SharkSkin

Bill, most likely what happened is the filter plugged up and the bypass opened. Anyway, glad to see you guys are being very meticulous about getting it all cleaned up. You're going to flush all of the plumbing, accusump etc I assume?

BTW, below is a message from our friendly weekend warriors at Porsche:

Bill Ball

Yep, galley plugs were pulled for thorough cleaning. I saw the WSM recommendation of new lifters. Shop was adament about that too, even though the lifters can be disassembled. The valves and seats were perfect. It will get a valve job and new guides.

Bill Ball

Marc: Appreciate the comment about the hose size. We actually had similar thoughts about that. I guess the filter could have gotten clogged and bypassed. The metal was pretty freely distributed around the motor. There was a lot in the filter, but I don't think it should have clogged it. However, if that wasn't what happened, we need to figure out what did. And yes, we have located stock guides.

Bill Ball

The filter clogging would be the simplest and preferred explanation from a troubleshooting standpoint: just don't clog the filter again and you should be OK.

The plastigage use has two sides. I've been told that the bearings are dimensioned to compress into rod end and journal. They are slightly long and thinner at the ends. Plastigaging a bearing is OK, but you can't use that particular bearing. Anyway, we are using another method. More later when we get to that.

Fastest928

Bill,
I've been told that the bearings are dimensioned to compress into rod end and journal...

Who said this? When you compress a bearing to measure it in the rod bore, do you then throw it away??? Or is it specific to the "assembled" and tq'd assy??

Again, I suggest that if you are going to measure the bearings, that you properly measure the bearing. Measuring properly requires that that you measure the journal and bore separately in multiple directions and that you mix and match to desired spec.

Cheers,
Marc

Bill Ball

This never got answered. We didn't compress the bearing in the rod bore. We didn't use plastigage. We took many measurements of the crank journal diameter, the rod big end opening diameter and the bearing thickness and figured the clearances from that. Sorted the bearings until we got things into the desired range. Despite the WSM showing Plastigage, every engine builder I know says that it may be fine for a street car but not accurate enough for a race motor, so pull out the micrometers. I can't refute that, so that is what we did here.

Jim Morton

As a suggestion for measuring the road bearing shells, use a micrometer that has a flat for the anvil and ball end on the measurement end. The type of mic is commonly used for measuring wall thickness.

Measurements should repeat within 0.0001 in order to have an acceptable total error for the stack up of all the measurements, crank journal, rod big end bore and bearing shell (x2).

Enjoy.

Fastest928

This methodology does not take into account bearing crush. Probably ok for street engines.

Marc

Jim Morton

Actually it does if you measure the bearings in the correct locale. Done it hundreds of times on dozens of race engines.

Come on by sometime and I'll gladly show you !

Rob Edwards

FWIW, I used a ball end mic on the Porsche 'yellow' rod bearings I used to replace 2 and 6 on the GT motor. The old bearings were 0.0588" to 0.0589" (they varied by <0.0001" when measured at 3 or 4 different places), and all 4 'yellow' bearing halves were consistently 0.0590 to 0.0591".

Fastest928

I measure the shell thickness "only" to characterize the bearing for reference. In my early years, I did the same as you and never had a problem, glad it is working for you.. For the last 20 years of engine buiulding, I crush the bearings to measure actual dims. Once I began begin characterizing the bores, shells and crushed dims against journals, beign matching and add a ton of other details, I found big difference in engine perfromance.

Go here for some general tips:

http://engineparts.com/it_bearinginstall.asp

Engine Bearing Installation and Fitting Tips
When measuring bearing measurements, they should always be taken at 90-degrees to the parting line to determine the minimum clearance. If measuring the bearing wall thickness, use a special micrometer with a ball anvil to fit the curvature of the bearing ID. The best way to determine bearing clearance is to measure the bearing ID with the bearings installed in the housing and the bolts torqued to the specified assembly torque. Use a dial bore gauge to measure the bearing ID at 90-degrees to the parting line, then subtract shaft size from bearing ID to determine the clearance. If the dial bore gauge is zeroed at the actual diameter of the crankshaft journal to be installed, the dial bore gauge will then read clearance directly and the subtraction calculation can be eliminated. About .001" clearance per inch of shaft diameter is a good rule of thumb. Increasing that by about .0005" will add a little margin of safety when starting out, especially for rods. Example: .001" X 2.100 = .0021" then add .0005", so starting out set clearance at .0026" for a 2.100 shaft.

If clearance adjustments need to be made, use either an extra clearance part for more clearance or an undersize part for less clearance. It is permissible to mix sizes if less than .001" adjustment in clearance is desired. When mixing sizes for a select fitting: a) never mix parts having more than .0005" difference in wall size; b) and always install the thickest wall shell in the upper position if installing a rod bearing or the lower position if installing a main bearing. When working with a reground shaft, always measure assembled bearing ID's first. Next have a shaft sized to produce the desired clearance since there are no extra clearance parts available for undersize shafts.

When measuring a bearing ID or wall thickness, avoid measuring at the parting line. The diagram illustrates there is a parting line relief machined into nearly all bearing shells. This relief is to allow for any mis-match between upper and lower shells due to tolerance differences, or possibly resulting from cap shift or twist during assembly. To determine bearing wall eccentricity or assembled bearing ID ovality, measure at a point at least 3/8" away from the parting line.

When installing any bearing DO NOT ATTEMPT TO POLISH THE BEARING RUNNING SURFACE WITH ANY TYPE OF ABRASIVE PAD OR PAPER. Bearing overlay layers are extremely soft and thin – typically .0005" on high performance parts. These thin layers can easily be damaged or removed by an abrasive media. Because the overlay layer is electroplated, it may exhibit microscopic plating nodules that make it feel slightly rough. The nodules are the same material as the rest of the plated layer and will quickly be flattened by the shaft. Bearing surfaces can be lightly burnished with solvent and a paper towel if desired.

Arriving at the correct choice of a high performance bearing for any given racing application is much like determining what clearance works best. From past experience, our knowledge of the intended usage and common sense can guide us in making an initial choice. Next, we can fine tune the selection process based on those results. The information given here is intended to aid in the initial selection as well as the fine tuning process.

The following table serves as a brief overview of the features included in each of the special Clevite 77® brand high performance bearing series.


P SERIES H SERIES V SERIES Z SERIES M SERIES
Rods Deltawall Mains Rods Mains Rods Mains Rods Mains Rods Mains
Eccentricity H H H-M M M L-M L-M M M L-M-H L-M
High Crush X X X X X X X X X X X
Hard Back X X X X X X
O. S. Chamfers X X X S S S X
Dowel Hole A A X
Thin Overlay X X X X X X
No Flash Plating X X X X X X X X
Reduced Wall Tolerence X X X X X X
Full Grooving X A A P A

Legend:
A = Available for some applications
H = High Eccentricity (up to 0.0015")
L = Low Eccentricity (up to 0.0005")
M = Medium Eccentricity (up to 0.0010")
S = Shortened length at fillet end
X = Applies to nearly all parts
P = Full upper and partial lower



© MAHLE 2009

Marc

Bill Ball

Thanks Marc. I think we did alright. We did not "crush" the bearings as I had understood that should be a one-time event, but I may have misunderstood that. Anyway, we measured the bearing thickness using the correct tools at the middle and rechecked around the middle to confirm consistency and used the math with the rod opening and crank journal diameters to get clearance. I think Dennis has about 7-10K miles on the motor, which is about 50X longer than it lasted on the last two rebuilds. We had occasion to pull the pan when we were investigating some oil pressure anomalies after the rebuild, and Jim & Dennis checked 2/6 while they were in there and it looked good. The oil pressure anomaly turned out the be due to an exposed cam oiling hole that we should have plugged. That's all fixed now and the car is ready for the track as soon as Dennis can get away from work.

Oh, and I did my first engine rebuild in 1964, so I guess I have 45 years of experience!

Alan

Bill - I think Louie gave you some really good advice earlier in this thread. Change the primary PCV breathing from the heads to the oil filler. Instead go just to dual balance lines between the heads - or better still 1 balance line and dual fresh air feeders from the filtered side of the airbox.

Plumb the intake vac line to a larger volume breather on the oil filler - see Louie's oil cap design or the simpler to fab up Provent attachment that DR came up with (even if you don't use the Provent). This can be implemented with or without an air/oil seperator or catch-can.

I investigated what Louie and others have done and am convinced this simple mod is a great direction for a better PCV system - it ensures oil drain back from the pass head is not impeded by the PCV evacuation flow during high blowby conditions - adding the fresh air head vents will likely enhance drain-back.

This should both reduce oil loss to the intake and at the same time keep more oil down in the sump.

Alan

Fastest928

Bill,

Good to know! Well done!

Glad Dennis' engine is now back to bullet proof with the addition of the omitted oil plug. Reliable, just like it was for 10 years under both Chris and Dennis' brutal ownership using a properly working accusump.

It ia amazing how well an engine holds up to track abuse using nothing more than a properly working accusump! Chris put that one on along with a few other goodies.

Failures will occur when the accusump is not working properly and unfortunately, it happend before. ...so check it before every track event to make sure all is working as designed.

mark kibort

Or not. (no accusump that is)