Timing and Advanced Timing.pdf
One of our customers asked about timing the camshafts on a four-valve
engine. I told him that there was a procedure in the Shop Manual (page
15-133), but that it was thoroughly screwed.
I think that I now have the correct info, and thought that I would post it
here for info - and for any corrections.
Add the following steps between step 3 and step 5, replacing step 4.
4a. Mount a dial indicator so as to measure the lift of an intake tappet on
cylinder #1. The indicator must be mounted directly in line with the valve
stem, which will require an off-set attachment for the indicator to get
around the cam. Preload the indicator by about 5mm, since valve lift will
be down, away from the indicator, then zero the dial.
4b. Rotate the crank about 540 degrees (about one-and-a-half turns), and
start watching the indicator. Stop when the indicator reads 1.6 +/- 0.1 mm.
4c. Check the crank dampener - the 20 degrees ATDC mark must be exactly on
the pointer. If it is, move to the other cylinder head.
4d. If the crank is not on the 20 deg mark, remove the distributor rotor,
and firmly install three M5 by 15 mm bolts in the rotor mounting holes.
Loosen the cam sprocket retaining bolt, counter-holding the washer. Do not
let the camshaft move!
4e. The cam sprocket is now firmly attached to the sprocket driver, but
both are free to move on the camshaft (the Woodruff key slot is slightly
oversize to allow limited movement). While holding the camshaft in place,
with 1.6 mm lift showing on the dial indicator, move the crank until the 20
deg mark is perfectly aligned with the pointer.
4f. While carefully counter-holding the washer, and ensuring that the
camshaft does not move, tighten the cam bolt to 65 Nm (47 lb/ft).
4g. Rotate the crank almost two turns, then carefully watch the dial
indicator and stop at 1.6 mm lift. Check to ensure that the crank is
exactly at 20 deg ATDC.
4h. Remove the 5 mm bolts and reinstall the distributor rotor.
4i. Repeat steps 4a thru 4h on an intake cylinder #6, but use 2.0 +/- mm
lift rather than 1.6 mm.
Note that in step 6, "cylinder No. 6" should be "cylinder No.
1".
Also note - these values are ONLY for the '85 and '86 engines.
For '87 engines, use 1.8 +/- 0.1 mm for #1; 2.0 +/- 0.1 mm for #6.
For the Club Sport (M28.41) and the '89GT (M28.47), use 2.8 +/- 0.1 mm for
#1; 3.1 +/- 0.1 mm for #6.
For '92 - up (M28.49/50), use 1.83 +/- 0.1 mm for #1; 2.08 +/- 0.1 mm for
#6.
As you can see, they left a bit out of the manual! If anyone has any
corrections, I would appreciate a prompt post, before everyone sticks a
copy of this into their shop manual.
Wally Plumley
928 Specialists
=======
That's definitely a much better description than what's given in the shop manuals. There's just one slight correction though. The three M5 by 15 mm bolts are tightened and the cam sprocket retaining bolt is then loosened as stated in step 4d above, but the three M5 by 15 mm bolts must then be loosened for the sprocket to be able to move in relation to the camshaft when doing the adjustment. The crankshaft is then moved until the 20 degree mark lines up with the pointer, the three M5 by 15 mm bolts are tightened, and the cam sprocket retaining bolt is then tightened. The three M5 by 15 mm bolts are used to make sure that the cam and cam sprocket do not move in relation to each other while the cam sprocket retaining bolt is being loosened or tightened.
Mike Schmidt
========Background:
It's been a few thousand miles since the engine was rebuilt (torn apart due to a
broken timing belt - no valve damage), so it's a good time to check belt tension
and compression. Belt was okay, but both sides were low compression (starboard
at 175psi and port at 155). The good news is that the cylinders were consistent
on each side - so that pointed to cam timing.
Otherwise, the engine ran well with no problems.
Day 1
1. Took off fans, PS reservoir, and valve covers (hate that starboard side!). It
was almost 4 hours work to get that far.
2. Used the manual to gauge and reset cams. Got a cheapie Harbor Freight
dial gauge and attempted to follow the instructions pages 15-132 to 15-135.
I had a heck of a time getting the gauge setup correctly because you need a hook
on the end of the gauge to rest on top of the lifter in such a way as
to avoid the movement of the cam lobe. The picture on page 15-133 is
deceptive because there just isn't that much flat surface on the lifter that
isn't obscured by the cam. Plus, the Harbor Freight tool has a short
operating shaft on the dial gauge - you have to rig up something to fit. I
settled on a bent wire taped and tie-wrapped onto the gauge shaft. It was
the best I could figure out at the time. Also, manipulating the gauge
stand in such a way as to get the gauge shaft parallel to the lifter is a
challenge.
3. Following the procedure, you're looking for the lift of the intake valves to
translate to the markings on the crankshaft balancer. I checked, and sure enough
both cams were 'out' - but not by much, maybe a few degrees.
After adjusting the cams, I checked again and once more to make sure.
Day 2
4. Figured it was best to come back refreshed and check everything again,
so I set up the gauge and re-measured. Everything looked good.
5. Buttoned up the valve covers (did I say I hate that starboard side?).
Cleaned up everything, double checked the belt tension, and put fluids back in.
6. Awright. Time for the test. Cranked over a few times, and she lit
up. Seemed a little weak, and immediately smelled rotten eggs. Hmmmmmm.
Waited a minute, then restarted. It was a little harder to start - not a
good sign. The engine would rev up, but definitely not very snappy. I
decided to do a street run, and headed out the driveway - for about ten
yards. This just doesn't feel right. So, back into the garage - and
popped the hood. Got some oil burning off, but otherwise stayed running
(kinda rough).
Wait. What's that?! Smells like ........like.....something's BURNING! I
see smoke coming from under the car and bend down to see the cardboard I used to
sop up oils has begun to burn because the catalytic converter is
CHERRY RED! I grab it and toss it into the yard where it smoldered and
burnt in the evening wind.
Checked the compression on the port side and it's now reading 150 psi.
Bummer. Apparently, the timing is so retarded that the fuel was collecting
and burning in the converter. No different than a simple 8-banger muscle
car.
7. It's getting late, so I decide to call the Big-Three to whine and ask
for advice. Well, it was too late to call one of them, so the West Coast
posse got stuck talking with me. Thanks Tom and Marc.
Day 3
8. Decide to change the port cam timing by moving it two notches more
advanced on the timing belt. Measure compression: 210 psi!
Wooooo-hoooooo. I check the starboard side, and it's 195 psi. So, I
slightly retard the port side to try to match compression of the other side and
wind up right at 200 psi port and the 195 psi starboard.
DILEMMA
Now, when the crank is TDC, the starboard cam notches line up but the port
side is off by two notches. How can this be? Remember, the engine had
been disassembled. Maybe the camshafts got mixed up (there are in fact
different lift specs and cam numbers for each side)? To hell with it - I
pull the cover off the port head and inspect the numbers. They're good -
which means the other side is good, too.
My 88 S4:
port intake cam 928 105 292 6R
port exhaust cam 928 105 294 4R
page 15-124 of manual:
port intake cam 928 105 292 04
exhaust cam 928 105 294 02
Just for grins, I set up the gauge again. As predicted, when the appropriate
lift is measured, the crank is far from the 20 degree mark (pg 15-134).
Someone can check my math because the Harbor Freight cheapie is in inches,
not mm. So, here were my specs:
1mm = .0394 inch
Cylinder bank 1-4 lift (page 15-135): 1.8mm +/- 0.1 mm
1.7 X .0394 = .067 in
1.9 X .0394 = .075 in
Cylinder bank 5-8
1.9 X .0394 = .075 in
2.1 X .0394 = .083 in
It seems to me one should be able to set cam timing by compression. If two
notches advanced got me over 200 psi, that wouldn't be too advanced, would it?
What would explain the big difference between timing gears?
My inclination now would be to rotate the starboard cam to match the port cam,
but this doesn't make sense because it would put them both out of sync with the
crankshaft (I did check - the balancer is on correct and not
backwards). The camshaft sprockets are the same part number, so that's not
an issue. The cam gears are installed so that the part number cast into them
faces the radiator and the little 'vee' notch for timing is pointing toward the
engine. The wider (1/4 inch?) casting notch opposite the 'vee'
faces the radiator. I don't have these on backwards, do I?
What shall I tear into next? I don't need any more practice taking out the
fans and pulling valve covers.
JP Rodkey
88 S4
Checked all cylinders to make sure there are no bent valves and all looksgood. I've re-rigged the dial gauge to something much more stable. It
just didn't seem you could get enough cam fine tuning using the method in the
book to get the kind level of retard I got.
I've downloaded Wally's (usual) detailed guide and hope some of you can weigh in
before tearing into it again tomorrow.
JP Rodkey
========
JP,
Making the extension is a bit tricky. I used a long thin bolt I found at the
hardware store. The rounded head of the bolt fits nicely on the top of the
lifter and the thin treads allow clearance of the cam lobe. The dial indicator
has a treaded end and some of the more expensive units come with threaded
extensions.
The one important thing to check is for the indictor to remain in contact with
the lifter at all times. I do this by checking the preload on the initial
setting TDC and then again on the 20 degree mark. The measurement on an S4 for
the 5-8 bank is 0.078 and the 1-4 bank 0.070. The measurement for the 5-8 bank
is made on the sixth cylinder intake valve lifter and the TDC mark in sync with
the cam. The 1-4 bank is measured from the intake lifter on the number one
cylinder with the cam out 180 degrees when at TDC.
I found with a new belt it was worth checking the tension often - every couple
of turns on the engine until it seats in. It took about twenty turns for the
belt to track on the center of the pulleys and for the tension to stabilize out.
I know the book says only a couple of turns, but more seem to be better. I
remove the spark plugs when doing this so the engine turns over easier.
As a best guess on the starting point the cam notches should be lined up almost
exactly with the marks on the cover when the crank is lined up with TDC. I tried
using only one bolt to hold the cam and found it slipped while I was adjusting
it. On the 1-4 bank you can mark the cam position on the Hall sensor plate as a
reference to see how much of a change each adjustment is.
If your cam belt is off one tooth then I suspect you will never get the timing
set right. Most of the time I have found the setting gives too small a reading.
I adjust this by loosing the cam pulley and moving the crank back about the same
amount the adjustment is beyond the 20 degree mark.
After doing this I run around a couple of times and find I have to reset the
dial indicator. Once the timing is set the dial indicator seems to stabilize out
and is consistent with less than a 0.001 deviation. I found the knobs on the
stand and the attachment to the dial indicator had to be tight for the
measurements to be consistent. You do not want the stand and indicator moving
with the lifter. I have been checking the setting for at least 5 revolutions
once I get it set right. Be sure to torque the cam bolt and use some blue
Loctite.
I did find when the setting was off on the 1-4 bank by a large amount the cam
chain tensioner was clicking when I cranked the engine over. Once I got the
setting dialed in the clicking went away. This might be a good tip off
the setting is wrong.
I hope this helps and good luck getting the car running right. I think with your
cam timing set right you will be impressed with the performance.
Dan the Pod Guy
Portia's Parts
=========Hi JP,
>My 88 S4:
>port intake cam 928 105 292 6R
>port exhaust cam 928 105 294 4R
>
>page 15-124 of manual:
>port intake cam 928 105 292 04
>exhaust cam 928 105 294 02
The cams that should be in your '88 are the ones on page 15-124a of the manual.
The numbers on your cams are the casting numbers, and not the part numbers as
are listed in the manual, so the manual numbers won't match those on the cams.
>Someone can check my math because the Harbor Freight cheapie is in inches,
>not mm. So, here were my specs:
>
>1mm = .0394 inch
>Cylinder bank 1-4 lift (page 15-135): 1.8mm +/- 0.1 mm
>
>1.7 X .0394 = .067 in
>1.9 X .0394 = .075 in
The 1.8mm lift for the #1 cylinder intake lifter is equal to .0709 in
>Cylinder bank 5-8
>
>1.9 X .0394 = .075 in
>2.1 X .0394 = .083 in
The 2.0mm lift for the #6 cylinder intake lifter is equal to .0787 in
>It seems to me one should be able to set cam timing by compression. If
>two notches advanced got me over 200 psi, that wouldn't be too
>advanced, would it?
If you mean two timing belt teeth advanced, yes that's too much. There are
48 teeth on a cam sprocket. That means each tooth is 7.5 degrees rotation of the
cam sprocket. Two teeth would be 15 degrees of the cam sprocket.
Since the cams turn at half the speed of the crank, that two teeth change would
be equal to 30 degrees of crankshaft timing. Even a 3-4 crankshaft degree
difference in the cam timing is enough to make a difference in where the engine
makes power in the RPM range. Also keep in mind that if you were to set the cam
timing for the best compression test psi numbers, that would mean that the cam
timing was optimized for best air intake into the cylinder at the cranking speed
of the engine. That would definitely be different than what occurs with the
engine running at high RPM. You'd definitely be down on power at the high end.
>What would explain the big difference between timing gears?
My guess is that you have the cams on one cylinder bank installed incorrectly.
There are those pointers cast into the cams that are shown on page 15-127 of the
manual. There should be seven chain links, or about 113mm of space between those
cast in peaks on the cams when the cams are rotated so that the peaks are
pointing upwards. The picture at the bottom left of page 15-127 makes it a lot
clearer than I can explain it in an e-mail. I'm guessing that you have the cams
on one cylinder bank off by one cam sprocket tooth in the chain that connects
them. This messes things up when you do the cam timing because you are measuring
the intake valve lift with the dial indicator, but the exhaust cam is the one
being driven by the timing belt and is the one indexed to the crank. If that
does turn out to be your problem, it must be a Milwaukee area thing or something.
Paul did the same thing when him and Jean-Louis installed his cams, and I found
the
problem when I set his cam timing for him. :)
>The cam gears are installed so that the part number cast into them faces the radiator and the little 'vee' notch for timing is
>pointing toward the engine. The wider (1/4 inch?) casting notch opposite the 'vee' faces the radiator. I don't have these on
>backwards, do I?
You have the sprockets on facing the correct way.
>What shall I tear into next? I don't need any more practice taking out the
>fans and pulling valve covers.
Trust me, even with more practice that passenger side valve cover will still be
a PITA. I've been in there three or four times on my car and once on Paul's, and
it never got much easier.
Mike
=======
I took some pictures of the engine I am working on to write up the cam timing
on my web site only to discover I had already done it. Here is the bracket I
made and how the dial indicator is set up.
http://www.kondratyev.com/porsche/technical/engine/valve.htm
Dan the Pod Guy
Portia's Parts
______________________
From: Wally Plumley [mailto:wplumley@bellsouth.net]
Sent: Tuesday, July 23, 2002 4:23 PM
To: 928
Subject: [928] Cam Timing
There was a question on the RennList Discussion Forum about cam timing. The
poster said that one of the cam sprockets on his '90 GT was half a tooth off the
alignment mark with the crank at TDC. I thought that the list might be
interested in my answer to him.
On the 32-valve engines, the cam sprockets can be adjusted on the camshaft - or
perhaps we should say that the camshafts can be adjusted on the cam sprockets.
This allows you to get the cam timing perfect, even though the sprockets may not
be perfectly
aligned.
There is a four-page procedure in the Workshop Manual. Basically, you set the
crank to 20 deg ATDC and see if the #1 intake and the #6 intake valves are
lifted a specific amount, which varies by model. If not, you turn the crank
until the correct valve is lifted the
specified amount, loosen the cam sprocket and lock the sprocket hub and cam in
place, then turn the crank/belt/sprocket until the crank is on 20 deg ATC.
Tighten the sprocket back to the hub, remove the locking bolts, and do the other
side.
Bottom line - the sprockets may not be exactly on the timing marks, but if the
cams are properly timed, it doesn't matter. You can either hope/assume that the
cams are timed correctly, or you can get the manuals and a dial indicator and
set them.
Wally Plumley
928 Specialists
www.928gt.com
From: Wally Plumley [wplumley@bellsouth.net]
Sent: Monday, January 21, 2002 10:28 AM
To: 928
Subject: [928] Cam Timing Info
I think that it is good for all of us to publicly demonstrate just how dumb we
are sometimes. I posted the following statement a couple of days ago:
>One of our customers asked about timing the camshafts on a four-valve
engine. I told him that there was a procedure in the Shop Manual (page
15-133), but that it was thoroughly screwed.
I find it amusing that after puzzling over this procedure many times, I had never noticed that my copy of the Shop Manual was missing pages 15-133 and
15-134! No wonder the procedure didn't make much sense! My only defense,
and it is a very weak one, is that my manual went from step 3 on page
15-132 to step 4 on page 15-135. Many thanks to Mike S. for sending me a
copy of the appropriate pages.
Since several people said that my home-made procedure was easier to follow
than the one in the manual, I am repeating it, with a couple of corrections
and additions. My apologies for the bandwidth.
For an '85 or '86 four-valve engine:
4a. Mount a dial indicator so as to measure the lift of an intake tappet on
cylinder #1. The indicator must be mounted directly in line with the valve
stem, which will require an off-set attachment for the indicator to get
around the cam. Preload the indicator by about 5mm, since valve lift will
be down, away from the indicator, then zero the dial.
4b. Rotate the crank about 540 degrees (about one-and-a-half turns), and
start watching the indicator. Stop when the indicator reads 1.6 0.1 mm.
Note - NEVER turn the crank backwards!
4c. Check the crank dampener - the 20 degrees ATDC mark must be exactly on the pointer. If it is, move to the other cylinder head.
4d. If the crank is not on the 20 deg mark, remove the distributor rotor,
and firmly install three M5 by 15 mm bolts in the rotor mounting holes.
Loosen the cam sprocket retaining bolt, counter-holding the washer. Do not
let the camshaft move!
4e. Loosen the three 5 mm bolts enough to allow the sprocket free movement
on the drive gear and the camshaft (the Woodruff key slot is slightly
oversize to allow limited movement). While holding the camshaft in place,
with 1.6 mm lift showing on the dial indicator, move the crank until the 20
deg mark is perfectly aligned with the pointer. Note - NEVER move the
crankshaft backwards! Louis Ott suggests that it is easier to put the crank
on 20 deg ATDC and to move the cams to get the correct lift, using
the cast-in flats. Tighten the three 5 mm bolts.
4f. While carefully counter-holding the washer, and ensuring that the
camshaft does not move, tighten the cam bolt to 65 Nm (47 lb/ft).
4g. Rotate the crank almost two turns, then carefully watch the dial
indicator and stop at 1.6 mm lift. Check to ensure that the crank is
exactly at 20 deg ATDC.
4h. Remove the 5 mm bolts and reinstall the distributor rotor.
4i. Repeat steps 4a thru 4h on an intake valve for cylinder #6, but use 2.0
mm lift rather than 1.6 mm.
Also note - these values are ONLY for the '85 and '86 engines.
For '87 - '91 engines (except as listed below), use 1.8 0.1 mm for #1;
2.0 0.1 mm for #6.
For the Club Sport (M28.41) and the '89GT (M28.47), use 2.8 0.1 mm for
#1; 3.1 0.1 mm for #6.
For '92 - up (M28.49/50), use 1.83 0.1 mm for #1; 2.08 0.1 mm for #6.
I find it interesting that following this procedure will put the camshafts
and crankshaft in the correct relationship, giving correct cam timing, but
may cause the notches in the cam sprockets to be off slightly.
Louis also suggests that you can adjust (retard) the cam timing to give a
slight power increase on the top end, with a smaller decrease on the
bottom. The opposite is also true - you can get a little more bottom-end
grunt with a slight loss on the top end by advancing the cams slightly. The
easiest way is probably to estimate 23 deg ATDC or 17 deg ATDC, rather than
the standard 20 deg., and using the specified valve lift at these points.
Thanks to all who responded.
Wally Plumley
928 Specialists
From: mlschmidt@sprintmail.com
Sent: Sunday, January 20, 2002 1:28 AM
To: 928
Subject: [928] Re: Cam Timing Info
That's definitely a much better description than what's given in the shop
manuals. There's just one slight correction though. The three M5 by 15 mm
bolts are tightened and the cam sprocket retaining bolt is then loosened as
stated in step 4d above, but the three M5 by 15 mm bolts must then be
loosened for the sprocket to be able to move in relation to the camshaft
when doing the adjustment. The crankshaft is then moved until the 20 degree
mark lines up with the pointer, the three M5 by 15 mm bolts are tightened,
and the cam sprocket retaining bolt is then tightened. The three M5 by 15
mm bolts are used to make sure that the cam and cam sprocket do not move in
relation to each other while the cam sprocket retaining bolt is being
loosened or tightened.
Mike Schmidt
'88 928S4 Auto Black/Black "PORSCHE" cloth
928 Owners Club Charter Member
PCA Chicago Region
From: mlschmidt@sprintmail.com [mailto:mlschmidt@sprintmail.com]
Sent: Tuesday, August 27, 2002 12:59 AM
To: 928
Subject: [928] RE: Thrust Bearing/Flex Plate
><Did first owners need to take the cars in for a belt tensioning after an initial belt stretch?>
>
>From the "Guarantee and Maintenance" booklet for my Euro 928 GTS:
>
>Maintenance 2,000 to 2,500 miles:
>Toothed belt for camshafts: Check tension.
So that would mean new, regular off the shelf, timing belts were used by
Porsche when the engines were initially assembled. If they didn't in some
way compensate for the initial belt stretch when the cam timing was
initially set, the cam timing would be off from specifications when the
belt did stretch. Since the engine rotates in a clockwise direction when
looking at it from the front, the passenger side cam timing should be
retarded in relation to the driver side cam timing when the belt stretched.
That's exactly what the situation was with my car when I checked the cam
timing.
Mike Schmidt
'88 928S4 Auto Black/Black "PORSCHE" cloth
928 Owners Club Charter Member
PCA Chicago Region
---------------
Hello Erkka,how are you? Hope you're well. Long time since we last had contact. You bought a diagnostic tool from us. Remember?I read your postings on rennlist quite regularly, and since you seem quite knowledgeable about the engine I decided to seek your advice.This is the story: a friend has a 928gts 1992 with a TBF. He's rebuilding it. All is done, and he's putting on the camshafts. Despite of several tries, he's unable to get the alignment between de shafts correct to factory spec. It seems simple: put the markers up, put the chain on, drop the shafts in and add the bearing caps. Final adjustment on the exhaust side cam wheel.This results in this timing:
Theo’s specs current value Difference (crank) conclusion Intake opens 13º after TDC 5º after TDC 8º early ?? Intake closes 61º after BDC 38º after BDC 23º early ??????? Exhaust opens 28º before BDC 28º before BDC correct OK Exhaust closes 12º before TDC 10º before TDC 2º early OK You can change the timing about 19 degrees by moving the chain one tooth, but that will affect open and close of the intake. I wish we had a factory tool (model) to put the camshafts in properly, but it should also not be difficult to do without. Is the spec maybe wrong?
Any ideas why one valve is that much off? Does this ring a bell with you?
Thanks for any thoughts.regardsTheo1992 928gts Midnight Blue (2006-)1988 928s4 Cherry Red (1999-2006)The Netherlands