Techline-May09-H-D 110" CVO -Part V: Lean running motors/overcooked cylinders (concl)

[admin]

This article concludes this thread.

It’s a pleasure talking to people for whom information and technical knowledge is second nature. As the guys at Axtell say, “A thicker, more stable sleeve than any other cylinder on the market. This 4" bore cylinder was designed to work in harmony with the 4-3/8" stroker motors that have become popular. This cylinder and piston kit has been known to help quiet engines and maintain excellent oil control. All stock components will work because this engine retains stock engine height. The 110" kit comes complete with Axtell cylinders, forged pistons, moly-rings, and MLS gaskets. The reverse dome piston yields a 9.7:1 compression ratio.” So, I’m happier now that I’ve also upped the compression a little from the anemic 9.3:1 to 9.65:1 plus a little due to milling the head gasket surfaces flat with a 0.007" cut, which will have a tiny effect on compression.

Axtell Cylinders
When comparing H-D CVO 110 cylinders and Axtell 110 cylinders, the Axtells look larger. And, in some respects, they are. These cylinders exude an aura of strength, rigidity, and stability. They are confidence-builders for the mechanic looking for superior products to combat the ravages of excess heat. The CVO 110 cylinder liner flange thickness is approximately 0.100" compared with Axtell’s thickness of 0.120". Both the CVO 110 and Axtell internal top liner thickness is 0.150". The thickness of the CVO 110 internal bottom sleeve liner is 0.160", and Axtell measures in at 0.200".

Conspicuously, the cylinder bottom flange length of the CVO 110 is a measly 1.000" compared to the beefy Axtell length of 1.630". The much longer flange length provides more rigidity, support, and stability for both the cylinder and its piston. At Bottom Dead Center (BDC), the piston must stop and change axis and direction. The piston needs all the support it can get in this area because of the super stress with which it must contend. The Axtell cylinders have two fewer cooling fins. The smallest fins at the bottom of the Axtell cylinders are missing, but otherwise have the same area as the CVO 110. The thicker Axtell fins have pronounced, vertical, thick-webbed supports perpendicular to the horizontal fins on either side of the cylinder, which adds extra rigidity and sustainability. These strong cylinders are all business.

The 0.630" longer Axtell cylinder flange must have relief in two places to allow moving and functioning. In mechanical parlance, the term relieve means to cut away interfering metal to allow clearance between functioning parts. On the right side of the flange as it sits in the engine, looking forward from rear to front, an area of the flange relieves to accommodate the piston cooling jets that occupy space in the right-side engine case cylinder spigot holes. A milder cutaway in the center of the cylinder allows connecting rod clearance. The connecting rods turning at BDC rotationally change axis and direction. Their combined angularity in relation to both the flywheel assembly and the cylinders is greatest at this point. The longer the stroke, the more exaggerated this female and male connecting rod overlapping angularity will be. Anyone familiar with building a stroker will immediately recognize this feature.

If you bore the spigots with the top stock case bolt installed, the boring tool will cut into the bolt. This can result in a loss of tensile strength of the bolt, which may allow a possible oil leak. If incorrectly reinserted, this machined case bolt may cause damage to the cylinder flange and mating piston. The stock Twin Cam case top bolt, which is the center bolt between the cylinders, goes through the left case and into a threaded portion of the right case. In other words, the bolt does not go right through both case halves. Axtell quite rightly recommends eliminating this system in favor of the case bolt going through both case halves for superior and more consistent clamping. Therefore, before boring the cylinder case spigots, remove the piston oilers from inside the right-case spigots. Drill the right case’s partial top bolthole with a 1/4" drill bit using a drill press or milling machine. Spot-face the outside of the cases around this hole, so there’s a flat sealing surface. Then reassemble the engine cases following the H-D manual specifications, except for the altered top hole. Insert the new 1/4" bolt and nut with the bolthead on the right-side case and the nut on the left one. Torque this top bolt to 85 in-lbs. (not ft-lbs!).

If machining the top-case bolt, instead of following the above procedure, ensure the bolt positions correctly through the case halves so as not to obstruct the cylinder spigots. If there is incorrect positioning, the bolt will distort the cylinder flange spigots, causing grievous harm to piston and cylinder alike.

The CVO 110 cylinder spigot flange has an outer diameter of 4.180". The Axtell diameter is 4.240". For referencing, the TC 88 is a much smaller 4.055". The CVO engine case spigot holes measure 4.208" for the sloppy cylinder spigot fit of 0.028" (4.208"-4.180" = 0.028"). Machining is necessary for all Axtell big-bore kits. The Axtell flange outer diameter measures 4.240" and, therefore, will not slide into the smaller CVO 110 engine case spigot hole of 4.208" (4.208"-4.240" = -0.022").

After installing the case bolts to specification, place the assembled cases into a milling machine or boring bar. Bore the case spigots 1.625" deep. Do not exceed this distance, as there is a danger of cutting into existing oil passages. Our Axtell flanges measured in at 1.630". The base gasket takes up this discrepancy of 0.005". The 4.000" bore cases in the CVO 110 require boring the spigot holes to between 4.210" and 4.215" diameter to 1.625" deep. However, our cylinders have a larger flange diameter than the prescribed spigot hole size. Our Axtell cylinders have a diameter of 4.240", so we bored out the Twin Cam case spigots to 4.250" to get a snug plug fit. If the cylinders were cast iron or ductile, we would decrease the spigot hole sizing 0.005" to 4.245" since the expansion rate of these cylinders is less than the aluminum casting. For reference only, Twin Cam kits with 4-1/8" (4.125") bore pistons require a 4.310"-4.315" spigot bore also 1.625" deep. Then step-bore the cases from 1.625" deep 0.250" farther at a bore diameter of 4.160".

As for boring and honing the cylinders for proper piston clearance, measure the piston thrust surface skirt 0.500" up from the bottom. On a piston with a skirt clearance, such as the one we’re using in our CVO 110 rebuild, there is a different procedure since clearancing interferes with the above measurement process. Measure the unclearanced piston on the thrust surface directly under the oil ring. Then measure the clearanced piston in the same place to ensure both pistons are the same size. Now measure the unclearanced piston 0.500" up from the bottom on the thrust surfaces. Use this measurement, plus the specified piston-to-cylinder tolerance, to determine final cylinder bore size. Thus, the critical area immediately under the oil ring and ring lands will have adequate clearance. For example, Axtell recommends 0.002"-0.003" clearance with its forged pistons when fitting them to aluminum cylinders, which all Evos and Twin Cams use. This clearance is substantially more than what’s required for Twin Cam cast hypereutectic pistons. Axtell recommends 0.0025"-0.0035" for the same forged pistons when fitting to cast-iron cylinders, which all Knuck, Pan, Shovel, and Ironhead XL engines use. JE Pistons adds in its instructions that specifications are gauged at 72 degrees F. The piston-to-cylinder bore tolerances also depend on bore size with TC 88 and TC 96 bores, which are 3-3/4", and TC 95 and TC 103 bores, which are 3-7/8" requiring 0.0025"-0.0035". A 4" bore like the CVO 110 requires 0.0035"-0.0045". If introducing forced induction, such as super- or turbocharging, or nitrous oxide, additional clearance of 0.001"-0.003", depending on application and, once again, bore size is required. The point is that forced induction requires more clearance.

Always consult your H-D manual for tolerance specifications when using its stock OEM pistons. Consult Screamin’ Eagle instruction sheets supplied with its piston kits when using its aftermarket pistons. Finally, when using Axtell, JIMS, S&S, or any other excellent manufacturer or supplier of quality pistons, always adhere to their specifications, boring and honing instructions, break-in procedures, and oil recommendations, if any.

Conclusion
That’s it for this month. In the next issue we’ll finish my recommendations for how to correct the problems with the CVO 110".

Donny Petersen
Tattoo Tony’s Heavy Duty Cycles
Toronto, Canada
www.HeavyDutyCycles.com