QUIZ, 20 FEB, 1997
Copyright 1997, by Harry Pellow, All Rights Reserved.

It was Monday, January 6, the First Business Day of the 1997 New Year and the day everyone returns from Holiday Vacation and calls the Maestro.

..... The Maestro's phone was ringing off the hook- he had one caller on hold, one on the phone and one about to drop off into Voice Mail.

..... Some of the things he learned were Enlightening and Uplifting. Others, downright Scary.

..... Let's take the nice ones first.

..... The first uplifting conversation came from a Doctor who just had his engine rebuilt by a Mercedes Mechanic.

..... "So, a Mercedes Mechanic rebuilt your 356 Porsche engine," repeated the Maestro with a wary tone in his voice.

..... "Why? Is that bad?," asked the Doc on the Phone.

..... "Well," said the Maestro. "It's not as bad as having your Porsche engine rebuilt by a Ferrari Mechanic, as we have data on them- they like to set the Idle Timing to 30 degrees advance "just to get it running". Which means once your Engine IS running, it has SIXTY Degrees Advanced Timing! Which means you have Engine Destruction within a handful of miles!

..... We have Data on the Volkswagen mechanic too, who THINKS he knows Porsche (by Osmosis) but doesn't. (The Worst case of this is when a VW mechanic attempts to "split" a Porsche case withOUT first removing the Flywheel. (On a VW engine you CAN split the VW case without first removing its Flywheel.)

..... But a Porsche Engine Case has two remarkably strong 8mm studs and their associated nuts, one on either side of the Cam Plug, that must be removed first, BEFORE one tries to "split" the Case. To gain access to these two nuts requires the removal of the Porsche Flywheel. Meaning: YOU GOTTA TAKE THE PORSCHE FLYWHEEL OFF BEFORE you can split the Case!

..... You can also tell when a VW mechanic has "put together" a Porsche 356/912 Engine, by these two MISSING nuts around the Cam Plug that they FORGOT to install because a VW engine doesn't use them! They are but the Igors who carry out the Curse of the Frankenstein Turkey.

..... "Yeah," said the VOP. "And that's why I bought your Book, Maestro- "Secrets of the Inner Circle". Unfortunately, my copy of "Secrets" arrived two days AFTER my engine arrived home, having been completely rebuilt by my Mercedes Mechanic."

..... "Yeah, geez, that's too bad," said the Maestro having heard this Sad Story many times before. "And, ain't it always the case that you get The Books a couple of days AFTER you did the Engine! It's one of Murphy's Universal Laws. And, now I bet you wish you had "Secrets" BEFORE you did the overhaul?"

..... "Oh, yes! In fact, after I read through "Secrets" do you know what I did?"

..... The Maestro confessed that he didn't know what the guy did after reading "Secrets".

..... "When I finished "Secrets", I went out to my Brand-New Porsche Engine, that had JUST been rebuilt by my Mercedes Mechanic, but never run-

..... AND TOOK IT APART!"

..... "Very Smart," said the Maestro. "And Very Brave too. I know how much it hurts to tear apart something you've just built. Takes GUTS!

..... But tell me, did you find anything Interesting inside your Mercedes-Mechanic-rebuilt 356 Porsche Engine to justify taking it apart?"

..... "YES, I did!" said the guy.

..... And that's the Question this week. What was wrong? And Why? The Maestro's Quiz: The Answer

..... As you know, a Mercedes Mechanic who was rebuilding a Doctor's 356 Porsche Engine put ALL the Porsche Pistons on Bass-Ackwards. BACKWARDS!

..... The Arrows on the Pistons were all pointing towards the PULLEY end of the engine, NOT towards the FLYWHEEL end!

..... So, how come the Mercedes Mechanic do that?

..... The Maestro did some cogitation on the Situation and SUDDENLY (Light Bulb Lights)

..... "Oh, BUT OF COURSE!" silently shouted the Maestro's Center of Higher Reasoning, simultaneously snapping the Maestro's fingers.

..... "The term "Front" to a Mercedes Mechanic may not be the same as "Front" to a Porsche Mechanic!"

..... Let's analyze that a bit further shall we, for therein lies an important point:

..... On a Mercedes, the "Front" of the Mercedes is the Front Bumper.

..... On a Porsche, the "Front" of the Porsche is the Front Bumper.

..... So, both the Porsche AND the Mercedes Mechanics will agree on which end of the car is which. That's a good start.

..... On a Mercedes, the notch or arrow on the Mercedes piston points towards the "FRONT" of the Car, (as a Gentle 356 Mailing Lister noted in a recent e-mail).

..... And on a 356/912 Porsche Engine, installed in the car, the Arrow on the Porsche Piston does indeed point towards the FRONT of the car- the Flywheel- too!

..... So, had that Mercedes Mechanic followed through with that Clear, Blue-Eyed Teutonic Logic from this good start, he would have been RIGHT!

..... But somewhere along the line the Mercedes Mechanic drifted off the road. Wonder how it happened? The Maestro thinks it happened something like this:

..... Being Mercedes-centric, The Mercedes Mechanic "Visualized", "pictured" in his head, the Porsche Engine as if it were installed,... IN A MERCEDES!!!

..... Clearly then, with the Porsche Engine installed in the MERCEDES, the Porsche Flywheel is, indeed, at the REAR of the Car. So, therefore reasons the Mercedes Mechanic, since the other end from "Rear" is "Front", the Arrows on the Porsche Pistons clearly must point to the FRONT of the Mercedes, er, I mean Porsche!

..... Q.E.D.

..... Absolutely Fabulous Teutonic Logic. Would get the Mercedes Mechanic an "A" at the University of Heidelburg.

..... But Absolutely, Fabulously, WRONG!

..... You should not picture the Porsche engine as installed in a Mercedes, or ANY OTHER car for that matter! You should picture the Porsche Engine as installed in a PORSCHE!

..... But that was the Mercedes Mechanic's Problem- he did too much "Visualizing", certainly more than was good for him.

..... "Did you find anything ELSE wrong with this engine?", asked the Maestro, knowing that ifin you find one Big Error inside, there likely be others.

..... Now, that could have been PART 3 of the Quiz of 1997, but it's too hard a problem, so I'll tell you.

..... Ah, Hell, on second thought go ahead and Guess.

..... WHAT ELSE WAS WRONG?

..... "YES!" Said the VOP. "After reversing the Pistons, I took your advice in "Secrets" and put solder and clay on the piston top and found the minimum Piston-to-Head clearance to be 0.029".

..... "Hummh, Twenty Nine Thousandths Deck Height, that's pretty tight," said the Maestro. Most everyone including the Maestro recommends at least a millimeter (.040) clearance between Piston and Head.

..... "But, " continued the Maestro flashing on the Right Thing to do. "Since you now have the Cylinder Heads OFF the engine, you can "CC" them- measure the Volume of EACH Combustion Chamber and set your Compression Ratio right where you want it!"

..... "How can I do that, Maestro?"

..... "Like it says in "Secrets, this can be done rather easily- by cutting (or having cut) a clear Plexiglas circle of 1/4", 3/8" or even 1/2" thick Plexiglas, of an inside diameter sufficient to fit inside the Cylinder Head and rest on the inside Sealing Surface of the Head- where the Cylinder normally seals.

..... Drill a 1/4" or 3/8" hole in the center of the Plexiglas circle as a way of adding fluid, and there you are- a "CC-ing device".

..... Coat the circumference of the side of the Plexiglas disk that'll be touching the Head with stopcock grease (or Bosch Distributor Grease, or PAM in an emergency). This helps to make a good seal with the head and keep the liquid in.

..... Then, with the Valves and Spark Plugs obviously in place, dip a 50cc Pipette (available from most any Science supply store unless banned by the Government by now), into some solvent or WD-40 and dump the entire contents of the Pipette - all 50 cc's +/-0.01cc at 23 deg C- into that Chamber of the Head that has the Plexiglas Cover in place.

..... Fill a 0-10 cc Graduated Pipette, and slowly drip the contents down the hole in the Plexiglas disk, while keeping the air "bubble" visible and centered under the hole in the clear Plexiglas cover.

..... Fill the Combustion Chamber with fluid until the air bubble goes away and the fluid is at the bottom of the hole in the Plexiglas cover. Read off how much fluid was required. That's the Head Volume for that cylinder.

..... Repeat on ALL FOUR Combustion Chambers. And then do it over again to get some semblance of statistics, after thoroughly drying the heads.

..... If you find the Head Volumes of all 4 "heads" is within 0.1cc, you get to sacrifice a Virgin because the Porsche gods have truly blessed you. Only a Matched Pair of Virgin heads, such as usually found on Industrial Engines, do that. (But when they do- WOW! Talk about a smooooooth engine!)

..... If the head volume variation side-to-side is within a half a cc, 0.5cc- that's Factory Spec.

..... If the Head Volumes are different side-to-side by say, 1.5cc's or more, that's too much. The "Net Squish Volume" of a 356/912 Porsche Engine is about 50cc's. A 1.5 cc difference in Head Volume is a change in Compression Ratio of about 3%. And 3% of say a 10:1 compression ratio is 0.3 compression ratio numbers.

..... So one cylinder may be OK at 9.3:1, but another might not at 9.6:1! Here, 1.5 cc's could make a significant difference.

..... Fortunately, by CC'ing the each Chamber and KNOWING what the head volumes ACTUALLY ARE, if one side IS 1.5cc's different from the other, you can bring them back into Spec by "Differentially Shimming" the small-volume side with an ADDITIONAL 1/4mm (.010") THIN copper gasket applied under BOTH cylinders of the lower-volume side. And There You Are- within Spec again!

..... A Rule of Thumb is: On a Big Bore Kit, Each 1/4mm thick Copper Base Gasket produces a volume change of about 1.5 cc's. (More accurate numbers are in "Secrets".

..... If you have a head where the head volumes differ by say .75 cc, you can put the higher volume chamber on #1 or #3 cylinder, and slightly reduce the compression on the most problematic cylinders. Thereby gaining Longevity.

..... There are lots of little "tricks" like these you can do once you KNOW the Head Volumes! Here, Knowledge really IS Power.

..... And once you know the Head Volumes, call the Maestro and he'll run your numbers through his Computer Program there'll calculate the Compression based on your Head Volume and most ANY Piston- from Stock ones of ANY diameter, to the 86mm NPR Big Bore Kit or any of the Shasta/JE pistons. Even Industrial Engine pistons.

..... Being a Doctor (hence the need for a Mercedes Mechanic), the guy did just that- and called the Maestro back the next day.

..... "Hi," he said. "I'm the guy with the engine the Mercedes Mechanic rebuilt that I took apart and found the pistons installed backwards!"

..... "Great," said the Maestro. "I've been hoping you'd call. Did you "CC" the cylinder head?"

..... "Yep," said the Doc on the Phone. "I rigged up a cover for the Cylinder Head and used some of my larger Hypodermic needles."

..... "And what did you get for Head Volumes," asked the Maestro, cutting to the Chase.

..... And This could be Part 4 of The Second Quiz of 1997: What WERE the Head Volumes: The choices are:

..... 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63 cc's

..... "55.1, 55.2, 56.1 56.6 cc's." said the Doctor.

..... "WHOA!" said the Maestro. "Again, you're One Lucky Owner- and one who has been doubly blessed by the Porsche gods for having the guts to take apart your suspiciously assembled engine!"

..... "Why is that Maestro?" Asked the Med School Graduate.

..... "Because," said the Maestro. "The Average 356C Porsche Cylinder head, when new, has 60-61 cc's in it. But YOUR Head has only 55 cc's! That's FIVE OR SIX CC's less! That means your Head mustave been Flycut a BUNCH! Probably Several Times!

..... There are ways to tell how much your head has been Flycut. You know that little raised section of Aluminum that forms a sort of "outline" around the Combustion Chambers of the head?"

..... "Yeah, I think so," said the Doc. "You mean The little "raised" area kind of "outlining" the Combustion Chamber?"

..... "Yes that's it," said the Maestro. "That little raised area is about oh, 1/16" or so- maybe 1-2 millimeters. So, ifin that "raised" area is completely GONE, your Heads have been Flycut a LOT- almost 2 millimeters!"

..... The Doctor looks at the heads and says "Why that's Amazing," Maestro. "The raised area IS almost COMPLETELY machined off! They've even started going into part of the first fin a little!"

..... "That," said the Maestro. "Is a sure Sign that the Heads have been intimate with the Flycutter on several occasions. Now, take a look at the Sealing Surface of the Head, where the Cylinder normally seals. Is that flat area or "shelf" where the Cylinder rests about a quarter-inch wide, or is it more like 3/8" or HALF-AN-INCH wide?"

..... "WOW!!, said the VOP. "Y'know, it IS pretty wide there- certainly more than a quarter-inch!"

..... "Sadly, that's another Sign of severely Flycut Heads- the combustion chamber must necessarily curve around to meet itself, so as you cut deeper into the Head, the "shelf" where the Cylinder rests gets wider and wider. I'd say this is more proof that these cylinder heads were Flycut a LOT! And I believe the 55 cc's you got for the Head Volume!"

..... Now, Five cc's may not seem like much, but to a Porsche 356 engine, a 5cc's change in the Head Volume is TEN PERCENT of the 50cc Net Squish Volume.

..... And a 10% change in Net Squish Volume means a 10% change in the Compression Ratio, too- In this case a 10% INCREASE! So, ifin the Compression Ratio before were 9.3:1 it'll be 10.3 to 1 NOW!

..... A 356/912 Porsche Engine with TEN POINT THREE TO ONE Compression Ratio running on the Reformulated Panther Pee that we now call gasoline would surely lead to no good.

..... Fortunately, the Maestro had his Compression Ratio Computer Program available that could run through the numbers quickly, even on the Shop's ancient IBM "XT".

..... And, yes, By George, the Compression Ratio on this Beastie with the Big Bore Kit would have been 10.3:1. And to bring the Compression DOWN to a 100,000 Mile Longevity 8.8:1 would require a .072" shim under the Cylinders.

..... But the Owner wanted to go a little faster and was willing to suffer shortened longevity. So, the Computer determined that a 1.0mm thick shim combined with an additional thin (1/4mm) shim for a total equivalent to 5 single 1/4mm shims, would give him sufficient Head and Valve clearances, AND a fun 9.3:1 compression.

..... So here we had a fully assembled, ready-to-go Rebuilt engine with TWO separate, hidden, lurking problems, any ONE of which would have maybe RUINED the entire engine within a VERY short number of miles- or at least required another tear down. The pistons would have slapped like Hell, having TWICE the

..... With the Pistons put in bass-ackwards the Piston "offset" is in the WRONG direction. So, instead of PREVENTING "Piston slap", the wrong offset CAUSED a Bahhhhddd Case of it!

..... Couple the Piston Slap tendency with the WAYYYYYY too high Compression Ratio, and that loud slapping sound would get mucho worse-o mucho fast-o.

..... Yes, clearly, the Mercedes Mechanic was certainly at a disadvantage here. Not only was he working on a Porsche whose Front and Rear were not clear, but that some of the parts inside were non-Factory Standard too!

..... And the Mercedes mechanic certainly DIDN'T KNOW that any engine a NPR Big Bore Kit almost ALWAYS must be shimmed with AT LEAST a 1.0mm thick copper base gasket to lower the Compression Ratio to something livable in these days of Methyl Tri-Butyl Ether. (And sometimes, ifin the Heads have been Flycut a bunch, you may even need a thicker shim combo to make things Right again.)

..... And since the 1.0mm thick copper base gasket DOESN'T come in the Porsche Top End Gasket Kit, the Mercedes Mechanic wouldn't even THINK of using it. "Mien Gott! Ifin it not be in der Gasket Kit Ve don't use it!"

..... This was case of Teutonic Thinking stabbing you in the back. Here the Mercedes Mechanic NEEDED a little Innovative Thinking in order to use (successfully) a set of non-Factory Pistons that required a Copper Shim that wasn't provided in the Factory Gasket kit. Teutonic Thinking sometimes prevents you from Innovative Thinking. Ask Adolph.

..... The Owner however wasn't of the Mercedes Mechanic persuasion and, being a Doctor, was sufficiently smart enough to realize that something might be wrong after reading all the Cautions in "Secrets", and man enough to take apart a BRAND NEW, NEVER-RUN engine.

..... Let's see, thanks to "Secrets" the Owner found two near-fatal Assembly Defects inside his engine and saved it from a Dose of Destruction, all for $29.95! Now, isn't THAT a Deal!

..... Saved in the Nick of Time! Fodder for yet Another Great Hollywood Movie. Or TV episode. Are you listening, Jerry? Mr. Seinfeld? *****************

..... But the Mercedes Mechanic, Visualizing more than was good for him, hung all the PORSCHE pistons the Wrong Way- with the Arrows all pointing AWAY from the Flywheel. Towards the Pulley!

..... (This is not unlike the Big Bad Boo-boo Mahle made that the Maestro saw a year two ago when a mildly-famous Importer called him in to IN-vestigate some 911 2-liter Pistons which had been placed inside 912 Cylinders in still-sealed Mahle Original Boxes. And since the 911 Piston is 80 mm diameter and the 912 Cylinder is 82.5mm diameter, the Piston-to-Cylinder clearance was a whopping 2.5 millimeter. That's TWO AND A HALF MILLIMETERS- almost an EIGHTH OF AN INCH Running Clearance- FROM THE MAHLE FACTORY.

..... Number 36, Inspector Costeau-like, passed this totally out-of-spec combination even though the 911 piston would FALL OUT of the 912 cylinder if the cylinder were turned upright. It was Terribly Teutonically WRONG in a Turkey sort of way.)

..... It took a LOT of cajones for this Owner to TAKE APART a Brand New rebuilt Porsche Engine done by a Mercedes Mechanic Two Days after getting " Secrets"!

..... After all, would YOU have torn down YOUR BRAND NEW ENGINE done by your mechanic who normally works on a different brand of car, just because you read something in some Book that came in the mail that day?

..... You'd BETTER!

..... Because the Owner found and CORRECTED not only this Disastrous Problem but another one too.

..... "Did you find anything ELSE wrong", asked the Maestro. Knowing that ifin there be one Big Error inside, there likely be others.

..... (And that could have been PART 3 of the Second Quiz of 1997, but it's too hard a problem, so I'll tell you.)

..... "YES!" Said the VOP. "After reversing the Pistons, I took your advice in "Secrets" and put solder and clay on the piston top and found the minimum Piston-to-Head clearance to be 0.029".

..... "Hummh, Twenty Nine Thousandths Deck Height, that's pretty tight," said the Maestro. Most everyone including the Maestro recommends at least a millimeter (.040) clearance between Piston and Head.

..... "But, " continued the Maestro flashing on the Right Thing to do. "Since you now have the Cylinder Heads OFF the engine, you can "CC" them- measure the Volume of EACH Combustion Chamber and set your Compression Ratio right where you want it!"

..... "How can I do that, Maestro?"

..... "Like it says in "Secrets, this can be done rather easily- by cutting (or having cut) a clear Plexiglas circle of 1/4", 3/8" or even 1/2" thick Plexiglas, of an inside diameter sufficient to fit inside the Cylinder Head and rest on the inside Sealing Surface of the Head- where the Cylinder normally seals.

..... Drill a 1/4" or 3/8" hole in the center of the Plexiglas circle as a way of adding fluid, and there you are- a "CC-ing device".

..... Coat the circumference of the side of the Plexiglas disk that'll be touching the Head with stopcock grease (or Bosch Distributor Grease, or PAM in an emergency). This helps to make a good seal with the head and keep the liquid in.

..... Then, with the Valves and Spark Plugs obviously in place, dip a 50cc Pipette (available from most any Science supply store unless banned by the Government by now), into some solvent or WD-40 and dump the entire contents of the Pipette - all 50 cc's +/-0.01cc at 23 deg C- into that Chamber of the Head that has the Plexiglas Cover in place.

..... Fill a 0-10 cc Graduated Pipette, and slowly drip the contents down the hole in the Plexiglas disk, while keeping the air "bubble" visible and centered under the hole in the clear Plexiglas cover.

..... Fill the Combustion Chamber with fluid until the air bubble goes away and the fluid is at the bottom of the hole in the Plexiglas cover. Read off how much fluid was required. That's the Head Volume for that cylinder.

..... Repeat on ALL FOUR Combustion Chambers. And then do it over again to get some semblance of statistics, after thoroughly drying the heads.

..... If you find the Head Volumes of all 4 "heads" is within 0.1cc, you get to sacrifice a Virgin because the Porsche gods have truly blessed you. Only a Matched Pair of Virgin heads, such as usually found on Industrial Engines, do that. (But when they do- WOW! Talk about a smooooooth engine!)

..... If the head volume variation side-to-side is within a half a cc, 0.5cc- that's Factory Spec.

..... If the Head Volumes are different side-to-side by say, 1.5cc's or more, that's too much. The "Net Squish Volume" of a 356/912 Porsche Engine is about 50cc's. A 1.5 cc difference in Head Volume is a change in Compression Ratio of about 3%. And 3% of say a 10:1 compression ratio is 0.3 compression ratio numbers.

..... So one cylinder may be OK at 9.3:1, but another might not at 9.6:1! Here, 1.5 cc's could make a significant difference.

..... Fortunately, by CC'ing the each Chamber and KNOWING what the head volumes ACTUALLY ARE, if one side IS 1.5cc's different from the other, you can bring them back into Spec by "Differentially Shimming" the small-volume side with an ADDITIONAL 1/4mm (.010") THIN copper gasket applied under BOTH cylinders of the lower-volume side. And There You Are- within Spec again!

..... A Rule of Thumb is: On a Big Bore Kit, Each 1/4mm thick Copper Base Gasket produces a volume change of about 1.5 cc's. (More accurate numbers are in "Secrets".

..... If you have a head where the head volumes differ by say .75 cc, you can put the higher volume chamber on #1 or #3 cylinder, and slightly reduce the compression on the most problematic cylinders. Thereby gaining Longevity.

..... There are lots of little "tricks" like these you can do once you KNOW the Head Volumes! Here, Knowledge really IS Power.

..... And once you know the Head Volumes, call the Maestro and he'll run your numbers through his Computer Program there'll calculate the Compression based on your Head Volume and most ANY Piston- from Stock ones of ANY diameter, to the 86mm NPR Big Bore Kit or any of the Shasta/JE pistons. Even Industrial Engine pistons.

..... Being a Doctor (hence the need for a Mercedes Mechanic), the guy did just that- and called the Maestro back the next day.

..... "Hi," he said. "I'm the guy with the engine the Mercedes Mechanic rebuilt that I took apart and found the pistons installed backwards!"

..... "Great," said the Maestro. "I've been hoping you'd call. Did you "CC" the cylinder head?"

..... "Yep," said the Doc on the Phone. "I rigged up a cover for the Cylinder Head and used some of my larger Hypodermic needles."

..... "And what did you get for Head Volumes," asked the Maestro, cutting to the Chase.

..... And This could be Part 4 of The Second Quiz of 1997: What WERE the Head Volumes: The choices are:

..... 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63 cc's

..... "55.1, 55.2, 56.1 56.6 cc's." said the Doctor.

..... "WHOA!" said the Maestro. "Again, you're One Lucky Owner- and one who has been doubly blessed by the Porsche gods for having the guts to take apart your suspiciously assembled engine!"

..... "Why is that Maestro?" Asked the Med School Graduate.

..... "Because," said the Maestro. "The Average 356C Porsche Cylinder head, when new, has 60-61 cc's in it. But YOUR Head has only 55 cc's! That's FIVE OR SIX CC's less! That means your Head mustave been Flycut a BUNCH! Probably Several Times!

..... There are ways to tell how much your head has been Flycut. You know that little raised section of Aluminum that forms a sort of "outline" around the Combustion Chambers of the head?"

..... "Yeah, I think so," said the Doc. "You mean The little "raised" area kind of "outlining" the Combustion Chamber?"

..... "Yes that's it," said the Maestro. "That little raised area is about oh, 1/16" or so- maybe 1-2 millimeters. So, ifin that "raised" area is completely GONE, your Heads have been Flycut a LOT- almost 2 millimeters!"

..... The Doctor looks at the heads and says "Why that's Amazing," Maestro. "The raised area IS almost COMPLETELY machined off! They've even started going into part of the first fin a little!"

..... "That," said the Maestro. "Is a sure Sign that the Heads have been intimate with the Flycutter on several occasions. Now, take a look at the Sealing Surface of the Head, where the Cylinder normally seals. Is that flat area or "shelf" where the Cylinder rests about a quarter-inch wide, or is it more like 3/8" or HALF-AN-INCH wide?"

..... "WOW!!, said the VOP. "Y'know, it IS pretty wide there- certainly more than a quarter-inch!"

..... "Sadly, that's another Sign of severely Flycut Heads- the combustion chamber must necessarily curve around to meet itself, so as you cut deeper into the Head, the "shelf" where the Cylinder rests gets wider and wider. I'd say this is more proof that these cylinder heads were Flycut a LOT! And I believe the 55 cc's you got for the Head Volume!"

..... Now, Five cc's may not seem like much, but to a Porsche 356 engine, a 5cc's change in the Head Volume is TEN PERCENT of the 50cc Net Squish Volume.

..... And a 10% change in Net Squish Volume means a 10% change in the Compression Ratio, too- In this case a 10% INCREASE! So, ifin the Compression Ratio before were 9.3:1 it'll be 10.3 to 1 NOW!

..... A 356/912 Porsche Engine with TEN POINT THREE TO ONE Compression Ratio running on the Reformulated Panther Pee that we now call gasoline would surely lead to no good.

..... Fortunately, the Maestro had his Compression Ratio Computer Program available that could run through the numbers quickly, even on the Shop's ancient IBM "XT".

..... And, yes, By George, the Compression Ratio on this Beastie with the Big Bore Kit would have been 10.3:1. And to bring the Compression DOWN to a 100,000 Mile Longevity 8.8:1 would require a .072" shim under the Cylinders.

..... But the Owner wanted to go a little faster and was willing to suffer shortened longevity. So, the Computer determined that a 1.0mm thick shim combined with an additional thin (1/4mm) shim for a total equivalent to 5 single 1/4mm shims, would give him sufficient Head and Valve clearances, AND a fun 9.3:1 compression.

..... So here we had a fully assembled, ready-to-go Rebuilt engine with TWO separate, hidden, lurking problems, any ONE of which would have maybe RUINED the entire engine within a VERY short number of miles- or at least required another tear down. The pistons would have slapped like Hell, having TWICE the

..... With the Pistons put in bass-ackwards the Piston "offset" is in the WRONG direction. So, instead of PREVENTING "Piston slap", the wrong offset CAUSED a Bahhhhddd Case of it!

..... Couple the Piston Slap tendency with the WAYYYYYY too high Compression Ratio, and that loud slapping sound would get mucho worse-o mucho fast-o.

..... Yes, clearly, the Mercedes Mechanic was certainly at a disadvantage here. Not only was he working on a Porsche whose Front and Rear were not clear, but that some of the parts inside were non-Factory Standard too!

..... And the Mercedes mechanic certainly DIDN'T KNOW that any engine a NPR Big Bore Kit almost ALWAYS must be shimmed with AT LEAST a 1.0mm thick copper base gasket to lower the Compression Ratio to something livable in these days of Methyl Tri-Butyl Ether. (And sometimes, ifin the Heads have been Flycut a bunch, you may even need a thicker shim combo to make things Right again.)

..... And since the 1.0mm thick copper base gasket DOESN'T come in the Porsche Top End Gasket Kit, the Mercedes Mechanic wouldn't even THINK of using it. "Mien Gott! Ifin it not be in der Gasket Kit Ve don't use it!"

..... This was case of Teutonic
 

 

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