Timing belt conundrum

I doubt anyone checked the flywheel timing and it was probably a couple of degrees off at the cam from the beginning plus a couple of degrees from belt variation. Rear bank wasn't too bad (2 and 3 degrees), front was 5 and 7 degrees.

 

So the short version is that if you have the time and inclination, that being that you think you can make the car run better than it is currently, during your next belt replacement you should:

Find TDC using a dial gauge
Use cam lobe measurement to determine when the cam is in the right orientation and for giggles mark it with paint
Change the belt pulley position to reflect this.

Did I miss anything?

Lester

 

Next time you check your valve clearances might make more sense. That's when I did my cam timing, belt change before last.

Be aware that checking/setting the cam timing on the front bank is a lot of work with the motor in the car. It's not conceptually difficult, but it's a finicky job done in an awkward position with less than ideal access and visibility.

 

Well I am waiting for cooler weather to do the big job: Replace heating hoses, replace vacuum hose, replace A/C hoses, replace high pressure fuel lines to injectors, replace injectors and bits, replace cam drive pulley and cam pulleys , and belts, I figure somewhere in there I'll do the valve adjustment. The upside being that I'll have the intake plenum off which should help access.


Lester

 

So the engine was conceived, designed, engineered and manufactured. The components were forged and ground to exacting tolerances then Mario's 13 year old nephew came along with a hammer and chisel and just kind of eyeballed it and punched in some timing marks?

 

HAHAHAHAAAA!!!

You know that the factory had to have a special tool that a fit the notch, was spring loaded and required just exactly the right amount of force to make the mark yet not bend the camshaft. Now new ones can be purchased through Ricmabi for $ 2000. (No, not really.)

Lester

 

My guess is the cams were notched accurately as part of the grinding process and were fitted with a relatively wide tolerance during assembly (the mix and match way of adjustment doesn’t make it easy.) has anyone checked how accurate the notches are using lift measurements?

 

Leave the Engine Bay Trunk Lid ON for MORE 'Difficulty Points, like I did, as I had no alternative place to put it.

 

My Flywheel TDC Pointer* was 'OFF' by over 1° from measured TDC and 3 of the 4 sets of 'Assembly Marks' on the Cams and Cam Caps are noticeably 'OFF' with the naked eye as well.

Once reassembled, I pretty much forgot those Cam/Cam Cap Marks as they, at that moment, more-or-less outlived their usefulness.

Those 3 Cams required Indexing** via the Pinholes in the Cam and Cog/Pullie and rotation of the Cam/Pullie as a single unit with or against the belt's direction of travel. What a PITA.

Measured ON the Flywheel:
1-4 Intake Events: 3° OUT.
1-4 Exhaust Events: 6° OUT
5-8 Intake Events: 4° OUT
5-8 Exhaust Events: 0° OUT.

ONLY the 5-8 Exhaust Cam 'Assembly Marks' were DEAD ON, and when measured with a degree wheel, the Cam was found to require NO Indexing.

Thank Goodness as that Cam is a REAL _=×$^^"%^er to get to with the engine in the car.

* - That OEM POS 'Pointer' had a such 'rounded point' as to be near useless. I made and installed a new one with a much, MUCH Finer POINT.

** - According to the Mondi 8 - QV WSM, as no 1981 308 GTSi WSM was ever published, the MAX Allowable deviation from 'PERFECT' Cam/Valve Event Allignment is ONLY +/- 1°

I am Assuming that allowable varience to be in CAM Degrees ... NOT CRANK Degrees, as the WSM is unclear to me.

 

From the assumption cam degrees +/-1 and the cam pulley is 90mm, I get 1,6 mm belt tolerance range or +/- 0,8mm.

Calculating the alu expansion I get 0.5mm from 20 degC to 100 degC. Just thermal expansion would eat up most of the tolerance on installation. I guess this should be accounted for, and I assume it is already included in full valve lift at a certain angle after tdc. The angle would be slightly different on a cold vs hot engine.

 

I HOPE I get this Correct, as the story was told here and to me in-person, quite long ago.

According to 2 DIRECTLY knowledgable members here who pretty much no longer post, Ferrari views(ed) their 'Road Cars' as something of an 'Acceptable Nusance' as they help fund RACING. Ferrari is, or was until they went 'Public,' a RACING Company, NOT a 'Car' Company. The only one of its kind in existance.

The 308* (& 328?) Series was even a bigger PITA for them. They built LOTS of them. They put the cars together and shipped them out the door. The End.

Being 8-Cylinder cars MAY have had something to do with the apparent 'distain,' as they both reported that the Testarossa/512TR line was given significantly more 'Tuning Care' before they left the factory. Still ... some 'slipped by.'

* - The 2V** cars will supposedly run 'just fine' to the average driver with quite a bit MORE Slop, than the WSM says is allowable. How much more? I have NO Idea.

I seek 'Perfection' (the very BEST my tools and abilities can do) anyway, so that number, whatever it is, is meaningless to me.

** - ALL the 4V cars are supposedly Much LESS 'Forgiving' to ANY Slop BEYOND the WSM tolerances. I have ZERO direct experience from which to speak as I don't own a QV or 328.

 

I never did. Have NO idea.

And like I said, using them purely as an ASSEMBLY Reference, then off to the 'Dead-Nuts ON' accuracy of the fly/degree wheel and their pointers for all event references, makes them largely useless.

 

The variantions in mating of a flywheel to the crank is largely irrelivant.

I brought the engine to TDC via a Piston Stop.

The flywheel pointer was OFF 'a little.' Perhaps a little over 1/2 a degree, but that's just a guess.

The flywheel 'pointer' also was quite rounded affording LOTS of Slop while reading it, so I made another with a very sharp point, painted it yellow and installed it pointing 'DEAD-NUTS ON' to PM1-4|

 

Lester,

What does, "Change the belt pulley position to reflect this" mean?

Using the pin and cam/pullie holes?

 

“I doubt anyone checked the flywheel timing”
I meant check the timing at the flywheel. I’m sure most people just use the marks, lock the pulleys, change the belts, and don’t change the pulley pins if a little off the marks.

 

You need a degree wheel and some method to find out valve opening and closing, right? Then cam covers need to be off. This is probably too much work for a diy.

 

Yep it takes a long time to get right with degree wheel and measuring lift,had to do this with the CATCAMS as there are no marks. Once set have scribed marks in to make the cambelt change simple next time

 

Yes.

 

Ok.

Got Ya.

 

It's been noted that the cam marks are like 3 degrees wide, IIRC of crank rotation?

So as ya'll are discussing, a degree wheel and using the gear holes is the only way to dial in the .5 degree tolerance of timing the Factory standard requires.

I recall JRV being proud of changing mine to "Euro Timing" of the (exhaust?) cam, so I know he spent the effort to do all of that.

 

And that should be duly noted. Changes in cam timing from the factor spec will mostly effect where the power is, top end, low end, or midrange. It will effect fuel mileage. But being off 5 degrees doesn't necessarily mean the engine won't run right. Mostly it will run differently. Depending on how you drive it may run better for you needs.

 

The 'Euro' timing of the 2Vi MONDI 8 (same motor as the 2V GTSi, for which there is NO WSM), is the same as US models for the Intake Side according to the WSM.

It is DIFFERENT for the Exhaust Side.

Exhaust CLOSES:

US - 14° ATDC
EURO - 10° ATDC

What does that change GAIN?

 

Are they also different cam profiles? If so, it's not surprising that the sweet-spot timing would also be different. Depending on the profiles, the actual opening and closing events could be happening at the same time with both cams.

 

More torque at higher RPM but also higher emission, and lower power at low RPM. US emissions standards are likely why US cars have earlier exhaust valve closing.

 

No idea as to the lobe profiles.

And I do have 2 EURO ICUs.