Setting the cam timing belts on a 355

Crap Ernie that is alot of extra work to set cam timing,(removing the head) hahaha. You are correct tho that is a good right up. regards, Vern

 

Agree about the heads but you can apply the techniques as well with them on

Interesting note how he mentions the adjustable tensioners make life easy while we are stuck with pins in the cam pulleys and moving the belts a notch, no one ever said working on Ferraris is easy though

 

That thread has little to do with engine timing and everything to do with engine building. The two should not be confused.

 

See, this is where the confusion exists. The holes in the pulley and the holes in the cam are not 1 to 1. There is a "vernier" adjustment that allows, while the cams are times correctly in relation to the crank and each other, the cam pulley to be placed (after the belt is installed and tensioned) exactly at a point where one of the holes in the pulley lines up with one of the holes in the cam flange. That way, the position of the belt cogs has no influence on the cam timing, if the cams are set properly in relation to the crank.

-Peter

 

I'd like to see how others set up the dial gauge, for me that was the most difficult task.

 

if you've set the belt to the pulley and rotate it so that you line up a hole on the cam you've adjusted the cam timing becouse you've turned the crank end to line up the cam. if you affix the crank end and the cam then line up the belt and pulley, the timing should not be effected. from there you can use the degree differences between pin holes to advance or retard the timing.

if someone has a spare 348 pulley upper/lower i'd be more than happy to redesign the pulley like i did for the 308/328 so that you'll have a vernier adjustment and no pins to pull. cost could be an issue though, like the 308/328 ones they were coming in a $1300 cost.

 

Oooh Plugzit my fellow Stooge.............someone is calling you.

 

umm thanks?
okay i give up, (gary coleman) 'what you talkin about ernie?'

 

F-Chatter Plugzit has a spare 348 engine sitting in his garage.

 

ahh okay, thanks.

 

I think that's a cool idea, but for me, I'd rather yank out all 4 cams and place electro-activators over each valve (if I was going to invest the time to make a change that large). Computer control the whole thing with infinite valve timing settings (in real time!) along with existing ignition timing and fuel/air settings/adjustments.

For that matter, might as well replace each vertical valve/stem with horizonal iris shutter-type valves, too.

 

This thread is going down hill quickly. People post but do not read what other posts. I can see why the pros are going nuts. I now understand tbakowsky's cry.

NoDoubt...it is late Sunday night. You have to work in the morning please stop drinking...

Your pal Moe

 

OK, here goes.

Firstly, I'm of the school of thought that the reference marks put on the cams are pretty good usually... certainly, in my experience, I've never found any to be wildly out... always within the rough tolerance of the line width, which is easy to see by eye. I only dial cams in by request or for investigation purposes.. NOT as part of std service schedule. If I happen to know or even feel (nearly 20 years experience) that cam timing is correct, I'll happily just replace belts to save expense if it's enomically viable or requested.

Recently, I've done belts and cam timing on a 355 that I suspected of having bad cam timing since PPI... due to poor power/throttle response initially, lack of the full on WAAAAA noise (despite bypass working correctly), but subsequently and more recently (18 months into new ownership) the C/E light came on for cat failure.

Now, and here's the crux... I reckon there's many areas for human error in dialling in the cams. I've dialled perhaps 10% of the belt changes I've ever done, and I always triple check my work in this regard.

Upon dismantly, the recent job was found to have significant mis-timing DESPITE perfect belt wear/tension conditions.

To check... firstly we have to establish a true TDC mark... 348/355/360 dont have crank markings, so we need to find the centre of the TDC dwell and mark it... I have a simple tool I drop in the clutch vent hole, and put a mark on the flywheel edge as the front pulley radius is too small for accuracy. This has to be done for both 1-4 and 5-8 banks.

The flywheel is on a spline, so the tiny amount of slack has to be considered... But it's not much and easy to set.

Then, we use the dial gauge to measure valve lift at TDC... on the inlet we must use the lateral (side) valve and not a central one of the 3. On the exhaust, either is ok. (In fact, it's interesting to compare valves... some discrepancy in the cam grind is quite common). I DON'T measure the point of max opening on the 5 valve cars because it's all too restrictive to get the tooling in the hole with any real accuracy, but I DO prefer this method wherever possible).

Now, it is ESSENTIAL that we measure lift in a perfect line with the valve... if we measure on an angle, the lift is effectively reduced, (plus, the likelihood of the pointer skidding increases dramatically) so I've made a specially bent pointer to wrap a round the cam to achieve perfect alignment.

To measure the timing, the CRANK PULLEY MUST BE TIGHT... as the helical gear otherwise allows the timing gears to retard a little.

Arrange the dial gauge perfectly in alignment, and turn the engine to TDC as marked... the lift should match the spec values. bear in mind the cam sprocket only allows 1.5 degree increments of adjustment, which is 3 degrees of crank rotation, so perfection is sometimes impossible to achieve.. in which case set the timing with new belts to be a little advanced, as it will retard with stretch.

On my recent job, the 1-4 bank was found to be just about perfect, but the 5-8 bank was considerably out...

I've included a few pics...

You can see my crank TDC tool which positively locates in the vent hole, the tape just stops it falling out and acts as visual reminder to take it out!!

You can see the marks that look really accurate, and you can see the ones that are clearly out as deliberately set previously by error... you can see also the amount of crank misalignment the incorrectly timed cams had.. about 12 degrees on one and 9 on the other... 4 holes and 3 holes on the cam sprockets...

When they were all adjusted... guess what happened with the reference marks.... they were all VERY close to perfect.
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Now that my friend is a great write up and i for one thank you for doing it
You have also answerd my question that others avoided answering regarding "whats the average degree that a 355 is out", in your first few lines. In which i thought as much
Very nice write up and i shall be keeping this in my files....Good that man

 

Thanks, you're welcome.

 

Thanks, Phil! Terrific, as usual.

Scott, wasn't suggesting moving the crank to have the holes line up. Was proposing what you suggested which was to line everything up (after using true TDC and a dial indicator to verify marks are correct), then install the pin in the matching holes...

Thanks, Peter

 

Thank you for your writing. Just one question for my understanding.
By a combination of sproket/cam alignment AND eventualy 1 (or several?) tooth shift between the sproket and the belt, isn't possible to have an adjutment increment of less than 1.5°? I will try to compute the minimum increment according to sproket, cam, and teeth angles ...

 

I have those specs, I used cam software to figure it out. They are in another computer. I agree that it is MUCH easier, particularly in terms of accurate reading of the dial indicator.

Jay

 

i thought that's what you were saying, i must of read it wrong. my appologies.

 

Thank you, Phil. Great write up.


Could you bear a couple of questions from a layman??
1. where is the degree wheel in your process? Not required... or just so obvious that everyone but me gets it?

2. must the heads be pulled to consistently measure/set the precise cam timing (e.g. is measuring valve lift the best or only way)?

3. the Ferrari workshop manual keeps talking about moving back 1/4 to TDC. Do they really mean turn the engine forward 3/4 to TDC?

4. would the 348 only require one mark on the flywheel for TDC?

5. is there any way that you could "show" how you are determining TDC dwell?
6. is there any way that you could show the physical process of setting the cam/pulley (e.g. special screw, cog installed, crank turned to mark)?

 

Done some computation:
angle between holes on the cam : 22.5°
angle between holes on the sproket : 24°
angle between teeth : 11.25°

For a given position of the belt on the pulley, the adjustment increment is indeed 1.5° (24-22.5) at cam level, so 3° at crank level.

If, without moving the cam, the pulley is skipped by 1 tooth wrt the belt, then the adjustment increment (wrt the previous position) is only 0.75° at cam level, 1.5° at crank level. Suppose a hole coincidence between cam and pulley, moving the pulley by 1 tooth give a shift of 11.25°, with 1.5° difference between hole spacing on the pulley and the cam, you will be able to find a new coincidence at the 7th or 8th hole plus or minus a relative displacement of 0.75° (0.75 = 11.25 - 7 * 1.5 and -0.75 = 11.25 - 8 * 1.5)

 

1). No degree wheel used... Only reference point is TDC.

2). No, Valve lift is not strictly speaking what is measured.. we measure bucket lift.. the hydraulic tappets don't move the valve perfectly so you are correct in saying that valve lift is still not truly measured. And if you look at the pic in the manual, you'll see that their measuremnts are NOT taken in perfect alignment (by the pic anyway)

3). No, turn the engine back and forward as directed.

4). No, You need a aTDC for each bank at least. Each piston if you want to be really anal!!

5). TDC is a dwell period. True TDC is the middle of that dwell period. It's only very small though. If you don't understand it, you shouldn't atempt it.

6). NO WAY... my banana fingers struggle like the rest of you!!

 

I always try to preserve the original pulley position if possible... as they are marked for quick reference by the engine builder in the factory...

If you move the pulley to chase a nano degree... you introduce an area of irregularity should there be any query later in the service life.

If you MUST move a pulley... remove the old marks by grinding and seal with paint, and then re-mark the pulley/cover reference point.

 

That makes sense. Thank you to share your experience.