07 May Adding Bump to Your Stick and Squish to Your Dish Part II
As indicated before, the purpose of this four-part series of articles is to show you the detailed process of building a performance engine; in particular, performing maintenance and modifications to an existing engine and assessing the difference. In Part I, we looked at the process of tearing down an engine and some of the things to keep in mind along the way. This month (Part II), we’ll look at the process of inspecting and machining engine parts.
To review, the 2017 cc (78.4 mm x 90.5 mm) engine featured here was originally built in 1994, having covered 80,000 kms (50,000 miles) to date.
The Engine Case
Inspection revealed that the 1994 Brazilian AS41 engine case was in excellent condition, needing no align bore. Some machine work was still required, however. As noted in Part I of this series, the engine originally had hydraulic lifters, but we planned to convert to solid lifters and a higher lift camshaft. Prior to doing so, the engine lifter bores were machined oversized and silicone bronze inserts were installed (refer to photo #1). This process not only ensures that the lifter bores are true, but the silicone bronze inserts also provide a stronger surface area for the lifters, virtually eliminating ovaled lifter bores with high-lift camshafts. This level of precision also helps to ensure that the lifter will spin freely in the lifter bore, evenly distributing camshaft lifter wear across the face of the lifter.
New head stud inserts were installed into the case. To ensure that the cylinder seating surfaces were perfectly true and that the heights were all equal, the case was milled down .030″ (refer to photo #2). Note that the case was milled after the new head stud inserts were installed (refer to photo #3). This ensures that the inserts don’t impact the cylinder seating surface, which can contribute to crooked cylinders, uneven cylinder wear, and oil leaks. Part of the milling process also involved lightly cutting the case cylinder bores to ensure that they were true and the depths were accurate, followed by carefully deburring the case of any loose or sharp edges (refer to photo #4).
You will recall from Part I in our series that loose threads were found in the hole for the oil sender. Art Thraen (Aircooled Engineering) addressed this by boring the hole oversized, followed by tapping it for an aluminum insert (refer to photo #5). The result (photo #6) provides much stronger threads than the original magnesium threads, providing leak free operation.
Art created the next modification to the case following a long distance road trip he made with his 1966 Cal-Look Beetle. His generator had failed during the trip far from home. Despite the fact that he had dual carburetors, freeing-up room around the generator, he spent a lot of time trying to remove the generator in order to install a new one. Anyone who has tried to remove a generator with a wide, late-model “doghouse” fan has encountered the challenge of the fan and backing plate being too wide, hitting the back of the generator stand. Removing the generator stand is also not an option, as it can’t be lifted high enough to clear the generator stand studs in the case, as the generator stand hits the bottom of the generator. The solution is to remove the generator stand studs, installing bolts, permitting the generator stand to simply slide backwards after removing the bolts. This allows the generator/fan to easily slide backwards for removal.
The problem with using bolts in the case for the generator stand, however, is that you risk ruining the soft magnesium threads when tightening the bolts into the case to secure the generator stand. Art addressed this by having a tool and die maker fabricate a tool (refer to photo #7) that permits you to remove the original studs, bore the hole oversize and run a tap, followed by installing an aluminum insert which provides strong threads for the bolts. The tool ensures that the holes remain square to each other and are drilled and tapped perfectly straight. With the use of dual carburetors, generator/fan removal can now be done in minutes versus hours.
Crankshaft
Initial inspection of the welded 78.4 VW crank indicated that it was in excellent condition. Following a thorough cleaning and polishing, however, small hairline cracks were found in one of the rod journals, including the journal surface and oil hole (refer to photo #8). This may have been there for some time, and Art believed that it was likely due to the initial welding process when the crank was originally offset ground to 78.4 mm. While welding and grinding the crank could have repaired this, the cost of doing so rivaled the cost of a new crank.
A new balanced, counterweighted, forged and nitrated CB performance 82 mm crank was therefore purchased from Aircooled.Net. While the difference was only 3.6 mm in stroke (refer to photo #9 – old crank on the right, new crank on the left), the slightly larger crank was chosen for increased torque (greater leverage due to longer stroke) and increased port velocity (greater piston speed due to longer stroke).
Rods
The modified VW rods were found to be in excellent condition. We spent some time speaking about the rods, and despite their excellent condition, decided to replace them. Why? The rods had endured a lot of road miles, and were not new when they were originally installed in the engine 80,000 kms (50,000 miles) ago. Due to the intended use of the engine (long road trips and the occasional blast down the ¼ mile) and power (approximately 150 flywheel horsepower), we decided to replace them with a set of magnafluxed and rebuilt VW rods. These rods were already clearanced for a stroker crankshaft, and came with heavy-duty rod bolts (refer to photo #10).
Another option would have been to send the original rods out for magnafluxing and rebuilding, but the cost of doing so rivaled the cost of a “new” set of magnafluxed, rebuilt rods.
Pistons & CylindersThe 90.5 mm Mahle pistons and cylinders were also found to be in excellent shape. Due to the mileage, however, the cylinders were honed and new Deves piston rings were installed. New rings are inexpensive, ensuring that you don’t encounter any compression loss or “blow-by” down the road. Following a thorough cleaning, the cylinders were painted with a fresh coat of flat black paint to aid in heat dissipation and prevent corrosion.
Cylinder Heads
As indicated in Part I of this series, the cylinder heads were purchased used in 1998. The ported VW 043 heads were originally built by Jeff Denham, running 40 mm intake valves and 37.5 mm exhaust valves. At the time of purchase, they had approximately 5,000 kms (3,000 miles) and 30, 12-13-second ¼ mile passes on them. The heads were then installed in this engine for an additional 30,000 kms (18,000 miles) and 6 additional ¼ mile passes.
After a thorough cleaning and inspection, the heads were found to be in good overall condition, but required a valve job, which was understandable due to the number of 7,000 RPM ¼ mile passes on them. Art performed the valve job and installed new dual ERCO valve springs.
Having trial assembled the motor to check the deck height (more on this in Part III of the series), Art determined that he needed 58 cc chambers in the cylinder heads in order to achieve the desired compression ratio of 9:1. As the cylinder heads had 60 cc chambers, the cylinder seating surface was milled in order to decrease the chamber size and provide an even sealing surface (refer to photo #11). The completed cylinder heads were now ready for many more street and track miles (refer to photo #12).
If you plan to build a performance engine, or are contemplating changes to your existing engine to extract more horsepower, the cylinder heads should represent a substantial portion of your attention and investment. As the saying goes, “the horsepower is in the heads,” and port velocity (not simply volume) is what makes a great street engine. Resist the urge to buy a cheap set of unported heads, or alternatively, simply “hogging-out” the ports for a high peak horsepower number. Focus on producing a broad torque band and strong horsepower, and speak with several cylinder head porters and manufacturers to find out what combination is best for your intended use.
In Part III of the series, we’ll look at the process of reassembling the engine.
