Got the Wonderbus's cylinder heads off, am hesitating before removing cylinders from case -- waiting for clarification from RAMVA on Bill Spiliotopoulos's brief statement, "pull the cylinders 1/4" out to seal the joint between the cylinders and the case. Clean the oil remains and apply some Curil T to seal the cylinder bases" before proceeding. (This is in thread "Having Fun and Thanks!"
While I ponder my next move, I read in Muir that the surface between the cylinder and the head would be expected to have a copper gasket. And there should be a paper gasket between the cylinder and case.
I found no gasket between the head and cylinder, and if there is a gasket between the cylinder and case, it is not visible -- just a bead of some compound.
Toss the Muir manual. Get a "real" manual, like the Bentley for Buses, '68 thru '79. The copper gasket rings went out with "Flower Power".
No gasket between head and cylinder. Paper "gasket" between cylinder and case. The paper often leaks oil which is why the sealant (silicone caulk works) is suggested.
Note that this is for Type 1 engines only; Type 4 ('72 and later) were different.
AFAIK, no stock ACVW engine ever came with a head gasket.
For the cylinder to case interface, I use high-temp RTV silicone gasket maker stuff. Comes in a tube. Get a bit on the finger and smear a _little_ around the base of the cylinder.
http://63.230.74.177/ghia/MVC-442F.JPG I probably used more than needed, but you get the idea.
Noted, and thanks. I saw that Bentley did not mention the cylinder-head gasket, but did say that if you found a paper gasket between cylinder and case when you took the engine apart, to use a new one upon re-assembly.
Okay, so a bit of digression here. I can see why the seal between the cylinder and case needn't be super-duper: there isn't much in the way of pressure there, and we just want oil not to dribble out. But between the head and the cylinder is another story -- lots of pressure there, I reckon. How do ACVW engines get away with having no gasketing there?
The ancient 36/40HP engines (which Muir was referring to) *did* have copper gaskets between head and cylinder. I think VW found that they caused more problems than they solved and opted to have the cylinder "mated" carefully to the head. Leakage (compression) from that junction is not one of the problems the engines are noted for. Jim
So a really tight fit is solution enough. Make the surfaces really flat and smoosh 'em together real hard. Simple. Elegant. Gas-tight. I like it. Is this standard practice in other automobile engines?
think the copper head gasket was only on the 25 HP (very early) and 36 HP and went out w/ the 40 horse. The head is lightly lapped w/ a cylinder and some valve lapping grit, cleaned and assembled dry. Not sure about cyl to case.
It's is not, it isn't ain't, and it's it's, not its, if you mean it is. If you don't, it's its. Then too, it's hers. It isn't her's. It isn't our's either. It's ours, and likewise yours and theirs. -- Oxford University Press, Edpress News
I suspect that, because of the horizontal engine arrangement as being air-cooled, the amount of expansion results in fairly high clamping pressure. Note that the head-studs are only torqued to 18 foot-pounds (for 8mm studs) which doesn't seem like much. And it isn't when the engine is cold. When hot, there is a _lot_ more tension on the studs. Bob Hoover posted a figure for this some time back, but I can't remember what it was.
Make the surfaces flat... they should already BE flat. This is a chore taken care of during blueprinting, not assembly.
Smoosh 'em together real hard... Stop. Torque them to spec. NOT 'real hard,' just to spec.
NOW come a touch a elegance... because as the engine reaches normal operating temperature the alloy case & heads expand more than TWICE as much as the cast iron barrels. In effect, the heads and the case try to expand AWAY from the barrels. But they can't because of the head studs. They still expand but now they expand AGAINST the barrels. And that's where the real hard smoosh comes from... giving you the sealing pressure you'd get from about 170 lb-ft of torque (instead of a paltry 23). The point most folks will miss here is that there ain't no way in hell you can torque a VW head-stud to 170 lb-ft... but if you know your onions engineering-wise, you can achieve that amount of pressure through thermal expansion WITHOUT having that amount of tension appear in the studs. Now THAT's elegance.
Of course, this is another reason you need the thermostat and the complete cooling system, because the principle only works when you maintain a relatively even temperature across a fairly narrow range.
You see, the folks who designed the thing are what we call 'engineers.' They know about coefficient of expansion, thermodynamics and other unimportant stuff, whereas the folks who print those neat magazines and sell POS engines to the Kiddie Trade and tear the thermostat out of their engines are what we call 'experts.' :-)
The VW factory in Germany issued a bulletin in the 80's, instructing their own rebuilders to LEAVE OUT the paper gasket from between cylinder and engine case.
There was NEVER anything used between cylinder and head, they mate WITHOUT any gasket, just metal against metal.
You can however install "crush" type copper head gaskets in there, if you can find them. Makes for an interesting compression ratio calculation, because without some experience, you don't know how much these suckers "crush".. FYI: they are around 3mm thick when new, and when the head is torqued down to spec, they lose HALF of their thickness. Or close. It's vague, I know, and in most cases you want to be SURE what CR you are setting the engine to run at.
Anyway... this I told you only as a curiosity piece, as you won't be needing these crush rings. They can be used as an alternative to head sealing surface machining, as they cover the possible ridges and un-even spots and offer a straight, soft surface for teh cylinder to seal against. Any imperfections in either mating surface will be "embedded" into the soft copper. GREAT seal! But what you SHOULD do is have the heads flycut slightly my a machine shop to get a smooth, straight sealing surface, and equal depth for all bores. Then use a good sealant between head and cylinder (VERY little of it) or install dry like most people do.
The gasket kits sold today have these in them. Just ignore them. I never use the paper gaskets for the cylinders.
The VW tech bulletin I mentioned in another reply (of which I have a copy at home) was actually meant for the Type 4 engine, but I can't see why it couldn't cover type 1 too, as they share the same basic configuration. Anyway, my way works. Just note that removing th epaper gasket will raise the compression ratio ever so slightly. And using "RTV Silicone sealant" will result in lower CR than using the (in my opinion) proper, thin sealant. Conclusion? Use the rtv silly-cone sealant if you found a paper gasket and decided to leave it out. End result is close to being same CR. (The difference in CR is marginal this way anyhow, I'm just saying it to reveal some of the "finer details" I talked about yesterday :) )
Dunno, but they do. Any possible small leaks will soon be blocked by carbon residue from the combustion process...
The cylinder tops need to be CLEAN and smooth, and teh heads should be machined absolutely flat too. When you torque the head down, the soft aluminum of teh head will give a little, and the hard cast iron cylinder will sink into it a little. Pretty good seal. Look at your old heads, you will see the "image" of the cylinder top imprinted in the head mating surface.
BTW, the thin walled 87 and 88mm "big bore) cylinders will *really* eat into the head... :)
Modern cars all use head gaskets. It's a nice "fuse" in case of engine trouble, and saves the metal surfaces from needing machining during engine rebuild. Or so they think. Aluminum heads suffer from warpage anyway when they overheat (when teh head gasket blows), and/or during improper disassembly and assembly. Machine shop time...
Valve lapping compound is a nice touch that I would recommend (and I do) for large bore cylinders (94 and up) but isn't really needed if the heads were machined flat to get a fresh, smooth sealing surface. That's my route normally and has proven to be enough for stock or mild street engines with stock size cylinders.
Finer details. I just bought this bus because it was a good price, seemed in good condition and was cool to drive. Now I'm learning about how paper gaskets and silicone RTV sealant lower compression ratios, and thinner stuff can raise them. This is a life?
I'm glad I am not the only person using lapping compund to check for a good sealing surface between cylinder and head.The mark left will show a bad sealing surface.I mark the cylinders and heads to keep the mated surfaces together.
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