The stock parts
The flywheels used on Type 4 engines can be classified into two different categories: VW and Porsche. The Porsche 914/912E used a different flywheel than the VW cars (411, 412, and Bus). The Volkswagens used four different flywheels, each having a different diameter clutch disc and pressure plate. The very early 411 used a 200mm clutch, thus it is compatible with the popular aftermarket Type 1 clutch discs and pressure plates. Next came the 210 mm, 215 mm, and the 228 mm flywheels.
The 914/912E flywheel had a 215 mm diameter face and used a unique pressure plate and disc to mate it to the Porsche transaxle. This flywheel differs from the VW flywheel in that the starter ring gear is offset differently and will cause a VW starter not to engage properly. This flywheel will be necessary only if the car you will be installing the Type 4 into uses a Porsche transaxle, such as the 901 or 915. The rest of this tech article will cover using a Type 4 engine with a Type 1 transaxle, as you can use the stock Porsche starter to finish the Porsche setup.
The Type 4 200mm flywheel was only available on the 1969 VW 411. This car was only available in Europe in limited numbers, so finding this flywheel is quite difficult. Due to this scarcity of the 200mm flywheel, Kennedy Engineering, the makers of the famed KEP pressure plates and adaptors, offers a 200mm flywheel for the Type 4s. By using this flywheel, or the original 200mm, a Type 4 engine will slide right into a standard 12V Type 1-3 transmission. These flywheels also give the engine builder a large variety of proven pressure plates and clutch discs. A standard 12-volt Type 1 starter meshes up perfectly, with the self-supporting Bosch SR17X being my favorite.
The Type 4 200mm, the 210mm, and the 215mm are all the same outside diameter and are basically identical with the exception of the clutch face diameter. The starter ring tooth count is the same as a 12V/200mm Type 1 (130 teeth). The 228mm flywheel has the same starter ring, but the raised portion on the outer edge of the flywheel makes it larger overall and requires the use of a self supporting starter.
As the diameter of the pressure plate increases, the issue of pressure plate height becomes an issue. The larger pressure plates are more likely to have clearance issues in the bellhousing where the housing slopes from the input shaft to the outer lip. It is here that you will run into problems with the 228mm flywheel. It is possible to clearance safely for the 215mm, but the 228mm leaves the bellhousing quite thin.
Now let's take a look at the issues of flywheel selections and the best options.
Forged vs. Cast
Probably the one weakness of the Type 4 flywheel is the fact that most Type 4 flywheels are cast iron. A forged flywheel, like the one used on the Type 1, is much stronger, and for organizations like the NHRA, are often necessary. The Type 1 200mm flywheel was forged from the factory, so it's a non-issue for the Type 1 crowd.
A careful reader will notice that I said that most Type 4 flywheels are cast; as there are a few forged options. The 228mm from the Wasserboxer, the 200mm 411, and the Kennedy Engineering 200mm are all forged options for the Type 4 engine builder.
But this is only of concern to the few Type 4 engines being built. For 99% of the street engines out there, the cast flywheel does the job quite well. It's rugged and easily obtainable from a manual transmission Bus or 411/412.
Pilot Bearing modification
All Type 4 engines have the pilot shaft (also called the input shaft) bearing in the crankshaft. There is no pilot shaft bearing installed in automatic transmission engines. The input shaft of the transaxle must be extended to reach the pilot shaft bearing if you are using a Type 1 transaxle. The input shaft of a type 1 trans is shorter to accomidate the pilot sahft bearing in the gland nut. When a short type 1 input shaft is mated to a type 4 engine, the input shaft falls short of the mark and simply rests in the hole in the Type 4 flywheel. To "fix" this condition, remove the old Type 4 pilot shaft bearing from the flywheel. Next, purchase a new Type 4 pilot shaft bearing (this bearing is also the exact same one used in the Type 1 gland nut, so you can use a replacement one from those too). Take the flywheel and the new bearing to a competent machinist. Have the flywheel center hole enlarged so that the new pilot shaft bearing may be PRESSED into position. It should be positioned so that it's flush on the "clutch" side of the flywheel. The thickness at the flywheel is about 0.400" so the new pilot shaft bearing will stick out the backside and end up partially in the crankshaft. Thats why the old one must be removed. A light dab of wheel bearing grease finishes the job.
Just as a sidenote: the KEP flywheel already has this modification done to it, so it's a bolt on solution.
Much like the common practice of adding dowels to a Type 1 crankshaft, some tuners have found that adding a dowel between each bolt hole that mounts the flywheel to the crank aids in keeping the flywheel attached, even under severe use. Some tuners feel that this modification makes the center of flywheel too weak, and thus do not recommend it.
If you are building a Type 4 for drag racing or off road racing purposes, I suggest that you look into this matter and make the decision for yourself. Talk to your engine builder or to your machine for their opinion.
A common sight on modified Type 1 engines is a lightened flywheel. Lightened flywheels are usually used on cars used for drag racing or for road racing. Most street engines would be better off with the stock weight to retain long bearing life and higher gas mileage.
Lightening a flywheel decreases the rotating mass of the crank assembly, and results in fast acceleration. Of course, less momentum is stored as a result, and it results in fast rpm drops when you make off the flywheel. This will also result in decreased fuel mileage, so knowing how you are going to drive your car will be best determining if lightening is for you.
Commonly, a lightened flywheel weighs anywhere from 12-13 lbs; any less than this and the engine suffers with bearing failure. It's is important to remove the weight from the outer edge of the flywheel, closest to the starter gear. If you remove too much weight from behind the clutch surface closer to the center, flywheel warpage can result.
For the average street Type 4 engine with a Type 1 transaxle, I recommend using any of the 200 mm, 210 mm or 215 mm VW flywheels. They will all slide into a 12V bell housing with little to no clearancing. The 228 mm is out as far as the type 1 bell housing is concerned. The pressure plate will require too much clearancing , could sacrifice the structural integrity of the transaxle case. Leave the 228 mm for the Bus people.
If you envision your car hitting the drag strip or seeing time in the Baja 1000, it's advised that you look to a forged flywheel. The forged flywheel is necessary according to NHRA rules and it is a lot stronger. If you are using a Type 1 transaxle, go with the KEP 200mm flywheel, as it allows the use of the common KEP high performance pressure plates to regain the extra clamping force.
If you are using a Bus IRS transaxle, then go with a Wasserboxer 228mm forged flywheel. It will give you the large clamping of the 228mm clutch, along with a softer pedal and the strength of the forged material.
As for lightening, this is a personal preference. Some people like the instant throttle response that a lightened flywheel provides, others prefer to have the full weight to keep the engine from dropping rpms quickly when backing off the throttle. If you do lighten the flywheel, remember go no lighter than 12 lbs.
An interesting bit of trivia
The wasserboxer engine, the watercooled Vanagon flat 4, shares the same bolt pattern for the flywheel. This means that a Wasserboxer flywheel is the same as a late model 2.0L Transporter. This also means that a Wasserboxer could use a Type 4 200mm flywheel, allowing a wasserboxer to bolt up to a Type 1 transaxle.
Thanks to Joe Locicero of Oregon Performance Products for the modifications of a Type 4 flywheel in a Type 4 conversion.