Timed on #1 or #4 cyl?

[keith m 131]

Hi All,

I was reading in the thread listed below and Parrish states that the TC should be timed up on #4 and not #1, can someone explain why this is, I would have thought that it would not make any difference if the engine was timed with either #1 or #4 on the compression stroke, the crank at TDC and with the rotor arm pointing at the relevant terminal on the dizzy cap. Am I missing something here?

http://www.131mirafiori.com/smf/index.php?topic=4042.msg31705#msg31705

Regards

keith

[Thotos]

Are you talking about ignition timing or camshaft timing? Parrish is correct about camshaft timing: With the crank and cam pulleys set to their correct timing marks, the rotor arm should point to number 4 cylinder. Get the ignition timing 180 degrees out and you'll get flames out of the carburettor(s) instead of in the cylinders. If you don't believe that I'll show you a badly burnt ITG air filter  

[mirafiori76]

Fiat should have put the marks on the pulleys for first cilinder instead of the fourth. Would have been a lot easier.

[keith m 131]

Hi Guys,

Both cam and ignition timing Theo,

Cam Timing...What position should the cam lobes be in when fitting a new belt to correctly time the cams?

Ignition Timing...On the standard engine with the cams and crank lined up with the relevant marks on the cam pulleys and the cam housings and with the crank lined up with TDC, is the distributor installed with the rotor arm pointing at 1 or 4 . Which cyclinder should be on the compression stroke? then the other would be on the exhaust stroke, or does it not matter. I ask this because I have read that a timing light should be attached to #4 lead.

Dare I say it but Haynes state that when fitting a timing belt, it should be set up on TDC with #1 on compression .. They also say the same when fitting a distributor and that the rotor should point to #1 and not #4. I know that people on here say that the manual should be put in the bin but surely there must be some truth in what they say, thats why I confused at being told that it should be set up on #4.

Mirafioriman, I dont understand what you mean by " Fiat should have put the marks on the pulleys for first cilinder instead of the fourth. Would have been a lot easier". Surely the cam marks are the same for setting both cyclinders, with the belt fitted then would it not be a case of just rotating the engine until #4 is on compression or #1 is on compression and then set the dizzy. What is the answer to my question under cam timing above, if I know the answer to that then my confusion should disappear.

Regards

keith

[Thotos]

With the crank and cam wheel marks lined up to their marks, the rotor arm should be pointing to number 4 cylinder.
When setting up ignition timing, connect your timing light trigger to number 1 cylinder.

[keith m 131]

Hi Theo,

I was editing my post when you replied can you read my last post again especially relating to the cam timing. For instance if I were to line up the cams to the relevant marks and then rotated the pullys 360* then would the cam lobes return to the same position,  if not I think this is where I might be going wrong when fitting the belt. I havnt taken the cam covers off yet to see what happens everytime the pulley is rotated 360* I have just thought about it now following your comments. 

Is this what you mean by setting the cam timing to #4

Keith

[Thotos]

if I were to line up the cams to the relevant marks and then rotated the pullys 360* then would the cam lobes return to the same position

You are confusing me now    The camshafts are turning at half the speed of the crankshaft, so when you say "rotate the pulleys 360 degrees" do you mean of the camshaft? which would be two revolutions of the crankshaft which would be a complete turn of the distributor (driven by the 'in block cam' or layshaft). If you rotate the crankshaft by 360 degrees, you'll only rotate the camshafts by 180 degrees so if you start with rotor arm at number 4 it will be at number 1. There are four strokes of intake, compression, combustion (power) and exhaust in a four-stroke engine and they occur during two crankshaft rotations per power cycle.



So if you are putting a new belt on the engine, line up the crankshaft pulley to its TDC mark, line up the two camshaft pulleys to their timing marks, line up the idler shaft pulley so the rivet is pointing to approximately 2:00 o'clock (so the distributor rotor arm is pointing to number 4)  and fit the belt. Then when the engine is started (hopefully!  ) connect your timing light to number 1 cylinder and set the timing to 10 degrees BTDC (set the idling as low as you can for this so the advance weights don't have any effect).

[keith m 131]

Hi Theo,

Thanks for the graphic,  

I think Ive got it, If I line up the crank to TDC and the cam pulleys to their marks should #1 valves be on the overlap whislt #4 is on compression.

As I said i havnt got access to take the cam covers off until the weekend but from what I can remember by looking at #1 is that the inlet cam lobe is about to open the valve and the exhaust lobe is just after closing. So in this position is #4 on compression? hence the rotor pointing to #4.

I thought that in this position that #1 valves were closed but I have realised that they are not closed but in the overlap position. I have been fitting the belt in this position which it would appear was actually correct relating to #4. But I thought I was setting up #1.

Is what I am saying now making sense.

Regards

keith

[Thotos]

Yes, I think we're in agreement now 

You need to take the cam covers off to satisfy yourself but with all the marks lined up, number 1 cylinder is starting its four-stroke cycle, hence the reason for the marks being where they are    That means number 1 piston is at TDC having just finished the exhaust stroke and about to start the intake stroke so the exhaust valve has just closed and the inlet valve is about to open. At the point of number 1 starting its 4-stroke cycle, with a firing order of 1,3,4,2,  number 4 is half way though it's cycle; so it's finished the intake cycle (1) and also finished the compression cycle (2) and it's about to go into the power cycle (3) hence the rotor arm is at the point ready to fire number 4 spark plug. 

When it comes to using a timing light to time the ignition, you are not concerned about the position of the cams but only concerned with the position of the crankshaft (i.e. the pistons) and as there are two revolutions of the crank per engine cycle, you can connect the ignition light to either number 1 or number 4 cylinder. But I find it more logical and easier to connect to number 1 cylinder.

 

[keith m 131]

Thanks Theo,

Yeah I have got it now. I realise where I was going wrong in thinking that #1 valves were closed but in fact were overlapping and about to start its cycle.

You may recall from my previous posts in the Garage section, 2ltr cambelt query and valve clearance, I am having problems with the engine bottoming out at 80-85 mph. I have reset the valve clearances, I have replaced all the electrical components, all the jets in the carbs etc are as spec and clean, the float level is correct. I am now thinking that my problem may be to do with the advance in the distributor.

With the static advance set at 10*BTDC the full advance is only approx 25* including the static 10 at 3500 rpm. I am basing this on the distance between the 10* mark and the TDC mark (approx 12mm) and my full advance looks approx one and half times that again. I can try measure this accurately (got any tips) but is this in the ball park. Although I have read in the Guy Croft book that it should be in the region of 37*

Whats your opinion on this, could this be causing my speed problem. Is there an easy way to check that the advance springs are working ok? I have centrifugal advance.

keith

[Thotos]

The standard 131 distributor has just centrifugal advance weights. The weights are controlled by two springs and I've seen a million (only slight exaggeration there  ) different types of springs. Unlike the 124 springs that are both the same, the 131 seems to have two different springs: one with slight tension and a tighter one with elongated 'loops' offering no resistance at all to start with.  I have experimented a lot with these springs and I can tell you that they make little noticeable difference.

I was always under the impression that static advance is 10 degrees and full advance is at 24 degrees so your measurements seem correct to me. It's important to have a very low idling speed when setting the static advance to make sure the weights are not advancing the ignition. If you can't get the idling slow enough (<500 rpm) then either disable the weights (cello-tape is good for this!) or set the 'idling' static advance to about 12 degrees. A lot of people now set the static advance to 5 degrees due to the low octane fuels but I found no problems running unleaded with 10 degrees advance. You can of course set up the static advance 'statically' but not so easy with electronic ignition.

I am certain that your limited top speed problem is nothing to do with ignition advance or with the ignition system at all. In fact from your description of the problem I'd say "it can't happen"!  If you have no loss of power in lower speeds (which you claim you don't) and you are not running out of revs at 80mph (which you claim you don't) then I can't see why the engine is not pulling beyond 80mph. Are you sure it's not fitted with a lorry-type speed-limiter? 

[keith m 131]

Now there's a point I forgot to look for a limitor, Ha.

Seriously I am getting really fed up trying to solve the problem, this engine was running superbly in the super and now its no better that the original moggy 1098cc engine, that used to do 70mph.

Something else I have thought about is the fuel return line, I have connected it and on reading guy croft book last night I came across this article. I have replaced the block mounted mechanical pump with an electrical pump fitted at the tank, based on what he says maybe the problem could lay here, under high rpm could some of the fuel be by passing the carb and returning to the tank?

keith

[Thotos]

under high rpm could some of the fuel be by passing the carb and returning to the tank?

That would be equivalent to running out of fuel. So I think the engine would cough and splatter not just 'not-go-any-faster'.

[keith m 131]

Oh darn it

[david]

Easy way to set the ignition timing and get it right is to drive it down the road and advance ignition timing until it pinks and retard it until it doesn't, It will take few stops to get it right but will be spot on.
Re your power/speed problem are you sure the second choke is opening ?  I know I asked this before but as Thotos said it makes no sense !