Thursday, November 23, 2006

VW - Engine Break-In

I think I need to re-check the head-torque before I run it... Is there a preferred pattern to loosening the nuts?

If the engine has never run, you’re probably safe in unbolting it willy-nilly, but I tend to work form the outside in, top to the bottom. Make everything finger-loose. Check for ‘tight’ nuts. Don’t disturb the washers; there should be sealant under them. With everything backed off, use MEK or Loc-tite’s ‘Klean-n’-Prime’ on the thread between the nut and the washer (you’ll need the little nozzle, or a laboratory spray bottle, or Q-tips, or... I use one of those lab bottles).

If you really can’t get in there, take off the nut so you can get at the stud. If you got tight nuts, replace them or chase them.

When you like the way things fit, put a dot of medium strength Loc-tite on the primed thread right up by the washer, run the nuts up finger tight plus a twist ‘o the wrist, start sneaking up on the torque. I resent my clicker three or four times, starting at about 12, ending up with 25, 26, or 27 ft/lbs, depending on temperature, type of crankcase, direction of the wind... :-) If it’s an early case with thick studs, use 23 ft/lb. Later cases with stud-inserts and the small (8mm) studs have a lower torquing spec, but never exceed 18 ft/lb. After retorquing the new engine, let it sit over night then check the torque again before you close it up. Just check for the last value; you’re looking for ‘lazy’ studs that have elogated as a result of torquing.

To me, First Fire doesn’t really count as part of the break-in, it’s merely the final step in the assembly. I get it started, pick it up to about a thousand rpm, let it run until it has a certain ‘hot’ smell, never letting the speed settle, up and down a little, senses very busy. Mebbe three minutes, max. Oil is 10W-Something; thin. Then I drain it out into a clean container, go off and think about things for a while. Slowly decant the flushing oil, drain the last little bit into a glass dish, slosh it with MEK like a placer miner looking for gold.

I’ve just cleaned the inside of the newly assembled engine. It really isn’t a part of the break-in cycle. Back when I was building a lot of engines, I might even use the same flushing oil on two engines, or put the same oil back in the engine, if no residue was found (but I usually throw it away; about four bucks. Cheep).

After it’s flushed, I re-check the valves and timing; anything that might have kicked loose; anything I might have overlooked. (Yeah, me too.) Then I refill it, fire it up, warm it up . . . never takes long with a new engine . . . bring it up to about 2,500, hunt around that speed range while I’m crawling all over the thing. It’s on the test stand, I’m not wearing ear muffs. I’ve got all the sensors cranked up to nine; smell, sight, hearing, hearing, hearing, touch. I overload in about fifteen minutes, have to shut it down and think about it. I might run it a little more to get more data on a particular thing but most often drain it, let it cool down. You always throw away this oil; it’s your first break-in cycle. Check it for chunkies of course. You’re real interested in any drips at this stage. There shouldn’t be a single one so if you see one it usually means the thing goes back into the shop, gets torn down. This is about the worst thing that can happen. And it does, but no oftener than once in every hundred engines or so. And yes, it’s usually my fault. Just plain damn stupidity or carelessness, like letting my cuff drag across the parting line just as I’m closing the case; dumb stuff. All that work ruined. But I’m getting better at it :-)

I usually keep an engine on the test stand until the rings are well seated and the temperature comes down; about six hours, on average. Then too, I tend to build ‘tight’ engines; you have to be careful breaking them in, giving them plenty of time to cool down between runs, keeping the oil changed even with the filter installed.

After a couple of hours you and the engine are pretty well acquainted; they’re all a little different. You’ve got the carb(s) tweaked down to the fine numbers, the thing will start on the first revolution of the crank, the case is dry, the blow-back is next to nothing and it’s starting to develop its own unique sound that will allow me to identify it years from now, assuming the muffler and intake are the same.

An apparently mindless part of breaking in an engine is seating the rings. We call it Bumps & Grinds. You slowly open the throttle to about 2500 then drop it, just let it shut. Anyone hearing you would think you’re just playing with the poor thing, up and down, loud then quiet. You’ll be wearing your ear muffs by then; you’re breaking it in, not checking it out. You never do any of these things for very long; mebbe 20 minutes at the outside, more like fifteen, then shut it down and go do something else; let it cool off. If you’re doing more than one engine you’ll have to dismount it hot, put it back on its scooter, put the next customer in the chair. (I’ve done as many as five engines for one customer, all as a series. Five is mebbe one too many for one man at a time.)

You keep records. If you’re using a test stand you’ll usually have a Hobbs meter; a kind of clock. If not, just your watch and and a note book. Doing one engine, you can’t get too confused.

The engine will start flattening out its curves after five or six hours of running. Fuel consumption will have dropped down to some steady figure, as will the temperatures. Oil pressure will have come up. You’ll want to verify that with a wet & dry compression check and a leak-down test, if you’ve got the harness. You will have to take a last look at the valves . . . unless you’re running hydraulics.

Breaking in an engine with hydraulic lifters is a little different than with solids, first because the valves probably won’t tell you anything at all. They’ll always be running a perfect zero-lash. But hydraulics in a freshly machined magnesium crankcase can generate a bit more ‘mud’ than with solids, or even hydraulics in an aluminum crankcase. So you take it easier at first, accumulating about 45 minutes of run-time before you start seating in the rings. Understand, the engine has never been allowed to sit about at an idle. Breaking in an engine means wearing-in an engine; it is a kind of controlled friction. But the mud does bad things to the minute clearances of hydraulic lifters, which are having an especially hard time because the engine is running hotter than it ever will again. So you do more short runs and longer cooling-off periods when you break-in a Type I fitted with hydraulics. That is, during the first two to three hours. After that, there doesn’t seem to be any difference, except the hydraulic engine will run quieter. And a little more efficiently, but you won’t see that until you’ve got mebbe six hours on it, by which time it probably will have been installed in a vehicle and roared off down the road.

Air-cooled engines have pretty loose tolerances compared to their water-cooled cousins. And with the inherent rev-limiters built in the the VW carburetion, cam and valves, you could run a factory-built VW right out of the box and not have any problems. That was then. No telling what kind of an engine you’ll wind up with nowadays. It’s best to pretend it’s a custom-assembled one-off design and break it in accordingly, taking lots of time to correct any problems, let the thing cool between runs (and I mean at least an hour), change the oil at least twice in the first six hours, and doing anything else you can think of to ease the birthing pains.

The complete wear-in cycle continues for about a hundred hours, after which the engine’s curves will stay substantially the same for the next thousand hours of engine operation. (Ed.Note: In a vehicle.) Understand, the engine is still wearing, still experiencing friction. But now it is wearing-out, not in. The wear during its service life will be very uniform and consistently small, but after a thousand hours or so you will see the first signs of terminal wear from the valves, the weak links in the VW system. The lower end should be good for at least 1,500 hours and will probably run 2,000 without a whit of trouble (say, 100,000 miles) assuming you’re running a full-flow filter. Beyond that, it will depend on if you’ve got a shaft seal, how well you’ve done your maintenance, your particular driving habits, and the vehicle in which the engine is installed, with early buses providing about half the service life of a sedan engine, later buses falling somewhere between the two.

Given the fact this is your first engine, I’m really looking forward to you having a successful installation. Please keep the list up to date on your efforts. Although you may not believe it, your success will cause of at least three other subscribers to take the plunge. It isn’t just one engine you’re bringing to life here but four.

1 comment:

Anonymous said...

hi from athens , greece :-)

your post, is the best info page i found, about the break-in process for vw aircooled engines.
It is a week now that i am searching and reading pages @ web, about the breakin for vw engines.
Your page is the best informative page -tech point per tech point, hour per hour- i found all these days.

thanks for all the work you are doing :-)