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Newbie Valve Adjustment Questions


ChrisMinelli

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Hello,

 

I managed to get a heater for my garage so I’m spending this weekend doing a full tune up on the Plymouth.  My goal is:

 

1.) Compression Test + Check Spark Plugs

2.) Adjust Tappets if Needed

3.) Check Dwell and Timing

4.) Adjust Carb with a Vacuum Gauge

 

I have never adjusted valves on a flathead before.  I have reviewed the manual and I am thinking this is what I am to do:

 

A.) Check cold clearances *between* the bolts.  (See photo - this is the biggest question I have).  Set to specs as the manual indicates.  
 

B.). Fire up engine and let it get to operating temperature.

 

C.) When running, check clearance again and adjust as needed to hot specs.  
 

My questions are: is the space where the arrow is pointed what I am measuring, and is there a “rule of 9” issue when the engine is running?  I suspect no on the second question given the engine is running but I am only familiar with overhead camshaft engines at this point and doing those while running is impossible.  
 

Thanks!

158959EB-094F-4D36-BD76-B6EF262AFF86.jpeg

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Seen here is a removed tappet. 
Green lines represent the lower wrench. It holds the tappet firmly in place. Preventing it from twisting. 
 

Red upper line represents the tappet adjustment wrench. You twist the top nut to increase or decrease valve to tappet clearance. 

 

BC37BB54-523A-4708-8B31-DFFC502AC285.jpeg

Edited by keithb7
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You are to measure the gap between the top of the tappet, and the end of the valve stem. Exaggerated here for clarity.  Area indicated by red arrow. 

By twisting the top tappet hex cap, you are either increasing or decreasing the tappet overall length. Changing the measured gap. 

 

4A613E77-CDC1-4A49-9E0D-38C83F937796.jpeg
 

What I’ve learned: It may take a few times to get them all set properly. Don’t beat yourself up when one or two valves may be clacking away when you’re done. An automotive stethoscope may help you dial in the exact valves that are still ticking. Use It while the engine is running. Get back in there and re-set the clicking ones again. 
 

Why do we need to set valves when hot?

 

1. Siamese block castings: Each two pairs of cylinders have no coolant flowing between them. This creates uneven cooling within the engine.

 

2. The water distribution tube: Valves nearer to the waterpump get cooler water than the valves at the rear of the engine. So the valves will operate at different temperatures. Metal expands when it heats up. The hottest valves will create tighter clearances, as those hot valve stems will elongate more.

Some folks set the valves when they are hot. Some folks, even set them while the engine is running. 
 

Lots of guys will take the published hot tappet clearance spec and add .002”. Then set them all when cold. I’ve done it both ways. Both methods provided good results.  
 

Start with Piston number 1 at TDC. Compression stroke. To ensure, grab a tappet at #1 between your fingers. You should be able to wiggle both intake and exhaust tappets a teeny amount. Up and down. This is your valve clearance that you’re feeling. This is usually positive insurance that both valves for #1 are fully closed. Check you valve clearances. Adjust as needed.

 

Turn your fan blade 60 degrees. (Easier to rotate engine when all spark plugs are cracked loose) Go to the next cylinder. (Firing order 1,5,3,6,2,4)  Repeat all the steps described and set valve clearances. Repeat until all valves have been set. 
 

Something to consider: A valve clearance that is too tight gets tighter when the valve gets hot and elongates. Now this valve will be lifted off it seat sooner. It also takes a little  longer time to set down in it’s seat again. This severely limits the valve’s cooling time. Less cooling time means you’re probably gonna burn that valve. It gets so hot chunks can burn away. Then that valve won’t seal and you’ll have a dead cylinder. 


Have fun! It’s rewarding. 

Edited by keithb7
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8 hours ago, ChrisMinelli said:

Oh I should note the photo is a screenshot of a video I found.  My manifold will be (and still is) on the car. 

LOL! Here I was getting ready to ask you what oil you ran because your engine is so clean in side.

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8 hours ago, keithb7 said:

You are to measure the gap between the top of the tappet, and the end of the valve stem. Exaggerated here for clarity.  Area indicated by red arrow. 

By twisting the top tappet hex cap, you are either increasing or decreasing the tappet overall length. Changing the measured gap. 

 

4A613E77-CDC1-4A49-9E0D-38C83F937796.jpeg
 

What I’ve learned: It may take a few times to get them all set properly. Don’t beat yourself up when one or two valves may be clacking away when you’re done. An automotive stethoscope may help you dial in the exact valves that are still ticking. Use It while the engine is running. Get back in there and re-set the clicking ones again. 
 

Why do we need to set valves when hot?

 

1. Siamese block castings: Each two pairs of cylinders have no coolant flowing between them. This creates uneven cooling within the engine.

 

2. The water distribution tube: Valves nearer to the waterpump get cooler water than the valves at the rear of the engine. So the valves will operate at different temperatures. Metal expands when it heats up. The hottest valves will create tighter clearances, as those hot valve stems will elongate more.

Some folks set the valves when they are hot. Some folks, even set them while the engine is running. 
 

Lots of guys will take the published hot tappet clearance spec and add .002”. Then set them all when cold. I’ve done it both ways. Both methods provided good results.  
 

Start with Piston number 1 at TDC. Compression stroke. To ensure, grab a tappet at #1 between your fingers. You should be able to wiggle both intake and exhaust tappets a teeny amount. Up and down. This is your valve clearance that you’re feeling. This is usually positive insurance that both valves for #1 are fully closed. Check you valve clearances. Adjust as needed.

 

Turn your fan blade 60 degrees. (Easier to rotate engine when all spark plugs are cracked loose) Go to the next cylinder. (Firing order 1,5,3,6,2,4)  Repeat all the steps described and set valve clearances. Repeat until all valves have been set. 
 

Something to consider: A valve clearance that is too tight gets tighter when the valve gets hot and elongates. Now this valve will be lifted off it seat sooner. It also takes a little  longer time to set down in it’s seat again. This severely limits the valve’s cooling time. Less cooling time means you’re probably gonna burn that valve. It gets so hot chunks can burn away. Then that valve won’t seal and you’ll have a dead cylinder. 


Have fun! It’s rewarding. 

Excellent, thanks for the photos and explanation, Keith!

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Set mine cold after the rebuild 15 plus years and 50000 miles ago. Added .02 to the factory settings. Haven't touched them since.  Some have mentioned that high mileage engines may have some tappets that are worn cupshaped where the indented wear prevents accurate measuring and setting.  I guess the important thing to remember is the clearance amount is to assure the valve is in full contact with the seat. This is especially important for the exhaust valve as it only gets cooled when closed and in full contact with the seat.  So a bit of lifter noise from a slightly loose measurement is preferably to a too tight setup which may leave the valve not fully seating when things get up to temp.

 

A few years ago I noticed my snow blower motor was shooting blue flame out the muffler under load. So I thought to adjust the valves.  I found that no matter where I measured, there was zero lash on the exhaust valve.  So I pulled the head and count the valve was indeed just barely closed with the cold engine.  No amount of adjustment would allow it to close fully.  So I pulled the valve and ground a little off the end of the stem, put it back in and was able to do a proper adjustment. So I don't know but over the years, either the valve seat erroded or the valve stem stretched.  I don't believe this would occur on a car engine but I guess it shows you never know what can happen over the life of an internal combustion contraption.

 

 

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19 minutes ago, greg g said:

 So I don't know but over the years, either the valve seat erroded or the valve stem stretched.  I don't believe this would occur on a car engine but I guess it shows you never know what can happen over the life of an internal combustion contraption.

 

 

Not so much a problem on our flatheads as they have steel seats, but many older engines without seat inserts suffer from seat recession with unleaded gas. Some are so bad that the head/block has to be cut for aftermarket seats.   I doubt if the stem stretched, but set recession and valve face wear are common on older engines of all kinds.

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1 hour ago, greg g said:

Set mine cold after the rebuild 15 plus years and 50000 miles ago. Added .02 to the factory settings. Haven't touched them since.  Some have mentioned that high mileage engines may have some tappets that are worn cupshaped where the indented wear prevents accurate measuring and setting.  I guess the important thing to remember is the clearance amount is to assure the valve is in full contact with the seat. This is especially important for the exhaust valve as it only gets cooled when closed and in full contact with the seat.  So a bit of lifter noise from a slightly loose measurement is preferably to a too tight setup which may leave the valve not fully seating when things get up to temp.

 

A few years ago I noticed my snow blower motor was shooting blue flame out the muffler under load. So I thought to adjust the valves.  I found that no matter where I measured, there was zero lash on the exhaust valve.  So I pulled the head and count the valve was indeed just barely closed with the cold engine.  No amount of adjustment would allow it to close fully.  So I pulled the valve and ground a little off the end of the stem, put it back in and was able to do a proper adjustment. So I don't know but over the years, either the valve seat erroded or the valve stem stretched.  I don't believe this would occur on a car engine but I guess it shows you never know what can happen over the life of an internal combustion contraption.

 

 

Some of the small outdoor equipment engines use a camshaft compression release mechanism to hold a valve slightly open for easy starting.

Many require the piston to be at 1/4" past top dead center to properly check valve lash.

Just more info on small engines...of course does not apply to the MoPar flathead engines..??

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Used to work on a lot of HH series Tecumseh's....company now gone.

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