Quarter Scale Merlin V-12

[petertha]

Wow again
- dumb question, but after you profile mill the block outlines from solid bar stock, now they are little islands but still attached. Do you then flip the bar over & mill the backside to 'release' the parts? If so, what keeps the parts from flying around once the end mill breaks through?

- Is the center hole for oil lubrication? If so, where does the waste oil get picked up?

- just curious (sorry if you already mentioned), what did you receive for plans & instructions package? I'm visualizing a volume set of Encyclopedia Britannica... but suspect something less Are they kind of builders notes with pictures or set of plans only? Are you modelling in SW as needed or just when required?

 

[mayhugh1]

Peter,
The hole you see was drilled for an oil passage and it will be plugged with a screw. The waste oil collects in the head and splash lubricates the cam lobes. When the level gets high enough it drains back into the sump through the cylinder stud tubes.
The documentation I received was about 100 sheets of drawings and some 30 pages of notes. About a third of the notes are 'boiler plate' talking about the need to straighten the castings, etc. There isn't alot of hand holding, which is OK, but it feels like some key basic information has been left out. For instance there are ports that aren't documented, and so I'll probably end up plugging them until I realize what I should have done with them. I'm only modelling portions of the engine that will help me understand and/or visualize some of the more difficult (for me) workings. For instance, I'm really struggling with the two camshafts which are not identical and not at all intuitive due to the crazy rocker assemblies.
These particular cookie sheet parts were cut apart on a bandsaw after being milled, and a secondary milling operation brought them to their finished height. Terry

 

[Scott_M]

Hi Terry
Looking fantastic !
I can recall working on some automotive cylinder heads ( aluminum ) that had different torque values for the head bolts. The reason was the head was structurally weaker in some places and would distort. Just a thought, you may want to try bolting the head to the block and see if the cam still spins. It would be one of those things that would be nice to know before final assembly.

Scott

 

[mayhugh1]

Well, Scott, that didn't occur to me. I can't test it in any meaningful way, though, until I make the liners since the heads sit down on them and not the blocks. In my previous mock-up I used some delrin spacers to simulate the portion of the liners above the blocks, but the delrin would compress in a torque test, and the result wouldn't be meaningful. Something else to worry about, I guess. - Terry

 

[Scott_M]

Oh man,I didn't mean to add anything to your worry list. :-[
And I'll bet you can deal with it at that time. Just sneak up on your target torque values while testing for cam rotation. Chances are good that you will be fine.
I just thought it would be worth mentioning.

It really is looking fantastic.

Scott

 

[mayhugh1]

The bearing blocks support not only the camshafts but also the rocker arms above them. After gaining confidence in their keyed alignment, I drilled and reamed the blocks for the rocker shafts. Again, I reamed the blocks .002" over the diameter of the shafts. Although the drawings specify the shafts with zero clearance to the blocks, I didn't want to risk the possibility of them affecting the alignment I had already achieved. I later realized that this clearance is also needed during assembly because in order to install the rockers the shafts must be slid in from the rear of the head through the already installed blocks. The alignment of the rocker shaft bores was verified using a length of the drill rod that was eventually used to make the shafts.
Each assembly uses six individual rocker shafts rather than a single continuous shaft. This is done so the shafts can be axially drilled for a central oil passage to lubricate the rocker arms and cam bearings. The cam lobes are splash lubricated with waste oil that accumulates in a trough that runs the length of the head. This waste oil is eventually returned to the sump at the bottom of the engine through the stud tubes. Special slotted washers under the stud nuts on the outer (lower) studs provide the return paths.
My castings and bearing blocks are a bit different from those in the photos I've seen of Gunnar's completed engine. Gunnar started construction, in 2006, of one of the first engines sold, and his is the only completed engine for which I've been able to find any construction photos. From what I've been able to tell from translating a copy of a diary he sent me, he also helped debug the Quarter Scale documentation. Evidently, the bearing block design evolved into the version in the drawings that I have. Gunnar's photos show two screws in the top of each block that were likely used to secure the ends of the rocker shafts. A gap is needed between the adjacent tubular shafts so oil can flow out from between them and down through a drilled hole in the center of each bearing block. It's this oil that lubricates the cam bearings. My drawings call for a single screw in the center of the block which I assume is now used as a separator between the shafts to establish the required gap. Since there's no provision other than a recommended close fitment to prevent the rocker shafts from spinning, I drilled and tapped the sides of my blocks for set screws to secure them.
Another major difference is that oil is pumped into the top of the bearing block in the center of the assembly in Gunnar's engine. My drawings show the oil being injected into the side of the rearmost bearing block. This was a peculiar change because most of the oil port in this new location is blocked by the bearing block's mounting studs. Even though I would have thought it best to inject the oil in the center of the assembly, I decided to follow the revised drawings. There was probably a good reason for the change, and it might have been that the original top-ends were being flooded with oil. This would also explain the change to the head castings that included a deeper waste oil trough.
While the blocks were out of the assembly to be drilled for the rocker shaft set-screws I also engraved their sides with their current positions in the assembly. This will insure the blocks always go back into their original tested locations.
The rocker arm design is rather novel and deceptively complex. I was able to do most of the tedious machining on the Tormach, but finishing them to their final width became an issue since there weren't two parallel surfaces to grip in a vise. After ruining all my spares by launching them across the shop, I machined a plastic fixture to orient the rockers so they could be held in a vise while being finished. I also machined a fixture to safely and accurately machine the slots for the cam rollers - four at a time. I substituted standard miniature ball bearings for the shop-machined cam rollers shown in the drawings. Curiously, the rollers in the drawings were an exact match to a standard bearing.
The Merlin has 24 rockers, and the exact same part is used on both the intake and exhaust valves in both heads. Using a common part simplified the construction, but it will also result in two very different profiles for the two camshafts. The effects of my short crankcase continued to bubble up through the top-end of the engine, and the rocker arms and shafts had to be modified to accommodate my shorter cylinder spacing. The camshafts will also have to be modified.
The machined parts needed to complete the cam block assembles included 24 valve rollers, eccentrics, and thrust washers. The number, intricacy, and small size of the aluminum bronze eccentrics would have made their machining very tedious on manual equipment. The valve rollers were hardened after being parted off from drilled-through lengths of drill rod. Care was taken when preparing the workpieces to make sure the holes were drilled through the exact center of the stock. If the shaft holes aren't centered in the valve rollers, the lash will be inconsistent as the rollers spin on the eccentrics. The tiny thrust washers for the valve rollers were turned from phosphor bronze.
I made two full sets of eccentrics having two different offsets. The offset of the eccentric wasn't specified in the drawings, and so I thought it best to have some options available when the camshafts and valves are completed. After thinking about it more, I realized it really wasn't necessary and was a big waste of time.
Adding the rockers to the cam block assemblies added another 200 parts to the engine. I'm going to take a break from the high volume stuff for a while and begin working next on the camshafts. - Terry

 

[Scott_M]

Again...Wow. Really nice work Terry !

Have you ever used Polycapralactone to hold odd shaped parts ? I works really well and saves a lot of fixture time. Tormach sells it.
Pretty handy stuff.

http://www.tormach.com/store/index.php?app=ecom&ns=prodshow&ref=31846

and

http://www.tormach.com/blog/super-soft-jaws/

Scott

 

[mayhugh1]

Scott,
I've been meaning to try it and have been planning to include some on my next order with Tormach. It does look really useful. I once used a football mouthpiece that I found in a local Walmart to solve a tricky fixturing problem, and it may have been made from the same stuff. After being heated in water it would conform and hold its shape. I only used it once, and so I don't know if it could be re-used like the Tormach product. - Terry

 

[Cogsy]

I bought some of the same sort of thermoplastic a while back and I have used it a lot, for everything from workholding to repairing items around the house (the button mechanism of the kitchen garbage can entirely relies on this stuff) and even replacing half of the nosepiece on my sunglasses (most people can't tell it's not the original piece). I haven't tried directly machining it yet, although I hold high hopes.

I can confirm it is a great product, but it is the same stuff sold on ebay under various different names (plastimake, etc) for much cheaper. I paid around $25 USD including postage for 1kg (2.2 pounds) of the stuff. But it goes a long way, my 4 kids have all made toys with it, various friends have created stuff and I have made many things, yet I still have 3 of the 4 250gm packets it came in unopened.

Long story short, grab some cheaply off ebay and have a play with it, everyone should have some on hand.

 

[mayhugh1]

The Quarter Scale Merlin's camshafts seem like perfect candidates for being built up similarly to the cam in Jerry Howell's V-4. The camshafts are almost ten inches long with diameters over most of their lengths on the order of a quarter inch. One of the photos shows a sketch of the cam blank that will be used in both heads. There are clearance grooves on each side of the bearings, and a narrow integral thrust bearing at the rear end limits the shaft's forward/aft movement. The necked down sections between the lobes are required to clear the valve spring assemblies. The rear of each shaft will later be fitted with a sprocket drive adapter, and I added a hex at the front of each shaft per John's suggestion to help with indexing the cams during final assembly.
I originally thought I would machine six spools for each cam with each spool having an intake and exhaust lobe pair separated by a turned bearing. I planned to bore these spools for a close slip fit on a length of known-straight drill rod. Done this way, the cam lobes could be easily machined with the spools set vertically in a simple fixture on a 3-axis mill. A difficulty with this built-up approach, though, is that a scheme is needed to accurately align the spools on the shaft before the Loctite sets up. If the parts are properly prepared this can occur almost immediately. Being roller cams I wouldn't expect the load on the Loctite'd spools to come anywhere near the shear strength of the adhesive.
I decided, though, to first try my hand at machining a test blank from a single piece of steel, mainly to see if I could do it. I considered more than half the battle being the machining of the cam blanks with the same fit that I had with the drill rods in my cam block assemblies. To machine the actual cam lobes I'll most likely later create a CNC program similar to the one I used to machine the crankshaft counterweights. My concerns with a single workpiece approach included warping as well as my own ability to stay focused throughout the lengthy and unforgiving machining required to complete the entire part. If the test part wasn't reasonably successful, I still had the option of making the cams as built-up assemblies.
I started with a length of ground/polished 5/8" diameter Stressproof that I ordered from Speedy Metals. I bought enough (surprisingly inexpensive) material for two camshafts plus a spare for about $15 plus shipping.
On paper I divided the cam blank design into six 1-1/2" long segments, and I made six worksheets with all dimensions referenced to the same lathe z=0 point at the rear of the camshaft. I kept the pertinent sheet immediately above my lathe at eye level to help keep me focused. My plan was to chuck the workpiece into the 5C collet chuck in my manual lathe and incrementally pull it through the collet just far enough to machine a single section at a time. The run-out of my lathe's chuck and collet combination is pretty lousy at almost four thousandths, and so I used a reference line scribed along the side of the rod to maintain a consistent alignment as the workpiece was pulled through the collet. I was careful to always tighten the chuck using the same key socket, and I used a dial indicator to verify the runout near the far-end of the workpiece after each repositioning. After every other repositioning I also found it necessary to pull the workpiece out of the collet and the collet out of the chuck and clean the chips off everything before reassembling.
Even though it wasn't initially needed, I started out using a live center in the tailstock to prevent the workpiece from whipping around as more of it was pulled through the collet. The rear end of the cam required some machining for a sprocket drive adapter, and so this was done on the mill before starting the lathe work. Part of this machining included the reaming of a locating recess where the tailstock center would wind up, and so I turned a center-drilled button to insert into this recess. My live center has a run-out of 1-1/2 thousandths, but in this particular set-up the tailstock is used only for stabilizing the far end of the workpiece and, so there's no first order effect on turning accuracy.
As a precaution I decided to turn the bearings a thousandth under the diameter of the test rod that currently fits my cam block assemblies, because I didn't know what to expect for machining-induced warpage. The completed ten inch blank will be somewhat flexible, and with seven bearings supporting it, the assembly itself might tend to gracefully straighten out a slight bow without binding. I also added generous fillets to the blank on each side of every lobe in hopes of reducing the tendency of the workpiece to warp during machining. I had no science to justify this, just gut instinct.
Most of the machining between the lobes was done with a full-radius Iscar grooving insert (GIP 2.39-1.20). This .093" wide cutter has sufficient relief to cut side-to-side chatter-free in steel for a depth of cut up to .010". I used this insert on my 18 cylinder build, but being designed for larger lathes it was necessary to modify its toolholder to fit my 1/2" Aloris clone tool post. Combined with the lathe's power feed, I found this insert capable of mirror finishes in Stressproof. The only polishing I had to do was typically to remove a few tenths with 1000 grit folded paper.
The machining of the blank's numerous features was, as expected, pretty stressful and required a lot of concentration. I spent nearly ten hours bent over the lathe making the test cam blank. I had to spread the machining time over a couple days to accommodate my knees, back, and frequent bouts with brain fog. A real disadvantage of this single workpiece approach is that a momentary lapse of attention can spoil a lot of invested time. To be honest, I'm not sure I can come up a single advantage of this approach over a built-up version.
The TIR of the finished blank, measured at its center between two vee-blocks, was only 1-1/2 thousandths - a very unexpected surprise. The blank fit nicely in my cam block assembly and spun so freely that I was left thinking that the extra thousandth bearing clearance that I had added wasn't necessary after all.
I ran into an issue, though, when I installed the rocker arms. For purely cosmetic reasons I had increased the width of the cam lobes shown in the drawings. What I hadn't realized was that the cam lobes actually run inside the rocker arm slots for a portion of their rotation. After going back and modeling this section of the assembly I realized that the stock assembly had been designed for only .007" radial clearance between the peak of each cam lobe and a portion of the rocker body inside the slot. When I machined the cam blanks I left an excess radial stock of .010" on the unfinished lobe disks, and this created interference. As I discovered, there's very little leeway in the design of the cam block assemblies, and the tight clearances between its numerous parts needs to be carefully followed. I was able to salvage my test blank by re-machining the widths of the lobe blanks. Since these were facing operations, they didn't affect the TIR of the blank even though I no longer had a reference line and had to use a different collet for the re-work. I left the excess radial stock, though, for the lobe profiling operations later.
With the test cam feeling like a success, I continued on and machined two more cam blanks from the material I had left. For these 'production' blanks, I didn't add the extra thousandth bearing clearance that I had used for the test blank. The TIR of the next two blanks measured .002", and even without the extra thousandth bearing clearance, both blanks turned freely in both assemblies. Except for the bearing clearances of the test part, all three cam blanks are essentially identical, and so I ended with an unexpected spare. The next step is to figure out how to fixture the blanks so the lobes can be machined without screwing them up. - Terry

 

[wirralcnc]

Terry great job on the cam blanks. As a lobe milling fixture can you not machine a vee block up. Keyed to the table of the cnc along the x axis. Then machine a slot 90 degrees to the vee. ( y axis ) for the lobe blank to sit in. Then you can machine each lobe and just move the cam along. A simple indexing plate on the end of the cam to aid indexing each cam lobe. Robbie

 

[mayhugh1]

A curiosity that I encountered with Stressproof but forgot to mention in my last post, is its tendency to become magnetized while being machined. If you look back at the second photo in my last post you'll see the chips standing up along flux lines created by drilling-induced magnetism. The residual magnetism of the final machined blanks was strong enough that they tended to stick to my metal work table without wanting to roll around. I've included a photo of a rocker shaft attracted to an end of one of the finished blanks. Before starting the lobe machining I degaussed the blanks using an ancient bulk tape eraser that I keep around the shop. Residual magnetism can create surface finish problems when chips clinging to the workpiece are re-cut. This issue wasn't noticeable while I was turning the blanks because I was using a drop-type coolant dispenser with the air flow turned up high enough to blast the chips away from the cutting tool. This magnetism may have been the cause of the poor surface finishes that I consistently experienced while trying to bore Stressproof a few months ago while testing its suitability for cylinder liners.
Continuing, though, with the experience I gained earlier while working on the crankshaft I was able to use the 'rotary machining' operation in my Sprutcam software to create the g-code to machine the cam lobes. The profiles of the intake and exhaust lobes on the Quarter Scale cams are identical, and so I compiled a single lobe profiling program and fine tuned it using some scrap material.
I found a local source for true flat bottom carbide end mills, and I was able to use them to mill rotating fourth axis surfaces flat and without chatter. Since the diameter of the cutter I used was wider than the lobes, the program didn't require any lateral moves. I had to hone a small radius on the tips of the cutter, though, to get rid of a slight gouge that consistently showed up on a portion of the linear ramps of the lobes. After making this modification, the surface finish was very smooth and required only a fine Scotchbrite pad to polish off the machining marks.
A significant issue, of course, was fixturing the long skinny cam blank in the mill. It might have been possible to machine the lobes with the blank supported in the cam block assembly itself. However, the same clearance issues that prevented me from line-boring the assembly also prevented connecting the blank to a rotary. Machining a similar assembly in a new form factor with rotary access seemed like a lot of work with no guarantee that the resulting clearances wouldn't create chatter that would degrade the surface finish.
The solution that I finally settled on was to support the cam blank in a collet chuck installed on my horizontal rotary. And, as with the blank machining, I incrementally pulled it through the collet just far enough to machine one lobe at a time using my already tested code. In order to grip the blank I machined three pairs of split brass collets to fit the finish-machined surfaces on the blanks.
After the blank has been chucked and referenced, the rotary can accurately keep track of its angular position, but when the chuck is loosened to reposition the blank this reference is lost. In order to get around this, I machined a disk having a snug fit over the tailstock-end of the blank. Once attached, the disk was prevented from slipping on the blank by a pair of setscrews tightened against the flats of the hex that was previously machined on the front end of the blank.
A centerline was scribed across the face of this disk and, with the blank secured in the chuck, the rotary was used to set this line vertical. The profiling code was then used to cut the first, or reference, lobe. The code machines a single lobe with its nose pointing straight up, but it also assumes the rotary is initialized to zero degrees before it is run. Since the lobe disks had already been machined on the blank, it was only necessary to position the correct one just outside the chuck and then approximately center the end mill over it. I color-coded and numbered each disk on both blanks to help me keep track of which lobe I was working on to avoid making stupid mistakes.
Setting the correct angles for machining the rest of the lobes is certainly simple in theory, but in reality there are a lot of opportunities for screw-ups. After the first lobe was machined the vertical line on the reference disk was used as the workpiece reference to set up the angles for the remaining eleven lobes. A machinist square set against the scribed line on the disk was used to reset the reference lobe each time the blank was repositioned. The angle of next lobe to be machined was computed from this reference. The main difficulty was keeping my brain from going into standby mode while going through the multitude of repetitive motions and remembering to re-zero the rotary before running the code.
Fortunately, both cams were completed without incident; and, as far as I can tell, they are correct. I usually have difficulty interpreting model engine camshaft documentation, but the Merlin drawing seemed well thought out and unambiguous. I decided to not do any further machining on the spare test blank but to save it in case one of the completed cams had to be replaced.
One of the photos shows a comparison between the two very different cam profiles for the port and starboard heads of the engine. The reason for this difference is that both cams turn in the same direction, even though the positions of the intake and exhaust valves are reversed between the two heads. The intake rocker is 90 degrees ahead of the exhaust rocker in the port-side cam, and the reverse is true for starboard-side cam. These rocker arm geometries create the need for a 180 degree difference in the lobe separation angles between the two cams which makes them look very different. The six lobe pairs on each cam are, of course, separated from one another by 360/6 = 60 degrees.
With the excess stock machined away from the lobes I was finally able to test the fit of the rockers with the cams installed. I thought I could feel a slight interference between the cam lobes and the inside corner of the slot where the design clearance mentioned in my previous post is minimal between the two. I disassembled all the rockers and filed a relief fillet on this corner, which probably should have been a part of the original rocker design.
The next step is to continue with some of the less stressful camshaft drive components. - Terry

 

[cfellows]

Terry, the quality of your work never ceases to amaze me. Now that the cams are finished, I guess it's all down hill from here, right?

Chuck

 

[mayhugh1]

Chuck,
On this engine it seems like everytime I finish the hard part, the next one shows up.
Terry

 

[DICKEYBIRD]

"...everytime I finish the hard part, the next one shows up." Terry

Them's powerful words pardner!;D

 

[makila]

Hi Terry,

Great work as usual, I have a question regarding the appearance of the cam lifting lobes. Even though you explain this in your post above. It still appears an odd timing sequence when you consider the rotation of the cams in any direction.

Looking at the cam lobes, the lifts on the Starboard cam look like they are closer to 180 degrees (I am guessing), whilst the lifts on the Port side look closer to 20 - 30 cam shaft degrees, (not crankshaft rotational degrees), the lifts look odd on the Port cam assembly as both valves appear to open within the same 180 degrees of crankshaft rotation (or 90 degrees of cam shaft rotation) -considering the 720 degrees of rotation (2 x turns) of the crankshaft for a complete cycle.
The Port cam, on the other hand, looks to be too close to 180 degrees, but this may just be an illusion given that I am looking at a picture. Generally, (but not always) a cam has lobe spacing within the same 180 degree quadrant? Hopefully this is part of the design based on the rocker configuration that act on the cams from differing pivoting points.

Just read again your post, the rockers act 90 degrees ahead on one side, 90 degrees behind on the other side, this explains everything, left the post in however as it must take a lot of thinking to create this engine!!

All the same, a great build that deserves to be followed by us all.

Regards

Steve

 

[mayhugh1]

The designers of the Quarter Scale Merlin greatly simplified the camshaft drive system when they converted it from a gear train of some dozen gears used in the full-scale version to a much simpler chain drive. They designed their system around a 3/16" pitch roller chain which, after an online search, I discovered is a fairly rare and difficult size to find. I contacted Nordex, the supplier recommended in the documentation for this chain, but was told they hadn't sold it for many years and no longer stock it. Fortunately, I received an email a few days later from a sympathetic sales lady who had come across a short length in obsolete inventory. The Quarter Scale documentation does mention that a more common .1475" pitch chain might be made to work with some sprocket changes, but I wasn't sure if its fit had actually been verified, and so I purchased the 3/16" remnant from Nordex.
The Merlin documentation includes drawings for machining the sprockets, but I used http://www.gearseds.com/files/design_draw_sprocket_5.pdf to double-check them. The tooth profile is rather complex; and this being my first experience with sprocket design, I found the Quarter Scale drawings a bit confusing. The reference helped me better understand the drawings but didn't completely agree with them.
I started with the 20 tooth aluminum sprockets that will be attached to the rear of each cam. The proper way to machine these miniature sprockets might be to first make a form tool similar to a gear cutter, but I thought I'd try to profile them with a 5/64" end mill that seemed to fit comfortably in the contours between the teeth. I turned the blanks on the lathe along with a fixture to hold them in a vise on the mill. The blank design includes 20 degree bevels turned on each side of the tooth contact areas.
I used a 3X speed multiplier (Speeder) for my Tormach, to reduce the machining time while using the tiny end mill. To lighten the load on the cutter I pre-drilled holes between the teeth in order to rough out the workpiece. The idler sprockets are about half the diameter of the cam sprockets, and were similarly machined from 316 stainless. These little sprockets were fun to make and came out looking great, but I haven't yet been able to test their fit with an actual chain.
The drive system uses two drive sprockets and three idler sprockets, and so I made a few spares while I had the equipment set up. The crankshaft sprocket will be machined as an integral part of the rear driveshaft, and that will be made later after I have the chain in my hands.
The cam sprockets are attached to the cams with two-part assemblies that provide for rotating the cams with respect to the sprockets when the engine is timed. A hub is bolted to the rear of each cam, and the sprocket is gripped between it and a retainer which, in turn, is secured to the hub with eight SHCS. The screws are loosened in order to index the cams with respect to the crankshaft. The hex that John recommended be machined on the front of each cam will be used to rotate the cam before the retainer screws are tightened. This arrangement provides a very high resolution timing adjustment compared with the several degrees available from a typical gear driven system. The hub was machined from drill rod and hardened whereas the retainer was machined from 6061 aluminum. - Terry

 

[dsage]

Hi Terry:

I've been watching silently in awe of your workmanship. Wonderful as usual.
Have you attempted to measure the lift and duration as well as lobe center angles of your cam lobes? Perhaps the drawings didn't specify actual duration, overlap etc. but sometimes it's interesting to measure and record it.
I usually set a dial indicator (with a proper sized tappet pad) over a cam lobe on the centerline of the shaft and use the rotary to measure the pertinent points in degrees like open and lose angles. Taking into account a bit of gap for desired valve lash.
For you, using the indicator with a flat tappet will of course give you different results than you will actually get on the engine since you are using a roller rocker, unless you can arrange a similar sized roller on the end of your dial indicator. Might be interesting to try.

Amazing stuff your doing. Keep it coming.

Sage

 

[dsage]

Oops. One more question.
Is it just clamping force that keeps the sprockets from slipping in the clamps / retainers or am I missing some small detail there.

Sage

 

[mayhugh1]

Dave,
I haven't made any actual measurements yet and will probably wait until the valves are installed so I can make them at the valve tips. The specs for the cam are:
intake opens 10 deg BTDC and closes 50 deg ABDC
exhaust opens 50 deg BBDC and closes 10 deg ATDC.
So, the valves are open for 240 deg of crankshaft rotation plus another 10 deg or so on either side for lash take-up.
Yes, it is the clamping force that holds each sprocket in position. If you look closely at the photo of the retainers, there is a small ridge turned on the rear of each retainer near its i.d. for this force to react against. - Terry