'll do some research on our TLR and S cams and advise us as to how good or poor they are.


cheers
 

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Discussion Starter · #3 ·
The cam bit...

No worries on the cams I have digital measurements posted elsewhere.



Here is a screen shot of the TLR exhaust camshaft profile plotted lift against rotation. Both traces are exhausts. (the program does inlet and exhaust side by side so its using two exhaust traces cos I only loaded one).





If you look along the bottom line you see the cam starts to lift slowly , this is the opening ramp. the next section is the flank where the valve is travelling at a fairly constant speed. the nose is where the valve slows to a stop and begins its return.

This is an R exhaust plot and just looking at it it looks smooth as a babies bum.

But.................

Lets look at what is happening on another level.........

This is a plot of the accelleration of the valve by the same cam.




As you can see the valve goes thru some quite abrupt changes and tho we might imagine its nice and smooth in the first plot it gets quite ragged as the valve sees it.

This plot is the changes in Velocity that the valve sees..




Where the line crosses the zero is at the top of the cam lobe. So the up line is where the valve is opening fast the down line is where it slows to full open at the zero line , going under is the speeding up to close and the last up bit is the last bit where it slows down to close.

When viewed like this we can see there is a good deal of stuff going on.
 

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You must have some nice software there.

But why aren't the rear ones failing like the front?
 

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Discussion Starter · #5 ·
The spring bit...

So now we have a fair understanding of what the valve is going thru in relation to the camshaft.

The Spring is left with the responsibility of controlling all those forces and motions.

It has to be strong enough to hold the valve shut when it is in the closed position. ( Depending on quality of design of closing ramps the valve may want to "bounce" , if you drop a spanner on the ground it will "bounce", Newton had a lot to say about this but lets not go there right now).
We have all heard of "valve bounce and it is frightfully destructive. It tends to cause heads to fall off valves and collet grooves to fracture.

It has to be strong enough to stop the valve from over shooting the full open position. and coming back and hitting the cam halfway down or not at all and just hitting shut after the cam has gone past this point.

And it has to have a frequency which is compatible with the forces put upon it by the cam shape itself.

So when a spring is pushed by the cam it is similar to a guitar string being plucked (use your imagination here). pluck a string calmly get a calm note, thrash it and the string jumps all over the place and can make more than one sound. so it goes with springs. Aggressive cams place higher loads on springs in all of the above considerations.

An analysis of the action of a cam on a spring is called a "fourier " analysis.

Here is a plot of a std TLR exhaust cam with the recommended lash of 6 thou...





RPM is plotted anlong the bottom and the instability / stability of the cam and spring assembly is plotted in the vertical.

The 100% line and above spells trouble.

Fortunately most of what we do is up and down revving so we drive thru critical periods before any damage is done and in this case the "bad spot "is from 7250 to 7750.

In top gear this is probably in the 100- 120mph range dependent on gearing.

So it sort of follows that if you were strolling along an Autobahn at this speed or these revs you could hold the revs for long enough for damage to occur.

Now because the rise above 100% is not great we could surmise that it could take a while for the damage to grow to a point where something fails.
 

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Discussion Starter · #6 ·
What happens in the bad bit.

When the spring passes into the critical range ie passes over 100% ( and this is based in this instance on some assumption I have made. but the shape of the plot doesn't change as I will show later) the spring loses its springiness.

Imagine you get a rubber band and hang a small spanner on it. if you hold the other end of the band and move it up and down the spanner boings up and down quite happily. now increase the speed or distance you move it and soon the spanner jumps all over the place.

same thing happens to the valve. feed it crap movement and soon it will lose control. It is because the frequency of the spring is unsuitable.

Making the spring heavier increases its frequency,. changing its design changes its frequency.

The shape of the plot is related to the camshaft design , not the spring frequency.

The purpose of the spring is to control the valve in the presence of the camshaft.

So what is happening at this rev range?...

Well if we consider the spanner and rubber band .. then things are jumping around of their own accord and the components are no longer tracking the cam

the valve and bucket are jumping off the camshaft and banging back into it. valves may bounce on the seats if the bad zone is "bad" enough. So bit by bit the cam bucket especially is taking a lot of hits rather than travelling up and down in an orderly fashion.
If you hit a follower often enough my suggestion is that it will crack.

Why will it crack in one line? well I reckon that eventually one point will get weaker and hollow out and the cam will ride on that one point more than another and the failure will happen.

Some buckets show small cracks happening in a circle and maybe this is the first stage.
 

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Discussion Starter · #7 ·
More about the problem

If we weaken the spring , or lower its frequency, or both.

then the plot will look like this.....



We can see the rev range is lowered, but the shape stays the same.

If we increase the parameters then the plot will look like this...




The rev range is raised..
 

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Discussion Starter · #8 ·
What about valve clearances.

This is going to shock you...........

we understand that we need valve clearances to stop valves burning out.. if they run out of clearance they will not close completely and the leaking gasses will torch the valve.( they actually look like someone has hit them with a blow torch!)

In direct conflict they need to stay shut as much as possible to allow them to cool down (heat is transfered form the valve head to the seat when it is shut).

The smaller the lash the more of the opening and closing ramps can be used and the easier it is on the valve and seat (on closing).A lower valve seating velocity

It also influences the shock loading placed on the spring.

here is a typical plot at 6 thou lash.....




If we open the lash to 8 thou.........



The "bad zone" is still in the same place but look at the height of the spike...


If we open the lash to 12 thou.......



The "bad zone" gets even higher in intensity..

Not only that but the much smaller spike at 5500 is now getting closer to the 100% line.

Now these are just plots based upon real data , some assumptions and some real physics and prepared with very clever software. 100% line is an indicator of trouble not a set in concrete its gonna fly to bits point. It shows us where the forces reach critical zones. certainly the peak of the plot where its over 110% is far more likely to do damage... you get the idea..

This particular paragraph is to highlight the need to run the specified lash clearances and not be drawn into making them bigger to be on the safe side.. cos its in fact less safe

Told you you'd be shocked!!.......
 

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Discussion Starter · #9 ·
You must have some nice software there.

But why aren't the rear ones failing like the front?
I don't really know the answer to this one but I would guess the difference from the front to rear is likely to be to do with the amount of oil around the assembly.

Perhaps the fact that the front exhausts would be submerged puts extra load on the assembly.

Perhaps its because in the presence of such copious quantities of oil the bucket skids on the cam and is not rotated as it should. (cams are not absolutely central on the bucket which makes the bucket rotate and offer a clean spot to the cam and spread the wear)


I do believe the buckets fail because they are allowed by circumstance to spend extended periods in a critical rev range.

Front or back thats a bit of a mystery...
 

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Discussion Starter · #10 ·
Where does that leave us?

Well I've got to blame Greg (cyclecamper) for raising the topic of choosing valve springs a couple of months back.
( and myself for getting involved but I do think accurate information is knowledge and some zoners will get something out of this)

TL springs are adequate for std cams and maybe for improved cams too. when used within the parameters highlighted in the plots.

The shape of the cam is the critical factor in the process. The plots showing various springs demonstrate this.

the Cams are adequate because in most situations no-one would hold the revs in the critical range.

Where to from here?

If you have a set of cams ( other than std) ( I have these) and want a plot.. no prob..

You will need to take them to a cam grinder with a "cam doctor " or 'cam pro" measuring setup. they can measure and print the data and also give you the files on disk ( take a USB stick) for further use. just email them to me.

You can also email me and I can send you a small program to generate the files on your pc, you will need a degree wheel (or protractor ) and a dial gauge.

If you can get the files I can do an engine simulation also and compare the likely power curve against the std power curve.
 

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Discussion Starter · #11 ·
The effect of cam frequency on power.

I have borrwed drew's (skanda) dyno sheet from his post to try and draw comparisons between the critcal points and power output.

TL's are known to have some smoothness issues and zoners correct this with fuel and ignition mapping. but it is quite likely that they arise from the cam events....


Skandas TLR..



There is a power dip at 4200 and again at 6500 and the power flattens at 9500. if we compare this to the fourier plot ..........



If I was out in my assumptions of spring frequency ...then if we slid the spikes down 1000 rpm... then each of the power dips would line up with the "bad zones" .

this may not be an absolute observation in this instance but it is absolutely true of other occasions with cams Phill (surecam.com.au) has shown me where engines have bad power ranges that can't be tuned out.
 

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Discussion Starter · #12 ·
Adjusted spring frequency

Until this point I had been using an assumed spring frequency of 30,000 cps as the base frequency to base the analysis.

below is a plot generated with an assumed spring frequency of 27,000 cps





Interestingly it now places the critical rev range peaking at 6750 which coincides with the power dip in skandas dyno chart.

It suggests that the actual spring frequency is likely to be 27000cps.

It also follws that if this is the case the previous assumptions need to be adjusted to fit the new data.

As said before the shape of the plot does not actually change just the time and intensity of events.

The conclusions remain the same the latest plot can just be considered to be more accurate.

Phew!!!
 

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holy brain overload! nicely done :hail opened up a whole new understanding of cam physics :thumbup I'm very familiar with engine, cams, etc, but this added to that :hail

interesting to see when you compared the graph to the dyno chart...

I usually rode my R 7-8k rpm (when I was fun riding) all the time :O my buckets always looked fine. but then again I wasnt in that range ALL the time, just when in the twisties. other than that it was mostly in the 5ish zone
 

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:stupid My S lived 6k+ when having fun, but even then it wasn't constant at any one rpm and sadly of the 60k I put on the TLS very few were while out having fun in twisties.

Mine have also been at the minimum lash forever. They were there when I got the bike (with 1k miles on it) and haven't really moved and I've not been motivated enough to set them to the middle - perhaps that makes the buckets happier:O
 

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makes me feel a lot better about always setting my valve clearances as close to the minimum spec without going under. I was trying to get the most out of the camshaft but now there are other really good reasons to do it.
 
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fantastic thread Stu, i learned a lot today :)

Suzuki gives you a range in between you have to set the clearance, and i bet they have set that range to have the most reliability... ( tight = burning valves, loose = buckets slamming )

i also learned that engines like lower revs, and maybe that's why i've never had anything happen to all of my TL-engines :laugh
 

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Ring-In, it's good to let people know the basics of what's going on, but it's easy for a little too much information to be worse than less. The people here that have experienced fractured tappets with production engines (no aftermarket cams, extra rpm, etc.) are probably because of the combination of racing use (short warm up cycle, consistent high rpm), modifications which increase power output (therefore heat, cylinder pressure, etc.), and therefore should expect a significantly shorter life cycle of critical engine components, which includes anything in the valvetrain.

The best thing to do would be if people with failed tappets were to list their modifications, running hours, maintenance schedule and lubricant. That would be the fast way to a general preventative maintenance schedule for the tappets, which is the most effective "fix" to this problem.

Regarding the tech stuff:

- Any engine component that has infinite life is either too heavy or too expensive. There should be no expectation that a highly stressed component like a tappet should have the same life under racing conditions as it would when used in production intent (non-racing) circumstances. The Suzuki TLR Superbike manual says to check clearance after every race (700 km) and to replace every 2000 km. Obviously they revved higher and used different hardware, but still preventative maintenance is key.

- Instability of a direct acting bucket is usually evident in the cam lobes. If the parts of the system are losing contact with each other, there is usually evidence of where they came back together (hard). The valve side of the failed bucket in the other thread may be indicative of this (semi-circular "chatter" marks), but it also may be a result of lobe/bucket/valve offset tolerancing or a perpendicularity/flatness issue on the valve tip/shim.

-Tappets (like anything else) fracture because of excessive stress. The simple calcualation is Herztian with all surfaces assumed flat or round, but like most simple calculations it falls well short of the real world where it is asking alot to call out flatness of a lobe or bucket to within a few microns. Since FEA is not realistic even where those resources exist, the Herztian analysis can at least give some indication of where the stresses are and relative changes.

- Cam characterstics are but one input to the valvetrain system, with the associated masses and geometry being equally as important in an analysis of stress (fauilure).

-Spring frequency varies with spring displacement. Valve springs gain inactive coils throughout their travel, as additional coils "go solid" the frequency of the spring changes. Linear is a safe assumption, so a line between open and closed frequency is usually good enough

- Your acceleration plot has alot of noise in it for simple second derivative (you can do this in excel, not until FFT's do you need something more powerful like matlab, yuck). I might be concerned about the resolution of the original data (lift/angle). If you don't have a access to an Adcole, find one and get time on it, this is critical data, and a small difference in accleration can be a huge difference in force.

This stuff goes on and on, and each point requires additional info to flesh out, which is why too little info is often better than a little too much. Good for you to take a deeper look into these things, there are any number of good texts and papers on valvetrain specifics that will really get into the meat of it. Cheers.
 

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Discussion Starter · #19 ·
Cf
Thanks for your comments.

FYI the data used was from a std TLR exhaust cam, all components were measured using industry std devices. and all assumptions were based on a std engine.

The resolution of the cam measurements was in 1/100ths thou per degree.(using a machine similar to the adcole) ( I service the machines so I'v had access now for ten years) files were generated using CamPro. and the analysis with Dr.Dr.

I think perhaps you might have missed some of the intent of the thread, which is to dispell some common myths associated with cams valves lash and springs.

We agree on what damages the buckets but not exactly the events that lead to that .

Yes it would be very helpful to have more collected anecdotal evidence and even more useful to be able to examine some failed components and the matching cams.

What is widely being assumed as the cause of these failures ranges from grit in the bucket bore to sticky valve stems. i don't believe that the buckets presented in the threads failed as a result of these conditions.


As to the complexity of the descriptions I give the zoners credit for being able to follow the gist of the thread if not all the detail. I could have made it far more complex but that would not have been appropriate.
 

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I think Duken4evr originally posted this article that talks about crankshaft acceleration and its effect on the valves and how it is possible for them to not follow the cam lobe profile. A good case for leaving the scissor gears in place :dunno

Interesting though.

Click for a bigger one.
 
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