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Thread: Ok.. It's head gasket time!

  1. #21
    DMC Midwest - 815.459.6439 DMCMW Dave's Avatar
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    Quote Originally Posted by TTait View Post
    Valves can be changed, but not the seats - the mating surface is milled directly into the head. Instead they get lapped, or resurfaced if you will. The machine shop can do it when they mill the heads, or you can try to do it by hand if you have the patience.
    The seat are steel inserts.
    Dave S
    DMC Midwest - retired but helping
    dswingle@DeLorean.com

  2. #22
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    Quote Originally Posted by DMCMW Dave View Post
    The seat are steel inserts.
    Typically the guides are reworked (or replaced if necessary) and the valve seats reground with a "Three Angle" grind. The valves are then ground and then each valve gets lapped into it's seat. Rare that you would have to do any more than that but there are things you can do if the seats are too messed up to fix by grinding. If a valve is bent or burnt they are usually just replaced. That is also not common but does happen. Springs are checked for pressure and replaced if not within specified length and pressure. Again, not common but can happen. I like to lap in my own valves as a check on the machine shop. It is a time consuming task so it is expensive so some shops will skip it to save the customer some money. My time is cheap so I do it myself. All you need is a twiddle stick, some lapping compound a a lot of patience. And a spring compressor.
    David Teitelbaum

  3. #23
    DMC Midwest - 815.459.6439 DMCMW Dave's Avatar
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    A severe overheat will cause the heads to expand and the exhaust valve seats will fall out, sticking the valves open. If you overheat an engine long enough this is what makes it finally stop running.
    Dave S
    DMC Midwest - retired but helping
    dswingle@DeLorean.com

  4. #24
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    Head Gaskets

    Quote Originally Posted by coreydmc View Post
    is it mandatory to grind the heads when replacing the head gaskets?
    Depends on how many times you want to do this. If you prefer to replace the head gaskets once, and have them seal completely and correctly, then a light machine cut is highly recommended. If you want to simply take your chances, well ...

    A light machine cut is only part of it. The machine shop should also do a pressure check to confirm that are are no cracks or leaky valves. If the heads have quite a few miles on them, the valve seals should also get replaced.
    Toby Peterson
    DeLorean Service Northwest
    DeLorean Parts Northwest

  5. #25
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    I've taken the head off of cylinders 1,2 & 3.
    have taken it to a machine shop and a pressure check shows that the valves are seating 100%.

    now i need to look at the mating service - if it is warped i can get it re decked . the question is "how much material can be removed" after all page 35 of the DeLorean Manual says ....
    Max bow of gasket face = 0.002"
    NO RESURFACING PERMITTED (Really??????)
    Cylinder head height =4.373" = .006"
    - that infers that no skimming - re decking of the head is permitted??

    This info is out of date. a 2 thou cut will show how true the deck is ...
    how much can be taken off?
    Currently resurrecting Vin # 11789 - the last of the batch of 50 exported to the Middle East. She's looking a bit sad !

  6. #26
    President, DeLorean Industries
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    Quote Originally Posted by SpudMurphy View Post
    I've taken the head off of cylinders 1,2 & 3.
    have taken it to a machine shop and a pressure check shows that the valves are seating 100%.

    now i need to look at the mating service - if it is warped i can get it re decked . the question is "how much material can be removed" after all page 35 of the DeLorean Manual says ....
    Max bow of gasket face = 0.002"
    NO RESURFACING PERMITTED (Really??????)
    Cylinder head height =4.373" = .006"
    - that infers that no skimming - re decking of the head is permitted??

    This info is out of date. a 2 thou cut will show how true the deck is ...
    how much can be taken off?
    Any cut to the cylinder head deck surface requires a companion cut to the top of the timing cover. As you drop the head surface lower the timing cover will protrude above this. The gasket does not have enough deflection to accomodate this. The mating point between the cylinder head, timing cover and valve cover will leak. If a head does not clean up within .005 discard.
    I'm sure there are people out there that have cheated this with sealants etc but the above is the correct way if you are going to surface a part designed not to be surfaced.

  7. #27
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    Because this is an overhead valve engine and the chain turns the cams, any materiel you remove affects the timing and the tension of the chains. You can also affect the geometry of how the intake manifold connects to the heads. Cutting the heads also reduces the volume of the combustion chamber affecting the compression ratio. All that said you could get by taking .002 off. To be safe whatever you do you should balance and do the other head too. As for checking, you use a straightedge and a feeler gauge. The inference is if you are more than .002 the head is warped and to flatten it you will have to take too much off. Just the act of taking off materiel can release built-in stresses and cause the head to warp even more. Bottom line, if your head is warped (bowed) more then .002, you overheated the motor and the head is junk. Probably both are.
    David Teitelbaum

  8. #28
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    So, the DeLorean workshop manual, states that the cylinder head height must be between 4.373" - 4.379 " and mine was 4.353, with a deflection outside of the .002 tolerance.

    It had a deflection of .004.

    This indicates that the cylinder head has been re faced before by 20 thousandths of an inch.
    So my head and one would have to guess "both heads" are toast!

    IMG_20190312_101258.jpg
    Currently resurrecting Vin # 11789 - the last of the batch of 50 exported to the Middle East. She's looking a bit sad !

  9. #29
    Delorean Guru
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    I would not try to mathematically determine the warpage. Get a straightedge and some feeler gauges and actually measure it. If the heads are really cut that much (I suspect that they were not) they are garbage. Did the motor look like it was part before? Why did you pull the head in the first place? BTW do NOT move the crankshaft unless you have liner locks installed. If you disturb the liners and break the seal you will have to pull the motor and reseal the liners.
    David Teitelbaum

  10. #30
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    Quote Originally Posted by David T View Post
    I would not try to mathematically determine the warpage. Get a straightedge and some feeler gauges and actually measure it. If the heads are really cut that much (I suspect that they were not) they are garbage. Did the motor look like it was part before? Why did you pull the head in the first place? BTW do NOT move the crankshaft unless you have liner locks installed. If you disturb the liners and break the seal you will have to pull the motor and reseal the liners.
    Hi David.
    The head was measured in exactly the way you state. - a straightedge and feeler gauges.
    The head dimension per the manual is 4.373 +.006 - so a newly manufactured head can be in the range 4.373 and 4.379.
    Mine was measured at the shop to be 4.353 - so it infers a 20 thou skim has been carried out before?
    the cylinders have fresh honing marks and it would seem like the engine has been apart before.

    Why did I pull the head? well, a number of reasons.
    - there was shards of ceramic in #3 - caused by a brand new spark plug shedding it's sleeve (thanks Bosch!)
    - an endoscope showed a small amount of water in #1 - but that could have entered when the spark plug removed?
    - if the the car has been subject to overheating then I wanted to reduce the risk of break down by having the head refaced - my good friend own a machine shop and will do this work for me very cheaply.
    - during the refurb of this car I had already removed/replaced a lot of components like exhaust etc so I knew the car was not going to fight me by snapping studs etc
    - this is my retirement project - so with that and all the above - taking the head off was the right thing to do - and no end of trying to get the shards out of #3 worked.

    I have since been contacted by an established DMC dealer that the heads would not be garbage after a 20 thou cut - he's done 100's of Delorean heads, so I would think that I could trust him?
    But I'd be interested to hear your point of view on why the heads are now garbage?

    Thanks on the heads up on the liners - The cam sprocket is held up and the battery has been disconnected and a sign put on the steering wheel saying "do not start engine"
    Currently resurrecting Vin # 11789 - the last of the batch of 50 exported to the Middle East. She's looking a bit sad !

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