Head gasket sealer on John Deere 750

   / Head gasket sealer on John Deere 750 #1  

Paul Campanis

Member
Joined
Dec 6, 2022
Messages
37
Tractor
John Deere 750 from 1982
A new head gasket leaked on my John Deere 750. Compression gases were coming into the cooling system after about 5 hours of use.

I bought a new head gasket from the John Deere dealer. What is the advisability of using head gasket sealer before installing it? If so what product would you recommend?

The engine manuel says not to use anything.

Should I have retorqued the head after a few hours of use?

Thank you
 
   / Head gasket sealer on John Deere 750 #2  
You need to check and be sure that the top of the engine block is flat and not warped, as well as checking the cylinder head contacting flat which mates to the block for warpage. This is usually accomplished by using a piece of inexpensive ground flat stock and wrapping a piece of wet/dry 400-600 grit paper around bar and drawing it across both flats. Block and cylinder head. Notice if the wet/dry paper is contacting all surfaces. If not your block, or cylinder head is warped.
What torqueing pattern did you use for the cylinder head bolts? Cross pattern I hope. You also need to draw up the torque in increments. Some engines use stretch bolts. Does Deere ask you to use new bolts?
I torque up cylinder heads, allow to sit overnight, then retorque next day to allow for possible relaxing of components.
 
   / Head gasket sealer on John Deere 750
  • Thread Starter
#3  
I have a proper straight edge and have checked both block and head for flatness.

There is nothing in the manual about replacing the bolts but I think that might be a good idea.

I'm certainly missing something. I'm also going to check and make sure the bolts are not bottoming out.
 
   / Head gasket sealer on John Deere 750 #4  
The cylinder head may need to be pressure checked. Cracks sometimes are found between the valve seats and extend into the water jacket. The cylinder head gasket may not be your problem source, a cylinder head crack maybe. Some don't open up until engine warms up also.
Simple method is to glass bead cylinder head combustion areas and then visually inspect for cracks. A handheld magnifying glass can help also.
Money costing would involve taking to an engine machine shop for pressure check and magnafluxing of cylinder head.
 
   / Head gasket sealer on John Deere 750 #5  
Sounds to me like either the deck (top of the block) or the head is warped or you have a crack in either and the only way to find out (if you cannot see it easily) is magnaflux them and I always replace head bolts with new ones because when you torque head bolts to spec, you actually stretch them.

What is the backstory on the engine? You overheat it or why are you replacing the head gasket, which is always replaced with no sealer of any kind.
 
   / Head gasket sealer on John Deere 750 #8  
My rule of thumb is that every time a head comes off it should go to a machine shop and be planed flat again. It's very seldom that a used head is perfectly flat.

I've watched my buddy in his machine shop plane a head many times. I've never seen one clear up on the first cut.
 
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   / Head gasket sealer on John Deere 750 #9  
Do keep in mind that when surfacing a head (any head), removing material to flatten it. changes the base compression ratio and may or may not require a thicker head gasket or spacer plate to return the compression ratio to stock. Why head gaskets come in different thicknesses and/or have spacer plates available.
 
   / Head gasket sealer on John Deere 750 #10  
Again, you guys crack me up 🤣 🤣 . This guy was encouraged by comments on TBN to tear down this engine without testing or experience and now he’s having issues and everyone acts like they have amnesia.
It is actually rather sad and happens quite often.

 

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