T-1
Type-1 Cylinder Head Inspection
Inspecting the cylinder head before rebuilding or re-installing it on the engine can save you time and money. Below you will find the common problems and areas that will need your attention before moving forward.
Once the head has been removed from the cylinder head studs the first area to look at for any damage is the spark plug hole. This area is probably the most common spot for cracks to appear. If you have had any long term experience with the Volkswagen T-1air-cooled engine, you may have experienced a spark plug coming loose or blowing out of the cylinder head. Care must be taken to have a close inspection of the spark plug hole for any cracks. Because of the heat generated in the head of a air-cooled engine, the probability of a crack starting here is very high.
The dual port cylinder head is prone to cracks much more than the earlier single port head. This is due largely to the size of the valves and the area between the intake and exhaust valve. The earlier single port motors tended to be smaller, less powerful, lower compression and therefore ran at a lower temperature. When the dual port cylinder head was introduced the size of the motor was also increased. The reach of the spark plug has also played a role here. You can notice that the thread length in your T-1 cylinder head is about half of your typical spark plug reach. With such a small amount of thread, a large amount of heat, the chance of there being a problem with the plug hole is far greater.
So once the head is removed, clean around the spark plug hole and look very closely for any cracks or damage to the threads. Any size crack can be a potential problem and a cause for concern. The crack can also be hard to spot, so if you have access to a solvent tank and or a sand or glass bead machine, this will clean the area properly to give you the clarity you will need to make an assessment. If a crack is found then you are really only left with a couple of choices. First is to have the area ground down and welded up, which can be quite costly and impractical. Unless there is something special with this particular cylinder head, having it welded is just not feasible. If welding becomes necessary, then at this time you may have the hole filled to then accept a ¾” reach plug. This will also open up a much larger choice of spark plugs and heat ranges available to you. Your other choice is to buy a new cylinder head, which in most cases today come with the ¾” reach as standard. The cost of brand new cylinder heads is usually well within the budget of most rebuilds and is a good choice. The only time that a cracked head may be used is when the motor is for an off-road vehicle. If the spark plug hole was to open up and eject the spark plug, you can probably limp it back to camp and load it on the trailer. Otherwise you may find yourself stranded out on the highway somewhere in the middle of nowhere without cell phone service.
If the spark plug hole looks to be in good working order than the next place to check is the area between the valve seats. With most dual port or single port heads it is quite common to find cracks between the seats. The manufacturer does allow for a crack to appear here without considering the head to be junk. Please check with your shop manual to determine how much of a crack is allowed before continuing with the rebuild. The important thing here is to make sure that the valve seat is in no way at risk of coming loose. If the seat was to come loose during operation, this could cause the head of the valve to become severed from the stem and fall into the cylinder. I do not think we need to go into any great detail as to how devastating this would be for your engine.
Once your head has passed inspection, you may still have a spark plug that is loose fitting in the hole. There are two typical fixes that are employed for solving this all too common problem. The first is usually referred to as a “thinsert”, a small threaded tube with your spark plug thread on the inside and a larger outside diameter. A reamer tap combination tool will cut new threads in the cylinder head spark plug hole to match the outside of the spark plug insert. You would then screw the insert onto the spark plug and with some thread lock screw the plug back into the head. These types of fixes can in some cases fix the problem. Yet when you attempt to remove the plug, the insert will in most cases come out attached to the plug, and bring a little bit of the heads threads with it as well. A more secure and permanent fix is commonly referred to as Heli-Coil. This type will remove less of the original material and once properly installed, is locked in place and will not be attached to the spark plug. This style is a steel coil of threads that match your original ones, effectively replacing the ones that were damaged.
Visual inspection of the exhaust and intake studs will easily tell you whether you may need to replace these. In most cases the worn stud can be removed simply by putting two nuts on the stud and locking them together. By using a wrench on the nut closet to the cylinder head you can then turn the old stud out and screw a new one in place. If the stud has broken off, then you may have to buy a stud extraction tool or take the head to a machine shop for them to fix. Sometimes the threaded hole in the head has been damaged and there is no threads left to screw a new stud back in place, so again a thread repair may work or a oversize stud may have to be used.
The Volkswagen air cooled head on the Type 1 will typically not have a gasket where the cylinder meets the head. You will need to have a look at this surface to determine if there has been any leaking. If the cylinder head nuts were loose when the head was removed, then you will probably notice black carbon streaks coming from the combustion area leading out of the cylinder head. Having this area repaired would require you to take your head to a machine shop so they can resurface this area so a proper seal will be created when the head is re-installed. If this area needs to be resurfaced, then once you get the head back the machine shop will be able to tell you how much material was removed. This can be critical depending on the motor you are building. If you are concerned with the compression ratio of your motor, you may then be required to add a shim to the bottom of the cylinder to compensate for the material removed from the head. In most cases a 0.010” [ten thousandths of an inch] flycut is not of any concern and would not require a shim to be installed under the cylinder. Anything beyond that will usually make a change large enough to the compression ratio to affect the engine. With the air-cooled engine, high compression means heat, and high cylinder head temperatures in an air-cooled head can spell disaster.
Checking the valves for wear is more of a visual task than anything. Have a good look at the valve retainer grooves for wear, even place one half of a retainer over the grooves to determine the fit between the two. The side to side movement of the valve stem with it placed in the valve guide will give you an idea of valve guide wear. One way of checking the fit is with a little oil on the stem, slide the valve into the guide, holding your finger over the exposed end of the guide, pull the valve out quickly. You should hear a popping sound if the fit is good, if not the valve will come out too easily without much or any kind of suction being felt on the end of your finger. If you are not familiar with the removal of guides from these heads, then I urge you to take the head to someone who has this experience.
I hope this gives you a good idea of the areas that you will need to give your attention to when working with your Type-1 air-cooled head.
All prices shown in Canadian funds.