Help re timing belt change!

[PaulB]

Hi all,
Newbie questions so please be patient.... Just about to change the timing belt and tensioner on a 74 Spider 1800 carb model. Originally had an air pump on the exhaust side....long gone but still using the double pulley. Have read all the posts etc but need to clarify. I have not yet removed the old belt....when I set the cam sprockets inline with the cam tower ‘pips’ by lining up the holes per workshop manual, the aux shaft pulley hole is at about 5 o’clock not 1.30. Also the crankshaft pointer looks about 15 degrees BTDC against the timing cover long mark.
The car has been running very well and obviously no interference issues with the aux shaft.
Question....should I replace the belt with pulleys in the existing positions? Or to do it properly does that mean turning the aux shaft to 1.30? And does that mean redoing the ignition timing?
Also why would the crankshaft pulley mark be so far off the timing cover mark?
Would really appreciate some advice. Thanks, Paul

[wetminkey]

I cannot answer your question, other than to re-state what the Fiat Shop Manual calls for,...and that is to align the hole in the aux. sprocket's spoke between the sprocket bolt, and the tensioner's spring retaining bolt. Changing it's position will not affect your ignition timing.
As far as your timing marks go,...it all depends on whether your engine has all of it's original parts. My '79 does not have timing marks on the timing belt cover, and the pointer would be on the passenger's side, but my engine is missing it's timing pointer entirely, so I had to make some timing marks while the engine was set a TDC #4. Your car runs good as is, so I'd just mark zero degrees , and use the mark for future reference.
Here, in Colorado, I would advance my ignition about 1 degree for each 1000 ft elevation, and a couple of degrees for crappy gas, but 15 degrees advanced is what I run my V8s at,...so I believe that your marks might not be proper.
Perhaps another member will post to tell us more about WHY the auxiliary shaft MUST be in this position, and if different Fiat parts could put your timing marks off so much,...
Welcome, PaulB!
Todd Compton.

[RRoller123]

This may help?

[18Fiatsandcounting]

Hi Paul, a few additional thoughts from me. As stated above, changing the auxiliary pulley orientation will not affect your ignition timing, but this is true only if you have the distributor mounted on the rear of the exhaust camshaft housing (as would be expected for a '74 spider). Also, my understanding is that some engines don't have any interference between the auxiliary shaft lobes and other internal engine parts, so the timing doesn't matter as the shaft only drives the fuel pump (if you have a mechanical version on the side of the block) and the oil pump, neither of which care about auxiliary camshaft timing.

But, you don't want to run into a clearance issue at higher engine speeds, so I would strive to get the auxiliary pulley reasonably correct. It obviously worked at the 5 o'clock position, but 1:30 is what is specified.

As for the 15 BTDC when the camshaft pulleys are lined up, I have found that the original timing marks on the timing cover are notoriously hard to read accurately, and shifting the timing cover around (mounting bolts loosened) can sometimes move the mark around several degrees or more, depending on the condition of the timing cover mounting hardware. What I do, once the timing belt is removed, is to remove the #1 sparksplug and insert a long screwdriver into the hole so that the tip rests on the top of the piston (caution so that you don't drop it or anything else into the hole!!). By moving the crankshaft pulley by hand, you can "feel" where TDC is by looking at the rise and fall of the screwdriver, and then you can check that against the marks on your timing cover. 0 degrees should be the longer mark towards the bottom. You can then install the new timing belt, get it running (don't forget to replace the #1 sparkplug) and then adjust the ignition timing to what's specified, or what works best. For my early-model-year Fiats, this is around 5-10 degrees BTDC. 15 BTDC could be just fine, depending on where you live (altitude, climate) and the general condition of the engine. As long as the engine doesn't knock, of course.

-Bryan

[seabeelt]

The Aux pulley hole needs to be at the 1:00 position or near enough to it It has a cam type lobe on it that tuns the mechanical fuel pump. It this is not in the correct position you have interference with the crank shaft and can possibly shear off. ( don’t ask how I know ) Then you end up with an unsecured pulley and a broken piece in the oil pan. Yup got to drop the oil pan to get that out. Please don’t go there. Align the pulley to 1:00

[wetminkey]

There ya go,...THAT'S why the auxiliary shaft MUST be in the proper position!
As the Fiat Shop Manual states,...the hole in the aux. sprocket's spoke should be positioned between the aux. sprocket's bolt, and the tensioner's spring-retaining bolt. That puts it at about 1:00,...

[18Fiatsandcounting]

Yes, that's exactly the reason for the aux. shaft pulley orientation. It's been a few years since I stared into the innards of a Fiat block, but my recollection is that the lobe on the aux. shaft (the lobe that drives the fuel pump) hits the connecting rod for the #2 piston if the aux. shaft isn't timed correctly.

Again, I have heard that some variations of this engine don't have an interference issue (could be folklore), but since you may not know definitively with a particular engine, please do as suggested and orient the aux. shaft pulley as it should be. Easy to do, and the consequences if not done could be very bad.

-Bryan

[PaulB]

Big thank you to all who took the time to respond. Very helpful....what a great international forum!
So, timing belt and tensioner successfully changed and car running smoothly. Actually a pretty straightforward job in the end. Even the tensioner spring bracket is easy to understand when you see it rather than just read about it.

My first ah-ha moment was realising the distributor on my car is driven off the cam not aux shaft so no timing implications in rotating the shaft. So as per advice, I set the engine at TDC off number 4 (using a wooden dowel in the spark plug hole whilst rotating by hand).....and the cam timing was already spot on. So locked the engine in 5th gear and went from there.

I did reset the aux shaft at 1.30 so all good. But out of curiosity I did play around .....very gently turning by hand with all plugs out...and sure enough there is interference.....and only a few degrees from where the PO (or the ‘professional ‘ that did the job) had left it. Maybe he was just really lucky. So yes....stick with the specified setting is the answer.

I reinstalled the aluminium timing cover with correct bushes etc replacing the random array of old fixings to try and ensure it is in the correct position. Then when looking directly front on from below the car.....the timing mark on the pulley vaguely lines up correctly with the correct timing mark on the cover. Close enough to declare victory anyway.

One other snippet in case helpful for others.....under certain conditions when hot my car would previously make a light grinding noise from the water pump area. A new pump had been fitted only 2 years ago before I bought the car. Turns out whoever fitted it did not install locking washers (or any washers) under the pulley bolt heads. So when hot....2 of the bolts were a tiny bit longer than intended where they bolt through the water pump threads flange....and just lightly scraping against the pump body. Sounded expensive but the fix was 3 washers.....1 under each bolt per that parts manual. Hard to explain...hope that makes sense.

Of course the job took way longer that planned. Doing it for the first time...and distracted by all those other ‘while I’m in there’ tasks. Cleaning/repainting components etc. Would be a quick job next time but hopefully not for a while.

Thanks again.....and for any other newbies....don’t be nervous and put off DIY. Take it steady...ask this forum when in need....much more satisfying than paying to get it done.

......Paul

[18Fiatsandcounting]

Paul, I'm glad it all worked out, and thanks for the additional information on the water pump as tips like that can help others in the future.

I do vaguely recall the interference between the auxiliary shaft lobe and the connecting rod was one of those situations where if either part had been located a quarter inch in the other direction, things would have been fine. But, with metal parts spinning at 1000s of rpms, there's no room for error with trying to be in the same place at the same time.

On the water pump: Way back in the recesses of my mind, I do recall having run across a similar situation, but gosh, it's been decades and so I'm fuzzy. Probably what happened is that I sheared off one of the water pump bolts and put in a replacement that was just slightly longer but then ran into the same problem you did. Anyway, glad you figured it out.

-Bryan