131mirafiori forum

Hi All,

1983  Fiat 131 2 ltr twin cam
 
I have been having a problem with engine power. The engine is flat out at 80 mph.

18 months ago it had a full engine balance and I fitted new main and big end bearings, the head was overhauled by someone else previously. Thought the lack of power was to do with a carb jetting issue. I tried various size jets but not much improvement. So now I am looking into the cam timing. 

I did a compression test with engine warm and WOT, cyclinders 1,2 and 3 were 172 PSI and 4 was 170 PSI. Which is approx 12 bar.

I have been checking the valve clearance ( cold engine) with the lobes perpendicular to the buckets/shims, the feeler gauge passed between the camshaft and tappet with just the slightest of gripping feeling and I have discovered the following:

Haynes states Inlet clearance as 0.018 in, (0.45mm) and mine measured correct.

Exhaust clearance Haynes states 0.024 in. (0.60mm) but I have clearance measurements of:
Actual clearance measured for cyclinders #1, 2 and 3 is 0.019 in. (0.48mm) and #4 is 0.016 in. (0.40mm)

As you can see there is quite a discrepency to the specification. I have just been looking at the Haynes manual page 186 supplement section again and there are two sets of listings on the page for valve clearance. Now I totally confused.
It reads as follows;

Valve Timing (valve clearances set at 0.031 in (0.8mm) and underneath it lists the inlet and exhaust opening and closing degrees. But at the bottom of the page it lists Valve clearances ( engine cold) and lists the dimensions for
Inlet ... 0.018 in (0.45mm)
Exhaust ..... 0.024 in (0.60mm) .

Now I am starting to get a bald spot from scratching my head. Hymmm. What dimensions am I supposed to work to?

With the belt on at the moment the crank and cam marks all line up but tomorrow I will check true TDC and the degrees of opening and closing of the valves and determine where full lift is with a dial gauge.

The head was overhauled by someone else and find it hard to understand how he could fit shims that are so far out, if that is what the problem is.

Could this be causing the problem of lack of power as mentioned earlier in the post?.

Are both standard camshafts identical in lobe shape etc?, do they have identity marks? Just wondering if they were fitted the wrong way round would that affect the valve clearance or does it not matter which side (inlet or exhaust)they are fitted on?

Advice please for what I need to do to get the clearance back to within spec. I have not done any shim etc. work before so some guidance would be appreciated.

Regards

keith

Clearances do change, that's why they're required to be checked periodically.

Not likely, those clearances aren't far enough out to be of major concern. Saying that, if I had the cam covers off I'd readjust clearances.

If they're standard cams, unless you need a drive gear for a cambox mounted distributor, the cams are interchangeable. The cam wheels are not, make sure you have them around the right way.


There's ya problem! The best use for a Haynes book is hang it on the toilet wall for emergency tear off sheets when the roll runs out.

Another possibility is they have mixed the cam wheels up as this would put the valve timing out but not by that much but would affect performance I would think.
I made my own tool for these years ago but now have the proper tool, I think Ricambio would still sell them ?
18 and 24 thou sounds right from what I remember.
0.1 mm  =  4 thou so it looks like some of those haynes conversions are out but thats no surprise.

Just checked for you :   If you look at the inlet camwheel the timing hole should be to the left of the locating peg
If you look at the exhaust camwheel the timing hole should be to the right of the locating peg.

Reading all of this i think the problem is not with the valves.

Perhaps a stupid question, but did you check the ignition timing? Do you have electronic ignition? Check the wiring inside the dizzy. If it's damaged you could lose a lot of spark.
Also check the mechanism inside. If that doesn't work proparly then you won't have the timing right at higher revs (sorry, don't know the expression in english).

Personally i think this last thing is your problem.

Ignition centrifugal advance.

Thanks, that's the expression i was looking for  ;)

Hi All,

David, thanks for the cam wheel identification I have checked and they are correct way round.

Tas131, you could be right about the Haynes manual. I have been reading Guy Crofts book and he states different opening and closing degrees for the valves. He is the man that knows about these things. So as I said I will check the opening and closing degrees of the valves and see who's spec is nearest. I have no reason to think that the cams are not standard so it will be interesting to see what full lift readings I get.  With regards to my current exhaust valve clearances that puts 3 valves out by 12 thou and 1 out buy 20 thou. why do you not think that those readings are not a major concern? If the clearance is not as spec would that not mean that the valves may not be fully closing?
Do I just remove the current shims and measure the thickness and deduct the 12 thou and 20 thou and simply order new sizes to the nearest thou.? What suppliers are in the UK.

Mirafioriman, the timing was set at 10 deg BTDC and the distributor was advancing. I take your point and will be checking it in more detail later but first I think that I should sort the valve clearance problem. I have just got a crank degree wheel so I will set up everything as accurately as possible and mark the max advance etc.

Please keep the opinions coming.

regards

Keith

Keith, If the valves were still open it would pop and bang and spit back through the valves and you would here this through the carb.
Was this engine ok before the work was done or had you never tried it and had the work done and ran it ?
If it runs fine but has no go it could be something else, I once bought a 131 sport that sounded fine but the car wouldn't do more tham 102mph on the clock and it turned out someone had fitted a 12/43 rear axle out of an automatic in it and the axle bottomed out at 102 mph but 80mph is a different kettle of fish.

Valve clearance is fine. 12 Bar !! It must be something else. Could be a wrong rear axle fitted, like David says.

Or....try shift to second gear... :D :D :D :D :D :D

firstly slightly tighter valve clearences (up to a point) will make the engine go better at speed but you will have a rubbish idle and fail the mot.
 what are you using to find tdc?, a classic mistake is to have the front pulley timing mark at 12oclock especially if your'e not using a cambelt cover. the correct mark (on the cover) is around about 2oclock.
you could have a blocked exhaust but this is near to hugely unlikely on non cat systems.
 lastly have another look at the carburettor, the alloy fuel delivery jets which straddle the barrells, its possible to fit the wrong way round blocking the fuel flow.

 where abouts are you? id quite like to take alook myself .
  

Just thought of something is the butterfly on the second choke seized solid with corrosion ?  I have seen this on webers.

The large OEM clearances are more than likely to allow for owners that don't maintain their vehicles, so parts can wear, gaps close up a bit, but no catastrophic consequences. I've got a set of aftermarket cams, the manufacturer recommends 0.007" clearance, intake and exhaust. I ran them at those clearances for several years without issues.


Yes, basically. But you'll require a special tool to push the bucket down and hold it while you remove the shim. Not sure about the UK, but some of the American suppliers have them. I've made my own several times over the years, crude but effective.
http://www.autoricambi.us/product/CH0-012/Valve-Adjusting-Tool/
I've bought bits from these guys several times, they're very good to deal with.

A good pair of screwdrivers will do also. A smooth one and a very edgy one. I'm doing it that way for over 27 years now.
And i still say the valves themselves are not the problem here.

Another dum question perhaps. But if you put down your right foot...does the trottle open completely? I once had that problem. Seemed the gaspedal was bend so i raised a little and my problem was solved. ;)

Hi All,

David, I dont get any popping through the carb.  My engine is fitted in my Morris traveller. I used to drive my 131 supermirafiori until 1996 when I was "T" boned and the car was a write off, so I bought the wreck back and stripped it.  All running gear is from the same car, engine, gearbox and rear axle so no mismatch with the axle. The engine was ok but getting a bit tired, burning some oil etc so I gave it an overhaul. It runs ok and idles at 950 rpm it just doesnt have the umph that I had when using it in the 131 when 110 mph was no problem. Thats why I know it is way under performing.

Strada, the current belt is fitted by lining up the cams to the marks on the cam housings and the crank TDC mark on the cambelt cover. When I was fitting the belt I used the screw driver down the plug hole to find TDC but having read up on how to use a crank degree wheel I realise that I may not have TDC spot on, so tomorrow I will set it up properly and see where true TDC is in relation to where I have it set. Although all the marks line up that doesnt mean that TDC is correct if TDC was not correct to start with. I believe that a few degrees out on the crank can affect cam timing and performance.
I the original cast exhaust manifold 4-2-1 set up with two silencer boxes, the front box is fitted approx 6" from the end of the downpipe and the rear box is fitted just before the axle.

I live in near Boston, Lincolnshire. If your near here you are more than welcome to pop in.

Mirafioriman, I have held the throttle wide open at the carb and the flap is fully open in vertical position, I have wedged the throttle peddle down and checked that the flap is also reaching vertical and it is.

Regards

Keith

Nice looking car ;)

Love the colour too ;D

Thanks Mirafioriman,

The colour is Fiat 124 Rosso Damask,

Regards

Keith

Did you check the carb as suggested by David earlier?

The Weber is a 2 stage unit with the second barrel providing the extra surge to accelerate and get the top end when you open the throttle.

Take the filter off and look down the carb.  The main barrel should be closest to the cam box.

If you open the throttle linkage the main barrel flap should open and squirt petrol into the manifold.  At about 3/4 throttle the linkage should engage the secondary barrel and both should then be open at full throttle.

Please check, as I checked a Monte Carlo carb last week that had siezed after being stood for a short time!

Hi Duncan,

I have checked and both barrels are wide open (vertical ) at full throttle and the throttle set up works smoothly.

Regards

Keith

Well did you get to the bottom of the problem ...

Hi Jason,

Ill health and work has prevented me from doing any further work to the car, but over easter I am planning on returning to the garage and will of course report back,

Regards

keith