CIMA/MAHLE Piston and Cylinder Tips

In the September 2010 issue of Hot VWs magazine we quizzed three Pro VW engine builders to get their secrets!
By Dean Kirsten | August 1, 2016

Photos by Dean Kirsten

The air-cooled VW engine is very unique within the automotive industry, in that we nearly all use a standard bore piston and cylinder. Unlike most automobile engines, which can be, and usually are, bored over-sized and fitted with larger pistons and rings, the VW uses, for the most part, standard bore parts. While we do use different diameter assemblies, they are all basically a standard size and rarely, if ever, are over-sized rings or pistons used (or available). For most of us VW engine builders, we are used to opening up a box of new pistons, rings and cylinders, cleaning and lubricating them, and installing them to the short block. Done deal. But not all assemblies are dead-on correct out of the box, and while the quality control is decent among most lines, there are things to look out for to insure that your next engine build goes without a hitch. To get a few pointers on what to look out for, we quizzed three different top VW engine builders and asked them to give us some tips on installing new pistons and cylinders on a VW engine. We talked to Dave Kawell of Kawell Racing Engines (Friendship, TN), Jason Lauffer of VW Paradise (San Marcos, CA), and Anibal Chico of Chico Performance Racing (Arcadia, CA).
The top compression ring found on this particular Cima/Mahle 90.5mm piston, is marked for correct position. In this example, this Mahle ring has been embossed with a large “M” to show which is up. If you look closely at the piston crown you will see that the actual piston size for this 90.5mm bore is 90.43mm. This number will vary depending on when this piston was made, as Cima/Mahle is known for production changes.
According to Dave Kawell, the one area that he pays particular attention to are the ring gaps, as many of the parts he comes across are too tight. This problem can cause a new engine run too hot, and be a bear to turn over once it is warm. A good telltale sign of tight gaps is to closely examine a well-run engine’s ring gap ends under a magnifying glass, to see if they are shiny. If so, they have been touching once the engine is warmed up as the rings expand, which is a big no-no. Dave likes to see gaps for these piston sizes between .016-.018-inch, .020 for a turbo engine (due to the extra heat that exists). Kawell continued as he makes sure the cylinders are extra clean and free of packing lube, but does add a small amount of assembly lube (Childs & Albert works well) to the piston skirts during assembly. Finally, he positions the ring gaps; top ring at 9 o’clock and second ring at 3 (in line with the wrist pin), and the two oil ring rails at 12 (lower) and 6 (upper).
Cima's second ring has a notch, which should face down when installed.
The next engine builder we talked to was Jason Lauffer. Jason told us that nearly all Cima cylinders have to be clearanced at their base, due to interference with the head studs (8mm and 10mm), which can prevent the cylinder from sitting flush on the deck. He increases clearance on a mill, but this can be easily done with a small Dremel tool. When asked about ring gaps, he likes to keep them between .014-.016-inch (which is very common out of the box), but increases them to .018-inch in engines with more compression/power. Ring gap locations goes like this; compression/top ring at 12 o’clock, second ring at 3, oil ring expander at 12 o’clock, oil ring rails at 9 and 3 o’clock. Jason likes to lubricate the cylinders lightly, and then wipes the excess off with a clean rag (for engines that will be run-in right away). For engines that will sit for a period of time, he usually adds oil to the top of the cylinder to prevent oxidation from building up on the bore.
Measuring the ring gap with a feeler gauge. You should check each cylinder at both the top and bottom to ensure there is no taper in the bore (gaps at both ends should be the same).
Our third engine builder’s input came from Anibal Chico. With the volume of engines that he builds, he rarely finds ring gaps that are way out of line. But for the most part, he likes to see gaps between .012-.014-inch, but more on turbo applications. He likes to position the ring gaps at; top ring pointing straight up (12 o’clock), the second ring at 6, and oil rings at 9 and 3 o’clock. For engines that he will run right away on the dyno, he only adds a spray of WD-40 to the piston skirts and rings, and keeps the cylinders clean and dry, using only fast-drying brake cleaner and a clean rag. For engines that will not be running for a long period of time (possible project delays, for example), he adds more oil to the cylinders for protection.
When we talk about where to position each ring gap, we are referencing the hands of a clock. If we say the top compression ring should be positioned at 12 o’clock, then, it should face straight up when installed. Each piston comes from the factory with an arrow stamped on the crown. These arrows should always point toward the flywheel.
Each of our engine builders pays particular attention to cylinder cleaning, to remove any honing oil and packing grease that usually exists. Rarely do these cylinders need honing, unless a different ring package is going to be used. Cima rings are known for easy break-in, and they do a reasonable job of sealing up with modest compression and rpm.
A Cima 3-piece oil ring uses a lower expander, which has painted ends (red and green). These ends should butt against each other and should NEVER overlap!
Chico likes to use a JayCee ring compressor.

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