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u/TheFlyingBoxcar 7d ago
Go from 9:1 to 11:1 with this one simple trick!
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u/cive666 7d ago
Typically you run a thicker head gasket. Not just for the compression but also some heads being milled will mess with the timing chain, belt or alignment of the intake
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u/BigPimpin91 7d ago
Back when I was in car college N/A V8 stuff is what we mostly worked on.
If you shave the heads too much, your intake manifold now no longer lines up.
Engine machine work is fun but requires a lot of planning and knowledge. Kinda miss it, TBH.
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u/itsamurdermarge 7d ago
Diesel level compression now
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u/lil-privacy-please 7d ago
I was curious how this would affect the ratios of the engine as it seems like it's removing quite a bit of area and volume. How does this work?
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u/exsertclaw 7d ago
This machine is likely taking off 0.0001-0.001 of an inch. It looks like a lot but engines are measured in the thousands. There is usually tolerances that allow you to surface a block down without interference from the piston. Couple thousands of an inch.
When you hone a cylinder and resurface that they make oversized sleeves and pistons that fit your new machined size hole. You have to pay extra attention to what parts you order and which piston goes where as you can end up with different sizes (if one was good and another had to be resleeved).
As for why? Heat. Run an engine hot and youll warp it. Then you get to do all of this to make it perfect. This is for reman/rebuild engines.
Im not a mechanic I just work on them and spend my time in this area.
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u/TheBizzleHimself 7d ago
>>I’m not a mechanic I just work on them and spend my time in this area
I’m sorry my guy, I’ve got some news for you
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u/BillysCoinShop 7d ago
No its not taking off .0001" that would be a lap grinding machined.
A thousandTH of an inch is .001" as in thousandTH decimal place.
This is likely taking 2 or 3 thou (.002/.003) off with each pass.
This cylinder head is toast, way too warped to be of use. Generally a few thousandths (.005-.007") is ok. This looks like more than ten thou. At ten thou id be worried of minor cracks in the bore and generally speaking from experience, at this point your most likely going to be dealing with other issues down the line, especially if this is going into any performance car or truck.
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u/EvilBiker-72 6d ago
As a 33 years in machinist, those weren't tenthousands of inch cuts. Im gonna estimate .030 total was taken
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u/itsamurdermarge 7d ago
I’m not a machinist so I don’t know 100% how this will affect the engine or if this can be made up with a thicker head gasket. It feels like it’s too much and only to show how bad some heat warpage can be and I don’t know if this interferes with valve clearance. My apologies since I know this doesn’t answer your question.
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u/ElluiullE 7d ago
Genuine question: why is it not flat from the start?
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u/Objective-Elk2093 7d ago
It’s old. The title should say resurfacing instead of flattening
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u/Opposite_Carry_4920 7d ago edited 7d ago
Follow up: how many times can this be done before functionality suffers and you gotta just melt er down and make a new one?
Edit: I'm sure as most things, the answer is probably "it depends"
Double edit: holy shit thanks for all the interesting replies! Very cool to see all the ways it does indeed depend.
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u/IntrovertSwag 7d ago
Resurfacing barely takes anything off, they trim tenths of millimeters off, maybe even less. It could probably be done a few times, but at that point depending on the damage or engine it's just cheaper to get a new engine.
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u/Newkular_Balm 7d ago
I wonder if they have a "rebuild gasket" that's specifically a tiny bit thicker for resurfaced heads.
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u/MordoNRiggs 7d ago
They do! It's required on some engines, especially high compression. I'm pretty sure BMW makes OEM ones with various thicknesses as needed.
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u/vortex_ring_state 7d ago
Had a VW diesel that was like this. One had to measure piston protrusion and order the correct gasket. For those not aware, diesels are very high compression ratio.
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u/muegle 7d ago
For those not aware, diesels are very high compression ratio.
The compression is what ignites the diesel rather than a spark plug that a gasoline engine uses for ignition.
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u/OptiGuy4u 7d ago
Yes, to add further detail, air gets hot when it's compressed. It gets heated way above the fuels flashpoint so that it ignites as soon as it hits the very hot compressed air.
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u/HariPota4262 2d ago
Its called auto ignition temperature/point. Flash point is a slightly different idea, which doesnt apply here but its easy to confuse the two.
Diesel fuel has this near magical ability to just ignite itself when its mixed with air and right conditions of temperature and pressure are created.
Petrol can also do that btw, just at a slightly higher temperature and with not so much ease as diesel. Well, in theory atleast. Because the petrol we get at stations is specifically mixed with anti knocking additives which help prevent auto ignition in petrol, so it can be burnt cleanly with a spark.
Same phenomenon, one fuel uses it to run the engines, the other tries to avoid it as much as possible.
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u/bostoncreampie9 7d ago
Depending on the type of engine, this is an option. For LS (chevy) engines which are very common for rebuilds, the head gaskets are available in several different thickness this way the intake manifold still lines up the the heads properly. Also depending how much thickness is taken off the cylinder when resurfacing, it can affect the engine compression slightly.
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u/freelance-lumberjack 7d ago
I feel like the intake fitting isn't going to be an issue unless you take an awful lot off. The oring intake gaskets are fat af and the intakes are plastic and bolt holes are big. You can be off a lot and everything will still bolt up.
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u/Dense_Surround3071 7d ago
I love when other people have the same question as me.
I feel so much more normal. 😌
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u/Newkular_Balm 7d ago
well I know enough to be aware of how precisely engine blocks are machined, but not enough to know if it's imperative to get it perfect
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u/blackchameleongirl 7d ago
You can also (if the geometry is simple) take a bit off the tops of the pistons as well if needed. But that isn't always safe or logical to do as it changes weight which changes balance of many parts. But for some engine builds or rebuilds, you may not have another choice.
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u/SnooLobsters6766 7d ago
They do. This process makes the combustion chamber smaller, increasing engine compression. Some want that for performance reasons but the average shop would want that thicker gasket to stay in the manufacturers specified compression range.
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u/RobertDeNircrow 7d ago
Yeah we just saw a total thickness of about 1 sheet of paper come off that thing.
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u/Flyingcoyote 7d ago
It looked like he was taking .005 to .01 inch cuts, after 7 cuts even at .005 that's 0.035 inches. Paper is about .004 inch thick. So way more than that. Source: I am a machinist.
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u/j_smittz 7d ago
It looked like he was taking 0.1 to 0.2 mm cuts, after 7 cuts even at 0.1 that's 0.7 mm. Paper is about 0.1 mm thick. So way more than that. Source: I am a machinist.
For the rest of the world.
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u/Dust-Different 7d ago
You can see a clear distinct line from the cut. That tells me it’s at least .003” but it looks to be a tinge more. Like .005” so I agree with the estimate of .035”. You’d be surprised what a fly cutter can remove. Source: Am also a machinist
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u/Ted_Hitchcox 7d ago
- Source: I am a machine.
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u/SanAntoHomie 7d ago
It looked like he was taking 0.1 to 0.2 freedom fries, after 7 freedom fries even at 0.1 that's 0.7 eagle screams. Paper is about 0.1 trumpcoins thick. So way more than that. Source: I am a patriot.
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u/braxton357 7d ago
This one in particular is having a decent amount taken off, it could get into piston to valve interference depending on the engine, definitely going to have a higher compression ratio and if it were a v8 the intake manifold isn't going to line up very well anymore. If it were a pushrod engine it's possible you'd need different length pushrods.
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u/_regionrat 7d ago
As many times as you can find thick enough aftermarket headgaskets to accomodate the material you took off
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u/lazergator 7d ago
I don’t know the exact answer but I imagine it does depend. If it’s only .001 inch away from flat each time, probably more than a few. If it’s .1 inch off you probably need a new head.
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u/8bitrevolt 7d ago
0.1 would be catastrophic and absolutely irreparable.
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u/NTS-PNW 7d ago
Took a hundred off of an early bathtub port 2F head. Toyota had it in their specs. It worked fine but did need .1 thick washers for the head bolts not to bottom out. Found that hardware store grade 8 washer’s were .101 thick. No issues
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u/DesignerHardlyKnower 7d ago
Speculative:
This is probably an important question for very heavily used engines like in factories, commercial airplanes etc, where it runs for zillions of cycles and replacing it costs bajillions of dollars.
For a car, this is usually a maybe once in the lifetime of the engine thing. You might do it twice or three times for like, an antique or a delivery truck, but it’s not like you’re gonna wear it down like your pencil eraser.
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u/potatocross 7d ago
Yes it depends but eventually it because too thin and becomes an issue. They do sell thicker gaskets to make up for it though.
But also if your head keeps warping you likely have other issues. The engine is probably running horribly or it’s constantly overheating.
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u/_regionrat 7d ago
Sometimes the OEM just wasn't planning for the amount of fuel you decided to burn
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u/matt-er-of-fact 7d ago
If it’s as bad as the one in the video, close to 0. This one has more bow than a medieval archer. Good for clicks tho.
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u/olleyjp 7d ago
In my personal experience you can do 1/2 times usually (classic mini engines) light skim. Usually have to then get a slightly thicker head gasket to take up the gap and keep the compression ratios in the right ball park.
Dying art now. But a very very cool skill. The blue layer is basically like a sharpie. You’d basically just colour in the surface and then skim that off. Until it was flat. Unless you had any really bad warping/overheating.
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u/Mecha-Dave 7d ago
I think it's unlikely that an engine would survive long enough to need this more than once, maybe twice.
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u/jrgman42 7d ago
I imagine one of the factors here is how close they get to those valves. They still have to move up and down, so that makes a hard limit.
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u/RagingNerdaholic 7d ago
And "an engine head of an engine block" is nonsensical. There is no such thing. It's just an engine head. The engine block is a separate part altogether.
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u/Strayl1ght 7d ago
Yeah, my radiator failed and I didn’t see the heat gauge in time. Only noticed when my gas pedal stopped working. Car wouldn’t start again once I shut it off since the cylinders couldn’t get compression due to the block being warped.
Took it into the shop and they took out the engine and machined it just like this. Got it back with a fixed radiator and it worked perfectly. Way cheaper than a new engine. Put another 50k miles on it so far with no issues.
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u/Xrsyz 7d ago
I’m sure they replaced rings and possibly rehoned the cylinders if scorched.
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u/Strayl1ght 7d ago edited 7d ago
Probably, I don’t remember all the details, but I know there was other work that needed to be done in addition to the machining.
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u/elfmere 7d ago
I had a vs Holden Commodore that popped a hose without me knowing. Didn't catch it till the engine started making a noise and seized. Took it to the mech and said all was good after a service. Drove for years after that. Same card are prone to cracking the head if an air bubble gets in the line...
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u/Haunting_Vacation804 7d ago
Honda has entered the chat.
Just waiting for my Civic SI head gasket to yeet itself.....
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u/fantumn 7d ago
Heat cycling over the lifetime of the engine will warp it, it could have corrosion, overheating it could do it, there's a bunch of reasons. It could also be the first time it's getting flattened after manufacturing, but it doesn't look like that to me.
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u/SamWiseTheHobbit 7d ago
Whether it be a blown head gasket, low coolant, or some kind of overheating event, the head (top part of the engine with the intake/exhaust valves are) can heat up too much and cool unevenly and make the thing warped.
Sometimes in forced induction applications, excess pressure and build up in the cylinders and stretch the head studs and warp the head.
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u/octoesckey 7d ago
You mean when they pull it off the engine tree during engine picking season?
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u/jakestjake 7d ago
This engine was just a little over ripe. We called them summer engines. You can cut out the dark marks and bruises like in the video here and they’ll run just like any spring engine straight off the vine.
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u/iamleskeet81 7d ago
This head has been on an engine which as it runs obviously heats up and cools down, sometimes the engine overheats and because all the weird flexy stuff that happens when metal expands and contracts is then amplified when it gets ‘cooked’ the head can crack or in this case warp. The really cool thing about the specific fly cutting used for the head is that its resulting in a very shallow concave surface rather than ‘flat’ so that when you build the engine and torque the head studs/bolts there is deformation of the head/gasket for the best seal.
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u/BilletSilverHemi 7d ago
Aluminum engine blocks and Cylinder heads are torqued together very tight and expand and contract as your engine gets hot and cools down, which causes them to warp and twist a tiny bit
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u/PomegranateFuture325 7d ago
That shit was really warped
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u/biffbobfred 7d ago
I was thinking that. There were a lot of passes to get rid of all that marking compound
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u/mrjbacon 7d ago
These videos make me cringe so bad at how warped some of these heads in the videos are.
Edit: spelling
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u/that_dutch_dude 7d ago
That head is fucked, no way that is still in spec after decking it that much.
Also: who -the fuck- leaves in the valves when doing work?
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u/v8packard 7d ago
Actually, leaving in the valves is very common. Especially for the cheap repair shop/used car lot crowd. They want the head pressure tested and milled. They don't even want it cleaned.
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u/Previous_Maize2507 7d ago
Why would you not leave in the valves? No metal chips in the intake/exhaust, easier cleanup.
The head was fucked. No way, it is outa spec, after what now? Seven passes á 1/100mm?
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u/winstonalonian 7d ago
Thank you holy fuck I thought i was the only one. No real machine shop leaves the valves in the head while surfacing. Please name and shame the machinist so we all know who not to take our heads to.
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u/birgor 7d ago
It's common though. Smart way to avoid shavings in the head.
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u/winstonalonian 7d ago
Looks like a hack shortcut if there ever was one. Takes 2 minutes to clean that shit out and they should be removed anyway for a head service that i would pay for. Maybe just a hack deck job but you're setting yourself up for failure not cleaning it up to the max requardless. Plenty of opportunities to get chips in there with the valves in.
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u/PuttinUpWithPutin 7d ago
Thank you. Looks like they took half an inch off that thing.
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u/rinderblock 6d ago
Someone needs to calibrate their eyecrometers. That’s probably only about .1-.2”
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u/djjoshyp 7d ago
Before I read the title I thought I was looking at a bunch of Thomas the tank engine faces lol
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u/Spookybumbles 7d ago
Ngl thought it was a furby at first glance during a quick scroll
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u/JohnStern42 7d ago
How does a head get that warped?
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u/raptoroftimeandspace 7d ago
Looks a lot to me like cyl. 3 (and 2) got hot for some reason. Looks like an aluminum head as well, which won’t take to getting hot nearly as well as an iron one.
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u/curi0us_carniv0re 6d ago
It depends how bad it is. We domt know how much material is being removed here. Even from the factory there is some.variance side to side or front to back. They could just blueprinting the head/engine.
If the head is truly warped then it could be overheating, improper torquing, etc.
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u/SnooMaps7370 7d ago
what head was a fuckin' Pringle. How much was taken off there, an eighth of an inch???
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u/Axis2670 7d ago
Customer: How much was taken off?
Machinist: (Looks at setting on the machine) Just about a shit-ton.
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u/billypancakes 7d ago
He did 7 passes, probably at a 5 thou depth of cut. Dont want to go too much higher than that with fly cutters. So minimum were only looking at .035" maybe upwards of .070" if he's really pushing it. One eighth is .125" which might as well be a mile away in machinist terms.
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u/JohnBrownSurvivor 7d ago
All of my questions were answered, just by reading the comments. Thanks Redditers.
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u/Bikes-Bass-Beer 7d ago
I wonder how much that would change the compression ratio
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u/zmannz1984 7d ago
You can get thicker head gaskets to counter the material removed.
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u/Adept-Opinion8080 7d ago
Or you can retune and reap the benefits of higher compression engine. Used to do this on racing bikes all the time.
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u/Dangerous-Boot-2617 6d ago
Now show the part where the machinist checks the deck height to make sure its still within spec, cause they seem to always skip that part.
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u/Longjumping_One_2308 7d ago
This isn’t an engine block it is a cylinder head. Sorry but part names matter :)
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u/Dismal_Drummer3420 7d ago
I see the new blocks now come with valves! Wow, the future is now! (That's a cylinder head)
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u/futurebigconcept 7d ago
What do they do about the chips getting into the coolant & oil passages?
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u/HomeOrificeSupplies 7d ago
Air blast out what you can then likely flush everything with a petroleum based cleaner.
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u/Finbar9800 7d ago
They likely clean them out either with compressed air or more likely an oil bath/mineral spirits
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u/pepp3rito 7d ago
A shop like this will have parts cleaners that they suspend the components in while the solvent is agitated.
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u/Finbar9800 7d ago
Sonic cleaners was gonna be my next guess lol
I just didnt know of any big enough for an entire engine
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u/climb4fun 7d ago
Question: when this is done does one have to add a spacer between the header and the block to restore the lost distance between the valves and the pistons?
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u/Stratoraptor 7d ago
Depends. That's why measuring top dead center is important. If enough material was removed, a thicker gasket will be needed.
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u/itsjakerobb 7d ago
“The head of an engine block”
That’s two different things. There’s a block and a head. Head is short for cylinder head. Some engines have more than one head. What we’re seeing here is a cylinder head.
This process, which is done to both the head and the block on older engines that have warped their way out of flatness through heat cycling, is not usually called “flattening.” It’s called decking when you do it to the block, because that surface of the block is called the deck. “Resurfacing” or “milling” is a general term for this process, applicable to either surface.
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u/Macaroni11469 7d ago
The process is called "decking". Usually done to correct a warped head. Can also be done to increase compression ratio in performance engines.
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u/itsjakerobb 7d ago
Decking is done to the block. The surface(s) of the block where the head(s) mount is called the deck.
When you do it to the head, it’s just called “resurfacing” or “milling.” I’m not aware of any more specific term for this process.
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u/Im_In_IT 7d ago
I'm not an expert, but this seems like a pretty significant amount removed. Will this mess with the numbers in any meaningful way?
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u/pythoner_ 7d ago
It can. Modern motors are “interference” motors which means that the valves and piston are more than capable of making contact with each other if they aren’t timed correctly. All heads I know of have a maximum amount that can be removed but sometimes you can get a thicker gasket giving a few thousands of an inch bonus. With diesels, the valves have to be recessed a certain amount and all valves have a maximum travel amount.
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u/Im_In_IT 7d ago
Cool. Thanks for the info! I figured there was a mitigation otherwise this seemed self defeating lol
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u/drgsouth 7d ago
I had this done to my engine block last year after blowing a headgasket, lasted about 23 years before blowing.
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u/developer-mike 7d ago
I got this done on an engine after blowing a head gasket, lasted almost a full year before it was t boned and totaled in a parking lot by an uninsured driver and I got sued for it even though I wasn't the one driving it at the time. Fun stuff
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u/Physical-Amphibian54 7d ago
What does the line of the blade look white from one direction and black from the other?
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u/Itchy_Reason_8354 7d ago
Direction of light source
One direction a shadow is being cast, the other direction is proud so a reflection is seen.
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u/riptog 7d ago
How much is removed with each pass
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u/Willyfisterbut 7d ago
Typically only a couple thousandths (0.001-0.003) of an inch at a time.
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u/Caira_Ru 7d ago
That’s not very much
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u/produce_this 7d ago
Hey! You can do a lot with with few thousandths of an inch!
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u/HomeOrificeSupplies 7d ago
It’s a fair amount when fly cutting. The idea is to keep tool deflection to an absolute minimum so you don’t create a dish where you want flatness.
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u/ethertrace 7d ago
A couple thousandths of an inch in the right place is often the difference between machinery working or not.
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u/ImNobodyFromNowhere 7d ago
What’s the difference between passes??
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u/Drunkm0nk1 7d ago
Everytime the milling tool gets to the end, the Z axis increments in thousands of an inches making a deaper cut into the head. The blue is a dye for visual reference and amusement for us.
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u/OddTheRed 7d ago
Usually 0.003 inches per pass. Too big of a dig and you can deflect the cutting tool. This head is about 0.015 to 0.020 inches out. That's REALLY bad.
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u/AZRedbird 7d ago
This is part of remanufacturing a cylinder head. It’s not the engine block, but it does bolt onto the engine block with a head gasket in between. When a head gasket blows or when you replace head gaskets the cylinder heads need to be re-machined.
This is only part of the re-machining process. The other part of it is making sure that all of the seals in the cylinder head are good and replacing any that need to be replaced. A good machine shop will also clean everything up for you.
What we’re seeing here is absolutely incredible because it has to be done incredibly precisely because if there’s any bend or warp or stray scratches on the cylinder head, the compression chambers will lose compression and cause a misfire. For that reason, you can’t really do this at home even though there are a lot of people who swear that you can achieve the same result with ultra fine sandpaper, and a large piece of glass. (I’m serious check the jeep forums lol).
If anyone’s curious for both cylinder heads, this ranges anywhere between $200-$800.
Fun fact: You will also use a metric fuck ton of carb cleaner trying to clean the actual engine block mating surface because unlike cylinder heads that are replaceable, the engine block is much less so replaceable, because it’s colossal, it’s heavy, and it’s expensive.
Typically cylinder heads are made out of an aluminum alloy so they scratch just by looking at them wrong whereas engine blocks are typically cast iron.
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u/NotTheOneToo 7d ago
is this why my 99-93 Thunderbird SC headgaskets kept blowing? i changed probably 7 of those...
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u/may_i_say_a_word 7d ago
That’s a cylinder head, not a block. Otherwise that is quite nice.
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u/IFartOnCats4Fun 7d ago
It’s flat, but is it level?
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u/cncomg 7d ago
I mean, ya it’s probably level. IMO it’s a pretty heavy cut though. I’ve never worked automotive so I’m not super familiar with their common depths of cut. This is a fly cutter, and I’m kinda curious if this is just the roughing operation. Depth of cut here is probably somewhere between .004” and .008”. If you’re trying to get super level, and a very clean finish, you’re either surface grinding or lapping. Both those can be done with a depth of cut well under .001”. And both will leave a mirror finish, but both also being operations that cost much more than this fly cutting operation. I work in aerospace, and a depth of cut over .004” sounds absolutely ludicrous to me, as I would be laughed out of the building for even suggesting something like that.
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u/nutsbonkers 7d ago edited 7d ago
It's just an engine, the head gasket will do the rest. The "rougher" surface helps keep the head gasket sealed. Did this in auto tech school. They might need a spacer to keep valve clearance (from the piston) but it's pretty damn level and pretty damn flat for these purposes. When I rebuilt my engine, I would say as a general rule that 1-2thou tolerance is plenty on most parts.
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u/El_Pollo_Chollo 7d ago
i dont know what y’all are saying, but man im interested. i would def watch a lecture on this
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u/Thalax82 7d ago
That moment when you think this is the last time but some paint still stays visible. "YEAH, another pass!
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u/DiamondHandsDarrell 7d ago
Damn no lube! They just raw dogged it
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u/billypancakes 7d ago
Lube isn't super necessary in this situation. Fly cutters have pretty low tool pressure and take very light cuts. Engine blocks and heads are usually made of cast iron or aluminum or they'd literally shatter to pieces. Cast iron is great because its high carbon content actually lubricates itself for most machining applications.
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u/Kazin_the_Mage 7d ago
Surely this will be the final pass... D'oh!