Engine Noises and Surprise in a Porsche 911 -

How often do seeming disparate problems converge with symptoms that seem to go together?  It’s rare but it happens.

This car – a 2003 Porsche 911 C4s - came in with a nasty rattle in the engine, and a fault code for a camshaft position error.  Like most mechanics the owner took that to mean the tensioner or the intermediate shaft bearing had gone bad, and the engine was in imminent danger of self-destructing.

We saw no reason to disagree with that assessment, and we expected the diagnosis to be validated on teardown.  When we installed the holding tools to keep the cams and crank lined up we found one cam slightly off.

But when we removed the transaxle and looked at the IMS bearing it was tight. 

There were no signs of metal in the oil.

All we found was slight grab marks on one tensioner, indicating it may have slipped back a bit.  We therefore had an explanation for the slack. But we didn’t have an explanation for the nasty rattle.  We looked inside with a fiber optic camera, and saw nothing.

The technician decided to put the flywheel on the engine, fit new tensioners, a new IMS bearing, and start the motor to listen without the transaxle in the way.  When he did, the result was surprising.  The cam position fault was gone, but the noise was unchanged.  The clatter sounded just like it was coming from the timing chains.

But it wasn’t.  As you see in this short video the noise was emanating from the flywheel.

With a new flywheel and new tensioners, the cam faults were gone, and the rattle was fixed.

The dual mass flywheel was not visibly bad, but its slop was at the extreme limit of the acceptable range.  The noise was obvious, though, once it was twisted hard.   

What is the takeaway from this?  Sometimes two totally different problems will appear virtually at once, and by combining their symptoms you can imagine a very different diagnostic path.  Many times motorists come to us with a list of problems and the hope that there is one thing - the magic bullet failure - that will cure them all.  We have to explain that worn brakes and oil leaks have nothing to do with one another.  And rarely - as in this case - the opposite happens.  A car comes in with seemingly related symptoms, but in reality it has two totally independent failures.

Or are they independent?  Thinking more on this, we theorize that the failing flywheel may have set up a vibration pattern at the back of the engine that caused the timing chain tensioners to vibrate internally, and one to eventually stick.  

Many techs would have changed those tensioners and then reassembled everything. And from outside, the noise would have seemed like chain noise for sure.  The next step – an unnecessary engine teardown.

No matter how much you know, cars can always surprise you.  

(c) 2015 John Elder Robison

John Elder Robison is the general manager of J E Robison Service Company, celebrating 30 years of independent Porsche restoration and repair in Springfield, Massachusetts.  John is a longtime technical consultant to the Porsche clubs, and he’s owned and restored many fine specimens.  Find him online at www.robisonservice.com or in the real world at 413-785-1665

Reading this article will make you smarter, especially when it comes to car stuff.  So it's good for you.  But don't take that too far - printing and eating it will probably make you sick.

Restoring seats in collector cars from Europe

One of the issues to be aware of when buying "restored" cars is that the examples offered for sale were often restored with the resale market in mind.  To that end, those restorers tend to focus on the things you'll be able to see at an auction inspection.  More substantive things - such as would be revealed in a two-hour cruise - are often ignored or even deliberately glossed over.

Sellers will often take exception to my characterization, but the facts speak for themselves.  If it takes $50,000 or $100,000 to do a cosmetic restoration on a car, you can assume that a similarly thorough mechanical restoration (almost all of which will be invisible on superficial inspection) will cost at least as much again, maybe more.  Doing both will price the car well above the auction averages, which are based on superficial restorations.

You see that in "show winning" cars that have to be pushed off the field because they barely run.  You feel it in a "concours" car when you sit in the seat and it feels like you ass is on the floorboards.  That is the subject of today's essay.

Cosmetically restored seats look good but feel awful

You can't really tell if a seat is restored by looking at it.  You can see wear, obviously, and you can tell if the seat is crooked or mangled in some way.  But a seat can look perfect and still be totally worn out and uncomfortable.  How can this be?  It's simple.  People put new covers over worn out old seats all the time.  It takes far more time to redo the innards of a seat than to recover it, and the cover is what a buyer sees . . . 

Prior to the widespread adoption of foam seat pads in the late 1970s car seats were often made with a metal frame that held a steel box spring like you'd find in an old bed.  Those of you who remember vintage summer camp beds know that box springs wear out, and when they do, they just go flat when you sit on them.  

The steel box spring is often capped with burlap, which tends to crumble but is otherwise trouble free.  Above the burlap you will often find a Spanish moss or horsehair pad, and above that a felt pad and then the seat covering.  Those things provide the "look and feel" of the seat but the comfort will never be there if the box spring is collapsed.  When they get old, the burlap, horsehair, and moss also provide the brown furry dust that tends to rain down underneath vintage car seats.

Here's an example of the junk that falls out of old seats.  In this seat the box spring is so loose that the seat cover has fallen right out of the grooves in the base.

It's possible to remake metal box springs but it's getting harder and harder to find the materials.  Today, most restorers fortify those old steel springs with robust molded foam.  In these photos you can see us doing that very job on a seat from a 1964 Porsche 356.

We start by removing the seats, which is pretty easy on an old Porsche - they just slide out.  The top and bottom are separated, and the cover is removed from the base.  The frame and spring and "everything else" are in two piles on the bench.

This particular seat has good leather, and the felt and padding are pretty decent too.  We're going to tighten up the rod that forms the pleat across the middle of the seat, as shown below:

The rod

The pleat

Now we're going to trim the original padding where we'll be replacing it with foam.  We're going to install a two-inch thick dense foam pad which will largely take the place of the collapsed spring.  The spring will be compressed by the pad, which will sandwich it tightly, and the whole structure will be a lot firmer.

The pad makes the cover fit a lot more tightly, which reduces the chance it will fall apart on the car. Here's the assembled lower cushion.  On close examination, you can see it looks a bit more "full" than before we took it apart but to the average person it would look unchanged

In this car we are also installing period headrests.  Some of you will say "Porsche 356 didn't have headrests" but I offer this page from the 1965 workshop manual - which we still have in original print - which says otherwise and shows how to fit them.

Here they are, and here's the finished seat.  With the exception of the headrest I'm the first to admit it hardly looks any different.  But the difference when you sit on it is striking.

Doing over a pair of seats like this is a full day's work, maybe more.  But if you want to drive the car - as opposed to just look at it - it's time or money well spent.

The seats in 1950s to 1970s BMW, Rolls Royce, Mercedes or Jaguar are all made in a fashion similar to what's shown here, and can be taken apart and restored using similar techniques.  Sometimes you can buy precut foam.  Other times you have to cut your own with a hot knife.  Some times the inside of the cover will require repair, and that can be complex if the seat has a pattern.  The worst is when the frames have rusted because it's tricky welding sheet metal seat frames and breaks can be tough to repair.

John Elder Robison is the general manager of J E Robison Service Company, independent restoration and repair specialists in Springfield, Massachusetts.  John is a longtime technical consultant to the Porsche and Rolls Royce Owner's Clubs, and he’s owned and restored many of these fine vehicles.  Find him online at www.robisonservice.com or in the real world at 413-785-1665

Porsche 911 blown air box failures

Back in the 1970s, Porsche went from carburetors to fuel injection in their 911 series cars.  The system they ended up using for most of the cars was called CIS, and it relied on a mechanical system of sensing air flow and metering fuel in response.

The incoming air was pulled through a box whose outlets were the six pipes to the intake and whose inlet was the metering flap.  There was just one problem with this arrangement - the metering flap went down(in) but did not go up (out.)  When the engine backfired through the intake, there was nowhere for the pressure to go, and the plastic airbox blew open.

This started happening as soon as the cars went on sale, and the market responded by developing a blowoff valve - a spring loaded valve that pops open and releases backfire pressure harmlessly while holding tight in normal operation.

This system was fitted to every Porsche 911 right through the appearance of Motronic engine management in the 1984 model year.  Amazingly, we still see cars that have never had the blowoff valve installed.  And they still get towed in, blown up!

Airbox with blowoff valve installed

Blown air box - the cost of not having a valve

The valve is under $100, and can be installed in less than two hours.  Fixing a blown air box is much more involved, requiring engine removal and $700 of additional parts.  

The moral of the story - have your car serviced by people who know the vehicles, and have them inspect the car from time to time.  An inspection by a qualified specialist would have revealed the missing valve and saved this most recent owner a $2,000 repair.

John

Robison Service is an independent Porsche service center in Springfield, Massachusetts.  They are a four-star Bosch Car Service facility with 30 years experience on Porsche automobiles.  Visit them online at www.robisonservice.com