Fiat Twin Cam auxiliary shaft pulley orientation

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Thotos
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Fiat Twin Cam auxiliary shaft pulley orientation

Post by Thotos » June 23rd, 2006, 1:22 pm

Dear Mr Croft,

Congratulations on your excellent new website. I wish you great success with it.

I'd like to start off you Q&A section with what might seem like a silly question but if I don't ask I won't know! I have a Fiat 131 Sport fitted with one of your engines and I recently noticed that the cam belt tends to ride slightly too far forward. I believe the position of the timing belt to be controlled by the tensioner bearing so I shall be changing it soon. But my question is about the correct position of the flange on the auxiliary shaft pulley. On my 1995cc engine the pulley flange is on the side of the pulley nearest the engine. I've noticed that on some of the photos on your site that the auxiliary shaft pulley flange is on the forward side of the pulley (i.e. furthest from the engine). Admittedly most or all of the photos that I can see the pulley clearly are 1608cc Twin cams. Is the orientation of the pulley different on different twin cams or is the pulley on my engine fitted the wrong way round?

Regards,

Theo Kyriacou

Guy Croft
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Post by Guy Croft » June 23rd, 2006, 2:56 pm

Hi Theo, try this, see if it helps.

Fiat ¢‚¬Å“ Lancia 8V TC AND 16V CONVERSION UNITS - CAMBELTS AND PULLEYS

(NOT APPLICABLE TO THEMA/DELTA, CROMA AND OTHER ‹Å“OE¢ž¢ REVERSED PORT ENGINES OE = Original Equipment ie: ‹Å“as it came from the factory¢ž¢)

All cam belts must have forward-backward guide flanges otherwise they will run off the pulleys altogether, and this function is performed by the following restraints:

- The back of the crank front pulley - that drives the alternator/water pump -stops the belt moving forward
AND
- The rear flange of EITHER the auxiliary driveshaft pulley OR inlet cam pulley stops it moving too far back.

You must NEVER run front flanged inlet with front flanged aux d/s and simply depend only on a rear flange on the ex pulley.

As far as pulley setups are concerned there is a choice of the following setups:
A. Std OE pattern ‚¾ belt:
1. Front flanged aux d/s pulley, rear flanged inlet, front flanged exhaust
2. Rear flanged aux d/s pulley, front flanged inlet, rear flanged exhaust
3. Rear flanged aux d/s pulley, flangeless 1" (approx) cam pulleys

B. GC race 1" belt
As 3 above

Any other setup is wrong and must be changed immediately.

The TC cam belt ¢‚¬Å“standard ‚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 special 3/8‚ automotive pitch and trapezoidal tooth form.

Never make fitting a cambelt a 5minute job. 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 ¢‚¬Å“ there should be no more than that induced by the clearance between the belt teeth and pulley teeth, there is some ¢‚¬Å“ and has to be 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.
Do not overtighten, as this will cause excessive wear between the cam and cambox journal housing. Make sure the tensioner pulley is on good condition and that the 10mm stud is secure in the block before fitting it. Do not paint or lubricate the tensioner baseplate. Painting will lead to embedding and loss of bolt holding strength. Turn the engine over several times by hand after fitting the belt, to check the belt runs true and is not loose, and double check the torque settings on the tensioner system. They are: 10mm thread main nut 32lbf ft, 8mm thread (13mm head) tensioner baseplate bolt and spring securing bolt ¢‚¬Å“14-16lbf ft. If you ever need to change the spring retaining bolt ¢‚¬Å“ it has a fine thread ¢‚¬Å“ 1mm pitch.

Do not adjust the tension after a period in service and do not remove and re-use the belt after period of running. Don¢ž¢t ask me why, Gates the manufacturers of most of the world¢ž¢s cam belts say so.

Make sure the pulleys and the belt do not rub on the belt cover ¢‚¬Å“ or anything else. Rubber dust inside the cam belt cover cam mean that something is rubbing ¢‚¬Å“ often it¢ž¢s the tensioner pulley.

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. Properly fitted ¢‚¬Å“ the GC 1‚ race belt will easily last a seasons racing at engine speeds over 10,000 rpm, or 48,000 road miles. The OE belt should be changed religiously at 36,000 miles and it is NOT recommended 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.

8V TC GC ADJUSTABLE ALLOY 1‚ PATTERN CAMWHEELS

The 6 off capscrews (M6) should be tightened dry or threads only lightly oiled to 8-10lbf ft. Do this twice, as they settle in the hard anodizing. The M12 fixing is 83lbf ft. These 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. The 1‚ belt usually runs slightly off the tensioner pulley, this does not matter, but always turn the engine over by had to make sure it runs true. Always fit the OE washer and make sure it is not cracked.

8V TC ‹Å“KENT CAMS¢ž¢ ‚¾‚ PATTERN ADJUSTABLE CAMWHEELS

These were originally designed for the 1608 type ‚¾‚ production type belt/pulley setup. They must have the correct flanged pulley on the aux d/s ¢‚¬Å“ in other words opposite to the one on the inlet cam. My preferred set up is front flanged auxiliary driveshaft pulley, rear flanged to the inlet, front flanged exhaust. Tighten capscrews as GC pattern above.

CAUTION - FUEL PUMP LOBE ON AUXILIARY DRIVESHAFT.

(Engines of 79.2mm stroke or longer ¢‚¬Å“ 1592, 1608, 1756 and all 2 liter).
Beware of pulley swaps if you do not know the history of the engine. The OE setup requires the aux d/s pulley timing mark to be set up at 34 deg clockwise from vertical (roughly in line with the right-hand edge of the hex-headed bolt securing the tensioner spring to the block).

A mistimed auxiliary driveshaft can hit number 2 con rod and cause damage or snap. If you hear a knocking noise when the engine runs ¢‚¬Å“ stop. By the same token never turn the engine over on the starter with the head off. If swapping the aux d/s pulley, make sure the shaft is timed so that the fuel lobe on the aux d/s does not strike no. 2 conrod ¢‚¬Å“ but better still remove it, cut off the fuel lobe, and plug the oil gallery, and run off an electric fuel pump like Facet ‹Å“Silver Top¢ž¢ from Weber.
Attachments
Front flanged aux ds rear flanged inlet OE pulleys.JPG
Cyril McMullen & son with GC spec 125 Samantha unit - standard pulleys and 3/4" belt.
Front flanged aux ds rear flanged inlet OE pulleys.JPG (151.36 KiB) Viewed 8322 times
Front flanged aux ds rear flanged inlet - Kent pulleys.JPG
Dave cannot's hillclimb-sprint 124 ST 1608 - a 'Kent Cams' pulley conversion.
Front flanged aux ds rear flanged inlet - Kent pulleys.JPG (18.38 KiB) Viewed 8317 times
16v conversion rear flanged aux ds, flangeless cam pulleys.JPG
Steve Parsons GC spec StIII 2 liter 16v conversion - late 16v head on 131 block - a 1" belt conversion on GC race pulleys as described above.
16v conversion rear flanged aux ds, flangeless cam pulleys.JPG (27.48 KiB) Viewed 8324 times

Thotos
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Post by Thotos » June 27th, 2006, 11:30 am

Thank you Guy for the detailed explanation. It all makes sense now.
My car has type 3 setup (Rear flanged aux d/s pulley, flangeless 1" (approx) cam pulleys). I had forgotten that the twin cams usually have flanged inlet and exhaust pulleys and I confirmed that at the weekend when I was looking at the engine of a 124AC at the Bromley Pageant.

I always thought that the tensioner bearing had a curved surface to keep the belt riding at the correct position and the flanges/stops were there as secondary safety. When the belt in my 131 was riding forward and was presumably being stopped from coming off by the inside edge of the fanbelt pulley on the crankshaft, the belt was right on the edge of the auxiliary shaft pulley and off the front of the tensioner bearing by a couple of millimetres. Are there different thicknesses of crankshaft belt pulleys like there are different thicknesses of the cam pulleys?

I think I need to have a closer examination of my engine and cambelt...
:!:

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Post by Guy Croft » June 27th, 2006, 5:12 pm

Theo, hi

that 'riding off' phenomenon can happen with the 1" belt, where it is fractionally overhanging the aux d/s pulley and the tensioner too, never found it to be too much of a problem. It's a problem if the belt is chucking rubber everywhere, that means bad belt wear.

It's due to the offset on the aux d/s pulley, thye do seem to vary, the best for the one inch belt conversion is the rear flanged plastic or early solid steel one. The one I always check when in build is the lightweight later one with big holes in it. I check it by turning the engine over many times with the belt on. If it doesn't 'walk' when turning it by hand, it won't when running. If it looks like something isn't safe, it all comes off for alteration.

I used to worry to death about it and shorten aux driveshafts, counterbore pulleys, pack out the tensioner but in the end I ran the 200bhp NHRA engine like with plastic aux d/s pulley and 1" adjustable camwheels to try it out, in the mid 90's - and here I'm talking end-of-straight speeds of 9500 rpm - and sometimes a bit higher higher. It ran quite happily, never dropped a valve or showed any tendency to wear, just changed the belt on 1/3rd season rebuilds.

A belt 'walking' backwards into the front seal housing is a more serious problem and is sometimes caused by a badly worn crank nose toothed pulley (they can grow a taper) when run with a front flanged aux d/s setup.

GC

Thotos
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Post by Thotos » June 28th, 2006, 2:18 am

Hello Guy,

...I used to worry to death about it ...

I think if you've stopped worrying about this, so should I.

Theo

SteveNZ

Post by SteveNZ » July 11th, 2006, 9:58 am

Guy Croft wrote:
that 'riding off' phenomenon can happen with the 1" belt, where it is fractionally overhanging the aux d/s pulley and the tensioner too, never found it to be too much of a problem. It's a problem if the belt is chucking rubber everywhere, that means bad belt wear.

It's due to the offset on the aux d/s pulley.

GC
Hi Guy, I have a riding off problem on an Uno turbo 1.3L engine. The belt is chucking rubber everywhere because it is rubbing on the crank V belt pulley. I have tried replacing all the pullies with some from a good engine, there was no change. It appears to the aux pulley causing the problem. do you know why?

I shimmed the tensioner bearing out to stop it from rubbing as a temporary solution. That was 2 years ago ..

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Post by Guy Croft » July 11th, 2006, 10:29 am

yes, seen this happen on TCs too.

That is head-block misalignment (faces not accurately parallel to crank axis) or cam housing dowels missing for sure.

GC

SteveNZ

Post by SteveNZ » July 11th, 2006, 11:12 am

Thanks :)

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Post by Guy Croft » July 11th, 2006, 11:31 am

Hi Steve

Some background, I was interrupted in the middle of writing my last.

Wandering cam belt - I have guided people thru this before, the steps I have taken people thru are:

1. Incorrect layout of pulley flanges *
2. Crank, cam, auxiliary driveshaft end float
3. Taper worn on crank nose pulley or cam pulley (s)
4. Cam nose length wrong (I have seen this once, fortunately before I fitted the cam)
5. Cam or crank pulley (s) not seating properly.
6. Cam pulley 'swashing' ie: cam nose not perpendicular to axis (bad grind) *
7. Badly worn tensioner bearings
8. Badly worn aux d/s or bearings especially the rear journal (shaft runs on a slant) *

* means I have actually seen belt wander & wear due to that cause.

If none of these apply I think it must be the misalignments I mentioned earlier, I just cannot think of any other cause. Have I missed anything?
I think the SOHC unit is very much at risk here due to the pulley setups.

GC
Attachments
2004_0203Image0002.JPG
John Valentine's X19 1500. There is a rear flange on the cam pulley but if the belt 'walks' forward it's going to rub severely on the crank front pulley.
2004_0203Image0002.JPG (62.88 KiB) Viewed 8252 times

pastaroni34
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Post by pastaroni34 » July 11th, 2006, 1:28 pm

dont forget to mention dirt/trash behind the tensioner bearing bracket or a bent bracket causting a tilted tensioner.
-Jason Miller
Miller's Mule Machine and Design Inc.
Houston, Texas - USA

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