The Foundation Of Your Engine From Borowski Race Engines Part I

The Rottler CNC block machine is capable of performing almost all cylinder block tasks. Here, the block is setup so that the decks can be machined.

The Foundation Of Your Engine From Borowski Race Engines Part III

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Over the past couple of issues (Part One and Part Two), we’ve looked at most of the steps necessary to carefully machine and blue print a cylinder block for a given application. We also looked at how Borowski Race Engines makes use of CNC technology to machine components. But there’s more to it than you might think.

Once the four axis Rottler F68A machining center is done, the cylinder block can be honed. Borowski Racing makes use of another Rottler machining center for this job. It’s an F85 vertical CNC hone.

According to Borowski’s Ken McCaul, “Honing is the final machining step in preparing an engine block for assembly. Its importance to the build quality of a high performance engine cannot be overstated. The following discussion and video will explain and demonstrate the basic details so that motor-sports enthusiasts can gain a deeper understanding into this aspect of engine building.

“The three key objectives of the honing process are to:

1. Impart the correct surface finish to the cylinder walls (as measured by a profilometer),
2. Bring the cylinder to the correct and uniform diameter (as measured by a dial bore gauge), and
3. Through use of a torque plate, ensure that the cylinder will be perfectly round once the cylinder heads are torqued onto the block.

“These three objectives can be achieved on a CNC hone (with a torque plate) to a far higher level of precision compared to what is possible with a manual hone. A CNC hone using diamond abrasives is able to perfectly replicate the dimensions and finish of the first cylinder in all subsequent cylinders as the wear of the diamonds is imperceptible from hole to hole.

“Cylinder walls require honing in order to allow the engine oil a means of both adhering to the cylinder wall and flowing up and down. The flow path is achieved by the use of a cross-hatch pattern while a specific surface roughness is needed for given piston ring sets and end uses (for example: naturally aspirated or boosted). Because honing removes metal, this process determines final cylinder size and shape. The angle of the cross-hatch is a critical parameter and it’s a function of hone stroke rate and RPM. Surface roughness is determined by the combination of abrasives used in the honing process and the metallurgy of the engine block. Aftermarket blocks will require very different abrasive combinations than OE blocks as aftermarket blocks typically use harder, higher tensile strength alloys.

“What surprises many people is that engine blocks distort when cylinder heads (or torque plates) are torqued down. When the engine blocks are bored, there is no such external stress being applied. The perfectly straight cylinder wall coming off our 4-axis mill is no longer straight after cylinder heads or torque plates are installed. In the video, you will see that there are resultant tight spots which the CNC hone removes by dwelling for additional time.

“In summary, a CNC hone, dial bore gauge and profilometer can produce a near perfect sizing, shape and finish in any given cylinder and replicate that in all that follow. This will have wide ranging ramifications to the completed engine's performance in areas including power, longevity and oil consumption. The results achieved using this level of technology simply cannot be duplicated using manual equipment.”

So, what’s a Profilometer? McCaul explains, “Surface finish is measured using a profilometer. These instruments report Ra (average roughness), Rpk (average peak height), and Rvk (average valley height). The manufacturer of the piston rings will typically specify their recommended surface finish for a given end use application. They may also recommend plateauing as a final honing step which, in effect, knocks the tops off peaks. This remove jagged surfaces, aids ring seating and prepares an ideal bearing surface over which the rings can travel.”

Check out this link to a video Borowski Racing produced on honing a cylinder block, using the above equipment.

Once all of the machining tasks were complete on my cylinder block (obviously shown here), the folks from Borowski Racing completely cleaned the cylinder block. Next up they painted the block, installed a set of brass freeze plugs, installed the cam bearings and finally, installed all of the oil gallery plugs. Just as a sidenote, they also install a test camshaft in the block once the bearings are installed to ensure fit.

Finally, the block was bagged, reinstalled in the original Dart shipping container, strapped to a pallet and shipped. Tracking numbers are provided and you can watch it every step of the way. By the way, Ken also supplied a bunch of photos of the block right up to the palletizing process. It’s a great reassurance for something costly and in these times, rare.

Just to provide you with a heads-up, I have a decent selection of engine building and measuring tools on hand. Before the article was even penned, I measured everything possible on the cylinder block. And yes, the specs are right on the money. Keep in mind, there were several special requests to suit my combination (finished deck height, lifter bore dimensions were two of them). Borowski Racing handled it all easily.

Building blocks? Bottom line here is, these guys really make it easy. For a closer look, check out the accompanying photos.

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The Foundation Of Your Engine From Borowski Race Engines

The Rottler CNC block machine is capable of performing almost all cylinder block tasks. Here, the block is setup so that the decks can be machined.

The Foundation Of Your Engine From Borowski Race Engines

The brains of the Rottler F68A is right here. Basically, the operator sets the various parameters (program, mode, etc.), and the CNC machine does the rest. As noted in the text, Borowski regularly upgrades the equipment, and that includes software, electronics and hardware.

The Foundation Of Your Engine From Borowski Race Engines

Our combination mandated a deck slightly less than the stock 9.800-dimension. The Borowski team accommodated us with an exact number.

The Foundation Of Your Engine From Borowski Race Engines

When I verified the final deck clearance (once the block was in my own shop), it proved to be dead on the money.

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