Cam timing question.....(pics)

[viking911]

I'm going to replace the right side cam seal on my 1976 2.7L engine. I was checking the overlap on cylinders 1 & 4 before I took anything apart. Using Wayne's book my cams (911.105.143.00 & 911.105.144.00) should have an intake valve overlap between 0.40 - 0.54mm. I'm only measuring an overlap of 0.32mm on cyl. no. 1? I wasn't going to touch the left side cam but given the measurment do I need to adjust this side also? FYI I didn't adjust the valves yet. The engine was running ok and I just dropped it to take care of an oil leak coming from from the back of right side chain case. The pics pretty much show step-by-step how I've made my measurements.


To start
Both cams are up.


Rotor at notch, cyl no 1.


Crank at Z1 Mark.


Dial indicator set to zero on Cyl no 1 intake valve.


Rotate crank 360 degrees and read cyl no 1 overlap. 0.032mm!!!! (dial indicator rotates CCW)


Now put Z-Block on cyl no 4 intake and zero dial indicator.


Verified cyl no 4 at TDC with rotor.


Cam position with cyl no 4 at TDC.


Now rotate crank 360 degrees and read dial indicator. About 0.44mm (dial indicator rotates CCW)


So, what do you guys think? I was just going to clamp left side timing chain to keep crank from moving and then take right side cam sproket off, change seal and put everything back and use dial indicator to put cam back into exact position. Does this sound like a plan?

Can I expect the cam timing to change after I adjust the valves?

Bob

[Walter_Middie]

Viking - it is critical that you adjust the valves before taking the measurements. All you have to do is adjust the intakes on #1 and #4 then repeat the cam timing measurements. Doing the cam timing first, before taking anything apart is an excellent idea. You will be very familiar with the procedure before taking it apart. It sounds like you are doing it correctly, you just need to adjust the valves first - and be accurate like never before with the valves. Use the dial gauge and get them spot on.

[unclebilly]

Could also be a worn chain / sprockets giving you a bit of slop. The chains are replaceable without splitting the case - PP sells a chain with a master link.

[Flat6pac]

There is consistant chain stretch and wear. My thought has always been set to the high side and let the chain stretch and it does with temperature change.
When you open the 46mm dont try to mark things, use the thrust that is there and set high @.54. Set and Match both of them and you ll run sweet.
As far as changing the chains I was always told, "if the chains are work out so is the engine" and that was the German Machinist talking..
Bruce

[unclebilly]

When I did the top end on my engine, the chains were pretty worn so I replaced them as well as updating the tensioners to the newer style hydraulic type (I was running the early style carerra tensioners and they were worn).

With bike chain drives you replace the chains and sprockets together, with the cam drive stuff, there doesn't seem to be enough stretch in the links to wear the sprockets but there can be enough stretch to make your timing out of whack. On a bike drive system, timing doesn't matter.

[911pcars]

Good advice.

Use the crank as a reference point for TDC for either no. 1 and/or no. 4, not the distributor. It should be more accurate.

Sherwood

[viking911]

Thanks for all the input.

Primary reason I started the thread was just for piece of mind that a I'm making the overlap measurement correctly.

I know everybody uses the term "chain stretch" but I was taught that chains don't really stretch. Any slop in a chain and sprocket setup over time comes from wear.

I wasn't going to replace chains and sprockets but now you've got me wondering if I should. Is this the "while I'm here" syndrome?

[Eagledriver]

Just do what you had planned and also retime the left cam. Save the new chains for a rebuild.

-Andy

[viking911]

I adjusted intake valves #1 & #4 today and rechecked the overlap. Both cylinders picked up .02mm in overlap after the valve adjustment. I've spun the crank enough and decided to jump in. I'd heard that it takes 2 men and a boy to loosen a cam nut but I was able to do it myself. Thats all the time I had for today, I'll try and get back at it tomorrow.

[db_cooper]

Be sure the timing chain tensioner is fully extended. I used to use those solid type tensioners to keep the timing chain tight when doing the cam timing. Any looseness will cause inaccuracy.

[T77911S]

Originally Posted by 911pcars

Good advice.

Use the crank as a reference point for TDC for either no. 1 and/or no. 4, not the distributor. It should be more accurate.

Sherwood

ALWAYS use the crank and never back up to Z1. if you go past, go around 2 more times. after you have them set, spin it around 4 or 5 cylcles and check again.

valve adjustment very important too.

what ever you set them to, make sure to set them the same. if you cant get one set where you want it, try setting the other side to match.

perhaps they could have been done like mine were done. instead of being set to .020 (80 on the dial) someone set mine so the pointer spun all the way around to the 20, which was really .080. about 12 deg advanced.

i have often wondered how much the timing would have to change before you could notice while driving. if he set his timing to .03, could he tell by driving? and, is the spec so tight so that the engine runs smoother or was porsche really concerned about the actual timing point?

[viking911]

I removed the chain tensioner and all the pieces off the end of the cam shaft. I found that the pressed stud for the tensioner is really loose! Is there an acceptable way to re-secure the stud? If nobody has one I'm thinking about threading the end that goes through the back of the chain case and making a thick washer to secure it again, is the stud hollow?. If I can't thread the back of the original stud I could turn a new one out of some stock, still would use a bolt to fix it to the chain case.

[theiceman]

subscribed .. great pics viking. I may PM you with some further questions at some point if you don't mind

[viking911]

Feel free to PM me if you like.

Update, I found a used chain housing but its going to take about another 1 1/2 weeks before I receive it. I can't wait to get this done. I'll update the thread when I finally get the housing. Better pics to follow, no more cell phone pics, I finally got a new camera.

[HKZ Bob]

Originally Posted by viking911

Feel free to PM me if you like.

Update, I found a used chain housing but its going to take about another 1 1/2 weeks before I receive it. I can't wait to get this done. I'll update the thread when I finally get the housing. Better pics to follow, no more cell phone pics, I finally got a new camera.

Hello Viking and all who participate on this great thread with nice pictures.

I have to go through the same process, but I would like to understand for the methodology of the measurement.

1)Both cams are up.
2)Crank at Z1 Mark.
3)Dial indicator set to zero on Cly no 1 intake valve.
4)Rotate crank 360 degrees and read cyl no 1 overlap. 0.032mm!!!! (dial indicator rotates CCW)

You are rotating the crank counter clockwise. Is it important to count the no of rotation on the dial gauge?

You are measuring the lift 0.032mm of the valve after 360 degrees crank rotation ccw when the valve is in the cylinder 1 is in exhaust PHASE.


5)Now put Z-Block on cyl no 4 intake and zero dial indicator.
6)Cam position with cyl no 4 at TDC. Dot is on the bottom on the right cam.
7)Rotate crank 360 degrees and read dial indicator.

About 0.44mm (dial indicator rotates CCW)

Now the task it to equal the overlap of both sides. Correct?Which side is my base, my nominal. Does it matter?

Notice I have no data of my cam. Bought is with regrinds cams.

Thanks for the help.

BR Bob

[T77911S]

i see you read the dial gage correctly. when someone did mine, they set the cam so the dial pointed to the BLACK 30, which was really 70! yes, it moves CCW!

[Flat6pac]

Rotate the crank ounterclockwise, Bob?

[HKZ Bob]

Originally Posted by Flat6pac

Rotate the crank ounterclockwise, Bob?

If you look at the rear of your engine you see the belt pully.

Do you rotate the pully counter clockwise or clockwise for this procedure.




BR Bob

[aigel]

Originally Posted by db_cooper

Be sure the timing chain tensioner is fully extended. I used to use those solid type tensioners to keep the timing chain tight when doing the cam timing. Any looseness will cause inaccuracy.

+1

No need to get anal on this IMHO. You can get those cams perfect and re-time them 500 miles later, I guarantee they aren't close to what you had them at ...

I would recommend a cam upgrade at this point in time. Then it is worth your while to retime both sides! Otherwise I wouldn't bother with the untouched side.

George

[Walter_Middie]

BR Bob,

You are rotating the crank counter clockwise. Is it important to count the no of rotation on the dial gauge?

You are measuring the lift 0.032mm of the valve after 360 degrees crank rotation ccw when the valve is in the cylinder 1 is in exhaust PHASE.

You rotate the engine the same way it normally runs - clockwise. The only reference above to CCW is the movement of the dial on the dial indicator. As the INTAKE valve on cylinder #1 drops, the dial indicator will move CCW. You are just measuring the amount of lift at piston TDC, but on the intake stroke (180 deg of cam rotation from the starting piston TDC).

Now the task it to equal the overlap of both sides. Correct?Which side is my base, my nominal. Does it matter?

Notice I have no data of my cam. Bought is with regrinds cams.

It is important to get them both the same - but you need to know what cam you have to find out what the overlap number for your specific cam is.