HEAD GASKET REPAIR

Ever since aluminum cylinder heads have become the norm, head gasket repair has become one of the most common engine repairs performed on late model vehicles. Aluminum cylinder heads expand and contract every time the engine is warmed up or cools back off, causing the cylinder head gasket to slowly wear until it cannot hold back the combustion pressure any longer and it fails. This is better known as a blown head gasket. The newer multi layer steel (MLS) gaskets are a lot better but they still fail, usually just not as badly as the older style gaskets.

Overheating can also contribute to a blown head gasket. If something causes the engine to overheat, say a coolant leak, there are tremendous stresses created in the cylinder head and it will generally cause the head gasket to fail.

We see on an average of three cylinder heads every day from cars or trucks that have had head gasket issues. Either a completely blown head gasket, or one that was just starting to leak and cause a problem. Either way, once it is determined that the head gasket is leaking, how do you go about repairing it ?

The head gasket repair procedure has four basic steps:

1. Remove the cylinder head
2. Have your automotive machine shop test the cylinder head to make sure it is not cracked or warped.
3 Machine the cylinder head to make sure the gasket surface is flat.
4. Re-install the cylinder head on the engine.

Sounds simple ??? Well it is far from it. We have seen just about every type of cylinder head and have seen mechanics make just about every type of mistake doing a head gasket repair. There are also a lot of misconceptions and misunderstandings about the procedures so I am going to try and cover as much as I can think of that will be helpful to either the Do It Yourself mechanic or the pro.

Basically I am going to go over the most common mistakes that we see when guys bring cylinder heads to our machine shop.

I am not going to cover the specific head gasket repair procedure for each vehicle. The step by step procedure in your service manual should be followed for a complete and long lasting repair. If you do not have a service manual I suggest buying a one time subscription to Alldata for your vehicle. It is very inexpensive and you will be able to access all of the correct factory service information. If you refer to have an actual printed book you can buy a Haynes repair manual or one of several others that are available.

Ok, here we go.

Before you start, please visit this page about abrasive disc cleaners

PLEASE DONT USE AN ABRASIVE DISC CLEANER

OK, now you can start your head gasket repair . . . .

Removing the cylinder head

1. Make sure that the engine is totally cold before removing the head.

2. Soak all of the exhaust manifold bolts with a penetrating oil the night before.

3. When loosening the head bolts, do so in reverse order of the tightening sequence. Usually this means you will start at each end of the head and work towards the center.

4. Once you have the cylinder head removed, DO NOT clean the gasket surface. Unless you are very confident that you can tell if the head gasket did fail, your machine shop should be able to look at the gasket surface and tell you, but only if you leave it in the same condition as you removed it from the car.

5. Remove any sensors or other items that might be damaged or lost during the trip to the machine shop.

6. Take the old head gasket with you to the machine shop, they see a lot of them and can usually show you exactly where it was leaking or completely blown. Click on this link to see some pictures of what a failed or blown head gasket looks like.

7. Either place the head upside down in the back of your truck, or make sure you place it on something soft. We have seen many heads that would have been fine but were scarred up by sliding around in the back of a pickup truck on the metal bed. On OHC heads this can result in bent valves too.

Checking the head . . . At the machine shop .......

1. The very first thing we do is a quick visual inspection of the head. A lot of times there are obvious cracks or other problems that will require extensive repairs. We see enough of them that we can usually spot them right away.

2. If there is nothing obvious wrong we will clean the head in our Jet Spray machine so that we can inspect it better.

3. The first inspection we do is to check the head to see if it has warped from the heat and if so, how badly. Almost any cylinder head that has been overheated will be warped some.

4. If the head is not warped too badly, the next test will be to see if it is cracked.

On cast iron heads, we use a procedure known as Magnaflux Inspection. This procedure sets up a magnetic field in the head and a special powder is used that “sticks” to any cracks and makes them visible.

Aluminum heads are not magnetic, so we use a pressure tester to check them. Basically this uses a set of plates to block off all the water passages and then air pressure is used along with a soapy liquid to find cracks, sort of like checking a tire for a leak.

5. If the head passes all of the tests and is deemed to be reusable, the final step is to resurface the gasket surface so the new gasket will seal properly. Make sure that your machine shop has the resurfacing machine to do this properly. Most newer cars with aluminum heads require a very smooth and flat sealing surface. A lot of older surfacing equipment is not capable of the correct finish.

Reinstalling the cylinder head

1. Make sure that the top surface of the engine block is clean and fairly smooth. We recommend using a razor blade scraper and then some fine sandpaper on a flat block.

PLEASE DO NOT USE an abrasive cleaning disc, sometimes known as a “cookie” cleaner. I have seen many heads and blocks that were ruined by the use of one of these tools. It is too easy to make the surface very uneven with one of these tools, especially on aluminum heads and blocks. The abrasives from these discs can also cause serious damage to engine bearings if allowed to get into the engine. If you didnt read the link above, you really should.

Make sure to stuff paper towels in the cylinders to keep from getting any dirt and grit around the pistons. When you are done cleaning the top of the block, use a shop vac to clean up any remaining grit that may have fallen into the cylinders. Then wipe the surface with a rag and a solvent such as brake cleaner. You want the surface clean enough to eat from !

2. Check the new head gasket against the head and block to make sure it is correct. If you still have the old gasket, compare the two. Mistakes do happen in packaging, now is the time to catch them.

3. Install the cylinder head bolts using either lubricant or sealer as specified by the service manual. I always put a little oil on the underside of the bolt heads to make sure they turn smoothly while tightening them. Tighten the correct amount and in the correct pattern as found in your service manual.

4. Squirt some oil on the valve springs, camshafts etc before closing up the top of the head with the valve cover.

In closing . . . .

These are the most common head gasket repair mistakes and hints I can think of. If you want to add anything, or have any questions please feel free to contact me I appreciate your suggestions and hope I can make this site better because of them.

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