Wyvern Cam setting

[Mike Ginn]

I have nearly completed this Wyvern (my first IC engine) and am seeking advice and guidance regarding pinning the cams. At present I am using M2x2 set screws which seemed to be a good scale size. However it is not possible to fully tighten these as the key depth is small and it jumps in the hex recess. I could move to M2.5 or even M3 but I am still concerned the cams will move when the engine is running. Ideally, I would like to pin the cams as per ETW’s drawings. I would use tapered pins.

I’m not sure how to do this and I am concerned that when done there is no adjustment.

I suspect that I will need to dismantle the cam shaft, reassemble using a timing disk to align the cams, lock them with the set screws and drill the 1/16th hole. Then reassemble onto the engine.

I would appreciate knowing how others have fixed these cams to the shaft with the correct timing.

Many thanks

Mike

 

[Vietti]

Have not built one but if I were to do it I would use next size bigger set screws,fine thread, and use two per cam at 90 degrees to each other

 

[Mike1]

I used two grub screws in each cam with no pins, over the years I had this engine the cams never moved, I also built a Centaur which has the same cam set up as the Wyvern the Centaur cams were also fixed with grub screws and no pins, the cams never moved and the Centaur is a powerful engine
Mike1

 

[Mike Ginn]

Thank you. Very interesting to hear experiences of locking cams with grub screws. This would be my preferred solution. At present I am using 2 screws and am thinking of increasing this to 3 and upping the size to either M2.5 or M3. I have machined a grove under each cam to prevent burrs and I am thinking of increasing the depth to allow a longer grub screw to be used - the advantage being that the socket recess would be deeper in a longer screw allowing a higher torque.
Mike

 

[DLM]

I have nearly completed this Wyvern (my first IC engine) and am seeking advice and guidance regarding pinning the cams. At present I am using M2x2 set screws which seemed to be a good scale size. However it is not possible to fully tighten these as the key depth is small and it jumps in the hex recess. I could move to M2.5 or even M3 but I am still concerned the cams will move when the engine is running. Ideally, I would like to pin the cams as per ETW’s drawings. I would use tapered pins.

I’m not sure how to do this and I am concerned that when done there is no adjustment.

I suspect that I will need to dismantle the cam shaft, reassemble using a timing disk to align the cams, lock them with the set screws and drill the 1/16th hole. Then reassemble onto the engine.

I would appreciate knowing how others have fixed these cams to the shaft with the correct timing.

Many thanks

Mike
View attachment 130545

I used 1/16 x 1/4 inch wood ruff keys in my cams & cam gear

 

[Mike Ginn]

OK DLM so how did you know where to cut the keyways to ensure that the timing was correct. I guess this is the bit I am missing. I do like keyways but not if their rotational position is critical! I don't really know how you achieved this!

 

[DLM]

OK DLM so how did you know where to cut the keyways to ensure that the timing was correct. I guess this is the bit I am missing. I do like keyways but not if their rotational position is critical! I don't really know how you achieved this!

The first thing i did was to broach the cams & gear then i cut the key way in the shaft
then assemble every thing turn the flywheel till where you want the piston to be for
intake then rotate cam lobe to where it just starts to open valve then mark the shaft then do the same for the exhaust valve now you can cut your key ways and hope every thing
is in the right place.
Don

 

[Mike Ginn]

Thanks guys for your help. Don, I like the keyway approach but there seems to be to many opportunities to mess up the timing. I will stay with the grub screw approach, get the engine running and if I have trouble then will revert to keyways. If I mess up I simply need a new shaft! I have ordered M2.5 x 3mm grubs to replace the existing M2 grubs and this should allow a higher torque with the 1.3mm key.
Now to the workshop
Mike

 

[Rustkolector]

Mike,
I have successfully used two set screws per cam lobe with standard cup head set screws. I usually relieve the shaft diameter about .010" under the set screws to allow easy removal and adjustment. Set screws and Small Allen keys often become worn with repeated use when building an engine and cannot be tightened properly. Once you have your cam lobe adjusted to your satisfaction, remove your set screws one at a time and install a new one and tighten with a good fitting or reground Allen key to the proper torque (see link below). The only set screw failures I remember are were in reciprocating motion applications.
Jeff

https://www.atlanticfasteners.com/tech-tips/simple-way-to-properly-tighten-set-screws/

 

[Mike Ginn]

Thanks Jeff
I have now changed to M2.5 x 3 cup head which has a more robust 1.3mm Allen key. I have also stopped using eBay SS grub screws which seem to have dubious tolerances in the socket. I will be using HT steel grubs from a known fastener supplier and from your and Mike1's comments, I believe I should be "good to go". Yes I have relieved the shaft by about 0.25mm to prevent the burr and also to get the grub head flush with the cam body - I think you can see that in my picture. I also have good quality keys. BTY I couldn't open the link you sent even using the Atlanticfasteners.com URL - strange.
I have the grubs at 60deg so that I could, at some point, pin but that seems like a lot of trouble.
My current headache is sorting out how to write/transfer the word Wyvern onto the side of the base but that's another subject!
Thanks Guys
Mike

 

[mayhugh1]

Mike,
After you have your timing set where you're happy with it, you might think about adding a drop of wicking grade threadlocker like Loctite 290 after the screws are tightened. It will fill any remaining reasonable clearances between the shaft and cam and as well as in the grub screw threads to add a bit more safety margin. Just be sure all the parts are cleaned before assembly. - Terry

 

[Mike Ginn]

Hi Terry
That's an excellent idea. I have never used 290 but I do use the bearing lock. The shaft gear is loctited to the shaft. I would use IPA (not the beer!) to clean taking care not to damage the surface finish on the steel. I would need to be very careful to control the quantity since it is red! I did wonder about using grade 603 which is slightly green and low viscosity.
I think my next step is to get the Wyvern to run and probably fight leakages in the valve system. Unfortunately I didn't use O rings and these cannot be fitted retrospectively - I would need to remake the head!
Thanks Mike

 

[awake]

In the two engines I have built (or am building - one in progress), I have used keys. I use a dividing head to set the position of the keys exactly to match the desired cam timing - key ways for each cam and for the cam gear. Using CAD software, it is not difficult to determine exactly what the rotation of the shaft should be be for each key way.

Of course, this means the design has to be right, and the cams and cam gear have to be broached correctly (e.g., with the keyway 180° from the "tip" of the cams, and with both the camshaft gear and crankshaft gear keyed on either a tooth or a valley as needed for the design).

As I said, I'm currently working on engine #2 ... but this approach worked for me for engine #1.