worn valve srpings

cpdtwo · May 31, 2007

belive I have worn valve springs on my 1500d. does anyone know what the presure is on the valve springs. I did order new ones but still would like to know what the spring presure should be. so when the new ones come and it does not correct the problem I could check the new springs. the valve are good and I'm replacing the seals so I hope the springs will stop the valve leaks.

normde2001 · May 31, 2007

How much valve spring tension you have has nothing to do with the valve's ability to hold air/water as long as the valves are closing. You need a valve grinding job.

cpdtwo · May 31, 2007

Have the head in shop, he checked valves say they are fine but springs are only 18lbs and not holding closed, tried shimms but would take too many to close. thats why the new springs but still need to know the correct valve spring lenth and pressure. The lenth new and minume leth for used, the coil lenth is what causes the tension and gives the return presure.

DieselPower · May 31, 2007

normde2001 said:
How much valve spring tension you have has nothing to do with the valve's ability to hold air/water as long as the valves are closing. You need a valve grinding job.

I would have to disagree with that. The valve spring tension has everything to do with how well a valve seals. Not enough spring pressure and the valve might not seat. You need two things for a valve to seal properly. A good valve sealing surface and proper tension from the spring.

cpdtwo - I'm not sure what your springs should be but if you have the head in the shop and they have already tested the old springs on a valve spring tester then they should be able to test the new ones and let you know what they are.

mark777 · Jun 1, 2007

FWIW: I've done a few Yanmar heads and on the very first one I was alarmed at how easy it was to apply pressure, with the palm of my hand, and open all of the intake and exhaust valves. I'm guessing 25-30#'s maybe?

After grinding the seats and valves I ordered all new springs (and seals), cleaned and reassembled the head and there appeared to be no noticeable difference testing the pressure with the palm of my hand. I made the assumption that Yanmar engineered a softer spring intentionally, rather than transmitting the pounding effect through the push-rods, cam followers and, ultimately the cam lobes via stiffer spring tension.

I do understand how a spring will become weakened by a tractor with several thousand hours...or one that has set for many years, valve under load, and collapsed from being in the open position.

Mark

normde2001 · Jun 1, 2007

mark777 said:
FWIW: I've done a few Yanmar heads and on the very first one I was alarmed at how easy it was to apply pressure, with the palm of my hand, and open all of the intake and exhaust valves. I'm guessing 25-30#'s maybe?

After grinding the seats and valves I ordered all new springs (and seals), cleaned and reassembled the head and there appeared to be no noticeable difference testing the pressure with the palm of my hand. I made the assumption that Yanmar engineered a softer spring intentionally, rather than transmitting the pounding effect through the push-rods, cam followers and, ultimately the cam lobes via stiffer spring tension.

I do understand how a spring will become weakened by a tractor with several thousand hours...or one that has set for many years, valve under load, and collapsed from being in the open position.

Mark

The next head you do, invert the head, drop the valves in the holes and fill the combustion chamber with liquid. I bet it will hold if you have a good grind job. Not to mention the compression pushing against the valve in a running engine. All the spring has to do is close the valve at the proper time so it can build compression. The seat and compression handle the seal. (IMHO).

mark777 · Jun 1, 2007

Norm,

I drop the valves in the bare head, fill the valve face area with 100 cc's of fuel and leave it that way the remainder of the day. With the gravity of the valves only, and a good valve seat and face grind (hand lapped with fine compound) it has yet to leak on any valve job I've done so far.

Going one step further I also assemble the head and inject air into the intake and exhaust ports with fuel on the valve faces double checking for air bubbles. Again, great success with the ones I've done.

cpdtwo · Jun 1, 2007

DID LEAK DOWN AND LAPPED VALVE AND STILL LEAKING. THAT THEN LEAVE SPRINGS

normde2001 · Jun 1, 2007

mark777 said:
Norm,

I drop the valves in the bare head, fill the valve face area with 100 cc's of fuel and leave it that way the remainder of the day. With the gravity of the valves only, and a good valve seat and face grind (hand lapped with fine compound) it has yet to leak on any valve job I've done so far.

Going one step further I also assemble the head and inject air into the intake and exhaust ports with fuel on the valve faces double checking for air bubbles. Again, great success with the ones I've done.

My point exactly, I never did one, but that's the way the hotrodders used to "CC" the combustion chambers back in th old days. With a steel valve face against a steel seat, all the spring tension in the world won't improve the seal.