Turning camshafts

westyguesty · 01-19-2013, 01:56 AM

I'm part way through putting my 911sc engine back together and really need to check everything is OK before i break something.

I have replace all lowers studs, 9 broken, gaskets, seal etc, however I didn't remove the camshafts from the heads, or have the heads rebuilt. Just carefully removed the complete unit and refitted after new studs, rings etc. The lower engine, pistons etc turns over freely, but now i am on to timing the cams.

I didn't think I had rotated the cams when I removed the head, but the left side has the 930 & key pointing down. read Rebuilding Porsche engine and on this forum I need to have both cams pointing up. Without the sprockets on the cams, I can't seem to turn either of them very far. They both turn a bit, but then strong resistance, obviously don't want to force them, but not sure how difficult they should be to turn.

With a completely standard engine, should I be able to turn the cams over 180 degrees without removing the heads again, or will valves and pistons meet.

Thanks, i feel i am getting close to getting the car running again, just unsure of this stage.

Flat6pac · 01-19-2013, 02:54 AM

You can turn the cams anyway you want, a bigger wrench is called for because youre fighting the valve springs.
I prefer to have the crank turned so the pulley is about 50 degrees before Z1, all the pistons are down inside the cyl and you can spin the cams without valve/piwston interference.
Put the dots up and then turn the crank to Z1, put the tensioners and chains on and pin the cams. Now you can dial them in.
Bruce

westyguesty · 01-19-2013, 03:08 AM

Thanks for the speedy reply. I think I am just surprise at the amount of resistance from the springs. As both sides feel the same, i'm guessing this is OK.

So if I turn the crank 50 degrees anti clockwise, i can turn the cams without any problems.

I still find it surprising that the left one is 180 degrees out as i don't think I turned it. Is the rule always start with 930 mark at the top on both camshafts.

Still i chance I can get the cams done and covers on this weekend

Flat6pac · 01-19-2013, 05:15 AM

If your heads are on already, you might be against a piston and need to turn cam the other way.
I set the crank before I put the heads on. If your heads are on already you need to get to the point of being able to turn both the cams and setting the crank. Once you have the crank set then youre free to turn the cams to the top.
Bruce

Daves911L · Daves911L's Garage

I don't know for certain about SC's, but earlier motors will most definitely have valve/piston interference when at TDC and I suspect even CIS cams will also. But you can work your through it OK. First, loosen the valve adjusting nuts and screw the adjuster feet out as far as they will go. Then Rotate your crank 60 degrees past (or before) the TDC mark and you will not have any cylinders at TDC and the best chance of moving the cams without the valves encountering a piston. If you encounter any resistance, rotate the crank slightly one way or another until the cam turns free again. Once the cam has moved past the obstruction rotate the crank back where it was, and when both cam marks are sitting straight up, put the crank back on the TDC mark.

westyguesty · 01-19-2013, 06:10 AM

Great, crank turned back 45 degrees with no resistance, and both cams now turn with only spring resistance, peaking every 90 degrees.
Both cams set straight up, crank now back at Z1, so time to try and get the cam timing correct.

Might be along for a bit more help later . . . . . .

JohnJL · 01-19-2013, 02:38 PM

OK, I'll be the $ick and say..why drop the motor and go throug all the trouble and NOT check the valves, heads and cams? You have done 90% of the work and if you have a problem, you'll have to re-do 50% of it?

My humble advice would be to take the heads apart and at least clean them, check for wear and renew the seals.

westyguesty · 01-25-2013, 11:40 AM

I did have the heads booked in at one place to have them done, although they look good, and I haven't really found much wear anywhere on the engine. They let me down, kept moving the date, and couldn't give me a fixed price. I may have them done over next winter if everything goes back together and engine runs OK, and get different cams at the same time.

On to my next problem / sanity check - the cam timing.

Crank at Z1, both cams pointing up, pins in, chains under tension, etc. Dial gauge at zero, then crank rotated 360 degrees. Gauge moves back and now reads 90. It's a 930/10 engine, so I think camshaft should be set at 0.9 - 1.1 overlap.
So do I now take the pin out the camshaft and move camshaft until dial goes round 90 (anti-clockwise), back to zero. Pin again and try again, keep going until the gauge goes round once, back to zero by just turning the crank. (Hope that makes sense).

Then do the other side ?

Thanks

Flat6pac · 01-25-2013, 12:01 PM

You need to pre load several MM on the dial guage so you can see the cam rotate. Set it at between 4 and 6mm, set the pointer and that point becomes zero and you have plenty of space. Load the cams as close to 1.1 as you can to get the match and have stretch of the chains built in.
Each time you move the pin it is generally equal to .15mm of valve movement.
Make sure you load pressure to the cam, turning clockwise to get the best reading after moving the pin.

westyguesty · 01-25-2013, 12:46 PM

I have preload on the gauge and put the pointer at zero.
To load the cams to 1.1, would I turn the crankand cams round by turning the crankshaft 360 degrees. When I did this the gauge moved back to show 90. Would I then unpin the camshaft and move it bac so the gauge goes back another revolution (1.0 ?)

westyguesty · 01-26-2013, 01:01 AM

I thinnk I have got my head round cheaking / adjusting the timing now after more reading.

jsut checking that it's recommended my cam is set at 0.9 - 1.1. Would 1.0 be exactly 1 full revolution of my gauge ?

Thanks

safe · safe's Garage

I agree with JohnJL.
I think you are fooling yourself, 9 out of 10 times the exhaust valveguides are shot, the rest of the engine can very often look pristine.

Flat6pac · 01-26-2013, 06:13 AM

Yes, 1 full turn is 1 mm, each .1 is marked as 10, .01 is each mark.
You cant expect the pinning to hit exactly so you pull the pin and replace it.
If when matching the right to the left and the numbers dont come in as desired, pull the pin and rotate the gear one tooth, you ll get a whole new set of numbers to work with. You do have to drop the tensioner to rotate the gear.
Bruce