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Engine Rebuild - Case Prep - Step 1

By Ryan Ballou

Beginning this month, I'm am going to be covering something that will span quite a few articles, something that will interest everyone regardless of what their performance expectations are for their engine. I'll be covering the process of actually building your own engine. I plan to take you step by step through each process as I encounter them on my own engine rebuild. This will include pretty much everything that the home mechanic could hope to do on his own with a few exceptions, most notably machine work, I'll leave that for the guys at the shop.

Whether planning a new engine or rebuilding an old one, the case is the first thing that you spend time on. New cases need a little TLC along with a few modifications, while used cases need to be looked over and checked for potential problems. For this article I'm using an old case of mine that's been garaged for a few years now and I'll take you through the steps that would bring it on par with my actual case, that happens to still be in the shop.

The very first thing you need to do is clean the case up. This isn't a final assembly cleaning; rather you just want to get the crud and oil off it so that you can work with a clean case and spot potential problems easier. Start by using a putty knife to scrap off any buildup, making sure not to scratch any machined surfaces. Once all the build up has been removed, spray the case down with a can of engine degreaser, inside and out. Let it soak for 5-10 minutes and then hose it off completely. You can either let it sun dry or dry it in an oven on the lowest setting.

If you used the oven to dry the case, then the next step will be an easy one, crack checking. If any cracks are present in the case, the heat will cause trapped oil to seep from the cracks making them quite easy to spot. If you let the case sun dry, then you may need to heat the case slightly to force the oil out. A hair dryer or heat gun works well here. Heat one small section at a time until you've covered the whole case.

Most of the time a crack means you're case needs to be retired to the trash pile. Some cracks can be welded or dealt with extending the life of the case for one more rebuild. If cracks are found, you need to discuss your options with your local VW machine shop. 

Once your case has been deemed crack free, it's time to check the main bore. The first and most obvious thing to look for is pounding at the center main bore. You will likely see the mirror image of the bearing shell worn into the bore. This is actually OK provided you can't feel any ridges in the bore. Rub your fingernail across the machined bore surface and if it catches on anything, then you're case will probably need to be align bored. Again, your local machine shop can help you determine what's acceptable, since this check relies on a feeling for what's right.

Before continuing or sending your case out to be bored over, you need to check the center main web for warping. With the main stud o-rings removed and the main web machined surfaces free from any debris, bolt the case halves together at the center main only. Torque the two 19mm nuts on the center main down to about 30 ft* lbs. Now while holding a flashlight on one side of the saddle, look down the other. What you're looking for is light shining through the case split at the main saddle. If any light shines through the seam while torqued, the case is warped and should be retired.

Next thing on the list is the lifter bores. You'll need to have your new set of lifters, cam and cam bearings to check these out. Blow some carb cleaner through each of the bores to clean them up. Lightly oil the lifters and slide them into each bore. The first thing you're checking for is side play in the lifter bores. Acceptable play is .001"-.0015". This can be measured with a dial bore gauge and compared to your lifter measurements, or again another 'feel' check. With the lifter in the bore about a half-inch from bottoming, there should be very little movement if you try to rock the lifter top to bottom. If you're unsure, ask someone at your shop to double-check for you. Worn lifter bores will wear faster and faster as the wear increases.

With the lifters still installed in the case halves you want to check for lifter to lobe clearance. With a stock cam/lifter combo clearance shouldn't be an issue, but if an aftermarket combo is used, this needs to be checked. Place the cam bearings in each case half, with a dab of assembly lube on each. Now set the cam into the bearings. Spin the cam until the peak of the lobe is over each of the lifter faces. This clearance should be at least .040", measurable with a feeler gauge. Place the cam in the other case half and do the same. If any don't measure up, you'll need to have the bores machined down to provide the minimum clearance.

Now is a good time to check out the oil pickup tube. Sometimes this can wiggle itself loose in the case. When that happens you're oil pump will start sucking air along with the oil. Aerated oil will quickly cause damage to your main and rod bearings ruining your day. A quick easy way to assure the pickup tube stays put for goods it to 'glue' it in place with some Loctite 518. Clean up all the surfaces really well before application and you'll be set.

Time to do a little cleanup on the case, but not the kind you're thinking of. You want to go over every inch of the case and de-burr casting flash, sharp edges, and any other flaws. Casting flash has a nasty tendency to break off under vibration making a mess of your oil pump and bearings if you don't run a filter. Sharp edges can lead to stress risers and eventually cracks. Other casting flaws in general will do the same along with slowing oil flow back to the case sump. With a Dremel/die grinder, carbide burr, and a steady hand, you can make short work of any casting flaws. A good set of hand files will work also but take a bit longer. Some spots you'll find are only accessible with a small round hand file.

The last thing on the list for now is to drill and tap the oil galleys. The reason behind this is to aide in the final cleaning process. Bits of debris tend to collect in the oil galleys at the factory plugs if they aren't directly in the line of flow when you're flushing the case passages out. This may seem a little daunting to some, but it's really easier than it sounds. Most shops will charge between $50 and $100 to do this service for you. Even if you have to go out and buy the drills and taps yourself, you'll still save some money or at least break even. You'll need a 1/8" NPT, 1/4" NPT, and 3/8" NPT tap.

To remove the existing plugs, simply drill and tap their centers to m6x1.0. You can then thread a spare exhaust clamp bolt into the plugs. Some people use dent pullers on the bolt to pop the plugs out, I was able to grab the bolt with a pair of vice grips and just yank them out. Once all the plugs are out, you're ready to tap the passages. Go slow and use plenty of cutting fluid. Since pipe taps are tapered, how deep you go is very important. Back out the tap often and use the appropriate sized plug to check depth. There are some passages where if you go to deep, the plug will interfere with oil flow, so look before you leap. On those that don't matter, I try to make the plug sit slightly higher than flush.

There are only three plugs to be tapped to 3/8" so start with those. They are the largest of them all, two in the front of the case, and one in the rear. The uppermost passage that gets tapped to 3/8" would be the one to use for the return line fitting if you choose to use a full flow oiling setup. Use a 9/16" bit to drill the first 1/2" of the passage out, this will properly size it for the 3/8" pipe tap. Next, tap the openings that receive 1/4" plugs. These will not need to be drilled out before tapping, as they are already the correct size. These passages include the oil pump outlet if you are going full flow. Then there is one on the front of the case and one on top, both entering the galley that the oil pressure light switch is located in. Finally there are five 1/8" passages. One passage is in the front of the case right next to the oil line return passage. One is to the left side of the case (facing the case), and three on the rear. These will need to be drilled out first with a size 'R' bit. An 11/32 bit is a close match if you can't find a size 'R'.

The three 1/8" passages in the rear of the case are of special interest, as is the 1/4" passage in the front of the case. It's possible that while drilling these out and tapping them that a burr will develop in the lifter bores or pressure relief bores that these passages enter. Not all pipe taps are exactly the same and may not require you to go that deep, on the other hand, some may. Check all of these by sliding either a lifter or pressure relief piston into their respective bores and de-burr as needed with a jewelers file.

Once these are all drilled and tapped, you've essentially done everything you can to prep the case for assembly. If the case needs to have any machining processes performed on it, now is the time. With the oil galleys drilled and tapped for plugs, cleaning all the shavings and swarf out will be much easier when the case returns from the shop. Possible machining operations are align boring/thrust cut, lifter bores sleeved, lifter bores machined for clearance, cylinder openings bored for oversized cylinders, and cylinder bore decking.

Now comes the hard part, sitting, waiting, and dreaming of the completed engine back in the car where you can drive it like you stole it.


1-The foundation for a new engine project, the case. Cleaned up and ready to start scrutinizing. You may notice this case was painted once before. Extra care would need to be applied to prevent flaking paint from entering the case, one reason I don't like painted cases.

2-Behind the #3 cylinder is the most likely place to find a crack. It would be in the recessed area just to the right of the main bore. Other common areas are around the cylinder bores, but check everywhere to be safe.

3-The wear marks are easiest to see on the thrust bearing saddle (leftmost) but it's the center saddle that will pound out first. If your fingernail catches a lip, you case probably needs to be align bored.

4-With a flashlight on the backside, check for light shining through case split. This case gets a pass here too.

5-Holding the lifter up 1/2" or so, very little play should be felt while rocking the lifter.

6-Since I don't have a .040" feeler I'm using a .005" and .035" feeler gauge together. Plenty of room here.

7-A quick wiggle of the pickup tube shows it to be nice and tight, just like it should be. You can just make out the oil weeping from the joint here; this is what a crack would look like.

8-A shot of the center main web shows some flash and quite a few sharp edges that will need to be cleaned up

9-The lumps visible here are some more casting flaws that should be cleaned up. A drum sander on a Dremel will make quick work of these. Always wear a mask when grinding and keep all flame sources far away. Magnesium dust is nasty when it catches fire.

10-The front of the case gets two 3/8" NPT plugs, one 1/4" NPT plug, and one 1/8" NPT plug. Notice the boss next to the oil line return passage has been clearanced back. This is to make room for the 90-degree fitting for the oil line. Drill and tap the 1/8" passage in this boss first so that you don't clearance into the space where the plug will be. Have your 90-degree fitting on hand while tapping this hole; you'll need to make sure it's pointing the right direction when tightened down.

11-Here we see where the 1/4" NPT plug goes on the top of the case, and the 1/8" NPT plug goes in the side of the Main galley where it feeds the lifter bores.

12Finally we have the remaining plugs. Three 1/8" NPT plugs, and one 3/8" NPT plug.

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