How To:

Repair your engine to allow the use of your new high quality HKS Metal Head gasket

HKS Power & Sports



Information provided is given free of charge in good faith without prejudice. Feel free to distribute in original form. Do not alter or modify this document.


Written by: Reg Riemer of SONiC {Supra Owners Network in Canada} 


    When people go to work on a head gasket replacement job, they sometimes tend to rush the engine back together. Rushing the engine together is the worst thing to do. When an engine is open be sure to take the necessary time to look for all the things that need to be looked at. This tech note covers all the areas that you need to be aware of, read it over carefully.

    We will discuss several important areas surrounding head gasket repair procedures and metal head gaskets; the three different types of HKS metal gaskets available for popular Japanese engines, how to determine if your engine will need machine work, how to find a good machine shop in your local area, how to be sure the work your shop does is suitable to allow the use of a metal head gasket, and SONiC lapping tools and techniques to allow repair of damaged block or bad machine work.


    Over the years of using HKS metal head gaskets, I have never seen any quality problems with them. They are without question the best money can buy. Any of the HKS gaskets will last for the life of the engine if they are installed into an engine that has been correctly prepared.

    When you purchase a gasket always make sure the dealer you buy it from packages it correctly for shipping. It is very easy to bend these gaskets when they are shipped.

    HKS metal gaskets come with a special type of rubber coating applied to the gaskets outer surfaces. This coating gives the gasket a good cold seal for when the engine is cold started after gasket replacement work is complete. As the engine heats and cools this coating also allows the metal gasket to settle into place between the cast iron engine block and aluminum cylinder head.

    Metal gaskets will not cover existing problems and damage to surface finish or bad preparation work of the engines cylinder head and block deck surfaces. I have seen a number of engines that were just back from the machine shop and the machine finish on the head and block deck were not smooth enough to allow the use of a metal head gasket.


    There are three different types of HKS metal head gaskets. They are listed as follows in order of popularity and cost.

    1. Bead Type {least expensive} 2. Stopper type {expensive design} 3. Grommet type {most expensive design}

    *BEAD TYPE gasket is the most common type sold and used in the Toyota engines in our car club. This gasket is inexpensive and delivers very good performance and will last the life of your engine when installed correctly into an engine that is correctly prepared for the gasket.

    *STOPPER TYPE gasket is the best gasket you can buy from HKS or any manufacturer. It is also the most expensive gasket design you can buy. This is because the manufacturing process used to produce this gasket is more complex as are its materials, therefore the cost to manufacture it is higher than the bead type gasket.

    * GROMMET TYPE is not a very common type of gasket and is presently only used in a few types of engines. If more of the GROMMET TYPE gaskets become available, I'm sure we will learn more about them.

    The three types of HKS gaskets are all designed differently and therefore require unique manufacturing procedures and materials to be produced. The purchase prices of the gaskets will vary considerably depending on the gasket type you choose and the thickness of the gasket required for your particular engine application.

    As any of the HKS gasket types get thicker, there are more layers of metal in the gasket design. The 2mm gasket has more metal layers than a 1mm and a 3mm will have more than the 2 mm. As each layer adds an extra sealing surface, it is my belief that the fewer layers in the gasket the better. I have learned that with mechanical equipment the simplest design is always the easiest to work with and the most reliable!

    All three of the gasket designs work very well. The difference between them is with the engine application they are to be used. The condition of the engine components will determine how thick the gasket must be. Remember that every 40 thousands of an inch is equal to 1 millimeter. Example: If your engine has not received any machine work before and a machine shop removes 10 thou from your cylinder head and 10 thou from the block deck the shop will have removed a total of 20 thou from your engines components. From this it follows that 20 thou is about .5 mm. Lets assume that the stock gasket in your engine was 1.0 mm. Then to retain the stock compression ratio of your engine after the machine work you will require a 1.5mm head gasket.

    Be sure to ask your HKS dealer for help before purchasing a metal gasket for your engine. You will need to know the past condition of your engine as well as the machine work it now requires before you can buy the correct gasket.

    As a rule it is best to use the thinnest gasket you can. Remember that the correct gasket thickness for your engine is based on the machine work done to the engine, not on what your friends think you should run.


    The following question is one that I have received from many performance car owners.

    >? >Hi Reg > >I know you are real busy and all but please just answer my one question? >When changing the old head gasket to new HKS metal head gasket, do I >need to do any other work on the engine like resurfacing the block or >can I just replace the head gasket. > >Please get back to me ASAP so I can start work on the bad head gasket in my 93 Talon >TSI all wheel drive turbo. >Thanks >-- >John Smith >Corning, NY

    Todays high tech engines from Toyota, Mitsubishi, Honda, and Mazda come from the factory with cylinder head and block deck machine finishes that are perfectly suitable for use with HKS metal shim head gaskets. The problem is this factory finish is next to impossible to duplicate in the real world should you require machine work to be done on your engine.

    Some SONiC members who have had machine work done to their engine when they installed a metal head gasket have experienced problems with combustion gasses leaking past the head gasket into the coolant jackets or oiling system. The marks from the machine tools can leave a pattern of fine grooves, on the engine cylinder head and deck surfaces. This rough textured surface allows the engines high-pressure combustion gasses to fizz through past the metal gasket.

    Because this smooth factory finish is very hard to have reproduced by the machine shops around the country several things must be kept in mind when machine work is done to your engines deck and head surfaces.

    They usually never admit it, but try as they might, many reputable machine shops have major problems obtaining a smooth enough finish to allow the use of a metal shim gasket. The reason for this is that they simply don't have good enough equipment, procedures, or technicians to achieve an acceptable finish to provide a tight seal when using a metal head gasket.

    Unless the shop is familiar with doing work of this caliber, they will not understand why you want a better job than what they have done. I have seen machine finishes bad enough to cause sealing problems when using a stock composite gasket!

    Because of this area of concern, I would only recommend that the engine block deck only be machined (resurfaced) if there is damage to the deck surface caused by the compression rings of the old head gasket. However, usually you will need to resurface the alloy cylinder head because the compression rings of the stock gasket bite into the alloy surface of the cylinder head.

    When we are talking about damage to the block or cylinder head finish we are talking about a very small amount of damage around the cylinder bores. This is the area where the compression rings of the stock gasket were compressed between the block deck and the head. This damage is not extremely visible, it may take a closer inspection to see it. Any damage in this area of three thousands of an inch or more is too much when use of a metal gasket is intended. The compression ring area around the combustion chambers of the gasket is the area of highest cylinder pressure.


    To find a solution to this machine finish problem I did a lot of research into the machine tools and the procedures that most shops can provide. As we have learned, there is only a small percentage of shops that can produce a good enough machine finish to allow the metal shim gasket to work as it was designed to.

    Shipping engine blocks and cylinder heads around the country so that a renowned good shop can do the work is counter productive. So lets talk about how you can find a good local shop that can provide quality work on your engine. I will also cover how to fix poor quality machine work already done to your engine, by using some special Lapping tools that I'm having manufactured.

    To find your quality machine shop you will need to ask the technical people that work at the shop if they produce any racing engines for the drag strip or road racing. Frequently shops that produce high volume production of general automotive machine work will not be suitable for your needs. Ask around town to find out where most of the people who build race engines get their machine work done. This approach will usually find you a good quality shop.

    As an example, I found a local shop in my area that can produce a fantastic machine finish. This shop happens to be an oil field machine shop located in Calgary, Canada. They deal with many of the large natural gas and oil patch companies. Their specialty is smooth flat finishes on valves and other gas/oil equipment. So this is another area you could look for a shop in your local area.

    The shop I found can make the surface of the block and head so smooth and flat that, in the words of the owner. With our quality finish you could run the engine without any gasket at all if you wanted too. I don't think I want to try this but his point was well taken. A good finish will provide a perfect seal in an engine with a metal head gasket.


    The machine shop I located in my local area also showed me a custom made 4-foot long lapping bench. With this bench you can make any machined flat surface perfectly smooth and totally flat.

    Lapping is a process that involves rubbing the cylinder head or engine block over a perfectly flat specially machined steel disk made of a special alloy material. Before the lapping procedure is started, the lapping bench is coated with a special SSCC compound. This compound allows the head or block to be moved over bench surface following a special pattern. 

    Lapping can remove enough material to clean up damaged areas or just add a quick polish to an already smooth surface. As much material as required can be lapped off the surface of the part. When a part is being lapped {polished} down to an exacting finish any errors in the previous machine work such as flatness and surface finish will begin to appear. Areas where the machine tools dive in or cut to deep will start to show up like a sore thumb. The lapping procedure is continued until all this evidence is removed.

    I have used this lapping procedure on several Toyota 7M-GTE Modified engines with fantastic results. The finish the lapping tool gives is better than what comes from the factory!

    You may ask, Reg, as its already hard enough to find a good machine shop in my small town, it is going to be next to impossible to find a lapping bench like this. What is your point with all this?Ó

    I decided to take the ball into my own hands and solve this problem for anyone that needs a solution. Based on using my shops procedure for lapping a finish, I have come up with a new idea! I contracted this shop to manufacture me a smaller version of their full sized lapping bench as well as a portable full sized version just like theirs. 

    These new lapping tools are now available for sale to any shop or person that needs to prepare the finish on their engine blocks deck or newly cut cylinder head. :-) The SONiC lapping tools are available in two sizes:

    - *The small sized lapping tool, available as part number # Lapkit sm-1 is an engine in the car block deck lapping tool disc that comes with the special SSCC lapping compound. An option for this kit is 14 each, 12mm x 1.25 pitch hex head set screws. The set screws are used to plug the head bolt holes in the block deck. Lapping tool kit with compound are available @ $249.00 US plus shipping and handling.

    - *Also available for shops with intent to finish many cylinder heads and engine blocks is SONiC part number Lapkit big-1 this lapping bench cannot be used in the engine bay. It is very large and heavy, 350 lbs. For more info on this, email Reg at put Lapkit in the subject of your letter. Full instructions for the lapping procedure are included with all SONiC Lapkits.


    By using this new SONiC lapping tool it is now possible to lap the deck surface of the engine when the engine is still bolted up in the car. Because this tool is smaller in diameter than the large bench it is a little trickier to use but with extra care following the procedure I have written for using this SONiC lapping tool the results are the same. The entire deck surface comes up smoother than it was when it came from the factory.

    If the engine in your car is in good overall shape but has a damaged deck surface there is now a good alternative repair to completely removing the block rebuilding it and decking it. By using the small SONiC lapping tool with the SSCC compound along with diligence the engine deck surface can be lapped back into spanking new condition. The same tool can also be used to smooth the bad machined finish on the cylinder head.

    This is how the small tool is used on an engine block deck that is in the cars engine bay:

    When using the small lapping tool on any engine block still in the car, a thick grease coating is put into the engine bores and oil galleries to keep any existing dirt from entering during lapping procedure with the Lapkit sm-1. As the SSCC lapping compound is quite thick and sticky it will not run down into the engine bores carrying with it any lapped metal, the grease in the bores is just a precaution. There is not a big danger of any contamination and clean up after the lapping procedure is quite easy.

    RTV Silicone can also be used to plug oil gallery holes to keep them free of any residual SSCC compound mixed with block metal. If you use the optional 10mm x 12mm 1.25 pitch set screw in the head bolt holes no compound will enter the bolt holes, thereby making this clean up area quick and easy work. These are available from most fastener sales counters or with your lapping kit at an extra cost. The ones I purchased were about $3.00 each so there must be a better place to buy them, I will look into this. If you are only doing the one engine, you may opt to clean the holes out one by one rather than spend the money on the setscrews.

    After all the prep work and lapping is done the grease and silicone is removed. The block will look better than new. We have successfully lapped up to three thousands of an inch from the top of a 7M-GTE block. Lapping out this much metal takes a bit of time but the results are worth the effort. 

    Follow the torque specs and pattern for your type of engine. As the HKS bead type gaskets do not have any high load areas around the bore holes, this gasket is basically just a multi layer flat shim. The load from the head bolts is distributed equally along the surface of the deck.


    If you are building a new engine you will want to clean up the new machine finish on your block and cylinder head, especially if the machine work looks too rough. The lapping process will move along much faster when it is used on a freshly machined surface. The machining should have removed enough material to smooth out the damaged areas, therefore the lapping is only touching up the newly machined surfaces.

    As the engine is not in the car, silicone or greasing the engines oil holes, bolt holes or piston bores is not required. These areas will all be cleaned by the shop when they finish the other machine work.

    The best order to have the machine work done on your new engine block is as follows; *Deck engine block with machine tools. *Bore or hone engine bores. *Lap deck with lapping tool. *Clean entire engine block.


    When the time comes to work on your overhead cam engines aluminum cylinder head there will be a number of decisions to make. You must find a good machine shop as discussed above. Be careful if the shop tells you they cannot machine it and you should not do this. Sometimes they are correct and in other cases they may be dead wrong. I wish this process was easier to explain, its not.

    Cylinder Head Warpage

    I hope that this section will help explain some of the thought process that must go into the decision of: Should I cut the head surface or leave it? Should I try to have the head straightened or leave it alone? Do I have to replace the cylinder head with a new one from Toyota or find another used cylinder head to have check out?

    Don't pay cash for a used head until it checks out. Most reputable salvage yards and parts dealers will allow you to have the head examined by the shop of your choice. If they will not let you do this take your business somewhere else. It would be an easy big money business to be selling scrap aluminum for three hundred dollars a bar. Valve guides in the 7M engines seldom need to be replaced. If the shop you are dealing with says you need new ones you should question this!

    To determine if your cylinder head is suitable to machine you must have a good understanding of the following test procedures, and the thought process relating to warpage. If you do not understand the methods of the testing, that's ok, leave this to your machine shop. However it is important that you understand the concept of what I am trying to explain. Read on as I will try to explain some of this below. I would recommend that you print this file so you can circle areas you want to ask questions about.

    Remember that the head is not just warped at the deck where you measure it, the entire head is warped along with the deck. This means that the ports, valve cover gasket seal area as well as the cam saddles {what the cams spin in} are all warped x.x thousands of an inch. Following this idea if you have say 10 thou warpage in the deck surface when you measure it, the cam saddles should also have this 10 thou warpage if the head has not been machined before. If you bolt the warped head back on the engine and torque it down this will pull the head straight again providing your block deck surface is flat. Think of it as a banana on a table, if you push the banana flat to the table it will look straight. When you let the banana go it will look curved again.

    Now lets consider what happens if you cut the 10 thou of the bottom of the head or the banana! The deck surface of the head is now perfectly flat, but the cam saddles, and basically the entire head is still warped 10 thou. The banana is still curved but it has one side that is flat. This is ok as long as the cams still turn smoothly in the head when you have it bolted down to the engine.

    Inspect the cylinder head for warpage in the deck and cam saddles. If the deck is warped less or more than the cam saddles you have a head that has already been machined at least once. If the head has not been machined before you will be able to tell because the warpage will be the same amount and in the same direction on the cylinder head deck surface and the cam saddles. It was all straight at some point in time. Because an in line 6 is a long engine a small amount of warpage is normal. 

    Carefully inspect the deck surface of the cylinder head for any compression ring grooves left by the gasket that are deeper than 5 thou maximum. The engine block must also be inspected very closely for grooves in the block surface. If there are marks in the deck surface of the block they will almost always be on the exhaust side of the deck surface. If they are deeper than 3 thou you should have the deck of the block machined as well to get a better than new repair (see above sections in this tech note). Remember to have your timing cover machined along with the block, it also must be machined down to the height of the deck surface. The shop will bolt it to the block and cut them together.


    Remember, if you do have the head and block machined and you want to use a metal head gasket be aware that the finish of the machine work is very critical to getting the gasket to work correctly. If you use a lapping tool on this fresh cut rough finish you will have a perfect gasket surface.

    The new style Toyota stock gasket is not as sensitive to block finish and small irregularity but it will also leak if the finish is too rough. The new style stock gasket can tolerate about 3 thousandths of an inch of groove damage.

    I hope this answers some of the questions regarding HKS metal cylinder head gaskets and engine preparation.


    Reg Riemer 1997



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