 Techline-Feb09-H-D 110" CVO -Part II: The valve springs and other issues
Note: This article will continue in the next thread.
This month we continue with excerpts of Chapter 3: H-D 110" CVO from Donny’s Unauthorized Technical Guide to Harley-Davidson 1936-2008, Volume II. (Some content has been altered to fit AIM’s style and format.)
Twin Cam Valve Springs
There are different styles of Twin Cam valve springs. The one to use depends on the application. The dual cylindrical valve springs (#18201-83 outer and #18202-83 inner) sit one inside the other. These are found on 1999-2003 Twin Cams, which have a .473" valve lift. This spring set is one of the few parts carried over from the 1984-99 Evolution motor. Valve spring design concentrates on both closing the valve when allowed by the descending cam lobe and controlling harmonics. We’ve all seen the pictures of a weaving and oscillating solid and fixed bridge in an earthquake. Well, valve springs, even though they compress and decompress, sometimes surge or fibrillate with the rapid movements and demands of the valvetrain. These inertia and momentum forces sometimes compel the confused springs to move opposite to normal. This is why there is an inside and outside spring, each having different coil pressure ratings. The coils-per-inch of each spring is also different to combat harmonics. If one spring surges, the other can, hopefully, counteract it. The lower valve collar sits over the valve guide, which is pressed into the head. Above the valve springs is the top valve collar, which has a hole in its center that fits over the valve’s stem. Two half-moon valve keys (sometimes called keepers) fit into a slot near the top of the valve stem. These keepers hold the top valve collar and the springs below it to a predetermined height. The ridges on the collars are the respective seats of each spring.
The beehive-shaped single valve spring (#18245-02) is found in some 2003 Twin Cam models and is the spring version in use today. The affected year bikes have .471" intake and .474" exhaust valve lifts up until 2007.
In 2008 and later bikes, valve lift was increased to .484". The beehive spring combats harmonics with a progressively changing coil distance and coils that taper to the top of the spring. Both methodologies work as the coils are constantly changing in pressure and shape. The bottom valve collar incorporates a valve seal. When the seal wears, the whole collar must be replaced. The 1984-2003 dual cylindrical springs fit over a separate valve seal that’s pressed onto the top of the valve guide. The Screamin’ Eagle beehive springs (#18013-03A) look the same, but, of course, allow for more valve travel (lift). The SE springs also have higher seat pressures to combat the potentially increased chance for unwanted harmonics due to performance camshafts. The recommended valve lift maximum is .575". Installed to a height of 1.800", seat pressure is about 205 pounds while maximum lift pressure increases to about 360 pounds.
The CVO 110" has triple valve springs, which easily accommodate a .550" valve lift with two traditional coil springs and an in-between flat wave spring. S&S Cycle has been using this method on its performance springs for years with great success. The wave spring interferes effectively with any developing unwanted harmonics. The valve collars are thinner to help allow for the extra valve travel, but have superior metallurgy to compensate for their thinness. The CVO 110 also has valve pockets in the tops of its performance pistons to accommodate the .550" valve lift cams. Stock TC 88 and TC 96 pistons are flat, since the stock valve lift for the 2008 TC 96 is .484", and most TC 88s have a .473" lift.
Valve Spring Clearances
When using performance valve springs in any Harley engine, the clearances between the springs and collars, and the surrounding parts must be checked. The new spring coils may be a little wider than the stock units. They may also be somewhat higher, especially when performance valves are also in use, as with the CVO 110. Performance valves not only have larger valve faces to promote an increase in airflow, but they may also have longer stems to accommodate longer valve spring packs, which give needed clearance for higher lift cams. In the case of the CVO 110 we worked on, all four upper valve collars were touching the inner face of the lower rocker box. Furthermore, the rear intake collar was actually rubbing against the box. We look for a clearance of 0.030"-0.060" between the spring pack’s upper valve collar and the inner face of the rocker box. I could tell that the lower box had had relief work done to it at the factory, but it was just not enough. The dealer had rebuilt this particular engine twice. Why had the dealership technician not checked this tolerance? This is Performance 101 stuff, which probably isn’t taught in standard H-D PhD courses. Anyway, they had three kicks at the can. Steve, my head wrench, properly clearanced the lower box with his Dremel high-speed grinding tool.
Valve Spring Travel
We also needed to check the CVO 110’s spring pack to see if it would accommodate our newly installed .603" valve lift cam and rocker arm ratio combination. The stock CVO cams have a .550" valve lift. The stock 2008 TC 96 valve lift increased to .484" from earlier stock lifts of .471" on the intakes and .474" on the exhausts. This simple measurement, however, takes a little time.
Here’s how to do it: it’s not necessary to install the lower valve collars over their mating valve guide appendages, which protrude into the head, unless the valve seal is part of the collar, as on the 2003 and later beehive valve spring packs. Always use a new valve seal during a rebuild. Therefore, replace the lower valve collar with a new one in this particular beehive application. If the valve seal presses onto the top of the valve guide, replace it with a new one. Then attach the upper valve collar onto the valve stem with two valve keys. Do this with the valve closed on its seat. Measure one valve at a time. You’ll need to hold the upper collar in place, keyed with the valve stem, since the valve springs are not in place.
A Vernier caliper is a slide ruler with a gauge that measures in thousandths of an inch. Use it to measure the distance between the bottom face of the upper collar and the top of the valve guide seal. Our measurements centered around 0.740". Traditionally, we use a clearance tolerance of 0.060", but some manuals are now advising an increase to 0.080". If we deduct the tolerance clearance of 0.080", we can safely use a valve lift up to .640". The manual says .650" and it is safe to use .650" valve lift cams here, as there is lots of clearance. Always check tolerances when doing performance work. Never take any measurement or guideline for granted. In any case, our cams come well within specifications with a .603" valve lift.
I sometimes find that the Screamin’ Eagle catalogs can be confusing, since they usually leave out key pieces of information that I need. In this case, it was difficult for me to discern whether the CVO 110 engines utilize .575"- or .650"-lift spring packs. If it is .575", which will accommodate the CVO SE255 .550" valve lift cams, then our .603" valve lift cams would certainly cause the upper collar to smash mercilessly into the top of the valve guide seal and perhaps the guide itself. Why there are .650"-lift valve spring packs in an engine with a .550" valve lift is a mystery to me. The spring packs may be generic to a series of cams with differing and greater valve lifts, although this is not the precise way to do this. The different valve lift cams require different valve spring seat pressures. For example, a .575" valve spring pack may have an installed seat pressure of 175 pounds with 450 pounds of seat pressure when compressed to accommodate the maximum valve lift of the camshaft. Secondly, a .650" valve spring pack may have an installed seat pressure of 195 pounds with 500 pounds of seat pressure when compressed to accommodate the maximum valve lift of the camshaft. Do not use higher seat pressure valve spring packs when they are not needed. Why would you slam the valves into their mating valve seats harder than necessary? A harder valve return leads to faster wear and less valve longevity. The performance mechanic always matches seat pressures to cam profiles. Less easily leads to parts collision, while too much leads to unnecessary premature wear.
Article continues in next thread. Check back issue for pix and extra information. |
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