Timing belt "walking".. Fiat 131 abarth 16v

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RedLexus
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Timing belt "walking".. Fiat 131 abarth 16v

Post by RedLexus »

Hey all , getting my Dad's 131 AR Rally Car ready for Rally Spain WRC and we have an issue with the timing belt moving out over the end of the cam pulleys . We fitted a new Gates 25.4mm belt , a new Tensioner , all the pulleys seem fine , with no wear , we've checked for crank end float , cam end float , all fine.... The two cam pulleys are Verniers , and don't have the raised guide piece like standard ones to keep the pulley where it should be . Apart from puttng a small metal shim under the tensioner to tilt it inwards slightly , are we missing anything?
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Guy Croft
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Re: Timing belt "walking".. Fiat 131 abarth 16v

Post by Guy Croft »

Set her up at tdc and take off the belt and alternator/front pulley. Use a straight edge to check the alignment of the front face and flange of the aux d/s relative to the crank nose pulley that drives the belt. It may be out of alignment with the the and the flange on the aux d/s pulley may be forcing the belt forward. The aux d/s may be a bit too long and need 1-2mm machining off the end.

The requirement for this mod depends to an extent on the setup height of the aux d/s pulley (must be rear flanged), the plastic one is the best for a bolt-on 1" belt conv and is not uncommon.

I assume I have interpreted your query correctly, cannot id any other cause of the 'top of my head'..

G
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Re: Timing belt "walking".. Fiat 131 abarth 16v

Post by RedLexus »

Sorry Guy , pardon my ignorance , but what do you mean by "d/s"? The pullys are a we bit different to normal , it has a secondary , smaller toothed pulley added on in front of the crank pulley . This drives the alternator and water pump as normal , but there is no flange on the bottom pulley or the auxillary or idler pulleys .

A very strange thing though , while fine tuning the carbs and ignition timing , the belt started "walking" to the other edge , and overhung it by a mm or so... then it gradually crept in to the inner edge... then back out a bit! We fabricated a nylon guide to keep the belt from going off the inner or outer edge , but it's still a slight worry .
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ASF72
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Re: Timing belt "walking".. Fiat 131 abarth 16v

Post by ASF72 »

Hi,
this has actually happened to me on my 8v Integrale vernier pulley's, the belt doesn't walk as such but does overhang by 1/2mm, scared me to death so now changed back to standards, now i'm wondering if its the vernier's we are using. I'm just having some drawn up on cad and then made to try and solve it.

Nino
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Re: Timing belt "walking".. Fiat 131 abarth 16v

Post by Guy Croft »

Tristan, hi

Now having your engine at my works I have inspected in detail everything that could cause this 'walking cambelt'.

Having told you the auxiliary driveshaft MUST have a rear flange* (!) I did not look there first, instead checked cam pulley runouts, bent crank, end float blah blah which of course were all fine. Worried about the head being miles out of true. So a moment of anxiety when I thought, crikey - what can it then be? Of course when I got to stripping the rest of the unit all became clear, see below.

Readers please note! Neither Tristan nor his father Pat built this engine. It was built by some complete clot in Austria, who, based on my estimate of his entire er, 'workmanship' on the unit, quite simply belongs in gaol.


G

*see - from this thread: ...the requirement for this mod depends to an extent on the setup height of the aux d/s pulley which must be rear flanged..
Attachments
PH 09.181 prep - (5) wrong pulley on aux driveshaft. MUST have rear flange.jpg
PH 09.181 prep - (5) wrong pulley on aux driveshaft. MUST have rear flange.jpg (114.06 KiB) Viewed 15809 times
PH 09.181 prep - (11) if you run the wrong aux ds pulley the belt walks into the front seal housing.jpg
PH 09.181 prep - (11) if you run the wrong aux ds pulley the belt walks into the front seal housing.jpg (117.73 KiB) Viewed 15809 times
RedLexus
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Re: Timing belt "walking".. Fiat 131 abarth 16v

Post by RedLexus »

Great to find a problem Guy , at least now we/you know the "why" now it can be fixed! What do you plan to do , fit a flange? Something like the one I had fab'd up for the Camshaft pulley?
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Re: Timing belt "walking".. Fiat 131 abarth 16v

Post by Guy Croft »

Yes, I shall have to re-vamp that setup with a rear-flanged pulley like the one below.

GC
Attachments
The use of this rear flanged pulley for dry-sump drive requires and accurate and robust marriage of the two pulleys, the aux d/s needs to be shortened and the flange on the back of the main pulley needs taking down a bit too..
The use of this rear flanged pulley for dry-sump drive requires and accurate and robust marriage of the two pulleys, the aux d/s needs to be shortened and the flange on the back of the main pulley needs taking down a bit too..
aux ds pulley mods to dry sump (4).jpg (110.55 KiB) Viewed 15768 times
shortened aux ds needs housing fitted without gasket to clear seal.jpg
shortened aux ds needs housing fitted without gasket to clear seal.jpg (112.33 KiB) Viewed 15765 times
miro-1980
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Re: Timing belt "walking".. Fiat 131 abarth 16v

Post by miro-1980 »

Wow!

Another intersting thread on engine build.

It looks like pulley selection and installation is almost a separate body of knowledge. It is also very interesting to see how many elements (not too mention failures by a poor mechanic) may cause timing belt "walking". With potential damage this may cause it is sort of important to avoid such problems (and poor mecahnics !)

Thank you Guy and Tristan.


Miro
www.Fiat-abarth-rally.com
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Re: Timing belt "walking".. Fiat 131 abarth 16v

Post by Guy Croft »

I have just edited my GC 'How To' on cambelts.

Yes I could write more but I don't get that much time to write these days much as I enjoy it.

Here it is in text and download.

GC

Fiat 8V TC AND 16V CONVERSION CAMBELTS AND PULLEYS
Auxiliary driveshaft – important note: To run a GC 1” cam belt you must fit a rear flanged aux d/s pulley in conjunction with the wide OE or GC race flangeless 29mm wide cam pulleys. The pulleys should always be wider than the belt and the belt must be allowed to find its own axial running position, never run flanged cam pulleys with the 1” belt. The 1” belt will run hard against the aux d/s flange – this is the constraint that stops the belt moving towards the engine and it is constrained from moving forward by the rear of the alternator pulley. The best auxiliary driveshaft pulley is the early solid steel or plastic one. The later sintered one with big holes in it has a different offset and should be used with auxiliary driveshaft shortened 1.5mm. When this is done the step on the hub on the rear of the aux d/s pulley may rub on the aux d/s housing seal and thus - either leave out the gasket and use silicon sealant or - machine 1.5mm off the hub. It is imperative to check the alignment of the aux d/s flange with the cam pulleys and the crank nose pulley that drives the belt.


Tension: The TC cam belt – std ¾” or GC race 1” is non-directional ie: may be fitted either way round. It is vital to ensure that there is no slack either on the tension or return side of the belt. Both belts are 3/8” automotive pitch and trapezoidal tooth form. Never fit a trapezoidal belt that is not this type. Typically the belt should be tensioned so that it is just possible to twist the belt 45 degrees with two fingers between the camwheels. Turn the engine backwards by hand to assess the slack between the crank and inlet pulley – there should be no more than that induced by the clearance between the belt teeth and pulley teeth, and there will be more on an engine with a worn crank nose pulley. This does not matter too much provided the belt does not go slack on the long straight when the clearance is taken up. Engines with adjustable camwheels should be tensioned with the camwheel securing screws loose. Do not overtighten the belt, as this will cause excessive wear between the cam and cambox journal housing, but too loose is worse as the belt will jump. There is no means to getting the tension ‘perfect’ without an ultrasonic tool so it’s up to you to do it right. I spend 1/2hr on this – every time. Never rush that job! When your belt is tensioned don’t forget to secure the camwheel screws.


Pulley: Make sure the tensioner pulley is on good condition, ie: bearings spin freely and are not ‘notchy’, and the outer sleeve is not worn and make sure that the 10mm stud is secured in the block (or head) before fitting it. Use of Loctite ‘Studlock’ is recommended on that stud. Do not paint or lubricate the tensioner baseplate or the block under it. Painting will lead to embedding and loss of bolt holding strength. Types of pulley vary but typically the 131/124/132 and Lancia Beta/ Strada 130/105TC models will all accept the 1” belt although the latter types have a shorter tensioner pulley and there will be a bit of overhang on the tensioner. This does not matter.


Wear: Do not re-use a belt that’s been removed after period of running. This directive comes from Gates, who pioneered cambelts. Belts suffer fatigue according to the load they are exposed to at natural frequency. That can vary from engine to engine. Belts go slack because they are worn beyond useable condition or have been over-stressed due to over-or-under tightening or because the pulley teeth are worn – especially true of alloy pulleys. Never retighten – replace! Properly fitted, the GC 1” race belt will easily last a season racing at speeds over 10,000 rpm and will endure 48,000 road miles easily. However ‘flat-shift’ gear change systems (eg: as used on ¼ mile) can cause aggressive wear to the belt and it should be regularly inspected. The OE belt should be changed religiously at 36,000 miles and it is NOT recommended by GC for racing as standing starts can throw it off the camwheel teeth. Make sure the belt is running true by cranking the engine before starting up.


Protection: Make sure the pulleys and the belt do not rub on the belt cover – or anything else. Rubber dust inside the cam belt cover cam mean that something is rubbing – often it’s the tensioner pulley. Beware of pulley swaps if you do not know the history of the engine. On units with an auxiliary driveshaft (eg 8V TC and 16v conversion) a mistimed auxiliary driveshaft can snap. If your engine does not ordinarily have the right aux d/s pulley, make sure the fuel lobe on the aux d/s does not strike no. 2 conrod (engines of 79.2mm stroke or longer – 1592, 1608, 1756 and all 2 liter). If in doubt remove it, cut off the fuel lobe, and plug the oil gallery. This service is available from GC. It is vital to shield the cambelt from stones, oil and debris, this is a common cause of belts jumping on race and rally events. All belts and alloy pulleys wear but operating the belt in dusty conditions with no cover or under-engine protection will lead to premature wear both. Inspect regularly if using in these conditions. Oil will not degrade this belt but will increase the tendency to slip so keep it dry.
Make sure your camwheels are not rubbing on the head or cambox/seal: This is not unusual because head and camboxes castings vary slightly. You’re the engine builder so if they are – get on and relieve the offending part.


GC 8v TC/16v conversion adjustable camwheels: capscrews (M6) should be tightened to 8-10lbf ft. The M12 fixing is 83lbf ft. Don’t use Loctite, it’s NOT needed. The pulleys are symmetrical, ie: can be fitted inlet or ex. They must be used ONLY with a rear flanged aux d/s pulley as described above. Always fit the OE washer and make sure it is not cracked.

Kent Cams 8v TC ¾ pattern adjustable camwheels: (see also GC type above) These were originally designed for the 1608 type ¾” production type belt, they require use of the original 1608 type front flanged auxiliary driveshaft pulley (ie: flange is on the outer face of the pulley, away from the block). Fit the rear flanged to the inlet and front flanged to the exhaust. Do not swap them round. Tighten as GC pattern above.
Attachments
Cam belts.doc
(25.5 KiB) Downloaded 564 times
aux ds pulley mod.JPG
aux ds pulley mod.JPG (61.14 KiB) Viewed 15681 times
aux ds shortened.JPG
aux ds shortened.JPG (66.41 KiB) Viewed 15681 times
Pulleys L-R Integrale 16v, 8V TC OE std belt, GC 8V_16V conv TC for wide belt.jpg
Pulleys L-R Integrale 16v, 8V TC OE std belt, GC 8V_16V conv TC for wide belt.jpg (115.08 KiB) Viewed 15682 times
tmvolumex
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Re: Timing belt "walking" and timing gear guides

Post by tmvolumex »

Guy,
I ran across a crankshaft timing belt pulley that has a built in rear flange belt guide. Are these used on later Fiat / Lanica engines?
All of my 1970's Fiat / Lanica engines do not have a timing belt guide (flange) built into the rear crankshaft timing belt pulley.
Was this done in the 80's around the same time as the flangeless cam pulleys? Is this rear flange sufficient by itself to control the belt at the rear?
Tom
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Guy Croft
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Re: Timing belt "walking".. Fiat 131 abarth 16v

Post by Guy Croft »

Fiat realised that if they put a flange on the rear of the aux d/s pulley they could run with no flanges on the cam pulleys. Obviously you cannot do that on models like the reversed-port and 16v designs as they have no aux d/s and the oil pump is run off the crank nose. Flanged pulleys used on the early models were dumped then.

The rear of the crank front pulley stops it walking forward and the rear flange on the aux d/s restrains it from going backwards into the crank front seal housing. No flanges are needed on the cam pulleys with 3/4 or 1" belt in that case.

G
tmvolumex
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Re: Timing belt "walking".. Fiat 131 abarth 16v

Post by tmvolumex »

Guy,
Thanks for the response. The crank cam belt pulley I was refering to has a belt guide on the back side, ie near the block. My guess is that pulley paired with a aux shaft pulley, that has a belt guide on the front of the pulley, may be the combination used by Fiat on later engines with no belt guides on the cam pulleys. All of my F/L engines have not had a belt guide on the back of the crank cam belt pulley. But those engines did not come from the factory with 1.25 inch wide cam pulleys without belt guides either.
Thanks,
Tom
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Re: Timing belt "walking".. Fiat 131 abarth 16v

Post by Guy Croft »

Hi Tom

I have never seen a flanged crank pulley on the TC 8 or 16v but it may have been taken from an X19 as I think one of them had it and I think it fits your crank.

It is customary to use the rear of the crank front pulley as the forward guide so, as your crank-nose cambelt drive pulley has a rear flange, I cannot see why any flanges at all would be needed.

The exception would be if the drive pulley flange did not align the belt 'properly' relative to the cam pulleys or aux d/s pulley or worse allowed the belt to walk backwards (ie: toward the crankcase) so far that it rubbed somewhere. In which case it's not much use is it?!

Moreover if you have too many flanges and sufficient space does not exist for the belt to find its true position during slow rotation (as it settles into place on the pulley teeth) it can chafe quite severely and I have often seen this - where the flange on one or other pulley is forcing the belt sideways. If you find rubber particles all over the place this is sometimes the cause.

This seemingly innocuous topic is actually very important and I take belt 'runs' & alignments very seriously during build and whenever any poor soul rings me 'just for a cambelt' - as some of the photos below hopefully demonstrate. I have captioned the photos prior to upload and hopefully that will suffice.

GC
Attachments
on this 124 16v head the flanges caused belt wear where arrowed.jpg
on this 124 16v head the flanges caused belt wear where arrowed.jpg (63.62 KiB) Viewed 12926 times
GP4 16v crank front pulley against which the cambelt runs.jpg
GP4 16v crank front pulley against which the cambelt runs.jpg (110.59 KiB) Viewed 12926 times
Gp4 belt check on cams.jpg
Gp4 belt check on cams.jpg (110.33 KiB) Viewed 12926 times
GP4 belt check closeup on aux ds.jpg
GP4 belt check closeup on aux ds.jpg (109.59 KiB) Viewed 12926 times
Gp4 belt check on the long run - note the belt running against the aux ds flange - but not so hard as to chafe and wear.jpg
Gp4 belt check on the long run - note the belt running against the aux ds flange - but not so hard as to chafe and wear.jpg (110.54 KiB) Viewed 12926 times
tmvolumex
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Re: Timing belt "walking".. Fiat 131 abarth 16v

Post by tmvolumex »

Guy,
Good info, I did not think of an X1/9 application. In addition, I dont know if the toothed section of those pulleys is the same width as the pulley without a guide rail. If the toothed section is sacrificed ion size for the guide rail, then it may not be wide enough for a 1 inch belt.
I have a couple crank pulleys, that are "as cast" on the back side and will not work as a belt guide without modifying the back of the pulley. The back of the pulley must incorporate a smooth angled surface to act as a guide.
Tom
GC_31
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