Question on plans for cam shaft follower push rods

[davidgeorge212]

I am working towards understanding some engine plans before I start building it. I have a question on how to make POS 35. This is the end tip for the pushrod that is used to follow the cams. The only thing that makes sense to me is that 35 is a sleeve that attaches to the 2mm diameter push rod. Then that assembly slides through 36 which is a guide. The plans have a lot of German terms which I am not sure how well they translate to English. I'm not sure what Kugel R1/ R2 means.

Thanks for helping.

 

[dnalot]

I entered "kugel german" in google search. The result indicates the work kugel refers to "ball, sphere, bullet ect". That suggests that indicated areas in your drawing have curved or rounded surfaces.

Mark T

 

[Charles Lamont]

35 is a tappet. The end of the pushrod is presumably also domed to seat in the spherical socket at the top of the tappet. This allows the pushrod to align itself and, again presumably, to move in an arc at the top end as defined by a rocker. I can't say I much like the design of that tappet.

 

[davidgeorge212]

35 is a tappet. The end of the pushrod is presumably also domed to seat in the spherical socket at the top of the tappet. This allows the pushrod to align itself and, again presumably, to move in an arc at the top end as defined by a rocker. I can't say I much like the design of that tappet.

I also thought this might be the case but I was wondering what if the push rods were to get mis aligned and fall out of the domed socket. Is there anything that attaches the pushrod to the tappet so it won't come apart but still move freely? Seems like if the pushed is just resting on top of a cupped surface it should be contained by a piece of heat shrink rubber tubing or metal sleeve.

 

[davidgeorge212]

Ok, I got out my old OS 60 open rocker engine to see how they did this. I was under the assumption these were supposed to be real shallow cups but they actually have a drilled down 1 or 2 mm so its actually more of a deep socket which contains the pushrod from slipping out. Its making more sense to me now

 

[Jasonb]

What diameter does he give for the pushrod? if it is 2mm then you really want the recessed hole to be slightly larger if you are going to drill deeper. so the rod does not catch the sides. eg use a 2.5mm ball ended cutter for a 2mm rod and then you could go say 2 - 2.5mm deep rather than the 1mm shown on the drawing.

In practice the valve would need to be depressed to release the rod and the valve spring keeps it contained (slight clearance) by pushing the rocker arm onto the rod.

Couple of sections from my Lil 36 midget that show the larger dia sockets, 2nd with valve depressed which frees the rod

 

[IanN]

Hi,

It looks like a well drawn , dimensioned and toleranced set of drawings - the H7 tolerance shows some thought has been given to the design and manufacture.

Rather than "get creative" and modify the design, I would follow the drawings - particularly the detail in the call-outs R1 and R2 which presumably detail the internal and external radii

Looking at the section B-B it would seem that the total travel of the tappet is about 1/5 of the length of the 4mm dia part of the tappet. The 4mm dia part is 8.4mm long so the total travel is about 1.7mm (the drawing of the cam will give you the true distance) The specified depth of R1 is given as 1.3mm. There is no way the push-rod with a total travel of 1.7mm is going to jump out of a 1.3mm cup

Ian.

 

[davidgeorge212]

Yes, the pushrod is 2mm diameter. Ian, you are pretty much dead on with the exact travel of the cam will be 1.695mm.
I appreciate all the help I get from this forum its really helping me to get a better understanding on how this stuff works.