BC

I had just bought it. I was comparing the plastigauge to the bore gauge.

GregBBRD

That depends...

Porsche is very screwed up on rod bearings. They send them two to a box but then want to bill you for each individual bearing...sometimes. Sometimes they will sell you the pair for the part number on the box...which is what they should do....

Anyway, the bearing come in three different "marked" sizes. Blue is the "tightest", yellow is the middle, and red is the loosest. They are marked on one edge of the bearings with a very light colored mark....which oil removes and therefore there is never any trace of. The general "range" between these different colors is .0004" (.01mm) per color...but that's not always the case.

Porsche will always ship (from Germany) either a blue with a red or two yellows. I guess they think that a red mixed with a blue equals two yellows. Hopefully, no one at the US distribution point messes with this and they ship this same combination to your dealer. They never will ship two "blues" or two "reds".

Anyway, here's what I would do, if I was in your position.

I'd order 4 boxes of bearings (8 shells) and a set of Glyco replacement bearings from your favorite 928 parts guy. Order a bearing micrometer (accurate to .0001) and learn how to use it. Hopefully, you will end up with 4 "red" bearings, from Porsche. Measure these and confirn that they are "thinner" than any of the other bearing shells. These should be your bearings for #2 and #6. Hopefully the bearings you get from Glyco will be "looser" than the "blue" bearings you get mixed with the "red" bearings. You should be able to find 8 "looser that blue" bearings to use in the other connecting rods. If you end up with a set of Glyco bearings that measure the same or tighter than the "blue" bearings...you are in serious trouble. Two "blue" bearings are almost always too tight for a "standard" crankshaft.

If Porsche sends you boxes with two "yellow" bearings and you can't find any "red" bearings...well, that requires a whole different approach.

Simple. Anyone can do this stuff. Why does my head hurt?

SeanR

Simple, you are thinking for the rest of us on a Sunday

blown 87

Well first off, just buying it does not mean it has not been damaged, and I do not understand how you could use a bore gauge and plastigauge together.

I use inside and outside mikes to measure the clearances, and for me the plastigauge is used as a last and final check.

GregBBRD

That makes sense and is probably a good idea. It is certainly a good indicator or what is actually going on. I've gotten to the point where I "trust" my measurements and don't use the plastigauge method. By the time bearings get actually installed, they've been measured several times and checked several times. It's just one less step that I have to do.

BC

I used a dial bore gauge on the rod big ends with the bearings in and the bolts torqued. I measured the rod journals with the micrometer.

I then assembled the rod journal and rod with the bearings in it with the plastigauge and torqued.

I compared the two readings.

Its making double sure.

IcemanG17

While I am an expert at destroying 928 engines......I am a total noob at properly installing rod bearings...since I have never done it.....the best I have ever done is check the 2-6 in my existing engine and it was pristine.....they looked nearly new..... but we didn't have a proper micrometer to test them at the time.....well 48 hours later the engine still runs...so it must have been okay....however I am sure they are showing some wear now.... :>)

blown 87

My cylinder bore gauge is to big for that, it is also very difficult to use right.

GregBBRD

.0015" to .003". Depends on what the engine is for, what kind of connecting rod it has, what kind of rod bearings are used, how much power it is going to make, which cylinder we are talking about, what kind of oil is going into it, who is going to break it in, and who is going to drive it. Other than that, I don't pay too much attention to it.

Seriously, you can't go very far wrong with the "age old standard" of .001" per inch of crank journal. I like to see a bit more in #2 and #6. I can live with a tiny bit less on #1, #5, #4, and #8. #3 and #7 can be tighter that #2 and #6, but bigger than the rest.

BC

Its an adjustable dial bore gauge with different length arms.