Jan Ridders Otto 4 stroke build

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NickG:
Doug,
It looks brilliant that. I've never seen a close up of the valves moving up and down like that before. Was it just me or could you see the valves bouncing slightly? I'm not sure whether it'll have any bearing on how it runs? I was just sure I saw a gap sometimes between cam and follower. I know this problem sometimes occurs if revving an engine high, race prepared or high performance engines sometimes have dual springs. I'm going to use that great excel trick before I get some sort of dividing thingymbom. Also, it looks pretty already to me, not rough!

Bogstandard:
Nick,

You will find on most engines you have to have some sort of gap between the cam and what they are operating.

If you start a cold engine up with no gap, and by the time it has warmed up and expanded, the valves could in fact be held open or the valve timing all wrong. You usually set the 'tappets' up with a feeler gauge so that when the engine is up to running temp there is still a small gap to prevent the valves being held open and givng the correct valve timing.

John

dbvandy:

--- Quote from: NickG on February 25, 2011, 01:32:08 PM ---Doug,
It looks brilliant that. I've never seen a close up of the valves moving up and down like that before. Was it just me or could you see the valves bouncing slightly? I'm not sure whether it'll have any bearing on how it runs? I was just sure I saw a gap sometimes between cam and follower. I know this problem sometimes occurs if revving an engine high, race prepared or high performance engines sometimes have dual springs. I'm going to use that great excel trick before I get some sort of dividing thingymbom. Also, it looks pretty already to me, not rough!

--- End quote ---

looking at the cam, it looks like at high revs the tappet is thrown up by the valve springs and rides along the cam relief for about 1/2 a rev, then settles down. The valves should not have enough mass to overcome the pressure of the springs as they are pretty stout.

I just bought one of these:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260731555933

I do not expect perfection, but it should work ok for what I am going to do with it.

Doug

dbvandy:

--- Quote from: bogstandard on February 25, 2011, 02:40:39 PM ---Nick,

You will find on most engines you have to have some sort of gap between the cam and what they are operating.

If you start a cold engine up with no gap, and by the time it has warmed up and expanded, the valves could in fact be held open or the valve timing all wrong. You usually set the 'tappets' up with a feeler gauge so that when the engine is up to running temp there is still a small gap to prevent the valves being held open and givng the correct valve timing.

John

--- End quote ---

Correct. I guessed at .008 gap like every other car engine I have ever worked on (the plans said nothing about it). If it turns out to be too much, I can cut another tappet a bit longer. I toyed with the idea of an adjustable tappet, but they are so easy to make I decided against the extra effort.

Doug

NickG:
Bogs,

Yeah good point, I know about the gaps - I remember setting them up on the older engines, turning the crank until each cam is at it's lowest lift then setting with the feeler gauge. Of course, most of the modern ones have these hydraulic tappets now which you just have to throw away when knackered instead of adjust!

I just thought it looked to me like the valves were bouncing at the bottom of their stroke with the inertia given to them by the cams. As you say though, this might change when warmed up. Not sure what speed you were spinning it at either. Should be ok, presume your springs are to the drawing Doug?

That rotary table looks like a good deal. I need to have a look at the Harrogate show, only trouble with going on the sat is, any bargains will probably have gone. At least I can go and have a play with them there though and get a feel for them

Nick

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