Issue with CAM and or tappet, need help

[borna]

Hello all
Got a problems with CAM and tappet and not sure where the problem is
As you can see in the picture, this is how I have it setup. Initially before starting the engine for the first time, everything was moving smoothly and CAMS were pushing down the valves just fine and smoothly. When I started the engine for the first time after a min of run, it stopped. Then I noticed I as I am trying to turn the engine by hand at certain position the belt is slipping. Further investigation, I noticed the exhaust CAM is getting stuck when is trying to push the tappet down to open the exhaust valve at the beginning stage and that was causing the belt to slip.
I don’t see any wears on either CAM or the tappet. Valve steam is straight and also moving freely in the valve guide. Can’t figure what could be the problem. Do you guys see any issues with the setup I have here?

Thanks
Borna

 

[camm-1]

I think you need to do tappets with bigger area on top when the force
for push them down minimize, the cam cant (dig in).

 

[borna]

So I can take the ball bearings out of the tappets and press sleeves with bigger area on the current tappets? Kind of like a dental crown J

 

[camm-1]

ohh, I didnt see the ballbearings, I thought it was just tappets without.
but anyway the angle of the touch can be hard maybe??

 

[borna]

so how can I fix the angle of touch?

Thanks
Borna

 

[kutzdibutz]

Hi Borna,

maybe you need a longer guidance for your tappets. I suspect when the cam is starting to press the tappet down there is a force that wants to tilt the tappet which then results in a blockage.
If that should be the cause you could also think about what valve lift you actually need and maybe adjust the cam. or keep the lift of the cam but increase the diameter so you can make the flank of the cam a bit more shallow. (if you know what I mean)

Good luck and hang in there!

Cheers, Karsten

 

[borna]

This is what I am also thinking, the tappet guides need to be longer.
This is what happens when a rookie design an engine

Thanks
Borna

 

[kutzdibutz]

Borna,

if there is a chance try to minimise the distance of where the guide starts to the tip of the cam. Reducing the free and overhanging part of the tappet and increase the guidance will improve. Also the connection of the tappet holder to the frame looks a bit thin. Is there a special reason you have the tappet holder in 2 pieces?

Cheers, Karsten

 

[borna]

Hi Karsten,
Reason tappet holder in 2 pieces is originally I had it on one piece and noticed the tappets are not moving freely because it was too thin. That I when I decided to add another peice on top to provide more support. As you said I think I still need to reduce the overhanging part of the tappet

Thanks
Borna

 

[pgp001]

You look to have a single point contact between the cam face and the ball bearing in the end of the cam follower.
This is going to be a very bad point of loading and will probably wear a line in the cam very quickly.

My engine has flat faced cam followers with sufficient surface are to ensure the cam is always pushing the follower along its axis.
Your set up looks as though it is trying to push the cam follower sideways.

The other thing to consider is that if you change the shape of the follower, you will also be changing the valve timing and duration etc. I cannot tell from your photo, but it looks like you have cams with straight flanks, these are very harsh on flat cam followers, I would consider having radiused flanks if you dont already.

Graham Meek did a good article on cam making.
http://modelenginenews.org/techniques/meek_cams.html
If you follow his advice you will not go far wrong.

Phil

 

[borna]

Hi Guys,
Again thanks for the comments. This is the engine I designed from scratch so it was a challenge.
However the problem is fixed. As it was suggested by Phil and Karsten the cam follower was pushing sideways. I added an extension and now everything is running smoothly. Tomorrow I'll try to run it and post a video

 

[vcutajar]

Glad you solved the problem. Looking forward to see it run.

Vince