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Is this possible

I'm not certain if this is even possible but ideally I would like to shorten 12 valves by .3 mm. A machine shop took off too much of a seat and the lifters are not allowing the valves to close completely. Valves are not sodium filled but I assume are hardened. Your thoughts please. There is only 2 mm above the keepers so should be alright if they can be shaved.
 

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Janger

(John)
Administrator
Vendor
Diameter of the valve? An inch? 0.3mm plus or minus how much? Is the overall length critical?

What’s a sodium filled valve?
 

PeterT

Ultra Member
Premium Member
We probably have some automotive experts (not me) but I'm going to guess valves are pretty hard as the seats are always ground not turned. It could be expected the top of the stems is similar if they contact rockers or lifters. In a lathe environment I can visualize holding the stem in a split cylindrical collet of sort so only the end portion is sticking out of chuck. Then a toolpost grinder ran across the end. 0.3mm is about 12 thou so it wouldn't take many passes & leave desirable finish. Turning this off accurately & with proper finish even with carbide tool tip might be dicey but its just a guess. The chuck & spindle ID would have to be able to accommodate the diameter of valve itself so something to check. There may be a better method using a dedicated surface grinder and maybe more consistent lengths. Also examine any kind of chamfer or radius the current stem top has, you would want to replicate that.

homebrew solution
http://www.mtfca.com/discus/messages/29/35243.html?1200779946

(sodium filled valves are for increased heat transfer under higher temperature conditions)
 
Inlet valve diameter 38mm exhaust 35mm. Material to be removed .3 mm tolerance plus .1 need to verify after removal.

Some engines use valves that are hollow and the void is filled with sodium. Sodium boils at around 900 degrees at the seating face of the valve then as the vapor travels up the stem it condenses similar to a mini AC system. This is very effective in removing heat quite often used in preformance engines and air cooled engines. Only problem is if fractured under load they pack a real punch and engine replacement likely results. They are to be disposed of as an explosive device just think pressure cooker without safety valve and 9 times the force. Not meant to be re ground.
 

DPittman

Ultra Member
Premium Member
If It am understanding you correctly....I would think the same machine shop should be able to grind that amoun off easily. Sodium filling is not typically in the stem.
 

RobinHood

Ultra Member
Premium Member
Rolls Royce used sodium filled exhaust valves for improved valve temp control as early as 1929 in their engines that were used in the Supermarine Spitfires which took part in the Schneider Trophy Races in Europe. Not sure who first came up with the idea, but they are very common in aviation piston engines.

0.3mm (0.012”) is possible to grind off the head of the valve. It could be done with a fixture in a spindexer and a surface grinder or holding the valve in a chuck of a lathe and using a toolpost grinder. Ideally, the work would be done on a cylindrical grinder.

I take it that you don’t have adjustable tappets to set your valve clearance that way?
 
This engine uses hydralic lifters but the increase of valve stem length is slightly past the extreme allowable tollerances.

I'm really not to keen to get any additional work done at that shop since the never followed my instructions to begin with. The sodium actually must travel up the stem a certain distance to cool and change back to liquid.
 

DPittman

Ultra Member
Premium Member
Don't take my word for this cuz I'm no expert but just relaying what I remember being explained to me by a fairly knowledgeable family member long long ago...
The sodium is in the head and top portion of the the valve stem to help cool the face that encounters most of the heat.
 

BMW Rider

Super User
It's pretty standard practice to grind the tips of the valves. Usually it is done with minimal material removal to clean up the wear marks on the tip, but can also be necessary to correct the valve stem height in some cases. How much can be taken off depends a lot on the valve construction. Some valves have a thick hardened cap on the tip that allows quite a bit of material removal as it is part of the engine design. Others are simply case hardened and have minimal allowable thickness to grind off.

The other concern with grinding the tips too much is how that will affect the protrusion from the spring keepers and cap. Too little and the rocker or follower cap can end up pushing down on the keeper or spring cap which can in a worst case situation cause the keepers to release the valve and destroy the engine. Looking at the picture of your valve, my guess is this maybe the bigger issue for you. Second problem with seats that are too deep (aside form a whole lot of problems with flow dynamics) is the spring length will need to be corrected with shims. As the stem protrudes more above the spring seat it causes insufficient spring tension which will affect valve closing rates and may result in early valve float.

Bottom line, my concern would be that if the valve seats are so deep that you have exceeded the working range of the hydraulic lifter, you have seats that need to be replaced as the proper corrective measure. Anything less would be a bandaid solution that may have a cascade of consequences. You need to verify what the design and engineering tolerances of your engine allows for in this condition.
 
Wow thanks BMW my biggest concern was the relocated position of the keepers but when I checked potential issues my concerns diminished but I did plan on a review. This engine allows the installation of repair valves which are 1 mm shorter in length. I did check and I'm at or a tiny bit above the limit which calls for shorter valves. My problem is the repair valves cost US$50 each a bit rich for engine which may only see 4ooo kilometers a year. You do however have me rethink a few things.
 

DPittman

Ultra Member
Premium Member
Don't take my word for this cuz I'm no expert but just relaying what I remember being explained to me by a fairly knowledgeable family member long long ago...
The sodium is in the head and top portion of the the valve stem to help cool the face that encounters most of the heat.

So just researching sodium filled valves and apparently they have more sodium in the stem and less in the head than what I was lead to believe.....
 

Everett

Super User
+1 to BMW Rider, thinking the exact same thing. As an auto mechanic I'd be concerned with the allowable specs and resultant geometry as well.
 
I'll send you a private message with regards to the shops name. A according to my measurements with the valves installed top of valve to cam bearing is at maximum height therefore the lifter should be out of usable range,(this I never measured before hand). Looking back at my notes specifications call for 106.6 mm I had measured 106.68 so yes they streached removing .3mm would correct everything. Yes I know new seats are prefered but this engine allows for 105.6 repair valves which are a special order. For giggles I'll price out new seats anyone recommend a good machine shop?
 
Thank you for your comments, advice and further education. I managed to locate another newer machine shop who has had some experience with this diesel engine. He has run into this issue in the past on the same engine and recommends shaving .35 mm off the top of the stems without issue. He claims to have the correct equipment for this task. In the coming few weeks I hope to find the time to visit his shop and then commit to using his services. With xmas coming and other commitments this project could well go into storage until spring.
 

John Conroy

member
Premium Member
The tips of those valve stems are hardened and you won't even mark them with a file. They need to be shortened on a valve grinding machine. It only takes about 1 minute per valve. The valves faces should probably be refaced as well while he's at the machine.
 
This is not a DIY im willing to tackle but I did find post 3 by Peter T gave me some valuable insight if I was inclined to handle this myself.
 
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