131mirafiori forum

Hi all,

Following on from my thread regarding valve clearance I have a query about cambelt teeth. I have a Powergrip belt 5022 - 148 x 3/4". Is 148 teeth correct for a late 2ltr 131.? The reason I ask is because I checked the degrees of opening and closing on my valves and the inlet is spot on with the haynes spec of , opening at 15 degs BTDC and closing at 55 degs ABDC, however the exhaust is valves are opening at 50 degs BBDC instead of 57 degs and closing at 20 degs ATDC instead of 13 degs therefore making the exhaust valves 7 degs late which in turn causes loss of top end power/speed and also causes a loud noise from the engine plus wouldnt that affect the scavenging process. I do have a problem with loss of power and noise whivh is why I started checking the cam timing.

Please correct me if what I saying about late exhaust valves is incorrect. When I realised that the exhaust cam is running late I ckecked the marks on the back of the cam and cam housing and noticed that the mark on the cam wheel is approx 4 mm to the left (looking from front of engine)of the mark on the housing, which confirms that the cam is opening late.

So with regards to my question about belt size and teeth, I have removed the belt to re-align the exhaust cam wheel (move it to the right) but with the belt fitted to the crank pulley at TDC and auxillary pulley I cannot get the belt to sit on both the cams in their correct positions, it either pulls one or the other out of position. If I fit the exhaust correct (centred on the marks) then it puts the inlet approx one and a half teeth advanced or retarded. If I put the inlet correct then it puts the exhaust into approx one and a half teeth advanced or retarded. At all times I am maintaining true TDC on the crank.

If this is the correct belt size then what could be wrong?  If I have to ccept that one of the cams will be out then which set up is the better of the two evils? exhaust cam on time and inlet advanced or inlet on time and exhaust advanced. Or do I just forget about the set up marks and set up the cams as follows... Inlet  55 degs before full lift, full lift being 110 degs and exhaust cam 56 degs after full lift, full lift being 112 degs. 

Hope this makes and that I have explained myself so you can understand my situation

Keith,

I read your story over and over again. And it's such a strange story. No way you can set the cams off 1 and a 1/2 tooth. A half maybe, but not 1 tooth further. And that half isn't so bad, as long as you turn inlet side inwards. I once had a 200 TC wich had the inlet cam 1 tooth inwards, on purpose. Stationary the engine was shaking a bit, but it gave a little more power in higher revs.

It doesn't matter how many teeth the belt has. As long as it fits the engine. But i believe 148 is right.

Again, the offset is strange. Keep the crank and cams in place...you could only be off half a tooth. And like i said, it's not the valves themselves. Not with the compression ratios you gave up earlier.

Hi Mirafioriman,

It is off by approx 4 mm ( centre hole to centre hole) to the left perhaps saying one a half teeth is excessive just wanted to get my point across. I have re-fitted the belt and will change the shims to get the valve clearance correct and see what difference that makes. If that doesn't improve the performance then I will install the cams as I said earlier and ignore the standard marks. I am just wondering if the cam box may have been changed to one from a different car prior to my ownership, and perhaps the marks are slightly different.

Yeah I have really good compression but something is holding the car back at 80mph. I think I will get it fired up again when shims are done and run it and if there is no marked improvement then maybe I will start checking out the possibility of a weak spark as you suggested. I have a new coil, distributor cap, rotor arm and electronic ignition module ( not sure of the correct name ) so I will try one at a time and see what happens.

I wanted to try and rule out one thing at a time rather than rush in and change lots of things.

Regards

Keith

Please let me see if I get this right:

• With your foot to the floor, the car gets up to 80mph and won't go any faster
  
• The car gets to 80mph in under 20 seconds
  
• At 80mph the rev counter is showing 4000rpm
  
• There's no misfiring; the car runs fine but won't go above 80mph
  

Set cams and crank, re do tension on belt, turn by hand twice and check . adjust cam by one tooth till alighed and repeat and repeat untill happy..

 you havent had reground or modifided cams have you ?...

  as long as there IS a gap in shims it will run normally ... 8)
  

The 2 litre uses a 148 tooth belt, I believe the 1600 and 1800 use 146 teeth, 1400 144 teeth, I think the 2 litre Croma uses 144 teeth as well. The tooth pitch is 9.2 or 9.3mm, it's more than 9 and less than 10 anyway. Having a cam wheel out by 5mm isn't going to cause your problem, I had an exhaust cam out by 1 tooth a few years ago, the car would still do more than 80mph, it did run better when I set it right. If you want the cams exactly right, you'll have to buy a set of adjustable cam gears. Jason Miller's are great, he does beautiful work and is a great bloke to deal with.
http://www.millersmule.com/MillersMuleStore/en/39-dohc-adjustable-cam-pulley.html
I'd be treating any cam timing specifications you get out of a haynes manual as bullshit.

What's all this Haynes manual hating?

Obviously factory manuals are better but I've often found Haynes manuals to be pretty useful

I have never found anything usefull in any manual. Always had to find out myself. And i even have the original ones, made by Fiat itself, used in the garages.

If you want a guide to changing spark plugs or a fan belt, the Haynes is fine, if you want technical specifications or tolerances, I'd seek a second opinion. As the original poster found, 2 different tolerances for valve clearances on the same page.

Hi All,

I have refitted the belt and after numerous trials managed to get the alignment nearer centre.

Thotos.... thats exactly right, everything as you say but stumped at 80mph maybe 85 with a tail wind, going down hill and in the slipstream of a racing car. LOL. I used to think that the shape of the car had something to do with the speed as the car is not exactly aerodynamic but then again neither was the 131 as that is shaped like a brick, no disrespect meant, I love 131's. As I said I had the original car and I know it is capable of more.

Jasonh131....I am not aware of any modifications do to the cams. As I said in my other post there is a gap, the inlet valves are all 18 thou so no problem there, the exhaust valves on #1,2 and 3 are currently 19 thou and #4 is 16 thou, they should be around 24 thou. you are saying that if there is a gap then it will run normally but I dont understand that because it is my understanding that the gap is to allow the valve to fully close but if the gap is too small then wont the cam lobe ramp come into contact with the tappet too early and start opening the valve sooner plus stay open longer than required for timing, also is there not a chance of binding on the spring if the valve is opening too much.  Maybe I have this wrong? Please can somebody advise so I know where I stand and I am not barking up the wrong tree.

Tas131.... I have read in the Guy Croft book that the dowel hole in the standard cam wheels can be redrilled to adjust the degree of the cam which is something I may do later. I hear that your not a fan of the haynes manual but I am a novice with limited knowledge and therefore I need to start somewhere to gather information.

Today I will order and then fit new shims, and as I said earlier if there is no marked improvement then I will focus on the ignition sysyem.

Some more info for you to ponder, before turning my attention to valves I carried out a vacuum test from the inlet manifold. The paperwork that came with the vacuum unit states that standard engines should read between 17 and 21 well mine sits at 22. The booklet explains what may be wrong ( valves, rings and spark etc.) upto 17 but nothing after that so I am not sure if 22 is a problem. What are your views on this?

Thanks guys for replying.

Regards

Keith

Not read all of the previous posts but have you checked to see if the second choke on the carb is opening? To me this sounds like a fuel problem/ spark.

Have you checked fuel pump pressure?

How does the engine idle at 850rpm?

Hi Sev131,

I have just checked the choke valves and primary and secondary flaps are wide open at full throttle. I have a Facet electric pump so plenty of fuel to the carb. Prior to fitting the electric pump I was using the standard mechanical pump and I had exactly the same problem, so the problem is not a lack of fuel to the carb. I replaced the carb inlet fuel filter.
It will idle at 850 but a little rough, it idles fine at 950.

You may well be right about the problem being with spark so will be looking at that next.
 
This may be a silly question but is there a way to check the strength of a spark, other than grounding the plug and checking the spark visually?

regards

Keith

Try using in line spark testers. Have you tried advancing and retarding the dizzy till it runs smooth and then try....forget the timing light for now?

Hi Sev

I set the static to 10* and then moved it about a few degrees but not much difference but I will try it all again. I have just put a mark to show 35-36* of full advance so tomorrow I will start it up and make sure that it is advancing to the max. Which degree of advance is most important, the 10* static or 35* full advance?

Do I provisionally set static to 10* at idle and rev the engine until full advance is achieved say 35* then lock down the distributor and what ever the static then reads is left. For example static may move to 15* or so. Am I understanding this correct. Or if at 10* static I cant achieve 35* degrees full advance does that highlight a problem within the distributor?

Thanks for the tip on an inline tester I have just bought a set on Ebay.

Regards

Keith

The shims are not your problem, neither is the cam timing, they're close enough for the engine to run better than you say it does. If you've fitted new ignition parts as stated, (although you don't mention plug leads), spark strength is probably not your problem either. It may be an ignition advance problem, but a timing light can easily check that. If spark strength was an issue, it would be more obvious under acceleration load than top end. Set static ignition timing at 10 degrees, don't advance static timing to try and get maximum centrifugal, you're moving the entire advance curve and increasing your changes of the engine pinging under load. If I recall correctly, the centrifugal advance curve is +/- 2 deg, so in the ballpark is good enough.

Several people have suggested a fuel problem, have you had the carb apart? You're trying to get the most complex parts of the engine to exact tolerances, and avoiding the simplest solutions. The problem you describe can be something as simple as a dirty air filter. I'd pull the top off the carb, give it a clean, check float level, needle & seat, blocked jets etc. It doesn't take long, costs nothing and can do no harm, it also eliminates a potential problem area.

Hi TAS

I have not fitted the new plugs (NGK BP6RES), and coil ( type listed below) etc yet. I said that if the valves dont make a marked difference then I will change the electrical components one by one and see if the problem is there. Your correct I did mention plug leads but I will some, what type do you recommend?

You say that the valve clearance is not the issue and that may be but since I have the cam box covers off I might aswell change the shims for correct size even just to eliminate something else. And the only reason I am looking at the valves is because I did start looking at the carb first and this is what I found.

I did take the top off the carb (34ADF 54/250) and checked the float dept which is set at 6mm. I replaced the float needle valve, checked all jets were correct and not blocked.
 
I re-checked the idle mixture screw and it is 2 & 1/8 turns out from seated.
The spark plugs are FIAT 1L45J, I got them from a Fiat dealer,  The plugs are a mid brown colour.
The coil is Motaquip RPC-115 BN17 for electronic ignition.
primary idle jet is 50
Secondary idle jet is 90
Primary emulsion tube is F20
Secondary emulsion tube F5
Primary air corrector jet is 170
Secondary air corrector jet is 175
Accelerator pump nozzle is 45

Air filter is a K&N set up. Which I washed and blew through with some low pressure compressed air.

So now you can see why I am stumped as to what is happening or not happening as the case may be. I also checked the inline fuel filters but I will check them again.

So I am not just focused on the complex parts of the engine, as I said I found myself looking there because everything else appears to be ok, but then again something cant ok.

Really appreciate your comments so please keep them comming.

Regards

Keith  

Yep, while the cam covers are off it's prudent to do the shims. Measure the gaps, the shims you've got, and work out what size shims you require. You can usually mix and match some of the shims you've got, so you only have to buy a couple of shims, or if the planets align correctly, none.
Once you've exhausted all your options, if you're still not happy with the performance and you're still scratching your head, it might be worth throwing it on a rolling road and getting some data of what it's doing in real time.

Thinking outside the box here:

1) Is the speedo accurate ie are you doing just 80 MPH or are you actually doing more (even if the speedo is at the 10% legal limit for inaccuracy you could theoretically be doing 88 MPH)

2) What's going on with the gearing. Is it possible for the engine to pull more than 4000 rpm in 5th with the current gearing? What happens when you go flat out in third and fourth gears? Does it rev to the redline in these lower gears?

Hi chaps,

Mirafioriman,...I checked the speedo against my sat nav and with the speedo reading 82 the sat nav read 79, so not much difference there.

All running gear is from the same standard car so no alterations to gear ratios etc to gearbox or diff.

I have taken it to 5000 rpm from 2nd through to 5th gear up to just past 80. What do you mean by redlining it? What rpm does that mean? It is not running at the mo, I will be doing the shims tomorrow so after that I can carry out any road tests you recommend.

Tas131.....I was thinking about going on a rolling road but wanted to try and sort out all the obvious possibilities before doing that. A Rolling road can be quite expensive.

Hopefully over the next few days and with the help of you all on here we can get to the bottom of this.

Thanks again

Keith

PS. David that is a super collection of cars you have there.

5th gear is an overdrive, I've read old magazine write ups that state 4th is better for top speed. Revving to 6k/rpm through the gears occasionally hasn't hurt my car over the years. It would be interesting to see what speed your car will pull in 4th gear.

You can rev the bollocks of these engines as long as they are properly mantained theres no problem as they are bullet proof.
The only time I knew of one of these failing was when it was being red lined in the wet and the driver went through a large puddle and spun up the rear and the revs went stratospheric and a valve broke and mashed the cylinder but this was a badly maintained car (no oil changes) and wouldn't have happened if he had dropped the revs a bit in the wet.

Thanks for that David, you've filled me with confidence.

I ordered new shims but wont get them for 10 days so cant do any road testing before then. So if I go quiet for a few days that will be why. I will be back on here when engine is running again.

Thanks guys

Regards

keith

shove a cable up the rear exhaust pipe ,i used a clutch cable . i had a pattern  back box on one 131 it  had a restricter plate in the middle of the box ? now i can get the cable 5 feet up the pipe .

Hi Jason,

Thanks for the tip I will try that tomorrow.

regards

keith

Here's my bit of thinking out loud....

It's not the shims (as most people said) since the gaps are good enough. In fact it isn't anything that will cause loss of power as the car gets to 80mph in under 20 seconds. As Dave suggested, it would be good to know if the car can actually rev to 6000rpm in lower gears (first, second, third). But it revs to 5000rpm so it's not cam timing or the cams. And it's not fuel starvation or carburettor problem if it revs beyond 4000rpm in lower gears; plus there's no loss in power.  And it's not a gearing problem as it's doing 4000rpm at 80mph in top. Like Dave, I too was thinking the speedo might be lying but the 80mph speed has been verified by Sat Nav and the rev counter. It's not a weak spark or ignition problem as that would cause misfiring. So there's only one possible reason for this problem: The engine's got the hump because it's in the wrong car!  ;D These twin cams have feelings you know....  ;D ;D ;D

I think you cracked it there  ;D  I once knew someone who put a fiat 1800 twin cam in a mk4 cortina ! (sacrilege)  and they couldn't get it to run right, needless to say I wouldn't have anything to do with it and felt sorry for the engine.

Hi Guys

I believe the engine has got a mind of its own, Theo. And you know what it is so bloody ungrateful because I could have let it go to the scrap yard but chose to save it and this is how it repays me.

I took the shims to my local engineering company and they reduced the thickness so didnt have to wait 10 days for new ones. Busy today so tomorrow I will get her (him) not sure what to call it anymore in case it gets offended) running and do some more checks as recommended on here and then I can do some road tests and report my findings.

Theo, I havnt replaced the electrics yet, I will replace them one by one in the next few days to try and determine what is causing the problem, that way if I find the fault I will know what is was for futuer reference.

Thanks Guys

Keith

Hi Keith

Just a thought................

This engine was designed to live on proper 5* petrol.  I have a 124AC and that used to love decent fuel!  The later models were designed to run on 4*, with only the latest setup for unleaded.

Unleaded fuel has nothing to slow the burn and therefore ignites and burns faster.  For this reason many 80s car models had adjustments to allow a change between leaded and unleaded.  All injected Vauxhalls had a reversible plug under the bonnet.

A common problem back in the day was to run a car on unleaded without adjustment.  In extreme cases the car can run lumpy at idle, then exhibit limited power at higher advance.

Try setting the static at 5 degrees and adjust the idle mixture to match.

Take the car for a run and see how it revs in each gear.  Listen carefully and see how the engine revs.  Beyond 3/4 throttle it should come alive as the second barrel opens.


Also, do you have points or electronic?

Wrong points gap can limit spark at higher revs.


Thanks
Duncan

Hi Duncan,

I will try setting the static timing at 5* BTDC and see what happens. I have ordered a new set of HT leads so should get them tomorrow and then I can try some of the things recommended on here by yourself and others and report back.

I have electronic ignition.

Regards

keith

Edit: Jason I can get the length of the clutch cable in through the rear box. It needs a bit of jiggling but it will go through.