Conversion - T4 Hayes

Rev - Nov 11, 2017


By - Bob Hayes -
Edited by - Jan Zumwalt (EAA #66327)


Hayes Type 4 Engine Overhaul

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PDF copy of this article for offline reading.



An air cooled VW engine rotates about 150 million times each 500hrs of flight. If the engine is correctly maintained, it is likly to have rotated nearly 1/2 billion times before needing replacement. If that scares you, then this is the wrong article to be reading laugh

This article will provide all the information needed to build a bulletproof, complete, reliable air-cooled Volkswagen TYPE 4 engine – no funny noises, starts instantly every time, no exhaust leaks, doesn’t catch fire, no motel rooms, no pulling the engine on the ramp of a strange airport, no oil leaks, no gas leaks,  no fumes, no backfiring, nice heater, quiet, it purrs – no nothin’. In other words, it goes anywhere and comes back without a problem.

We inlude special notes for the Type 4 engine! There is plenty of good information for the other VW type engines but you can’t skip over anything –  if you want success, you need to read and understand everything we're doing, and why you’re doing it. Along the way we explain what  works  and what makes sense.  This isn’t step-by-step but rather it's meant to be a guided tour that requires you to read the whole thing.

Old Seized Parts

If you have a nut anywhere on the exhaust system or anywhere for that matter but  particularly at the cylinder head, and you have a nut where it seems it’s so tight you’re afraid it is going to break a stud and  it just won’t move, STOP!! The last thing you want to do is break any exhaust stud off in the head. You may never be able to fix it and end up needing a NEW HEAD simply because of one broken stud. So you may end up spending  a couple days  few hundred dollars to put ONE NUT ON. Don’t break a stud!!

So, whenever in doubt, rather than risking a broken stud, heat the nut up red hot with a torch. It will likely come right off. This simple step can save you hours and hours of work and plenty of $$. Heat can save you a lot of time and money. Usually when something won’t turn, it means something is too tight. Making the respective hole bigger usually solves this problem and heat will do it. This even works on stubborn plugs in carburetors. Just use a real light flame and make sure it’s dry.


Take the flywheel off first with the clutch. It’s easiest to do it right away when the engine is still heavy to resist your effort on the long breaker bar you’re going to need unless you have access to an impact wrench.

When taking off the heads, particularly on type 4 engines, you may find the upper head nuts so tight that when attempting to turn the nut, the whole stud want’s to come out of the case. Use oxy-acetylene and heat the nuts – they’ll likely come off. A butane torch may work or at least help.

When disassembling the case, make sure you don’t miss any nuts because they’re so covered with glop you can’t see them. The two studs that pinch the front cam bearings and cam plug on type 1 engines are often covered and if you miss them and try to force the case halve apart, you can break the case and you’ll need to find another one.

For type 4 engines, never remove this bolt until you’ve remove the sump plate securing nut. Don’t forget this step or you can break the case:

The bolt in the above photo is unique – there’s only one like it in on the whole car. It’s 77 millimeters long including the head and 72 millimeters long not including the head. Thread is 8 x 1.25 millimeters – 8 millimeters in diameter and one complete revolution of threads for each 1.25 millimeters of length (pitch).

Notice how the non-threaded part of this bolt is bigger than the threaded part. This wider part is to provide support for the oil pickup tube.  Any bolt the with the proper length and proper thread pattern will work but this is the right bolt …

If you do not have this bolt, it’s best to try and find a used one. Thing is, there’s only one per bus on this planet. If you can’t find one, try to find a used bolt that is the correct length that was installed at some time in the past on a vehicle as new or from  any new car dealer. Most likely, a dealer will sell you a bolt sourced from the factory and it won’t be junk.  If you just buy a bolt  at Home Depot (junk) or Fastenal (junk) or anywhere like that, it’ll be Chinese and real soft and will bend easily when tightening it  and this can break the case. This is not me being anal – this is reality.

This is the pivot bolt for the alternator for 72 through 79 buses. It’s almost exactly the same dimensions as the proper bolt for the type 4 oil pickup tube. It’s the best thing to use if you don’t have the right bolt for the pickup tube. A bit of creative filing will be necessary but it’s the next best thing to the real thing and it’s a German bolt so you know it’s strong.

The starting point here for assembly is the everything is all apart. Clean or not, it can all be evaluated.

We start with valuable information regarding aftermarket aluminum cases.

Here’s a photo of a stock case:

And here’s an aftermarket aluminum case:

The aluminum case only comes with the vent hole shown in the stock case. There’s no lower drain  other than a small slot in the base of the web that divides  the crank and cam gear area from the rest of the case. When an aluminum case is assembled without drilling these drain hole, this area has no way to drain other than the small slot and the vent, which is too high for proper drainage. Realize also that the crank gear and the cam gear act like a giant oil pump. Without an upper vent hole and lower drain holes, this area fills with oil and the pressure created by spinning cam and crank gears (just like the oil pump) cause oil to leak past the oil return threads on the crank pulley and even a sand seal will not be an effective repair. If you drill the two holes shown in the picture,  you will have no leakage here with either the stock pulley or a sand seal pulley.

Except – you may have a leak with a stock pulley you may have leak develop here over time. To fix you’ll have to use a sand seal and a sand seal pulley to match. There’s two ways to fix this – with a seal designed to install without machining and one that requires machining. The no-machine type of seal can begin rotating in the bore over time but I’ve gone 40,000 miles with one of these and no problem with spinning. But with this configuration, a spacer is needed behind the pulley to make the pulley stick out from the case far enough to clear the seal. Since the pulled hub is very thin walled to accommodate the seal, it always looked like it might break. The machining necessary type seal allows the pulley to have more crankshaft within the hub since it doesn’t require a spacer and thus has more crank within it instead of empty hub.

This machining can be accomplished without disassembling the engine (you can do it in the car) but you’ll need a cutter – about $150. The pulley can be found many places online and the pulley comes in kit form, with the seal. All seals that come with these kits have no spring. Many seals for many applications have a spring – front grease seals, rear axle seals, the nose cone/hockey stick seal on the trans – every one of these seals has a spring. The spring keeps the seal lips tight against the thing they seal against. And technically, the no-spring seal that comes with all sand seal kit’s is really the wrong one for the application. It’s not meant for the rpm the pulley develops. Realize this seal requires machining of the case for installation. It’s the same in every other respect as the seals that come with the kits so it works with your machined hole and with your pulley.

Note – Gene Berg offers the seal with spring as standard. They sell the cutter (periodically – they make them and the sell out quick). For best results use the Berg pulley and hub assembly when you opt for the sand seal. It’s all steel, not aluminum. Realize that in order to use a seal, the hub on the seal must be smaller than stock. This results in a rather thin wall and can break. Happened to me. Started off with quickie, no machine seal. About 400 thousand miless later,  the case was cut.  The case was cut for the maching type seal. Spacer was removed since no longer necessary so pulley was pushed onto crank farther – maximum depth, maximum engagement with hub. It broke about 500 miles later. Needless to say, this was rather unexpected at best and in reality, very, very, very, very, very, very, very, inconvenient. It also very inconvenient.

You may think it’s insane to drill a couple holes in a brand new case. Well, in case you haven’t noticed, almost EVERY SINGLE AFTERMARKET PART, no matter what it is and now matter what it’s for – from door panels to engine cases – has something wrong with it. So if you want an engine that doesn’t leak – drill these holes!  And if you are using one of these aftermarket cases, you’re going to need to use a sand seal and a sand seal pulley. It seems these cases can’t account for the blowby found in a stock case and they tend to leak with a stock hub style pulley sooner or later (sometimes immediately) so you’ll either need to have the case machined for the seal or put one of the quickie, no machining type of seal but sometimes this type of seal can spin in the case so have it machined if you can. If the engine is already assembled or just a running engine, no seal will cure the problem if the holes aren’t drilled in the case. And that’s not the only thing wrong with these cases, besides what’s mentioned in the following. Keep reading. There’s a lot to learn …

The other thing that needs to be done with a new or never align-bored aluminum case is align bore it.  The center main is loose on these cases as the come with stock diameter bore. In other words, if you have a new or never align bored but used aluminum case (brand name Auto Linea) you need to align bore it to the first oversize – 0.020″ over or 0.5 millimeters. Without this step, you’ll have lower oil pressure than possible, the crank will be poorly secured,  and since the bearing is wiggling,  it will  eventually begin making noise. It varies, but sometimes it can even sounds kinda like a loose rod.

Evaluating the case

The back side of bearings differ from brand to brand. Some bearings have the oil groove on the case side, others have it on the crank side. With the oil groove on the crank side, it makes no mark so you’ll have to rely on two things to determine whether you need an align bore – a beaten look on the case bore surface and how the bearing fits into the case. Contrary to the popular belief of some, the ends of the bearing are supposed to stick of past the case a bit. The same is true for the rod bearings. When the case is assembled, the bearings form the proper diameter and a preload is created – a pinching together  of the bearing – that keeps if from moving around. It’s gotta be tight; rigid - it’s a car, not a toy.

The same goes for the rod bearings – the bearings are supposed to stick out of the bore a little bit.  How much? I don’t need to know. I’d worry if they didn’t stick up.

Here’s a crank from a 2 liter air cooled Vanagon engine.

There’s a lotta people out there that think type 4 cases never need an align bore. Hey, everything wears. When the center bearing was put in the case this crank came out of,  it wouldn’t even stay in. If one place the bearing half in the bore and case was tuned with the bearing facing the floor, the bearing would fall right out – there was no tension because the bore was bigger than the bearing. This should not happen – this center bearing should pinch when installed and the pinch keeps it tight. The looseness in this case caused the crank to bang around a lot and this constant pounding shattered this crank into submission. When I first saw this, I thought the defining marks were water stains. A bit of polishing and it was still there. I could feel it with my fingernail.

36 hp engines from fifties would sometimes break crankshafts. Since the broke across the cheeks of the crank, the car would still run on 4 cylinders – for many miles. I’ve seen one run for over a year like this. But if this Vanagon crank would’ve broken in the vehicle, since it’s right in the middle, it would’ve stopped immediately. Look close at all the parts in the engine. This problem could’ve gotten past a machinist polishing the crank for you and would’ve left you scratching your head a few weeks after assembly wondering why it happened.

Align boring keeps the bearings secured and thus keeps the crank secured on a fixed axis. A worn case, specifically  on the center main, allows the crank to flex and can cause breakage and apparently fracturing. So the answer to the question is type 4 cases DO NEED ALIGN BORING when they align boring or else!!

There’s basically two kinds of pickup tube and thus, 2 kinds of cases. The case in the photo had the wrong (long) pickup tube.

German Pistons

If your pistons are German, this matters - measure the clearance between the ring and the piston. You’re measuring ring land play. If it’s less than .005″, use the pistons and cylinders again. Forget all that stuff in the book – this is what matters. Buy new Hastings rings, clean the carbon out of the bottom of the ring land (use a broken ring or a ring groove (land) cleaner). Just clean the bottom of the groove. Hone the cylinders and put it together. It’s not out of the question for a high mileage engine with original pistons and cylinders to be usable. Brazilian pistons with 20,000 miles on them are usually way beyond usable. Chinese? I don’t yet. Don’t toss a German piston until you check. They’re high quality parts. And honing the cylinder makes it a teensy bit bigger – engine will rev quicker.


You need inserts if you don’t have them. Originally up to about 1972, maybe earlier, type 1 VW head studs were 10 mm in diameter and screwed into the case with an interference fit. This means the hole the stud screws into is tiny bit smaller than the diameter of the threaded end of the stud itself thus the hole offers resistance when the stud is screwed in and is supposed to keep it from ever coming out or stripping. This worked fine until VW increased the displacement to 1500 cc’s. The bigger displacement results in a  bigger explosion and the increased stress on the studs resulted in stripping. If you don’t have inserts, you must install them. It’s highly probable at least one bottom stud will eventually pull if none have already. It’s just plain sketchy to not put in inserts in a VW case. But if you don’t have them already, you’re lucky. This is because then you can choose the best ones and the best way to install them. The best ones are called Time-serts although there are other similar ones. Time-serts require a smaller hole to be drilled in the case for installation vs some others that require the drilling away  of a lot of metal before tapping the case for an insert and when it comes to drilling holes in places, less is more regarding diameter.

This is what deep studding number 3 exhaust (refer to location) stud is all about …

Non-deep studded cases have the bottom of the stud reach right above where the case tends to crack. The pull on the stud is literally trying to pull the case apart thus weakening it and often causing it to crack. When the stud is deep, the top of the threaded portion of the stud is pushing this area together rather than pulling it apart because it’s on the other side of the weak, crack-prone zone and thus deep studding helps prevent cracking.

But the thing is, there is very little material between the surface in the above photo and the hole the stud screws into regardless of whether it’s deep or not. Therefore, it’s a real bad idea to put an  insert here and since it’s the lower, longer stud holes that tend to strip and need inserts and the top stud holes hardly ever strip, there is virtually no reason to put an insert here and putting one in is a bad idea. And if the case is not deep studded and you have it done, you’re putting the stud in virgin material in the first place so it’s not gonna pull anyway and is much more likely to strip with an insert due to the very small distance between the hole enlarged for an insert and the area behind the flywheel  and then it will be the insert that strips in the case andyou can’t fix it, even with a “Big-sert”. If you drill the hole for this type of insert, you’ll see side of drill bit showing as it cuts through the case on the flywheel side. And with a “normal” insert here, since the metal is so thin on the flywheel side, it may strip just assembling the engine. It’s happened. Just don’t do it. Drill the hole and tap for the stud, don’t use an insert. How deep?  You use a bottom stud for this stud on final assembly. There’s 8 on every engine. The proper hole depth will result in the lower stud protruding from the case the same amount any outer upper stud.

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