Cub valve spring replacement

Matt E.

Member
I have a 1948 Cub, put a belly mower on it to use around the farm in Montana. I was out there last week cleaning up for winter and motor was running great for about 20 minutes. Started to miss. Went through diagnostics, found no compression on a cylinder and then removed the side cover over the valves. The intake valve spring broke on front cylinder. One keeper was laying there, I assume the other is down in the oil pan now.

Do I have to pull the head to replace the valve spring or is it possible to replace the spring without tearing it all down? This will be a job for next spring when I get out there again. Just want to have all of the needed parts on hand when I go.
 
All you need to do is remove the carburetor. Removing the hydraulic lines and the intake/exhaust manifold is really nice but not needed. You'll need a valve spring compressor and a magnetic tool to grab the
keepers. Should be all you need for that. Others shall chime in.
 
You might be able to make a special tool out of a brake spoon to hold the valve down. Then use a flathead spring compressor to put the spring in place
and retainer/keepers. Jim
 
I don't think I'll need to remove anything to get at it. After removing the cover plate, its in the open in front of the manifold. I'm pretty sure Dad has the right spring compressor in the shop somewhere. I'll have to pull the oil pan and hopefully the other keeper is down there. Thanks for the info!
 
Or get a pair of new keepers and leave it there. (much easier) If the valve moves upward when trying to put on th keeper, pushing down on the valve head
with a heavy wire or ? through the spark plug hole might be advantageous. Jim
 
When you do install the new spring and keeper, put something in the casting holes, rags etc that lead to the oil pan incase you drop something down there. Removing the oil pan now is a good time too, for cleaning especially if you never have. GOT SLUDGE? Easy to do, but does take patience especially on the rear bolts.
 
methinks that spring will come off, by pushing the valve open, and then sliding spring off. replace new spring. there is a washer that holds the
keepers on the valve stem (needed), get new keepers (needed) just replaced keepers on cub engine valve stem, they seemed to be worn (keepers dropped
off of valve stem)

i put a narrow board on top of the engine, so valve spring compressor would pull more straight. one leg of compressor on top of board.
also, i found a flat washer that was not so flat. it had been pushed so that the hole was pushed out on one side. formed a funnel like. i placed
this on top of the compressor leg, and this helped push the valve spring upwards, giving more room to put keepers in place. a bit of thick axle
grease on inside of keepers will help keep them in place, until you can get the compressor released
remove spark plug, a bent nail inserted (partway) through spark plug hole will help keep valve down , while compressing new spring. good luck
 
yes, someone replied, be sure to cover the oil drain holes, so that the keepers will not go into the oil pan. you will probably drop one. a pencil
type magnet is also helpful.
 
Yes you will need to reove the head so yoiu can compress the spring. The keeper will not go thru the oil pump as the screen will stop it. Is the washer still there that holds the spring
 
I plan to buy a new spring and two keepers. The washer on the bottom of the spring is there, it didn't come loose, only missing one keeper.

I think there is a different type of spring compressor that just compresses the spring, tongs on top and bottom. Not the large C-clamp type that you normally use with valve-in-head type. Janicholson, that is what you are referring to correct? Flathead spring compressor?

Good idea on the rags to stop the keepers from falling into the pan or galley.
 
i used the c-clamp type compressor. gives more room, than the other type that i tried and it holds the spring in place. you will need all the room
that you can get, while doing this.
 
easy peasy... get cyl. on TDC and apply 100-120 lbs of air to that cyl. to hold valves down. did many many valve seals that way on engines. no head removing.
 
Verry interesting you have a cycl that is bad because of a valve problem 70 yrs old and you say air pressure will hold a valve shut
 
he said the valve spring was broken, not a burnt valve. K. no problem changing springs with air pressure. dont matter if the engine 100 years old. and yes air pressure holds the valves closed.
 

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