There is nothing worse than spending the time replacing a head gasket only to have it fail shortly after. There are a few things that can be checked to make sure this does not happen to you. Measuring cylinder head warpage or checking cylinder head flatness is an important step in every head gasket repair job.
We spill the beans and let everyone in on the secrets to making sure your next head gasket replacement is a success.
A Clean Cylinder Head Is Important When Checking For Warpage
The most important step of doing any major engine repair is cleanliness.
After all, we all know the saying, cleanliness is next to godliness.
Cleaning starts even before the engine is disassembled. If you pop open the hood on the vehicle that you are working on and find a dirty engine, this is the time to clean it. A good engine degreaser and low pressure water will make quick work of any dirt or debris on the engine.
During disassembly of the engine take the time to blow away any dirt that you find and cap off any removed hoses to prevent any dirt from finding its way in internal engine passages.
Once the engine is removed you will need to clean the cylinder head sealing surfaces to properly measure for cylinder head warpage.
How to clean cylinder head sealing surfaces
It is very common for the sealing surfaces (surface that contacts the gasket) to have left over pieces of head gasket material remaining after removal. When left, these head gasket pieces will cause your measurement to be incorrect and also cause repeat head gasket failure.
It is important to clean 100% of any remaining material from the head gasket surface. Unlike other surfaces on a vehicle, you cannot jump to a grinder or sander to clean up the surface. A cylinder head surface is a highly machined surface and when the incorrect cleaning process is used it can cause issues that damage the cylinder head beyond repair.
Use a plastic scraper
The quickest and easiest way to clean the cylinder head sealing surface is to use a plastic scraper. It can be easier to use a metal scraper but this type of tool can put gouges into the cylinder head causing even more damage.
Always make sure you use a plastic scraper.
This part is where you are going to need to have to put in some elbow grease. Using a plastic scraper to clean a cylinder head takes time.
Once the cylinder head is scraped clean, spray the surface with brake cleaner and wipe clean with a lint free cloth.
Use a parts washer or hot tank if you have access
Not many home shops have access to a hot tank cleaning system. If you are looking for clean cylinder heads this is the best way to make sure the part is as clean as it can be.
Sometimes local shops may have a tank like this that for a small fee would be interested in cleaning your cylinder heads for you. Possibly your local high school has an automotive program that would love to clean your cylinder heads for you.
Witness marks may be present and are normal
Having replaced many cylinder head gaskets over the years I can tell you that witness marks will be present after cleaning. These marks are completely normal.
But, what are witness marks?
Witness marks can be thought of as stains in the surface of the cylinder head. Various portions of the head gasket leave marks in the cylinder head that can only be removed if the cylinder head is machined, or decked.
Generally the metal sealing surfaces are the areas that will leave witness marks .
Do not be tempted to remove these marks as you may cause irreparable damage.
Tools needed to measure cylinder head flatness
There are many tools needed to measure a cylinder head. Some of the tools that you will require are in your home tool box and others may need to be purchased.
A quality set of V-blocks may be overkill in this situation but will make your life easier. If you plan on doing a lot of engine repair, v blocks are an excellent investment. Even if you do not purchase these, a set could be made out of wood to be useful around the shop.
V-blocks are just what they sound like, a set of blocks shaped in a V. The V shape holds a cylinder head in various upright positions allowing you to clean, measure, and inspect much easier.
Machined straight edge
This tool is a must have for properly measuring a cylinder head for flatness.
It can be common to assume that something “flat”, such as a level will work for a straight edge. However, in this case when you are measuring to the thousandths of an inch. A homemade straight edge will not be accurate.
Invest, beg, or borrow a machined straight edge so you can measure to the thousandths of an inch when checking cylinder head flatness.
Quality automotive feeler gauge
The last tool that you will need most likely already lives in your toolbox. The best automotive feeler gauge will allow you to measure in increments of 0.001” to get the correct measurement.
Obtain proper measurement specifications
Measuring the cylinder is useless unless you have the allowable specifications. These can normally be found in the best online automotive repair manuals but can be found other places as well.
Generic specs for cylinder head flatness
If you are measuring a V6 engine cylinder head, flatness should not exceed 0.003”
If you are measuring a V8 engine cylinder head, flatness should not exceed 0.004”
If you are measuring across the cylinder head, flatness should not exceed 0.002”
How to measure a cylinder head for warpage
Now that the cylinder head is clean and you have the tools you need you can measure the cylinder head for flatness.
Place the cylinder head in your v-blocks or prop on some cloth rags to make sure that it does not move. Follow the simple steps below to measure:
- Place the straight edge lengthwise across the cylinder head.
- Open your feeler gauge to 0.001”
- Raise the feeler edge slightly and place the feeler gauge between the straight edge and the cylinder head.
- Attempt to remove the feeler gauge.
If you feel resistance the cylinder head has flatness under 0.001”. If it pulls out easily the cylinder head has warpage of more than 0.001”. Continue to increase the feeler gauge by 0.001” increments until you feel resistance. Whatever the feeler gauge reads is the amount of warpage your cylinder head has.
Measure in more than one direction
You will need to measure the cylinder head in more than one direction. I generally measure a cylinder head 8 different times. Take a look at the below graph to see which directions you should measure a cylinder head.
While it can be easy to skip this step, it is very important to make sure that it is done correctly.
If the cylinder head warpage meets or exceeds the specification you will need to repair. Depending on manufacturers recommendations this could mean replacing the cylinder head or possibly sending the cylinder head to a machine shop for machining.
If you do not measure cylinder head flatness the cylinder head gasket may fail again. If the cylinder head is warped a lot it can cause cylinder head failure shortly after the engine is started.
The only straight edge that you can use when checking cylinder head flatness is a machined straight edge. If you use any other type of straight edge you will get incorrect readings and may lead to another head gasket failure.