8N Valve Spring Question.

Ok, this is on my 8n. As previously stated, I rebuilt this engine one time but dirt dobbers managed to make nests in the engine while the pan was off.
I am re-doing the whole thing again. New everything and complete block wash. Down to the valves which were all new before but after close examination I noticed that the seats and valve face had become tarnished with no seat to valve mark.
That tells me that the valves were not seating properly??
After considerable reading up on this I realized that there actually 2 different springs, one for the 8N is shorter and a tight curl at one end. The one for the 9N is longer and equal curls.
The 9N seems to be much stronger. Mine are all the 8N type.
The 8N spring when installed can be turned by hand, the 9N spring is tight and can not be turned by hand.
So, the question is, which spring is best to use??
Also, can the 8N springs be SHIMMED with a washer to make the spring stronger and produce a tight seat fit?
Thanks for any help on this.
 
It seems to me that if your sump was open to the air long enough for the mud dobbers to move in, then valves that remained open during that time frame would have light oxidation naturally forming on their faces and seats.
 

The later springs are stronger, see,FO-4 , I would question if the valves were properly adjusted.
see paragraph 27 concerning the guides and springs.
 
(quoted from post at 14:20:10 10/25/16)
The later springs are stronger, see,FO-4 , I would question if the valves were properly adjusted.
see paragraph 27 concerning the guides and springs.

Ok. Fact is, after I put it together and started it up, it ran fine for a 2 to 3 minutes. My pressure dropped from 30 to 15 real quick. I cut it off and checked it all out and oil looked ok and then I started it again. It then developed a knock at the rear of the engine and that is when I cut it off and tore it back down. So it may have run 5 minutes all told?? Anyway the valves were adjusted 11 and 15. But here it the kicker, when it was running I felt some blowby coming from the carburetor. So that told me that maybe an intake valve was sticking?
But now after looking at those springs, I feel the springs are not strong enough to snap the valves closed when needed??
 
OK now this makes sense as my number, if I can recall correctly, is 8N 11149 and I could be off a couple numbers as I am at home and tractor is on farm.
So I will switch those springs out and use the longer ones?
 
To answer your last question, typically yes springs can usually be shimmed, but the sealing is done at the valve/seat contact area. Stronger springs don't necessarily guarantee a tighter seal, they only allow for proper seating at higher RPM's. Since the tractor engine in an N is a low RPM tractor, stiffer springs are not needed. That is not however suggesting your springs are good. They need to be tension tested. My book is out in the shed so I do not know the tension tests for valve open or closed or the free length.
 
(quoted from post at 17:15:09 10/25/16) To answer your last question, typically yes springs can usually be shimmed, but the sealing is done at the valve/seat contact area. Stronger springs don't necessarily guarantee a tighter seal, they only allow for proper seating at higher RPM's. Since the tractor engine in an N is a low RPM tractor, stiffer springs are not needed. That is not however suggesting your springs are good. They need to be tension tested. My book is out in the shed so I do not know the tension tests for valve open or closed or the free length.
Ok. I now have a set of 9N springs in my hot little hands, lucky me, and I will switch them out for the 8N springs. These are brand new springs and they should do the trick.
 
(quoted from post at 17:45:55 10/25/16)
(quoted from post at 17:15:09 10/25/16) To answer your last question, typically yes springs can usually be shimmed, but the sealing is done at the valve/seat contact area. Stronger springs don't necessarily guarantee a tighter seal, they only allow for proper seating at higher RPM's. Since the tractor engine in an N is a low RPM tractor, stiffer springs are not needed. That is not however suggesting your springs are good. They need to be tension tested. My book is out in the shed so I do not know the tension tests for valve open or closed or the free length.
Ok. I now have a set of 9N springs in my hot little hands, lucky me, and I will switch them out for the 8N springs. These are brand new springs and they should do the trick.

OK. Speaking of valve springs, in the process of installing the assembled valves back in the block another problem cropped up that puzzles me. The number one intake keeper is loose and will just move back and forth by hand. There is no pressure on it from the spring. The others are stable and can not move unless I push down on them as if to remove the keeper.
I have taken the #1 out and examined it, oiled it, babied it and put it back and same thing.
Any ideas here will be appreciated.
 

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