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Cylinder head bolts - am I doing it wrong?

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7 years 4 months ago - 7 years 4 months ago #3555 by Tyler
From an ASE study guide:

All of the following are true regarding cylinder head removal EXCEPT:

A. The engine oil must be drained prior to head removal.
B. The radiator must be drained prior to head removal.
C. The head bolts should be removed in the reverse order of installation.
D. The engine should be cold.


The stated correct answer is A.

Thinking about answer C... I'll be honest, I've never done this before :blink: Going back together, sure, follow the correct order. But taking the head off? I have a hard time believing this will cause any ill effects.

What say you? Is this hogwash, or have I been doing it wrong the whole time?
Last edit: 7 years 4 months ago by Tyler.

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7 years 4 months ago #3561 by Andy.MacFadyen
I have heard of it before a half century back, one of our local main Chrysler UK (Rootes) dealers used to insist that they allowed engines to cool over night before they removed a head, it might date back to the day when there were engines about with alloy heads and cast iron blocks, some of those were serial offenders for head gasket blowing.
We did a lot of head gaskets on the Imp range which had a gem of an all alloy engine that is if you could keep it water tight. We tried all the standard tricks but it never made any difference. There was a cure but as Chrysler had zero interest in their European operations they didn't spend the money.

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7 years 4 months ago #3562 by matt.white
I had it drummed into me. One of those don't question why deals. Never really understood it either. Don't really bother anymore either. :-)

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7 years 4 months ago #3566 by Dylan
Tyler wrote:

Thinking about answer C... I'll be honest, I've never done this before :blink: Going back together, sure, follow the correct order. But taking the head off? I have a hard time believing this will cause any ill effects.


Yep. When installing the head you start with the inside bolts and tighten them outwards. When removing it's the opposite. This is still written in OEM technical information.

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7 years 4 months ago #3568 by Dylan
Theory is that you can end up with a warped cylinder head or even crack it. But with a stone cold engine I don't really see the problem.....

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7 years 4 months ago - 7 years 4 months ago #3574 by Andy.MacFadyen
Back about 1970 we changed the gasket on a 1952 4 litre straight 6 sidevalve engine Humber engine with an alloy head. The cylinder head was much thinner section than on any modern engine and with a fairly thick copper asbestos gasket.
It would have been real easy to warp the head with the wrong procedures.

Same as this photo media-cdn.tripadvisor.com/media/photo-s/...umber-car-museum.jpg
I am extra extra careful removing and replacing cam carrier and other gasketless joints.

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)



Last edit: 7 years 4 months ago by Andy.MacFadyen.

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7 years 4 months ago #3686 by Tyler
Ah yeah, I see what you mean with that I6, Andy.

Thanks for the responses, everyone! So, it probably won't matter, but maybe do it anyway? Taking no chances and all that.

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7 years 4 months ago #3700 by Andy.MacFadyen
I tend to be super careful on engines with drop in cylinder liners or any open deck cylinder blocks --- experienced a few repairs that didn't go as planned.
Life was simpler when everything was made of cast iron.

" We're trying to plug a hole in the universe, what are you doing ?. "
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7 years 4 months ago #3729 by Doc
C & D for me every time Tyler.
A wouldn't matter in my mind, I would drop the oil after all repairs completed, before firing up for the first time.
B wouldn't matter as you would undoubtedly have to pull one or more hoses off anyway, therefore the coolant level should be below the level of the head gasket.
Cheers.

Youtuber specialising in Diagnostic techniques, sharing skills and helping technicians be the best they can be #Picoflu

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7 years 4 months ago #3730 by Andy.MacFadyen
On some FWD engines removing the lower hoses still leaves the coolant level above cylinder head gasket level. I usually clamp off the hoses to avoid excessive coolant loss, then disconnect and use compressed air pressure to push the remaing coolant out from the cylinder block.
Using a set of hose pinches saves a lot of mess.


" We're trying to plug a hole in the universe, what are you doing ?. "
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7 years 4 months ago #3733 by Tyler

Doc wrote: C & D for me every time Tyler.


Another vote for C! I guess I'm more of an ape than I thought :lol:

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7 years 4 months ago #3739 by Ro-longo
I just did head gaskets on a Ford 6.4L powerstroke. Took the head bolts off with my 1/2 impact :woohoo: (I did loosen them up in reverse order, just a habit for me know) And in the service procedure it says to NOT resurface the heads, just clean 'em up a d slap them back on. :silly:

"Silver bullets are for killing Werewolves, not fixing Cars." -Rob Longoria-

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7 years 4 months ago - 7 years 4 months ago #3741 by Andy.MacFadyen
On a lot of engines introduced in the last 25 years have tight restrictions on how much can be skimmed off the head face. I have never been a fan of skimming a head unless I had good evidence that was the problem.
Back in the days when antifreezes didn't give as good coolant protection as modern coolants we used get a lot of alloy heads skimmed or even welded because of corrosion. On engines with an open deck alloy block and cast in "damp" cylinder liners we used to get the blocks skimmed to leave the liners a few thou proud of the block

The guy that did our machining was ace he had 3 wooden sheds on the cannal bank -- in one he had 5 guys working, one was a store/office and in the third he parked his Roll-Royce.

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)



Last edit: 7 years 4 months ago by Andy.MacFadyen.

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7 years 4 months ago #3752 by Tyler

Ro-longo wrote: I just did head gaskets on a Ford 6.4L powerstroke. Took the head bolts off with my 1/2 impact :woohoo: (I did loosen them up in reverse order, just a habit for me know) And in the service procedure it says to NOT resurface the heads, just clean 'em up a d slap them back on. :silly:


They're worried about raising the compression ratio? So, I guess if you have a warped head (for whatever reason), then it just gets a new head :blink:

Coincidentally, the original question came out of an A9 prep book :lol:

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7 years 4 months ago - 7 years 4 months ago #3758 by Ro-longo

Tyler wrote: They're worried about raising the compression ratio? So, I guess if you have a warped head (for whatever reason), then it just gets a new head :blink:


That's exactly the reason for not machining the head, the compression ration is already high on those engines, add the extra pressure from the turbo and you can see why they don't want any more compression than they already have. After I cleaned the head, I had to check for warpage with a flat edge and a feeler gauge. Any problems and it gets a new head.

Also with many V type engines with overhead camshafts, machining the heads too much can cause timing issues. So loosening the head bolts in sequence on any type of engine is good practice. No sense in taking any chance on making the Cylinder Head even more warped. I do know they make Cylinder head shims, but I have only seen them used once and to me I wouldn't want to use them if I had to.

"Silver bullets are for killing Werewolves, not fixing Cars." -Rob Longoria-
Last edit: 7 years 4 months ago by Ro-longo.

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7 years 4 months ago #3786 by richiepearce
Reverse order every time for me whether it be sump, head, cam carrier or rocker cover. Just the way I was taught and I don't see any benefit from not doing it this way other than a small amount of time.

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7 years 4 months ago #3796 by paul.simpson
I take it you are removing them ?
I can say from experience if your doing them up and they are stretch bolts hope u replaced the old ones, going way back I made that mistake and a head bolt snapped off flush in the block ....engine scrap ! No machinist wanted to touch it.

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7 years 4 months ago - 7 years 4 months ago #3798 by Andy.MacFadyen
If you look at some manufaturers literature stretch bolts can be used up to 5 times provided some basic checks are carried out. The confusion arises because people confuse the elastic tensile limit of steel with the yeild point.

Before fiting a stretch bolt new or old:
The threads should be examined for damage and cleaned --- not oiled.
The fitted length of the bolts should be checked --- ie. before fitting the head screw the bolts in by hand and check there is enough remaining crush to fully compress the gasket without becoming thread bound.

It is a common misconception that a stretch bolt used once correctly has a lower tensile strength than a new bolt --- the failure load is exactly the same and the load at the elastic limit will actually have increased by a small amount.
BUT the overall length of the bolt will have permanently extended (strained) by a tiny margin.

When a normal high tensile steel bolt is tightened the load stretches the bolt like a spring but because it is working below the elastic limit it returns to the orignal length once it is undone. High tensile bolts have very high elastic load limit when they are over-loaded to failure point snap suddenly without any "give" because the load at the elastic limit is very close to failure load.

A stretch bolt is made of a steel that has a lower elastic limit but the load at yeild (when you can feel it give) is still quie high.
This means the bolt stretches (strains) elastically like a spring up to a certain load (the elastic limit) after which there will remain some tiny permanent increase in length (permanent or inelastic strain) when the tension in the bolt is released.
Next time the stretch bolt is used the length of the bolt increase again by an even tinier amount.
If used X times eventualy all these tiny increases (strains) in length add up until when the bolt is reused the total strain (elastic strain + inelastic strain) reaches the maximum strain the bolt can endure.

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)



Last edit: 7 years 4 months ago by Andy.MacFadyen.
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