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One ring to seal them

By Kip Woodring

“Plus ca change, plus c’est la meme chose.” In case you don’t recognize this truism in its native form, allow me the attempt at a rough translation into Harley-speak.

Almost 20 years ago, Evolution Big Twins developed a propensity to leak oil from the base gaskets. Funny (odd, not ha-ha), since they had been on the market for years even then, with no sign of this problem in evidence. Turned out, certain materials in the composition of the gaskets (some say asbestos) were banned by the feds about then, and those few alternative materials left to choose from at the time sucked—so they blew! The ensuing scramble to stanch the bleeding lasted longer than it should have, and involved several tries at different gaskets, new cylinder studs, new head torque sequences and methods, tools and techniques to ensure the mating surfaces were as flat as could be and more. But in the end, there was no admission that a slight redesign of the interface between case and barrel would have been the best solution. Instead, with no little irony attached in light of subsequent developments, the “fix” turned out to be rather simple. For all practical purposes, a rubber O-ring was overlaid upon and integrated into the gasket—problem eliminated! These so-called “print-o-seal” type gaskets still serve well on Sportys, which never suffered as badly as Evo Big Twins anyway, but when the Twin Cam came on the scene in 1999 a notable design feature was the absence of pesky base gaskets altogether! By that I mean the flat-sheeted material, laying on flat metal surfaces, simply clamped in place by torque in the top end stack, was ditched in favor of a more reliable arrangement: literally, an O-ring of certain dimensions, resting in a machined groove of complementary (and critical) dimensions in the crankcases—elegant and foolproof! At least in bore sizes used in 88-inch, 96-inch and even 103-inch displacements.

A fine point about fat O-rings
Apparently, as bore size approaches four inches and barrel spigots in factory crankcase castings get thinner to accommodate bigger steel liners, something upsets the nifty equilibrium of the “standard” arrangement. There can be little doubt that heat (or more accurately the inability to dissipate it) has a lot to do with it. It’s just plain tough for thermal loads from high performance air-cooled engines to move from the middle of the cylinder to the walls, so the heat can be transferred to the air via cooling fins—too far from the action—or not enough fin area—take your pick. That aside, the fact is early 110-inch Twin Cam engines are at risk for (perceived) base O-ring leaks, whether purchased as Screamin’ Eagle/CVO models done by the factory or as kits from the SEPP catalog and done by a shop or as a DIY project. Why that should be is a bit like the old “which came first—the chicken or the egg?” riddle.

Lessee—first, we put the O-rings in the grooves. Then we put the barrels over the O-rings. After that, we lay the head gaskets on top of the barrels. Then we put the heads on. Next comes the important part—head bolts on and carefully torque to spec. There’s more, but let’s stop with that torque business and its significance. The integrity of the top end “stack” is at stake obviously, so precision is paramount for that reason alone. However, things like stretch in the cylinder studs and pressure to seal the gaskets and O-rings are a critical part of the deal as well, and subject to change with temperature and load. There’s a great deal of difference in what the sealing elements in the stack have to cope with during, say, cold starts under no load versus drag racing at smokin’ hot temps. The barrels grow and shrink with every single “cycle” from cold to warm to hot and back again. The metal changes dimensions and shape too, but what really takes the hits (and the heat) over time is the head gasket. They get “scrubbed” constantly with use of the engine and once they’ve had enough, even though they might not “blow” in the textbook sense, they can easily destroy the integrity of the “stack” when they can no longer seal properly at any given temperature or under all conditions. Once the head gasket goes, crazy as it may sound, often the evidence is found at the base of the cylinder in the form of a leak. This is partly because the top of the barrel is a lot hotter than the bottom, especially if the head gasket is “chuffing” a little combustion heat out onto the head and cylinder like a tiny blowtorch. If the disparity in growth or shape between top and bottom is sufficient because of this, the bottom of the cylinder may well have insufficient clamping pressure and let oil sneak right past those O-rings. Of course another theory is that over time O-rings of less than superior resistance to either heat or (of all things) the effects of oil, might just get all stiff and “plasticky” or even crack and allow those base leaks. The point is, both the head gaskets and the base rings are equally responsible for keeping the top end stack stable and leaks under control. So (chicken and egg scholars) which really happens first—and does it matter?

What’s clear from this is the need for some serious precision when case-cutting factory parts to accommodate a 110-inch conversion, particularly the dimensions of the grooves for the base rings! What’s less obvious is the decreased distance from the cylinder flange to the studs, yet in many ways that’s a critical factor as well—especially when things get hot and heavy! (Having practically no distance between studs and case holes on 113-inch engines might be why they use gaskets instead of rings.)
For 88-inch, 96-inch and 103-inch engines the base rings are, in fact, O-shaped—as indeed they were until recently for the 110-inch engines as well. Current thinking seemingly involves a “slippery” graphite head gasket to allow for thermal expansion of metal surfaces on the head and cylinder top, while minimizing “scrub” of the gasket itself—and of course, filling the groove in the case with more than the rounded, slender edge of an O-ring to seal the bottom surface of the cylinder. By using a square-ring (or quad seal, if you prefer) with a wider surface, the gain is about 400 percent more sealing area. This should do the trick all right!

Squares and graphite—health food for Harleys?
In spite of the fact that “squares and graphite” calls to mind some weird breakfast cereal (or chicken feed), we’re really talking about what the factory has done to upgrade both the base rings and the head gaskets for 110-inch engines. Beginning April 29, 2008, The Motor Company began building 110-inch engines with new square base rings (#11907) which aren’t an “O” any more and appear (judging from the amber/orange coloring) to be a Viton-type material. This upgrade came on the heels of arguably more important new graphite head gaskets (#16801-07B) that were used in engines built after March 3, 2008. A very nice one-two punch! Owners of factory-built 110-inch H-Ds constructed after these dates have little to fear regarding leaks and the same is true of kits to build your own 110-inch engine. Meanwhile, The Motor Company has done the right thing for owners of older factory 110-inchers. Most of you know who you are and what H-D is offering, but for those few who don’t, check with your dealer for details regarding bulletins #M1225A (Product Program 905) and #M1226 (Product Program 906), which in essence provide these upgraded parts (and in some cases a lot more) for older CVO/SE factory-built 110s. These upgrades are free, but not forever. There’s a two-year time limit from the date these programs were established—call it August of 2010 give or take—so the clock is ticking! Mind you, there’s absolutely no safety issue here, so this is not a recall, and it applies to owners of 2007 and early 2008 model motorcycles equipped with “Registered P&A” or “Custom Coverage” (dealer installed and warranted) street-legal Screamin’ Eagle 110 c.i. engine kit numbers including: 29844-07, 29845-07, 29866-07A, 29909-07, 29910-07, 29912-07, 27800-08, 27801-08, 278802-08, 27803-08, 27804-08, 29844-08, 29912-08.

As for the folks who built 110-inch engines from kits and did not have them registered, or used kits that weren’t street-legal, or aren’t liable to get any help from the factory for whatever reason, best advice there would be to buy yourself a new top end kit (#17349-07), then wait and see. Better to have the parts and not need ’em than need ’em and not have ’em, after all. Besides, this whole situation doesn’t amount to anything like the problems with Evo base gaskets, back in the day—meaning it affects a small percentage of a small percentage of Harley’s production. There is one final (and curiously) noteworthy item for those who’d like to speculate further on big-bores and gasket integrity, and it is this: The biggest of them all (the 113-inch kit) doesn’t use base O-rings, it reverts to base gaskets. The 113-incher appears to eschew the use of graphite in its head gaskets as well. It’s not now, nor is it ever likely to be, even remotely street-legal. The 113 has a bore of 4.06″ and likely makes more power than a 110 ever will—and yet?

One can only speculate so-called “race engines” will be used far less, and taken apart (for other reasons) so frequently, that terms like “warranty” and “upgrade” become meaningless in that context. Or, to put it another way, most of the folks who simply must have a hot 113-incher couldn’t give a damn if it leaks a little, nor fret when they occasionally tear into it. (Sorta the opposite of the types who want 100,000 miles of pristine service with only routine maintenance.) I’d like to know what you think, but to me, it all boils down to the axiom we started out with: “The more things change, the more they stay the same!”

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