Is adjusting valves neccessary?

[edrobyn]

I have a Ford Model 1920 Diesel and the owners manual calls for the valves to be adjusted every 500 or so hours. The previous owner said he never adjusted them. My Dad also has a Ford tractor, which he bought new, and he has never adjusted his. If it's running okay should I just leave well enough alone or is this something I should definitely do? The owners manual recommends adjusting them with it running. I have never done this before and don't know how to go about trying to get a feeler gage in a tappet while it's moving.

What is your experience?

 

[Jerry/MT]

I have a Ford Model 1920 Diesel and the owners manual calls for the valves to be adjusted every 500 or so hours. The previous owner said he never adjusted them. My Dad also has a Ford tractor, which he bought new, and he has never adjusted his. If it's running okay should I just leave well enough alone or is this something I should definitely do? The owners manual recommends adjusting them with it running. I have never done this before and don't know how to go about trying to get a feeler gage in a tappet while it's moving.

What is your experience?

I think the theory is that wear will cause the valve lift to decrease reducing the air charge and thus the power will drop.

The more critical issue is valves adjusted with too little lash. Valves require contact with the seat to transfer heat and cool them. Too little lash results in too little cooling (valves are not in contact with the seat long enough) and thus the valves burn. So if you err on valve adjustment, err to the side of increased lash.

Having said all of this, I have not adjusted the valves on any of our diesel powered tractors but I probably should check the valve lash every 500 hours or so.
I have adjusted valves n our Ferguson TO-30 with the engine running and the biggest problem with doing that was oil spash. I made a little cardboard shield and dialed the idle down as far as I could get and still have the engine running. I really think that's the best way to do it. You have the engine operating at the running temperature and you don't have the problem of not having the cam positioned properly. that's my opinion anyway.

 

[Hooked_on_HP]

I think the lash should be checked. This can prevent wear on the rocker arms and valve stems. I warm up the engine and then set them with out the engine running. Set the intake valve lash when the exhaust valve is is almost fully opened. and set the exhaust when the intale valve is fully open.
Bill

 

[whistlepig]

Do all diesels have solid valve lifters? I'm kind of curious. I know we don't adjust valves on cars anymore. My tractor is coming up an a valve adjustment soon.

 

[dfkrug]

My Dad also has a Ford tractor, which he bought new, and he has never adjusted his.

Just a couple of weeks ago, I adjusted the valves for the 1st time on
my latest Deere project tractor. At 2018 hours, they have never been
done!

Well, I was surprised to see that half were in spec, and the other 3
were not too far off. Amazing. Nice Yanmar engine. It sort of
says that waiting this long is OK, tho I don't do that on my rolling stock.

The hardest part? Getting 10 y worth of dirt buildup off the top of the
engine before and after removing the valve cover.

 

[Jerry/MT]

Do all diesels have solid valve lifters? I'm kind of curious. I know we don't adjust valves on cars anymore. My tractor is coming up an a valve adjustment soon.

Most cars use hydraulic lifters which are self adjusting. Most tractors, dieselor gas, use tappets (solid lifters) which are not.

 

[Ford tractor]

I think the theory is that wear will cause the valve lift to decrease reducing the air charge and thus the power will drop.

The more critical issue is valves adjusted with too little lash. Valves require contact with the seat to transfer heat and cool them. Too little lash results in too little cooling (valves are not in contact with the seat long enough) and thus the valves burn. So if you err on valve adjustment, err to the side of increased lash.

.

I'm assuming you know your stuff, but your explanation is off a bit in my opinion.

Normal valve / seat wear will cause the valve to sit deeper in the head. That reduces the clearance (lash). That initially results in GREATER power because the valve is held open slightly longer. However, after a while the valve lash gets close to zero and the valve is not allowed to seal tight -- eventually it won't even close. Then the hot gasses leaking out will erode the seat and valve -- often called "burn a valve". That is NOT caused by the time on seat. The difference in time is negligible, but the hot high pressure gasses flowing in that reduced channel are far from negligible! In fact, they act surprisingly similarly to a plasma cutter.

The exhaust valve has a tough life as it deals with the hot gasses where the intake gets to deal with the cold intake air. That makes it wear faster and that's why it's far more common to burn an exhaust valve than an intake valve.

 

[flyingcow]

Yes, get them adjusted.

 

[Jerry/MT]

I'm assuming you know your stuff, but your explanation is off a bit in my opinion.

Normal valve / seat wear will cause the valve to sit deeper in the head. That reduces the clearance (lash). That initially results in GREATER power because the valve is held open slightly longer. However, after a while the valve lash gets close to zero and the valve is not allowed to seal tight -- eventually it won't even close. Then the hot gasses leaking out will erode the seat and valve -- often called "burn a valve". That is NOT caused by the time on seat. The difference in time is negligible, but the hot high pressure gasses flowing in that reduced channel are far from negligible! In fact, they act surprisingly similarly to a plasma cutter.

The exhaust valve has a tough life as it deals with the hot gasses where the intake gets to deal with the cold intake air. That makes it wear faster and that's why it's far more common to burn an exhaust valve than an intake valve.

Thanks for your comments.

As the valve lash decreases valve does not contact the seat (which is cooled by the water jacket and is relatively cool compared to the gas temperature and the valve temperature) long enough to transfer the correct ammount of heat to the cooling jacket and it thus operates at a higher temperature then when it has seat contact for the correct increment of time.This causes increased material oxidation due to higher valve operating temperatures. This is the point I was refering to and it can lead to the edge of the valve "burning out" but over a much longer time period of time.

As the lash gets small enough and the valve leaks, it is now subjected to peak gas temperatures and that is what causes a rapid burn out. This was your point , I believe, and I don't disagree. It's just that you don't want to get there if you can help it.
There are other ways of burning out an exhaust valve with the entire valve train being at spec. This applies to spark ignition engines. Operating with a too lean a mixture so as not to have any charge cooling due to fuel evaporation and/or operating with light detonation. In these cases the peak gas temperatures are greatly increased and the higher exhaust temperatures increase valve material oxidation and cause the valve to burn rapidly.

I wasn't trying to give a disertation about valve life. My point was when adjusting the valves, if you err err, on the side of increased lash so as to prolong valve life.

 

[Ford tractor]

Thanks for your comments.

As the valve lash decreases valve does not contact the seat (which is cooled by the water jacket and is relatively cool compared to the gas temperature and the valve temperature) long enough to transfer the correct ammount of heat to the cooling jacket and it thus operates at a higher temperature then when it has seat contact for the correct increment of time.This causes increased material oxidation due to higher valve operating temperatures. This is the point I was refering to and it can lead to the edge of the valve "burning out" but over a much longer time period of time.

As the lash gets small enough and the valve leaks, it is now subjected to peak gas temperatures and that is what causes a rapid burn out. This was your point , I believe, and I don't disagree. It's just that you don't want to get there if you can help it.
There are other ways of burning out an exhaust valve with the entire valve train being at spec. This applies to spark ignition engines. Operating with a too lean a mixture so as not to have any charge cooling due to fuel evaporation and/or operating with light detonation. In these cases the peak gas temperatures are greatly increased and the higher exhaust temperatures increase valve material oxidation and cause the valve to burn rapidly.

I wasn't trying to give a disertation about valve life. My point was when adjusting the valves, if you err err, on the side of increased lash so as to prolong valve life.

Hopefully, our clarifications will help others understand the importance of your last sentence! :thumbsup: