2ltr Cambelt Query

[keith m 131]

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

[mirafiori76]

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.

[keith m 131]

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

[Thotos]

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
  

[jasonh131]

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 ...
  

[Tas131]

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.

[mirafioriman]

What's all this Haynes manual hating?

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

[mirafiori76]

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.

[Tas131]

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.

[keith m 131]

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

[Sev131]

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?

[keith m 131]

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

[Sev131]

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?

[keith m 131]

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

[Tas131]

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.

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.