john gill

Thanks Geoff

DId you get your engine finish:cheers with those modifications ?

Did you finally get the seats out ?

you have all confirmed my suspicions that it is a machining job, I had hoped thAT they were threaded.

GregBBRD

A dry sump will not cure the bearing failure issues associated with 2/6. It will improve the problem, but not cure. If you are running an track engine with 928 style rod bearings, you should look at them once a year....regardless of the oiling system. If you have the ability to monitor the knocks and change the timing accordingly (Sharktuner), the magic knock number is less than 75 per 10,000.

2/6 tend to knock before any of the other cylinders. This knocking pounds on the "soft" rod bearings and distorts the shells. Eventually, the shells will be "loose" in the rod, will break off the locating tang, and spin the bearing. This is actually the first thing to check when inspecting "soft" rod bearings. The guys with the "Chevy" style cranks have a selection of rod bearings to pick from, which enables them to get rod bearings that are more resistant to this pounding.

Better oiling helps to cushion the rod bearings against this pounding from the knocks and delays the problem.

Indeed, the oil flow valves may not let enough oil by to properly oil a street engine, especially an automatic. I personally wouldn't gamble my "no longer available GT exhaust cam" on less oil flow, for the street. If the engine is going to live on the track, you don't need the huge volume of oil that is delivered stock.

Vilhuer

Easiest way to remove those valve seats I have heard of is to make thread into center hole, install suitable size long bolt into it and pull bolt up. This should bring valve seat with it. Hole in head is slightly larger than hole in the seat. If thread is small enough bolt shouldn't be in contact with head itself.

Other way to do it is to just simply drill seat out. Lower part of 944 S2 valve isn't in contact with head and thus it doesn't matter if hole walls in head are not exactly straight and true. As long as hole is ok down to lower of the two o-rings valve will work.

Maybach_Man

yes but what about the swarf in the engine????

Geoff

BC

What about the companies that make custom rod bearings - maybe they would make a salable batch for the stock 928 rods.

GregBBRD

This would certainly help, if one of those companies would tool up and make a run small enough to be practical to purchase. Of course, the ability to produce an alternative part doesn't always mean that you are going to get what you want.

Porsche was forced to change to much harder bearing rod shells, for the GT-3 engines to live. Even with all of their knowledge, testing, and ability to have things produced, they have had several iterations of these bearings.

Track engines generally need a different style rod bearing than street engines. Generally, soft bearings with good concentricity work really well for long mileage needs. The harder the bearing, with less concentricity, is generally better for track use. The huge selection of types and sizes of the "Chevy" rod bearings certainly makes this bearing convenient to use.

Granted, convenience isn't always the best thing. The "Chevy" connecting rod in the 928 application is certainly a prime example of this.

john gill

Thank you all

I am so glad I started this thread , so much good information being revealed ,

Greg do you know what these bearings are made of ??

TIA

GregBBRD

John:

Not sure of the specifics....I'm sure that there are trade secrets involved, here. The eccentricity and the hardness of the GT-3 bearings appear to be very similar to the "Clevite H Series" bearings.

john gill

AN update on the oil control valve seats ,

10mm threaded rod ,strongback (bit of angle),drill & tap for the rod , attach the lot & out come the seats easy .

Then the 944 valves slide straight in ,

Interesting though , when I exy outed the grub screw holding the stop for head ball valve no 1 there was no spring, any wonder this engine had an oiling problem.

Mrmerlin

the spring is to hold the ball closed so gravity would work. make sure the new seats dont move once they are installed if they do then you will have a lack of oil possibility due to the oil pushing the new seat upwards and cutting off the oil supply holes to the cams and lifters