Friday, November 24, 2006
VW - Jugs
(The following was in response to a Vintage VW List subscriber who was given an engine for free. Unfortunately, the engine was a POS with near-zero compression. The fellow wondered if he could simply replace the rings and make a quick sale.)
I'll tell you one thing that don't work. Doing a ring-job on a VW. The fixture to properly hone a VW jug is the size of a milling machine. I think there are two of them in southern California, which could well mean two of them in the whole damn country. The problem is returning the cast iron jug to a perfect circle AT OPERATING TEMPERATURE, close enough to the OD of available pistons to be sealed by available piston rings. To do this, the jug has to be distorted at room temperature to take into account their variable wall thickness (ie, the stud channels in the fins). VW stopped re-manufacturing jugs in the '60's, having found it impossible to equal the service life of new jugs at an economic cost.
If a set of jugs has less than 2,000 miles on them I might hone them and put in new rings. Otherwise, I scrap them. In the long run, it's cheaper.
If your 'free' engine has honed jugs, scrap them.
Jugs in General
First thing you do with a set of new jugs is wash them with clean mineral spirits. (Okay, gasoline, but don't get caught.) When they are perfectly, absolutely oil-free, take a cheap 1/2" paint brush and turn it into a 1/4" paint brush by cutting off half the bristles at the ferrule. That's what you need to get paint down into the bottom of the fins.
Now paint those puppies! Thin coat, please. Flat black Rustoleum in the can, not the spray stuff. Thin it out a little. Do a neat job of it; don't get any paint in the bores or the spigot sleeve, and keep paint off the sealing surfaces. (I didn't say it was easy.)
Let them harden up a couple of days. Inspect for holidays, touch them up. If you don't paint them, they won't last the twenty years and more they can last, when you're running a full-flow oil filter.
Once they are painted get a can of Bon Ami cleanser and scrub the bores. That pretty swirl pattern contains microscopic fragments of carborundum! It is embedded into the soft iron granules that are part of the matrix of cast iron, which unlike mild steel is far from homogeneous. Spend about twenty minutes scrubbing each jug. Use a sponge and lots of cleanser but not too much water. Scrub around the bore, not up and down. When you get done, give them a good hot water rinse, and I mean too hot to touch. Get the whole cylinder hot. Wipe them with a known-clean rag or towel. Spray the bore immediately with WD-40 (a San Diego product, by the way and a nice stock to own) and put them in a warm oven or drying box (ie, light bulb in a cabinet) to insure all moisture is driven out. When dry, you can oil them lightly and bag them, or store them back in their box if the cardboard is dry.
The hour or so you spend scrubbing your jugs adds about a year to their useful life but more importantly, saves you several hundred dollars in oil over the life of the engine. Those microscopic bits of carborundum come from the manufacturing process and will remain in the jugs, being polished deeper into the walls or taken up by the rings, unless you remove them. The pumice and diatomatious earth used in Bon Ami brand cleanser has a hardness of about 4 on the Mohs scale. Carborundum is 9+, right up there with bort, industrial grade diamond. It don't go away. Cast iron is harder than pumice or diatomatious earth, they do go away. Indeed, if you do a good job, there won't be any for the engine to flush away.
So why do people leave abrasives in engines? Because it lets the rings wear in almost instantly. If you're building engines on an assembly line, it is a justified compromise. Jugs on aircraft engines are cleaned with a series of hand-scrubbings and ultrasonics. They can last about 4,000 hours before catastrophic failure (which is why they are normally overhauled at about 2,000 hours). 4,000 hours on a Lycoming is the equivalent of about 300,000 miles on a in a VW.
(So why don't we use ultrasonics and all that high-tech stuff on veedubs? Some guys do! But the main reason is practicality. Your main bearings dictate the maximum useful life of your engine and right now, they're only good for about 150,000: they lack the surface area to survive longer. And it makes no sense to put 300,000 mile jugs on a 150,000 mile engine. The hidden lesson here is that engines are harmonious things, their parts work -- and wear -- in concert. Put new, tight jugs on a worn lower end and the poor thing won't last a year. Even worse, it's liable to suffer a catastrophic rod-bearing failure. But when new parts wear-in together they will give you plenty of warning as the end of their useful life approaches.)
No, you can't use that can of Comet under the sink. It contains chlorine, something you don't want anywhere near cast iron. And don't worry about the rings seating. Follow the break-in procedure I mentioned; don't be afraid to rev that puppy up. (Think of it as birthing pains.)
A set of VW jugs includes new pistons, pins & rings.
First thing you do, you sit down with one piston, take the rings off one at a time, make a sketch of its profile, mark down if its the top or middle ring, which side up, etc. You'll see lots of different types so don't put your faith in a book. Use the set you have as your book.
Make a good drawing. Keep it clean. Keep it in a notebook and the notebook in a drawer. It's like a penny savings account. You think it's just pocket change but when you need it, it turns out to be a lifesaver.
End gap should be okay but it only takes a couple minutes to check the whole set and you've got to take them apart anyway for balancing, cleaning, etc. So check the gap. Keep the rings together by sets; put them into baggies with a paper tag telling what piston they came off of. Mark the pistons clearly, either with a scribe or a punch. Mark the jugs too -- sometimes you find a wild one in a set, a couple thou larger or smaller than the others, with rings gapped to match. At the factory, they dealt with thousands of jugs from conscientious suppliers. Aftermarket stuff runs from junk to sublime, you have to decided what you've got.
Boring subject. Big bore means opening up the case to accept larger spigots. Type IV is 100mm and up. Biggest practical bore on regular bug engine is 94 for a late case, 92 for early (and they'll still leak), in the real world don't go over 88 & 90 (old & new). It has to do with the compression seal and how much 'shelf' space is left after you open up the bore. The jug has to seat on a flat, parallel surface to insure no oil leaks, fretting, etc between jug and case. Open the case too much, not enough sealing surface, engine goes to hell. And not just from leaks. There are purely mechanical considerations here as well. The total stress of jugs, studs & heads is concentrated at the base of the jugs. The jugs will pound into the case during the first five-six hours of running. Smart builders do it on a test stand, dismantle tin, re-torque. Do it again about 50,000 miles, maybe pull the heads then, too. Don't gasket the jug/case joint, use Permatex, the non-hardening kind (light tan?) or that new gray RTV gasket stuff. Paper gasket is a joke between cast iron & magnesium subject to heat cycles (as VW learned). Best builders O-ring the spigot bores. Tricky to do (needs special tooling) but works like a dream. (See Larry Pauter's all-billet aluminum cases. About six grand each.)
J.C.Whitney Big Bores
I've never bought any from them. I've seen too many different brands, too many unbalanceable sets. You're going to have to trust to luck and understand it's on your shoulders. That's why balancing becomes so important. You are not just assembling an engine, you are manufacturing it.
If the things claim to be Big Bore but also say they don't require machining the case, walk on by. The biggest stock bore was 85.5mm. The only way you can fit a bigger jug into the stock spigot hole is to make the skirt and cylinder wall thinner. Thin sections of cast iron don't do well when subjected to rapid heat cycling. Such 'big bore' jugs distort, leading to sealing problems and uneven wear. They certainly don't hold up as well as their heavier walled cousins.
Standard Size Jugs
Regular jugs have stricter standards in both material and workmanship. I'd be more willing to try a mail-order set of standard jugs. I've a hunch the odds would be on the side of getting better quality than the so-called Big Bore things.
(After dismantling the free engine and finding the cam was off by a couple of teeth, he wondered if he could simply button it back up without replacing the jugs, balancing, or replacing the exhaust valves & guides.)
Run What ya' Brung!
Sure, it'll run. Might even last a year or two if you're careful. But it won't be sweet. Its life is 90% over before you begin. If your only option is to sell the thing to a kid, I guess that's the way to go. But you must understand that once you touch something with a wrench you own it. First sign of trouble, the kid's going to come knocking on your door. Or maybe his dad. Have that thing sitting out in the drive, dripping oil, swallowing a quart a hundred and blowing smoke all over town, everybody knows. At least, all the mechanics do. (Big scarlet 'M' sewn to your shirt? Same thing.)
Unless you're all packed and ready to move I think it would make real good sense to build the best engine you can, make sure the buyer understands any corners you've had to cut and the down- stream consequences. Do a good job, it's going to be around for a long time. And every time people see it some of them will remember who built the engine.
Come on! A week ago you didn't have a spare engine, now you do. Make it the best engine you can build. Every engine will teach you something; every engine will instill habits. You want to learn the good habits, have them teach you the right stuff. And none of the really good mechanics die rich.