T.D.C. on the P1 2.0TS Engines. - Alfa Romeo Forum
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(Post Link) post #1 of 13 Old 13-05-15 Thread Starter
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Hmmm T.D.C. on the P1 2.0TS Engines.

I know that this has been discussed many, many times but! I have now confused myself and talked myself into an issue that may not even exist?

Basically....

Cambelt and balance belt change on a 2.0TS Alloy top engine, the advice is always "Two full revolutions of the crankcase". I removed the camshaft on the inlet side in order tyo replace variator and upon putting the camshaft back in its place, i simply tightened the camshaft using the cam locks to secure the top end at TDC with the the other cam caps installed also.

So, ..... am i driving myself mad or does the crank not need need to be turned two revolutions as it takes two full revolutions to turn the camshaft one full revolution, so, do i just turn the crank until TDC on No1 cylinder ie: only one revolution needed and then mount the belt/s?

Sorry if this appears a silly question but i have this doubt in my mind before i attempt starting the engine after a full belt change and at the moment cannot think straight!

Thanks in advance as always.
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Were you at TDC before you removed the inlet cam?
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I was Dan, its just the crank has been turned several times after belts were removed as TDC on crank was attempted several times using both long screwdriver and then a TDC guage. The car was initially (with old belts on) turned to TDC on the camshafts via crank before belts were removed.

The problem is i do not know how many times the crank has been rotated with belts off, am i right in thinking that two revolutions of crank is only necessary when bottom end is linked to top end ie: cambelt on? Otherwise as long as crank is TDC on no1 cylinder ie: one revolution of bottom end then im good to mount belts?

Or am i missing something?
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Sorry, to answer your question the inlet camshaft was removed once TDC on camshafts was achieved using Cam locks. On rreplacement it was bolted inwith camlocks and other bearing caps. It was not rotated upon install until belt had been installed.
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Ah OK, you just need to time the cams & crank back up, it doesn't match "which TDC" you are on as you've had the belts off. The ECU will know as soon as the engine spins up as it'll get signals from the crank & cam sensors.
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Number 1 cylinder at TDC, both cams installed, both cam locking tools installed, and then follow the rest of the cambelt change procedure (pulleys loosened etc). You can't go wrong
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Think i have it? I understand how easy it is to drive yourself insane.

Where i was confusing myself was the Compression & Combustion cycle.
The cycles are determind by the camshafts, therefore as long as camlocks are fitted and first two lobes of Intake cam are pointing up and towards rear then the cams are set for Compression stroke.

The Crank reaches TDC on every revolution as demonstrated on crank pulley and lower plastic engine cover. It is the camshafts that dictate if its Compression or Combustion.


Am i right?
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Cheers Dan, you posted as i was explaining what was going on in my head above.
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glad you got it straight now.


but how could you turn the crank without belt with the exhaust cam still there?

and since you have the tdc gauge now, did you notice how much you can turn the crank without seeing the screwdriver move?
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Hi Cuore, with exhaust cam at TDC i read that the crank can be wound without touching any valves and that was what i found.

The screwdriver was deployed at dwell on TDC and double checked when my TDC guage arrived, the screwdriver was good enough in my opinion and TDC guage was used for peace of mind.
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If no.1 is at TDC, then just fit the cams using the cam-locks.

The two rotations is just to get the cam-phase back to where it was before (first rotation switches it between inlet and exhaust phases) if the cam-belt is on while you're doing the rotation.


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Cheers Ralf, i got there in the end but nearly drove myself mad in the process.
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Member car:

Alfa 166

The TDC gauge is there to fine gauge between the piston reaching the top of the stroke and then returning back down.

But what you find is there is quite a bit of slack BTDC ATDC. You are meant to mark half way between those points as true TDC.

I think each alternator pulley has two marks on it if you refit it and the crank cover to show a rough estimate.

Between those two marks you can get the ignition to advance or retard slightly.

Same with the camshafts as they are virtually on verniers with the movement. Although you are supposed to just use the inlet pulleys for tightening only.



But as PUD says. Doesn't matter how many times the crank is turned. Its got two movements up and down. So doesn't matter where in its rotation its at so long as its at the top and in between BTCD and ATDC.

You can get away with quite a bit of movement each way. But it'll effect fuel consumption.

Currently my car as I do a lot of motorway I've advanced the exhaust as to open up earlier the scavenging at higher revs. Only a couple degrees. But even that makes idle a little rougher. But allows smoother high rev's and better mpg during motorway driving.

Regards
Scott
Alfa 166 2.0 Twinnie - LPG and a few trick performance parts
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