2000 Tc engine doesn't run

[mirafiori76]

Hi everybody,
I have a serious problem even since I am a Fiat mechanic for 25 years and am rebuilding a group 4 car.
I have a 1978 (one of the first) 131 Racing which won't run. The engine simply doesn't start. I already checked timing and compression, changed cilinder-head, double carbs, complete ignition but it won't run. Towed it three blocks and changed ignition-timing several times. Somewhere between big flames coming from the carbs and big bangs from the exhaust there must be a moment that the engine will run, I think. Does anybody have a suggestion? What am I missing here?
This engine has the following: race-cams with adjustable camwheels,
                                                bigger valves which are perfectly timed.
                                                new timing belt, timing ok
                                                new ignition coil, new cables and sparkplugs
                                                new distributor
                                                double 44 carbs which can breath freely
                                                4-2-1 exhaust manifold

HEEEEEEEELP
Thanks,

Mike

[curt]

Hi Mike -as you are already a mechanic Iguess youve checked this.
It sounds like from what you describe as flames and banging that the distibutor drive is 180 degrees out.Is it a cam or block dizzy ?
First Id check timing belt is correctly on i.e. all marks aligned correctly.
Id double check by removing the cam covers and looking at the cam lobes on cylinder one being on compression stage and crank pulley on or near TDC.
Then you can pull off the dizzy cap and check the rotor arm is at or near cylinder 1 plug lead ready to fire. I would then turn the engine over by hand and check the rotor moves round freely and aligns correctly in the right firing order as the cam lobes all come into position on their compression stroke .
You are obviously getting ignition hence the flashbacks you are getting .
Failing that All that is  left is either a very weak air fuel mix or very bad valve seats across most or all of the cylinders

Hope this helps

Curt

[david]

As I recall when the front cam wheels and crank are all in alignment the fiat twin cams fire up no 4 cylinder first so you want the rotor in the distributor pointing at no 4

[curt]

Cant remember that far back 
But a quick look at the cam lobes will tell you which cylinder should be firing

[Thotos]

As I recall when the front cam wheels and crank are all in alignment the fiat twin cams fire up no 4 cylinder first so you want the rotor in the distributor pointing at no 4

Yes that's right and I can confirm that if you don't do that you can burn your rather expensive ITG filter with the flames that come out of the carburettor!  I still have the burnt filter somewhere if you want proof     And I can still hear Simon saying "I told you so..." 

As Curt said above, it sounds to me that your problem is distributor out by 180 degrees. With the static timing marks on camwheels and crankshaft all lined up the rotor arm should be pointing at the number 4 cylinder HT wire.

[djape1977]

ha a similar problem on my twincam lada last year...
turned out to be a faulty ignition coil.
also, electronic ignition unit (comutator or whatever you call it in your part of the world) could be faulty.

if you have a source of LPG or ACETYLENE you can bypass carburetors and feed the gas directly tru the carb into the engine. helped more than once to eliminate fuel system as a source of the problem.

still, sounds as if you have an electrical problem.

[djape1977]

change the coil. preferably take one from a running car for a test to be 100% sure that it's ok.

[curt]

I dont mean to' teach your grandmother ' as we say but -
 I know you say you changed the cables 1-4 and 2-3 but that wont help if the rotor arm is mid position between two cylinders -The spark will just arc and jump to the nearest contact tower in the distributor cap which could be any cylinder.
For peace of mind and you may already have done so I would physically check that the rotor is smack on with the distributor tower of the correct cylinder.
Another thing maybe is that the rotor has not located correctly on the shaft-had this happen before !
With the popping and banging as you say from either inlet or exhaust it has to be an ignition timing or valve timing problem.Valves are closed for approx 180 degrees of the four stroke cycle-both exhaust and inlet fully closed for 90 degrees of crankshaft revolution on compression stroke-therefore for flames to erupt from inlets or exhaust popping-either ignition is way out of time or there is a major arcing/tracking fault in the distributor cap or LT release side.If all that is OK then it has to be valve timing.
Ignition has to be occuring when either inlet or exhaust valve is open to cause that to happen.I know this is silly but you have definitly got 2 and 3 the right way round ?Once again I would say remove the cam box covers and physically check the cam lobes for timing -maybe the marks are in the wrong place
Good Luck

Curt

[parrish]

Camshaft timimg!
Remember camshafts are timed in No: 4 @ TDS on a Fiat TC.
If you have the original camshaft pulleys you cant really go wrong, however if you have aftermarket vernia pulleys the chances are that you have timed them in with  No: 1 on TDC and  not No: 4, that will put your timimg 180 degrees out.
Go back to basics and check the timing/camshaft alignment.
Regards
Steve

[curt]

Posted by: parrish  Posted on: Today at 05:04:04 PM 
Insert Quote 
Camshaft timimg!
Remember camshafts are timed in No: 4 @ TDS on a Fiat TC.
 
Sorry to correct you -Dont you mean TDC 

Just pulling your Leg 

[djape1977]

pall, had a same problem, even changed the head too, turned out to be ignition coil in the end. even had a backfire trough carb.

[curt]

Well if youve checked everything that much and youve changed all the ignition components and carb then it has me stumped as well 
My next advice would be sticking valves or bad valve seating or broken valve spring or shim bucket jamming or just badly adjusted but youve changed the head as well 
It really is a mystery -time for scooby doo 
Will keep thinking -but Im stumped -let us know how it goes on 

Gut instinct still says timing though 

Just a silly thought -when you replaced the head were the manifolds already on it -I know of people that have covered the inlet ports with tape to stop dirt ingress and not removed the tape before putting the manifolds on 

[Tas131]

After reading through this thread, I'm voting for a weak spark. If the cam timing is correct, and the ignition is not 180 deg out, with enough fuel it should at least fire a couple of times on a squirt from the accelerator pump. I'd be checking cam timing and applying a dab of white paint on the crank and cam pulleys so I could check with a timing light while cranking. With a timing light on number 4 plug lead I'd be checking crank and cam timing, if the spark is +15-0deg from TDC on the crank it should run, if not I'd be suspect of the quality of spark at the plug.

[curt]

Just had another thought-some dizzys had a shear pin in the drive dog/gear.
If the pin does shear than even though the rotor shaft may be seen to turning over by hand -friction on the shaft is all that is turning it -when cranking they can slip to another position.

[curt]

when you say checked - have you physically taken the cam box covers and dizzy cap off and turned the engine by hand looking at the cam lobes for firing positions and also physically checked TDC by taking a plug out and ' feeling ' the cylinder is there ? I know its a pain but marks and pulleys can lie -mechanical positions cant! It still says timing- Have you ran a compression test by the way ??
Another thought-you say that you changed all the ignition components-and it still wont go - have you checked the low voltage side -ground and feed to the coil when cranking over - it may have an intermittent power feed or too low a voltage when cranking
this could cause the problem -a volt meter would show this up