If you're looking at a disassembled motor and wondering do you have to resurface heads when changing head gasket , the short reply is that while it's not technically a law, it's usually the distinction between a restoration that lasts years and one that fails in a week. It's one of those "while you're in there" tasks that seems like a hassle, although skipping it is easily the most common error DIY mechanics plus even some spending budget shops make.
Let's be true: pulling a cylinder head is the massive pain. You've spent hours unbolting manifolds, draining coolant, and fighting with stubborn head mounting bolts. When the head is actually off the block, you just want to clear it up, throw the new gasket on, and get the car back upon the road. Yet the reality associated with internal combustion will be that things obtain hot—really hot. And when metal will get hot, it goes.
Why Flatness Is Everything
The head gasket has a pretty impossible job. It has to seal the incredible pressure of the combustion chamber while concurrently keeping oil plus coolant from mixing or leaking out there. To do that, it needs two perfectly flat areas to squeeze against.
When a head gasket "blows, " it's often because the engine overheated. When an aluminum head gets too hot, it tends to warp. We're not talking about the warp you can easily see with the naked eye; we're talking about a few thousandths of an inch. Even a tiny curve in the metal makes a low spot in which the gasket can't get a proper "bite. " In the event that you put the brand-new, flat gasket onto a somewhat curved head, the seal won't become uniform. Eventually—and generally sooner instead of later—the combustion gases can find that weak spot and flashlight right through the gasket again.
The Problem With Modern MLS Gaskets
If your car has been integrated the final 20 years, it probably uses a Multi-Layer Steel (MLS) head gasket. These things are good for long life, but they are usually incredibly picky regarding surface finish. In contrast to the old-school composite gaskets that had been thick and "squishy" enough to absorb minimal imperfections, MLS gaskets are slim layers of spring steel coated with a tiny bit of rubber-like material.
These gaskets require the surface which is not only perfectly flat yet also incredibly easy. If the head has any pitting from old coolant or scratches from a Scotch-Brite sleeping pad (please, don't make use of those), the MLS gasket may not close off. This is the reason why when people request do you have to resurface heads when changing head gasket upon a modern vehicle, the answer is nearly always a resounding yes. The device shop doesn't just make it smooth; they give this the specific "RA" (roughness average) finish how the gasket demands to do the job.
Just how to Check in case You Can Miss It
I actually get it—some of you are working on a "beater" or perhaps a budget project where every dollar counts. If you're identified to avoid the machine shop, you can't just eyeball it. You need a precision machinist's straightedge along with a collection of feeler gauges.
Lay down the straightedge throughout the head in many directions: lengthwise, crosswise, and diagonally in an "X" pattern. Try to slide a feeler gauge under the straightedge. Most manufacturers designate a maximum warp of about. 002 to. 004 inches. To give you an idea of just how thin that is, a human hair is definitely usually around. 003 inches. If a. 003 gauge photo slides under that straightedge at any point, you definitely have to resurface it.
Even if it's "within spec, " you still have to cope with the surface finish. If there is any staining, fire bands, or pitting about the water spencer, you're playing an unhealthy game by without having it machined.
The Hidden Dangers of the DIY "Clean Up"
One of the biggest temptations when you have the particular head off is to grab a die grinder or even a drill along with a bristle disk to "clean up" the old gasket material. Stop right presently there.
Those rough pads are the foe of aluminum canister heads. They may be made to remove material, and they do it unevenly. It's very easy to accidentally create a dip in the metal that you can't even see till the engine is back together and seeping. Furthermore, the resolution from those parts can get directly into the oil pathways and wreck your own bearings.
A machine store uses a huge, incredibly precise milling machine or a belt surfacer to shave off the tiniest layer of metal—sometimes only. 003 or. 005 of an inch—leaving a surface that appears like a mirror. You just can't replicate that in your own driveway having a scraper and some sandpaper.
The Price vs. The Labor
Think about it this way: What is the value of your time worth? An average machine shop will charge anyplace from $60 to $150 to resurface a single cylinder head. Compared to the expense of a full engine rebuild or the ten hours of labor this took you to get the head off, that's inexpensive insurance.
If you put it back together without resurfacing plus it leaks, you're out the price of another head gasket, another set of head bolts (since most are "torque-to-yield" and may only be used once), more coolant, more oil, and one more entire weekend of your life. Carrying out the job twice is always more expensive than performing it right the 1st time.
When Do You Absolutely Have to Do It?
There are a few scenarios where it's not even a question. In the event that any of these apply to you, don't even bother checking this having a straightedge—just take it to the particular shop: 1. The engine severely overheated. If you drove until the vehicle died or maybe the filling device was pinned within the red, that will head is bended. 2. You're using a good MLS gasket. As mentioned, these require an almost perfect surface. 3. There is definitely visible pitting. If the area across the coolant passages looks "eaten away" by corrosion, the gasket won't have a solid surface area to press towards. 4. The old gasket failed between cyl. This particular often leaves a "fire track" or even an eroded path in the metallic itself.
Don't Forget the Block
While we're speaking about the heads, we should probably mention the engine unit. While cast metal blocks are very much more unlikely to warp than aluminum heads, they aren't invincible. You should execute the same straightedge test on store shelves deck.
If the block is bended, you're in a very much tougher spot since that usually means pulling the whole engine to send out the block to the device shop. Fortunately, it's rare for a block to warp unless the engine was dissolved down into the literal puddle. Generally, a good, cautious cleaning with a razor blade (held flat! ) plus some brake cleanser is enough regarding the block aspect.
The Judgement
So, do you have to resurface heads when changing head gasket ? If you want the reassurance that you won't be doing this identical job again in three months, then yes.
It's tempting to cut corners when task management is dragging upon, but the cylinder head is the heart of the engine's sealing system. Taking that trip to the machine store gives you the chance to have them pressure test the head for cracks, check the valve seals, and make sure everything is ideal.
At the end of the day, a head gasket repair is a big-deal. You've already done the hard part by getting the motor apart. Spend the particular extra bit of money, get the heads surfaced, and relax easy knowing that will the seal will be better than it had been when it left the factory. Your car (and your sanity) will thank you.