Finding No. 1 Cylinder TDC - rebuilding

While removing the harmonic balancer & pully assembly to replace the front oil seal, the pully, harmonic balancer, and mounting piece all separated. This creates two problems for me, I think.

1. Stupidly, before removing the assembly, I did not put the crank in the Z1 position. Now, although it is pinned, I don't know of a way to reassemble it so that the markings on the pully match the crankshaft positions. All three of the above pieces separated. If they had stayed intact, it would have been no problem, because the pinned mounting piece would mate up exactly in the correct position. Since the the pully and harmonic balancer are attached by 9 bolts, there are several ways that they can go back together.

2. I think the harmonic balancer & pullys were most likely "balanced" originally. There are small weights attached to the pully indicating that they were dynamically balanced as an assembly. Now that they are separated completely and I have no idea how they were originally mated (I didn't think to mark them), I have 1 in 9 chance of lining them up correctly, and an 8 in 9 chance of getting it wrong.

Any ideas??

Can I take the assembly to a tire place and have it spin balanced?

Any clue how to find TDC?


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Steve
'89 Carrera 4
'62 190 SL

Not familiar with the C4s but what about this...

Aren't there supposed to me markings on each camshaft that when doing rough valve timing you set pointing straight up?
So, if you remove the chain covers, see where the markings are pointing, then you should be able to rotate the crank until they face up, then the balancer and pulley should line up with the original holes, because with the markings facing up on a timed engine then the carank is at TDC.

Please god, don't take my word for it...ask someone else if this makes sense...but I think the theory is sound....


Best of luck,...I'm having a hard time imagining a harmonic balancer as my car dosen't have one.

Thanks for the thought. It would work, except the chains were not installed when I pulled the balancer/pulley assy off.

Well, it would have been helpful to tell us just where you are at the reassembly stage you are ...

If you turn the engine 'til #1 & #4 pistons are up at top (dial indicator, heads off) ... you are set to decide the cam timing at that point.

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Warren Hall
1973 911S Targa

I'm not sure what poses the biggest quandry for you: finding TDC or getting the crank assembly back into synch with the engine. Here's how to find TDC:

Since the notch on a production crank pulley may be off a few degrees due to manuf. tolerances, here's an old hot rod trick to find true TDC - important for accurate cam and ignition timing.

Take an old spark plug and remove the guts (porcelain and middle electrode), then create an internal thread through the middle of the hollow spark plug or weld a nut (about 5/16 or 8mm) to the spark plug shell so you can thread a long bolt through it. Now install this new TDC tool into No. 1 cylinder (with bolt backed off).

This procedure works best if the chains are off. Loosen the rocker arm adjusters fully (you don't want to introduce valve head to piston), as you will rotate the engine around without the valves in synch.

Install the crank pulley and rotate the engine (CC or CCW) so the crank pulley TDC notch is about 1/2" or so from the TDC line on the crankcase (for No. 1 cylinder). Thread the bolt in by hand until the bolt stops against the piston. A nut snugged on the bolt helps hold this position. Place a temporary mark on the pulley opposite the TDC mark on the crankcase. Now rotate the engine (by hand) again in the opposite direction. As you approach TDC, slow down, then gently continue until the piston stops against the TDC bolt. You'll feel the resistance. STOP and again mark the pulley opposite the TDC mark on the crankcase. You now have two marks on the pulley. True, absolute TDC is exactly halfway between the two marks. Repeat as often as you like to validate. If halfway between marks happens to land on the factory notch, great. If not, create a new notch as this is your new TDC reference point for accurate cam and ignition timing. Paint it with white paint for visibility and don't forget to remove your TDC tool.

I'm not familiar with the balance weights on a C4 factory pulley. They were either part of the factory crank, flywheel/clutch assembly balance or for the crank/vibration dampener only. If it's the former, I don't know what to suggest. Teardown for just this may or may not be critical or justified. If the weights are just for the latter, you could have the 3-piece pulley assembly balanced by a shop.

Hope this helps,
Sherwood Lee
http://members.rennlist.org/911pcars

Hello

Never been there, but just try if the holes will not aligne in only one position to rematch them perfect. ( I think the y have a slight irregular/uneven boltpattern )

Finding TDC on the engine is very easy just use the distributor marks.

Grüsse

Sorry Warren. Present status of build up: pistons, cylinders, heads, cam towers, & cams installed. Chains fit into place, but not timed.

I now think my main problem is finding TDC without tearing it down again, because on reinspection I realized that before tear down (in April) I did mark the balancer to match the pully tdc mark. Of course, I forgot this when the mess came apart in my hand. Of the three pieces, I'm able to put two (balancer & pully) of them together with confidence. If Roland is correct about an asymmetrical bolt pattern, I might be home free.

I'm a little nervous about Sherwood's hot rod trick since in involves introducing the piston to a bolt! But, it reminds me of a time I found "rough" TDC by watching a pencil, inserted through the spark plug hole, ride up and down while rotating the engine. I think that would get me back in the ball park, but don't know if it would work with 2 plug heads due to the angle of approach into the cylinder.

The crank has a locating pin "hole" on the front end. Does anyone know if that has any relation to any particular cylinder position?

Why o' why didn't I replace that seal when everything was open & apart??

[This message has been edited by sms1305 (edited 05-27-2001).]