2007 Cayman S 987.1 – Full Engine Rebuild – Inspection

In the article here, I discussed the tear down of the engine to its basic components. Next I’ll discuss my inspection of the critical parts. This is a new to me 5 owner car with about 108k miles on it. My reasons for tearing the engine down are discussed in the article here.

The most obvious visual issue that I noted was the condition of the main bearings on the crankshaft. They haven’t failed per se, as the bronze or copper base material is not showing. But they don’t look pristine either. So chalk up one area where I am glad I tore the engine down, as these bearings are definately going to be replaced. BTW, what you are looking at is the crankshaft carrier, laid open in its two parts. This is a truely impressive casting, with 7 crankshaft bearings i.e. each cylinder is straddled by a crankshaft bearing. About as rugged and stiff as they come. I believe the dark scalloped areas surrounding the bearings are a non-aluminum material, probably a carbon steel with a high modulus of stiffness. You can also see that each main bearing is captured by a pair of bolts. The narrow slots in the bearings are where the oil is injected into the bearing interface.

The crankshaft carrier with the intermediate shaft on top.

The next bearings of interest are those on the big end of the connecting rods. Compared to the bearings on the crankshaft these looked pretty good. Nevertheless, they will get replaced. I don’t have a good picture, you’ll have to trust me.

Of course, the big topic of interest with these engines is bore scoring. After cleaning up the bores, I found no evidence of bore scoring. The first picture of the 1-3 side is a bottom view. The picture of the 4-6 side is a top view. Using my finger, there was a negligable “ridge” at the top of the bore.

I cleaned up the crankshaft and inspected it. To my eyes, it looked very good.

I also took a look at the 4 camshafts. No issues were noted. I moved on to some physical measurements. I have posted these below. In summary, the crankshaft measurements were very consistent. Not that I expected it but there was no journal that deviated in size from its bretheren i.e. no journal had been ground.

The most interested measurements were those for the cylinder bores. This 3.4L engine has a nominal cylinder bore of 96 mm. My measurements are all in inches. I used a “bore gauge”. It is designed to easily find the true maximum diameter point, as it uses 3 points of contact. It does not measure diameter directly, rather you can find the maximum diameter and set the dial gauge to zero. From there it shows the deviation. Generally speaking, my cylinder bores, which I understand started life as perfectly round holes, had worn themselves into an oval shape, especially at the top of the bore. Ovality ranged from +0.0025″ on cylinder 6 to 0.0045″ on cylinder 2. The “clean” area of the bores measures roughly 3″ down into the bore i.e. the stroke. At the bottom of the stroke, the ovality was not nearly as pronounced, with a maximu ovality of 0.001″ on cylinder 4.

One additional indicator of potential future problems, if not addressed, was the wear on the skirt of the pistons, especially bank 4-6. There is a coating on the skirts and it is definately showing signs of distress.

So if there is a “smoking gun” here, it is the ovality of the cylinders and the wear on the pistons. This is not surprising in that there is a “thrust load” on one side of each piston with every firing stroke. Although all piston/connecting rod/crankshaft type engines have these loads, it’s a harsh environment, especially as power levels rise. I will pursue getting this “fixed”, which for these engines generally means the introduction of new cylinder liners.

Regarding the cylinder heads, there isn’t anything there that I can readily measure. I will leave that evaluation to my selected machine shop. In general, I would expect the valve seating surfaces to be ground and possibly some or all of the valve guides will be replaced.

So that is it as far as my mechanical inspection is concerned. I did not find any broken parts. No metal or plastic bits resting at the bottom of my oil pan. Which is not a surprise, as the car was running well. But you never know. Now I am in the process of selecting a machine shop. And I am thinking about which items on the engine that I want to replace, mainly to improve reliability. FWIW I am not contemplating any performance upgrades such as increased cylinder displacement or head work. I just want to get the engine back to a good baseline, as it left the factory. More musings on where to go next will be left to an upcoming article.

Below are some spreadsheet images of my measurements. I am not a machinist! My instruments are not calibrated. Take these with a grain of salt. When you see a number stated to 4 decimal places, rest assured the final decimal place was just an estimate. As noted above, I am mainly looking for deviations. I used a fairly decent bore gauge and a set of Starret micrometers that I found years ago dragging around after my wife in an antiques store. My only significant find in years of visiting antique stores! They are Starret but your guess is a good as mine regarding the state of calibration.

Top, axial is measured at the top of the bore (below the ridge) parallel to the crankshaft axis.

Top, lateral is measured at the top of the bore (below the ridge) perpendicular to the crankshaft axis.

Bottom, axial is measured at the bottom of the bore stroke parallel to the crankshaft axis.

Bottom, lateral is measured at the bottom of the bore stroke perpendicular to the crankshaft axis.

EDIT: I forgot to mention that the coolant pipes leading up under the car and the water pump appeared to be very clean with no deposits, discoloration, etc. I did replace the coolant hoses under the front engine mount last year and added fresh, genuine Porsche coolant to the system at that time. I don’t know if that made any difference with respect to the current condition. There is also a chance that a previous owner had the water pump replaced at some point. If anyone has any data on the “lifespan” of the Cayman S waterpump, I would be interested in the feedback.