Timing belt replacement
Hi all.
Just wondering if we really need the "special Porsche
Belt tension tool" Wouldn't it be possible for someone (anyone) who is
lately doing a belt tension with the proper gauge to do one with a
generic belt tester like the ones at this web address
http://hmc-international.com/
<http://hmc-international.com/>
, as well so we can find out the tension
in real world figures, not Porsche figures.
these gauges are about $9 American. And would save
everybody the hassle of hiring/buying a gauge just to check the tension
on their cars once in a while.
I would see this a great public service to anyone in
the know... or currently doing a belt job.
Or is this simply too much to ask????
Cheers,
Jes
==============================
Jes,
I have recently installed a new timing belt. I borrowed the official tool (from
the GB club) to set the tension. I then measured the tension, so that I can
re-set it in the future if necessary. This is what I did:
With the right hand side (facing front) timing cover removed, and all others in
place, the lower belt run that is exposed is from the tensioner pulley to the
right hand camshaft. Push down on this section until it touches the center
section cover. I measured the force at 15kg and the movement at 12mm.
You will need to cut a piece of wood to allow you to get a straight, vertical
push on the belt, and something to measure the force (I used bathroom scales).
This method produced very reproducible results, even after turning the engine
over. All measurements were done with the engine in the timing position, i.e.
TDC no1 firing.
Smiffy (1980 "S")
=========================================
Hi Jes,
Last time I set the timing belt tension I had a play with the tool as compared
the readings with those I got
from using a depth dial indicator I have ( similar to a normal dial
indicator but with a depth mic base)
there were interesting correlation's but I was a bit suspect of the Porsche tool
( from the dealer a real
worry as you could see where it had been dropped and damaged) I though try it
again next time and get some
results this will be soon and I'll see if I can gain any good info.
Its really a matter checking belt defection etc. but the load needs to de
applied correctly it may be a
matter of checking the reading on the Porsche tool to a conventional belt
tensioning tool. Something I will
look into next time I re-tension the belt after run in ( if I get time as I can
generally get access to the
tool).
I found some info about the RDK and which points to bridge but where did I store
it in the computer I'll
find it and post it ( or I'll go back to the wiring diag as it was easy if I
Regards
Eddy
==============================================
Eddy,
My own experience with an intermittent t-belt light left me wanting a way to
get two identical measurements in a row. I would welcome a belt tensioning
tool or method that was easier to use and provided consistent readings. As
a non-engineer I would think a good indication of belt tension would be the
number of degrees you could twist the belt with the engine at TDC.
Kevin Berez (kaberez@mindspring.com)
================================================
Kevin,
I think the tool is not a really easy thing to use and I test my belt quite a
few times to ensure repeatability. I was watching some "Porsche
trained "
people and I though it was a bit hit and miss.
I don't like this tool or the method but while I agree twist or deflection for a
given load could be used I thought I might contact the belt manufacture and get
some info ( Gates was a supplier for Porsche some years ago as the original
parts had a Gates logo and Part number in a Porsche box) I used to buy direct
from Gates so I thought I'd start there.
I' keep you posted but it all takes time.
Regards
Eddy
==================================================
Dear Bora:
To the best of my knowledge, all 928 timing belts need to be retensioned
about 1500 miles (2500 km) after installation. The reason is: new belts
will "stretch" a bit, and retensioning removes that stretch. YMMV.
On a personal note; This past July, the tensioner warning light came on my
90GT. I searched the service records to find that the belt was 2.5 years
old and there was no record of retensioning. Fortunately, another PCA
sharkster (Pete L.) had a belt tensioning tool and offered to show me how
to use it. Upon inspection we found the belt to be in good condition, but
its tension was 4.0. We retensioned to 5.1. So far, all is well.
Merry motoring. ~Ed~
==================================
I don't know about your mechanic having delusions, but a new timing belt
needs to be retensioned between 2000 and 2500 miles per the Porsche
Maintenance Checklist for the 928, although Kim Crumb recommends between 500
and 1000. The belt should be retensioned every 15,000 miles thereafter and
changed between 45,000 and 60,000 miles.
I don't have the maintenance manuals so I don't know what they say.
Good Luck,
Ted Childs
===================================
When he stops swearing, direct him to the top of Page 15-14 in Volume I of
the 928 shop manual, which says "Make sure new drive belts are retightened
after driving car approx. 1,000 km."
That page is dated July 1983, and, as several others have pointed out, the
factory now recommends a greater distance before retightening, but it has
always been the case that retightening after a little while has been what
the factory (and good sense) direct.
Your (former?) mechanic's vehement-but-dangerously-incorrect statement is
just the kind of claptrap that 928 owners used to be vulnerable to before
the 928 community organized.
====================================
Dear Dave:
I have only serviced one tensioner, so I hope those with more experience
will correct any mis-information mentioned below.
There is oil in the tensioner, but it's in there to act as a damper. It is
not internally fed to the tensioner, nor will it cause the tensioner to
automatically take up any stretching of the belt. Instead, there are two
access holes for the oil. The lower one is the inlet, and the upper is the
outlet. As I understand it, gear oil is the recommended fluid, which will
behave as a slow damper. YMMV.
Merry motoring. ~Ed~
====================================
> <snip>
> You mention "be sure to at least do it as described in the Chilton's
guide". As I have never seen this (probably not published in the UK) can you tell me
what it says.
>
> Smiffy, 1980 "S"
Sure, this is what is sometimes referred to as the 90 degree method. When the
belt is at the
correct tension you should be able to twist a "relaxed section of the
belt" 90 degrees. It is,
of course, not as accurate as the very expensive and sensitive tensioner tool.
The trick is to
know how hard to twist the belt! The original tool, from which this technique
was derived, is
Special Tool 9131, which I guess is no longer available, although I would love
to have one.
It's use is pictured on pages 15-15 to 15-18 of the factory service manual.
I believe you can order a copy of the Chilton's Guide from 928 International or
maybe from one
of the other Big Three. It was prepared for the earlier models including yours.
Daniel Shapiro
'82 928 5 speed 226k
===============================================
Anyway, I hope it is helpful. The reason I got my 83S-auto for only $4k
was that the PO found that the power steering hose was leaking (spraying
the side of the engine) and when he went to the Porsche dealer they told
him $284 for the hose only! He realized he was not yet able to handle
that kind of expense, so he dumped it. But the useful info is that I got
a power steering hose from my local NAPA for $65! I was worried when we
ordered it that the replacement hose would not have the restrictor in
the middle of the rubber part (yes I sawed the line apart to see what
was in there!), but the NAPA part was spot-on. A perfect fit. I did have
to weld up a 17mm crow-foot wrench to get the line connection on the
back of the pump. Whatta BITCH!
Another note: In my T-belt replacement job, I found that the little
roller that mounts right on the water pump was a little noisy. I tried
to press the bearing out, but I took too much force so I just pried out
the shields on both sides of the bearing and carefully cleaned it with
multiple baths of lacquer thinner. Then a gentle and SLOW spin with the
air hose to get rid of any little particles, re-grease it, pop the
shields back in and presto, it is smooth and quiet. This little roller
is about one-half the size of the crank sprocket so when the engine is
turning 4K, it is turning 8K!
I took the belt tensioner all apart. The o-ring felt about as hard as
industrial diamond, so I chipped it out. NAPA had a 1/16 X 1.125 o-ring
that is close enough to 1.5 X 28mm to work OK. The dust cover, for which
I find no separate part number I replaced with a piece of nice leather
from an old pair of boots I keep around for such things. And the leather
will outlast the original rubber boot anyway. This tensioner thing is
interesting. There are some cavities in the front of the engine that
match cavities on the back of the tensioner. The oil you pour into the
fill hole while waiting for the excess to bleed out the bleeder hole
fills the body of the tensioner as well as these funny cavities on the
back. I guess the purpose is to conduct the engine heat intimately to
the bimetal disks that maintain the belt tension. Sure seems like a
complicated system!
--jer
83Sauto
=================================================
> -----Original Message-----
> From: Mark Rosenfield [mailto:chefmark@pacifier.com]
> Sent: Friday, March 03, 2000 12:02 AM
> To: 928
> Subject: [928] Belt Tension Light
>
>
> I am in the process of fixing the toothed belt warning light on my 89 S-4. The previous owner had it disconnected because it was sending faulty signals. The microfiche doesn't give me anything to go by so I am soliciting information from the group. I have examined the system to the lead on the belt tensioner. Can anyone tell me what part on the tensioner is the switching mechanism for the warning light? A part number would be very helpful as well as any information regarding part replacement.
>
>
> Thanks in advance,
>
> Mark Rosenfield
> 89 S-4, 122k
>
mounted on the carrier for the tension roller is a simple copper strip which
connects to the pushrod on the end of the tensioner housing---the "warning
system" is looking for a constant ground--if the tensioner arm bounces away
from the tensioner usually under hard acceleration/deceleration the light
flickers on---the timing belt is pulled around by the toothed gear on the
crankshaft along the way it turns the oil pump gear, turns the drivers side
cam, the smooth back side spins the water pump, it pulls the passenger cam and
finally goes around the tensioner pulley before it gets back to the
crankshaft gear--in this system the tensioner is there to take-up the slack
on the no-load side---like a bicycle chain there is a tight side and a
no-load side. One important note the tensioner is not hydraulic, it does not
self adjust, it is not supplied with engine oil. It is a simple mechanical
tensioner stacked inside the housing are a number of slightly cup shaped
bi-metallic washers these washers when heated change shape to loosen the
belt to compensate for the thermal expansion of the aluminum block. As the
design progressed the tensioner was filled with 90 weight gear oil, to better
transfer heat to the washers, the next step was to drill two holes on the
back of the housing and put a gasket between the block and the housing
allowing oil to run into the webbing for better heat transfer-There are no
oil holes in the block- You must still fill the tensioner when changing the
timing belt--engine oil for later models- the last improvement was to insert
a baffle with a controlled orifice like a shock absorber inside the
tensioner--this was to help limit the bounce of a loose belt when the engine
is cold- Back to the "belt warning" system--it is very unreliable-and
can
only warn of a possible loose belt--it cannot tell when the belt is worn, too
tight, has cracks or teeth have broken off--it is good to have it working but
do not depend on it saving your engine.
================================================
The question of the belt tension tool appears somewhat regularly on this
list. Anyone doing their own engine work will think of alternatives
to
that expensive tool. I will share my little escapade from 18
months ago.
Original tool is now manufactured by one maker in Germany. It's
profile
(size) is important because it fits in the required area for tension
measurement. It's also important that it measures the belt between
the
crank and camshaft gear on the passenger (US) side. Other areas of the
belt
are either too difficult to get to or will not give reliable/repeatable
measurement. I rented the proper tool and purchased two 'Kriket'
tools
from NAPA (with different ranges). Correct tool has rollers that fit over
and under the belt to take the reading. Procedure requires pressing
down
on the tool until it is pressed against the air pump bracket (going off
memory here). All of this is important because it reliably positions
the
tool and uses a fixed surface - the mounting bracket - as a reference for
every measurement.
My plan was to take measurement with the 'correct' tool and use a Kriket to
find a reference. If you use the location described above (belt from
crank
to cam gear), there is little actual belt available. Most
importantly, the
ribs face up. This pretty much cancels using the Kriket because it
works
by pushing down until enough belt deflection occurs to overcome the Kriket's
little 'snap' at which you then read the scale on the tool. After
many
variations and attempts, I could not get reliable, repeatable results and
had a heck of a time manipulating the position of the tool.
Another alternative is the old 'squeeze' tool for measurement. It
works
pretty much like the factory Porsche tool, but it's actuated by squeezing
down on the actuator with your palm while holding the tool in place with two
fingers. Because of it's size and geometry, measurement must be
taken at
the top of the belt - the part exiting the cam gear on passenger side.
There is no room to fit the tool in the proper place on the lower belt.
I could not make any other method work to my satisfaction. I
believe that
for 16 valve engines, the 'finger' method of twisting the belt is probably
good enough. Not so sure I'd trust it for 32 valves.
Why take the
chance? I decided to rent the tool (the Big Three all provide this
service) whenever needed. It's entirely possible I may have missed
something or should have tried another variation - so by all means see what
you can do and be sure to post your results!
JP Rodkey
79 euro
==========================================
Hi guys (and gals),
I'm in need of some desperate help. I'm taking apart my front end to do
the t-belt, water-pump, pulleys and so forth. I release tension from the
belt in preparation for removal, and then slide the belt off the sprockets.
I look at the passenger side cam sprocket only to notice in horror that the
sprocket has moved 4 teeth counter-clockwise.
The belt must have still has some tension on the top end and pull the
sprocket when set free.
Oh Sh#t!!!!!!!!!!!
I'm at TDC, can I simply rotate the sprocket clock-wise 4 teeth and line it
back up with the mark?!? Seems to feel tight, I'm guessing this is just
the valve spring I'm feeling?
Please advise if I'm F#CKED!
Thanks,
Joe.
89' 5 speed and first time t-belt do-er.
==============================================
Joe:
Not to worry. You've called it correctly...the valve springs and cam
position
move the p-side sprocket as soon as the belt is removed.
This must therefore be addressed during reinstallation. 17mm box wrench in
the
hands of an able assistant will allow you to proceed with the proper
"threading" of the new belt.
Best regards,
David Lloyd
================================================
Hi everyone
Well maybe I know the answer to my long and boring threads on variation of
tension in the timing belt
I found when running the engine without covers that there was CONSIDERABLE
harmonic vibration in the belt at most rpm's This did not seem right
Looking at the tensioner adjuster wheel with a strobe light ( i used
different plug wires to see it in different positions ) I noticed that the
belt appeared to part company with the idler as it rotated. Took the whole
thing out and checked bearings, seemed fine, but greased them up anyway!
So , I then put it back and reset tension with finger thumb method . OK
this is not a good method ( I know everyone knows this) as it is difficult
to calibrate one finger/thumb unit. But I did find I could tension the belt
past where it was before and still get a 90 degree twist. What I did was to
tension till I could not quite get 90 and then run back a notch or two.
Result:
Tension in all positions. Now I realize when the belt is too loose it
allows the tensioner to come to its stops in travel ( spring loaded I
assume) and then there is NO tension in the belt and it is completely
loose. Clearly this is way too looses as it ceases to drive the water pump
As the PO had a new T belt fitted just before I bought it and I now have
2000 miles it clearly needed a bit more tension.
Running the engine now, there is no visible harmonic vibration and I can
still do the 90 degree twist reasonably comfortably.
Conclusion
1) I'll rent / beg / borrow a tensioner tool asap.
2) Too loose causes significant harmonic vibration in the belt with probably excessive belt and cover wear as the tensioner cannot extend enough to take up the slack in some engine positions.
3) Too tight can cause serious wear problems as well, though I really don't
see how this could directly cause drivers side camshaft breakages unless
there is a marginal oil feed to one of the bearings and the extra load
causes it to pass its limit ????
Makes sense?
Any comments?
Phil
===============================================
Phil:
I agree with your methodology. Personally, I use 1.5 Fingthumb Units
(FU's?) of tension.
Can't get too close to a 90 deg. twist - maybe 45 degrees. My book says to
use SAE 90 oil in
tensioner, but I don't know what year yours is. Does it have two
fittings? If so, one is the
fill port and the other is the bleed hole. I really can't imagine breaking
a camshaft from
too much tension, but maybe so. Mine would just make noise if I got it too
tight. Used to
race Nissan V-6 engines - 850 hp at 8500 rpm. We used what I think was a
larger belt than
standard and tensioned it so tight I couldn't believe it. No broken
camshafts or belts or
problems of any kind. I am not convinced of the necessity for a tension
gauge...
Gary - living on borrowed time - Casey
86 5 sp
===================================================
Too tight caused excessive cam sprocket wear on my 88. When I got the
car, the dealership had
simply been cranking down the tensioner adjusting bolt to extinguish the light
(t-belt
warning) for the PO. Don't let anyone do this. It had been doing
this for a year or so with
him. I knew the guy and the dealer and several other techs that had seen
the car.
When we took the front off to change the belt and re-build the tensioner, we
noticed
considerable wear in the sprocket faces, looked like 1/16" grooves where
the belt ran. Not
good, lucky it didn't break a camshaft. I have heard of broken sprockets
too, I guess several
things could cause this but "too tight" would sure be one of
them. Went ahead and replaced
all wear parts, water pump, etc. and replaced the front seal.
Same with camshafts, several things can cause failure, but don't write off
"too tight" as a
possibility.
It may be interesting for some to note that again in the past 6 months I have
seen times of
intermittent t-belt warnings. We knew the belt was right, we check it
often, especially with
this "phenoma". Finally Mo took it personally and went
nuts. Took the computer out and
replaced it with a known good one. No luck. Wires had continuity,
all seemed OK. Were about
to tear into the pod and look around when Mo decided to completely inspect the
tensioner
mechanism. He found that the 3" long metal "sensor" that
breaks the ground to trigger the
warning lamp, had a fracture (crack) in it near the 90 degree turn the metal
takes near the
attachment points.
A crack. Not a complete break, but still hanging on. This explained
the intermittent nature
of the warning. Sometimes it worked for a month or two as it should, other
times it would
display the warning for a month. Came on about 3 or 4 minutes after
driving (normal warning
mode for a problem in the circuit).
Now after replacing the arm, no problems. Tip: Carefully inspect all
parts and connections
(even for little cracks) as I believe even with a 60% crack in the metal, it got
enough juice
to satisfy the warning system. At 70% it didn't.
Weird, huh?
Marc White
======================================================
There is a lot of variation in loading on the timing belt, which leads to
flutter and jerking of the belt. This jerking and fluttering can cause the
"switch" in the tensioner to lose ground contact, sending a signal to
the
warning system computer that the belt is loose. The tensioner oil appears
to serve two main functions - damping these fluctuations, and transferring
heat from the engine block to the bi-metallic washers that serve as the
spring in the tensioner so that they compensate for engine expansion due to
heat. Failure of either of these functions could lead to false belt tension
warnings.
To fill the tensioner on a later car with two nipples:
Get a trigger-type pump oil can. Fill it with 90 wt oil. (One tech sheet
from Porsche says to use engine oil, but I prefer to go with the heavier 90
wt called out in the shop manual - I think that it will give better
dampening.) Get a foot-long piece of clear plastic tubing that fits on both
the spout of the oil can and the nipple of the tensioner.
Remove the rubber caps and open both bleed nipples.
Attach the tube and oil can to the inner-most (upper) nipple. Pump oil
slowly (that's the only way it will go in!) into the tensioner until you
get a solid stream from the outer-most (lower) nipple.
Close both nipples and re-install the rubber caps.
Check the engine below the tensioner for oil leakage for the next week or two.
If you add oil to the tensioner and it promptly leaks out, you need a
tensioner rebuild. The rubber cap gets hard and brittle with heat and age.
Wally Plumley
928 Specialists
===========================
The sensor is nothing but a strip of copper attached to the tensioner arm,
when the tensioner pin is touching the arm it grounds the circuit and the
central warning brain is happy -- if the contact strip starts to break the
resistance can be too high and reads as no ground as does a loose wire .
This system is so primitive it should never be relied upon but should not be
ignored .
Jim Bailey
===========================
Although I'm mainly a lurker on the post, Mr. Kempf was kind enough to allow
me
to try his version of the Porsche T-Belt indicator as a beta user. I've
owned a
'79 for over 15 years, and have replaced the belt three times now. The
last
time, the tension was set using his new indicator. As I mentioned to
Jay, I
took and made a very fine scribe line so as to see if I could actually see and
possibly graph the belt stretching over a period of time. The reason I
even
contemplated this exercise, was that I felt that I could get enough
repeatability between readings so as to be worthwhile, along with my curiosity.
Alas, I decided to maintain tension, rather than to attempt to chart an
ever loosening belt. The belt relaxed very little over the next 5000 miles
and
after the third adjustment hasn't moved for over 7000 miles. Actually the
third
adjustment probably wasn't necessary, and probably wouldn't have been noticed
except for my scribe line. I recently acquired a '89 s4, but so far
have not
taken the time to run a base line tension check. I have no qualms in
recommending the new tool. Not being one attempting to impress others by
how
much I can spend for 'Porsche' tools, how can you miss with this one.
Keeping the rubber side down
Byron
=======
There was a question on how to calibrate or check the "Kempf" Timingbelt tool. A simple answer is: attach a string to the assembly to simulate the timingbelt resistance to twist and attach 5 lbs (2.2Kg) of weight to the string. That should make the indicator stay right at full scale of the "calibration window".
regards
Theo