801 Ford Diesel exhaust valve cap clearance

riveroadrat

Well-known Member
Does anyone know where I could get one of those mics for the exhaust valve stem end to cap clearance? What do y'all do about that ? I thought maybe just buy new caps and hope for the best. I'm pretty sure the factory clearance of .003 is probably gone from wear. I think those caps are for rotating the valve.
 

Are we talking about valve lash here? If so, all that requires is a simple feeler gauge that can be had at any auto parts store.
 
(quoted from post at 17:59:02 02/12/18)
Are we talking about valve lash here? If so, all that requires is a simple feeler gauge that can be had at any auto parts store.

Learn something new every day. :lol: I see what you're talking about. I've never been in a diesel 172 before. Plasti- gauge?
 
No, only the exhaust valves have caps on them. There is supposed to be around .003 clearance between the top of the stem and the top of the cap on the inside of the cap. Mine look like they are probably flush. It shows the tool in the repair manual. I'm still trying to figure out how it takes the measurement.
 

I see the issue in the OEM Ford shop manual, but not a special tool for that. Do you have a manual other than the Ford one, or can you point me to the page/diagram?
 

Those caps are rotators, just ignore them. Treat them like they are the valve stem and use a plain old feeler gauge.
 
(quoted from post at 18:30:59 02/12/18)
Those caps are rotators, just ignore them. Treat them like they are the valve stem and use a plain old feeler gauge.

There's a specified clearance between the end of the valve stem and the inside of the cap. I learned about it just moments ago by scanning the Ford service manual. One is not going to gauge that with any feeler gauge.
 
I think they have something to do with keeper wear. Instead of the rocker pushing on the valve stem it pushes on the keepers, My 2 cents. I will take a pic of the page and try to post it.
 
Its in an original August 55 manual. Try the pic.
a256778.jpg
 

Interesting! Mine's a 1961 printing. I don't see anything like that in figure 23 where it shows that cap clearance. Now you've got my curiosity up too.
 
The new caps are $19 each at CNH. I cant grind the valves once installed but I can lap the caps on emery cloth. It might be possible to make that tool from an old mic by removing the center lock and making the bottom piece.
 

Use to tail end of a pair of calipers, a depth micrometer works better if it will fit between the valve and lock, measure the height of the valve from the lock, then measure the depth of the cup, your looking for .003 difference in those measurements.
10657.jpg
 
I can tell all of my old ones are bottomed out by the polish on the inside of the caps. I have a few that are showing indents on the top of the cap. The exhaust heat must make the keepers wear faster.
 

You looking at it wrong, if you don't see the inside of the cup polished you have a problem.
When the valve is opened the rocker arm pushes down on the cup, the cup pushes down on the lock moving the lock away from the shoulder of the valve, the inside of the cup then contacts the valve pushing it open.
Valve springs have a natural twisting motion when being compressed and uncompressed, with the lock pushed away from the valves shoulder the valve is loose, not effected by that twisting motion the valve moves straight down.
When the valve closes the lock moves back up against the valves shoulder and the twisting motion of the spring rotates the valve.
The valve may only rotate .001 or .002 per event but at 1800 rpm that's 900 events per minute.
To tight and the cup will hold the valve not allowing it to rotate
To loose and the hammering effect will flare the valves shoulder making it tight in the cup.

I'm not the best at explaining things, hope this made sense.
 
I was thinking that they were for pushing on the keepers to keep them locked tight when the valve is opened. I think that keeps the lock top edges sharp so theres less chance of dropping a valve. On a side note, I had a valve job done on a head and was adjusting the valves. One valve kept going out of adjustment. I kept looking at it and finally pulled the head off and found the bottom part of the valve sitting on top of a piston. Talk about nipping trouble in the bud, I was relieved to catch that.
 

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