Camshaft timing

[MikeHynes]

Sometimes the very basics can get confusing.
Cam timing is cam timing, ignition timing is ignition timing. They are NOT the same thing.

Cam timing marks line up when the engine is at TDC for cylinder #4 (and cylinder #1) and the #4 cylinder is ready to fire. That means the valves on #4 are both closed. It also means the valves on #1 are both open (an equal amount). If you said that the cam timing marks line up when the #1 cylinder is on split overlap (both valves open an equal amount), you're correct too.

The ignition timing marks line up when the #4 OR #1 cylinders fire. Either #4 or #1 can be used for ignition timing.

 

[carl]

This business of setting the cam at #1 or #4 has me confused. At least with a stock cam wheel, you set the crank at TDC, using the correct timing mark (plastic cover for 1300 or block mounted timing plate for 1500), the cam wheel is pegged to the cam so can only go on one way, rotate the cam wheel to the appropriate mark (mark on engine mount for 1300 and mark on belt cover mounting bracket on 1500) and install the belt. These are all set marks with no 180 degree out confusion. So if all the marks are hit correctly, the cam is timed correctly. Ignition is set using the #4 wire position on the ignition cap and other than a bit of fiddling to fine tune the ignition timing all is done.

The 1300 cam wheel is different from the 1500 cam wheel because of the different timing index marks on the two motors. They are not 180 degrees from each other an thus not interchangeable. One of my 1500 motors had a 1300 cam wheel but it was timed using the timing mark on the engine mount so technically that was OK. Admittedly cam talk makes my head spin.

 

[EricH]

The 1300 cam wheel is different from the 1500 cam wheel because of the different timing index marks on the two motors. They are not 180 degrees from each other an thus not interchangeable.

Not interchangeable, but if you do make the mistake of installing a 1500 cam pulley on a 1300 motor and then line up timing marks and install the belts.... the car will crank but not start. Now if you rotate the distributor to fire #1 instead of #4 it will fire right up and run, not well but well enough to make you think you were on the way to fixing your crank-no-start problem.

 

[rx1900]

Hey Bob. In case you are not perfectly clear on all this.....

On a 1300, the timing marks on the cam pulley are supposed to line up when #4 cylinder is at TDC and ready to fire. At that point of course both of the #4 valves should be closed - that is when both the cam lobes for that cylinder are pointing up. And of course the crank is at TDC.

At that point....on a 1300....the timing mark on the FRONT of the cam pulley should align - NOT with the pointer on the sheet metal timing belt guard - but with the pointer cast into the snail mount. That is how Fiat designed it. And that should also be used with the VAS cam pulley.

On some - but I dont think all - 1300 cam pulleys - there is ALSO a timing mark on the BACK of the cam pulley. Yes, that mark should align with the pointer on the sheet metal timing belt guard of course only again at #4 TDC.

Thus you could use either set of marks to align the cam. Take your pick...

However - in your case - I believe the VAS cam pulley ONLY has the FRONT mark on the pulley. To save cost they did NOT also put a mark on the BACK of the pulley. Thus you must ONLY line that mark up with the pointer on the snail mount. Of course this means that any other timing marks - like the pointer on the belt guard - are useless for you and should be totally ignored.

Got it ??

Now of course you could ignore all the timing marks on the cam pulley and time the cam via split overlap method on any cylinder you choose. But at the end of the day....when you rotate the crank to TDC and #4 valves are closed....those marks should line up....

 

[B0b]

Thanks for the comprehensive writeup.
Now of course you could ignore all the timing marks on the cam pulley and time the cam via split overlap method on any cylinder you choose
Which is what I did, because I preferred to be sure about the cam timing, given a new cam, a new sprocket, and some machining on the head.
I expected I would need an adjustable sprocket because of the 0.75mm head machining, but, as I mentioned above, the belt fit and held the timing.

Referring to my earlier photo, here is what it looks like with the crank turned 360 deg - in this position the #4 valves are fully closed:
The 1.3 mark lines up with the snail projection.

So, at the end of the day, I could have just installed everything using these marks, although I think that by using the cam lobe center approach I am comfortable that all is OK.
And I am embarrassed that I did not read pages 47 and 48 of the factory manual where it describes using #4 cylinder.

 

[rx1900]

Yes....."my" method would have only got you...close....

Close....would only be perfect ...IF....the dowel hole in the end of the cam was indexed perfectly....AND...the dowel hole in the cam pulley was indexed perfectly.....AND.....the head and block were NOT machined down !!!

In theory....if you shaved the head and/or block...for sure the cam would now be retarded. Absolutely !! And would have to be corrected by using an adjustable cam pulley ( or re-drilling the dowel hole ). And yes...could only be checked/adjusted perfectly by using a degree wheel and dial indicator.

In theory...in your case....you should have found your cam timing now a couple of degrees out ( retarded ). Guess you could calculate how much by pi x d of the cam pulley and the amount you shaved.

If....you swear ( by checking with degree wheel ) that your cam timing is perfect within 1/2 degree.....then surely you got really lucky and your particular cam and/or pulley was machined incorrectly ( and in the opposite direction ) by the same amount as your shaving. Go buy a lottery ticket......

 

[B0b]

Which is why I said earlier that one gets lucky sometimes.

I did the calces before shaving 0.75mm from the head.
Math shows about that the timing should get retarded about 2 crank degrees per 1 mm of shaving. I expected about 1.5 degrees.
Maybe all the tolerances stacked up in my favour.

All of the points you raise are why I chose to ignore the marks and do the timing using degree wheels and a dial indicator.
I checked it a half dozen times and am satisfied its correct. Half a degree is very tough to accomplish, but I am within 1 degree.


Going to put it to bed until April, when I will have to decide on ignition timing given my new compression ratio.

Thanks to everyone for their input.

 

[CnC79X19]

Which is why I said earlier that one gets lucky sometimes.

I did the calces before shaving 0.75mm from the head.
Math shows about that the timing should get retarded about 2 crank degrees per 1 mm of shaving. I expected about 1.5 degrees.
Maybe all the tolerances stacked up in my favour.

All of the points you raise are why I chose to ignore the marks and do the timing using degree wheels and a dial indicator.
I checked it a half dozen times and am satisfied its correct. Half a degree is very tough to accomplish, but I am within 1 degree.


Going to put it to bed until April, when I will have to decide on ignition timing given my new compression ratio.

Thanks to everyone for their input.

I'm guessing we must have been lucky too Bob since I wasn't aware that you could install the flywheel 180 degrees out (but the white dot lines up somewhere on the transmission degree markers so we guessed right), the crank pulley marker also lines up somewhere on the toothed tab that attaches right next to it on the block and the timing cover plate pointer seems to line up to the the 1.5 marker (opposite the 1.3) on the Vick Auto adjustable cam pulley depending on what angle you eyeball it from? I'm not really even sure what it does or how to adjust the thing anyhow? Also wasn't aware that the snail mount had markers on it. We just stuck a length of weed eater line in #1 piston until it seemed to be at TDC (or thereabouts?) and lined up the distributor rotor somewhere around #4 on the cap? Used on old timing light and turned the distributor til the light was around 10 degrees and snugged it I think? Not sure if we messed anything up but it seems to run ok although strong smell of rich fuel maybe? Obviously it gets way more precise than this so I might need some help when the weather warms.

 

[Dr.Jeff]

So then according to this photo, the cam pulley is correctly marked?

I've never had a 1300 SOHC (only 1500's) so I assume that method of cam alignment is only for the 1300?

 

[B0b]

Dr. J, yeah , its correct. Thanks to Doug for his info.
Cliff, i have all the stuff to set everything accurately, so lets plan on getting together when it warms up. Ideally you have the detailed cam spec. If not we can measure it.

 

[CnC79X19]

Dr. J, yeah , its correct. Thanks to Doug for his info.
Cliff, i have all the stuff to set everything accurately, so lets plan on getting together when it warms up. Ideally you have the detailed cam spec. If not we can measure it.

Great, thanks Bob