John Dunn

Tappet clearance HOT vs COLD

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I've just redone the valve job on my 38 RC humpback and now setting tappets. I've got some original manuals from 1935-41 and a 50s vintage MoPar shop manual on the industrial engine versions. The 35 book shows .006" intake and .008" exhaust, 41 Dodge truck manual shows .008" intake and .010" exhaust, and the industrial engine book shows .010" intake and .014" exhaust with up to .018" for the sodium cooled exhaust valves. THEY ALL say to check and set with engine at normal operating temperature and one place even said to do adjustment with engine running at idle. I've adjusted  overhead valve engines while running but can't imagine doing these flatheads like that. Has anyone ever adjusted valves on Mopar flathead 6 while RUNNING with the HOT exhaust manifold in the way? 

What clearance should I set while cold with engine apart???? I'm guessing clearances close up a bit when engine is hot? I was thinking maybe .010" intake and .014" exhaust cold. 

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Yes. Not really hard to do but takes some practice.  The only accurate way to set them is hot and running.  Hot and not running is okay if you start and run the engine after setting every four valves.

On my Pontiac you needed one extra wrench because the adjusters had a lock nut.  That is why I put WPC adjusters in my engine at the last overhaul.

Edited by Tinindian (see edit history)

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An absolute must has to be running and hot....otherwise you will get a nasty slapping sounds on the valve train...I always put a tray under the engine and keep a magnet stick around....if your not experienced things tend to fly around and out of your hands....

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Once you get them adjusted to specs let the engine cool completely and mark the clearance cold. Let us know what they read.

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I've done several Mopar flatheads while running...no danger nothing exciting happens.

Just keeps hands and wrists away from the hot manifold.

If the truck has the original engine set the valves to the factory specs.... but .002" wider won't hurt it at all say for heavy use..

Just don't set them too tight.

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I found reference in one of my old books for cold setting spec, believe I went with .010" and .014". It runs great, I've put 150 miles on it. maybe just a bit of clack from one valve when just off idle that seems to go away once warmed up. 

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The major thing that happens setting tappet clearance while running is that the feeler gauge is pounded and becomes thinner as you proceed. At the end it is pretty malformed. I learnt this on a 1936 Chev.

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I prepared my car by taking the right front wheel off. Then removing the inner wheel well window. I put the wheel back on. I lined up all my tools, jack and jack stand ready to go. I then went for a drive to get everything warmed up to operating temps. I pulled into the driveway and quickly jacked up the car and got into the valves while they were hot.  I shut off the engine and set a couple valves. Then started up the car again for s bit to keep things hot. I did it this way so I was not sticking my wrenches into the moving valvetrain. My wrenches were not a good fit while the engine was running.  Engine shut off,  I had no problem with my wrenches. 

 

I did start up the engine and tested the clearance with my feeler gauges, while running. When set just right the feeler gauge gets slowly tugged inward by the motion of the valve and tappet. Too tight and you won’t get the feeler gauge in. Too loose and the valve ticks until you put the feeler gauge in, then the ticking stops.  These clues are telling when the clearances are spot-on or not. My engine has been running very well since I set the valves hot.

 

If engine is shut off, as I did above remember the valves must be set with the highest point of the cam lobe pointed straight down, away from the tappets. Start at #1 piston TDC and set its valves. Turn your crank 120 degrees and go to the next cylinder at TDC in the firing order. 1,5,3,6,2,4 I believe it is.  Here is a link to a video I posted on YT.

 

https://youtu.be/aameeYT7SXQ

 

Edited by keithb7 (see edit history)

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