Novice engine rebuilding Z1 TDC predicament.........

[boyt911sc]

The engine rebuild project for this high compression (10.3 : 1), twin-plug, EFI, individual throttle body, distributorless, crankfired, TEC-3 system, etc. went smoothly with minimal problem last summer. While I have rebuilt 9 SC engines before, this was my very first non-stock 3-liter engine project.



The engine was turned over to the owner about 3 months ago and sat on a cart awaiting installation into the car. Transmission was bolted to the engine. And the owner noticed how difficult it was to turn using the alternator belt. It just kept slipping and not rotating the crankshaft a bit.

It was decided to remove the spark plugs, transmission and starter. Still difficult to turn the engine. And finally, all the rockers were loosen to relieve the pressure on the cams and this where problem originated!!!! The crankshaft pulley was @ Z1 when all the rocker arm screws were back off without determining whether it was Z1 (TDC) for cylinder #1 or #4 (???).

Since this engine is distributorless and crankfired, I have no way knowing what Z1 is? Without the OEM distributor (ignition) how could I set it to Z1 compression for cylinder #1?

Any suggestion, recommendation, or comment are highly appreciated. Thanks.

Tony

[Emo993]

Hi Tony, not an expert...but if number 1 is at DTC and Number 1 cam lobes are in a closed valve position, that is Z1 TDC. Having rocker arms screw backed off does not change that. If I'm missing some thing, we need Walt to chime in. mark

[KTL]

Backing off valve lash screws doesn't change the timing. It just screws up the valve clearances.

YOu can back off a valve screw wherever you want in the rotation of the engine. I'm not necessarily endorsing this, as some of the screws are loaded pretty good by the valve springs depending on where the rocker's cam following pad sits on the cam profile.

Z1 TDC is always going to be either the #1 or #4 cylinder's TDC. So check your cam lobes to see which lobes (both intake and exhaust) are on the "closed" side of the cam lobe.

Also, you can take a look at the timing teeth on the trigger wheel. If it's a 60 minus 2 wheel, my recollection is the static timing should be at the trailing edge of the 11th tooth when at #1 TDC. That's how my HPV-1 electromotive was baselined.

[boyt911sc]

I have re-set the valve gaps @ 0.10 mm for 1-6-2-4-3-5 cylinders using Z1 TDC (??) as my stating position for cylinder #1 and so on. Re-checked the gaps three (3) times and I could not be more happier. I have to go back and inspect the cam positions when doing #1 and #4 cylinders. Will keep you posted.

Tony

[lindy 911]

While rotating the crank, TDC (Z1) for #1 will be just after the intake valve closes and the piston reaches TDC. You can use a pencil in the spark plug hole to see when the piston is at the top and align the crank pully Z-1 mark with the crank case seam on top.

I don't see how this has anything to do with the engine not turning easily. Using the crank pulley bolt, the engine should turn with minimal resistance with the plugs removed. If the cams are out of time the valves will hit the top of the pistons.

[KTL]

Does the engine have a "special" flywheel? I've seen that Fidanza aluminum flywheels typically have tight clearance against the engine case and you have to massage the case material near the M8 nut locations for the case parting line

[boyt911sc]

Originally Posted by lindy 911

While rotating the crank, TDC (Z1) for #1 will be just after the intake valve closes and the piston reaches TDC. You can use a pencil in the spark plug hole to see when the piston is at the top and align the crank pully Z-1 mark with the crank case seam on top.

I don't see how this has anything to do with the engine not turning easily. Using the crank pulley bolt, the engine should turn with minimal resistance with the plugs removed. If the cams are out of time the valves will hit the top of the pistons.

Lindy,

The engine turns using the crankshaft pulley bolt. But using the alternator nut/belt to turn the engine does nothing and just kept slipping. So it was decided to check what's the problem. The transmission was disconnected, spark plug removed, and finally all the rockers adjusting bolts were back off. And still the engine won't turn using the alternator nut/belt.

Now looking back, the slippage is probably due to the after market crank pulley that is not grabbing the belt like the OEM (???). The engine turns easily using the crankshaft bolt.

There is plenty of clearance between the valves and the pistons. I have rotated and tested the engine over a hundred times after cam timing and valve adjustment. Plus lubricating oil and assembly lube made the cranking easier. Thanks for comment.

Tony

[boyt911sc]

I have used the crankshaft bolt for turning the engine during cam timing and valve adjustment. And never once used the alternator nut/belt. Now that the engine has the motor mount bracket, using the alternator nut is very convenient to use turning the engine but not in this case.



The engine was cranked close to a hundred times (total) during the process for testing the clearance between pistons and valves. Plus actual travel was measured accurately using a dial gauge.



I had the original ignition distributor installed on the engine during the course of the rebuild and was removed after everything was completed. So I never paid attention to the cam lob orientation and relied solely on the Z1 and rotor position. Without the distributor installed, I was somewhat lost. Now, I know what to watch out and observe. Thanks.

Tony

[KTL]

Often times you have to apply some pressure to the midpoint of the belt span to get it tighter on the pulley. Then you can crank the engine over with the fan pulley

[Dr J]

^^^^
What he said.

[boyt911sc]

Originally Posted by KTL

Often times you have to apply some pressure to the midpoint of the belt span to get it tighter on the pulley. Then you can crank the engine over with the fan pulley

Kevin,

I've been pressing the alternator belt since I started tinkering 911's but this practice is not doing anything to turn the pulley/crankshaft. The engine spins OK using the pulley head bolt. So there is the question on the coefficient of friction between the new crankshaft pulley and the new belt. It does not seem to grab the pulley even if you apply pressure to the belt during cranking. I have to look further and investigate this anomaly. I'll keep you posted. Thanks.

Tony

[snbush67]

It is strange that the belt is slipping with proper tension. Perhaps it is just the coating on the new parts, are you using a new belt? Sometimes belts get glazing from slipping and then they don't grab at all no matter how tight. Sometimes you can use hair spray to get them to grab.

[boyt911sc]

Originally Posted by snbush67

It is strange that the belt is slipping with proper tension. Perhaps it is just the coating on the new parts, are you using a new belt? Sometimes belts get glazing from slipping and then they don't grab at all no matter how tight. Sometimes you can use hair spray to get them to grab.

snbush,

The belt and crankpulley are new. I'll borrow (swipe) my wife's hair spray can tomorrow and try it even if it sounds silly. Would a belt spray used to prevent squealing noise help? Will keep you posted.

Tony

[Walt Fricke]

Tony - I think about the only thing different here from the 3.0s you are used to is that the valve to piston clearances are more critical. So the window for setting the cams without interference is smaller. But with all your checking of this, it doesn't sound like you missed anything there.

Could you try various used fan belts? Maybe somehow you have one with the wrong side angles or is too wide? Not enough belt tension would be resolved with the finger on the belt trick you know as well as the rest of us. The Clewett pulley works fine on my race motor.

But what's this business of powder or other coating of the fan pulley half which is built into the fan? Huh?? Might the friction coefficient of that be too low?

You have a later fan (lots of small holes, and typically used with a smaller diameter pulley half with lots of small holes). I've successfully used an earlier, larger effective radius, fan pulley half with fewer, larger holes in this application without the kind of problem you have, so I don't think that is the problem one way or the other. But that paint - - -

[KTL]

Originally Posted by Walt Fricke

But what's this business of powder or other coating of the fan pulley half which is built into the fan? Huh?? Might the friction coefficient of that be too low?

VERY good observation by Walt. I think he hit the nail on the head with that sharp eye of his!