Speaking of 355 cam timing............

I found this on a UK forum.

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, 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.

(i guess that means all the above work is a total waste of time)
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Interesting PP.

 

This thread pops up after i was working on my mates Twin Turbo 1000hp (Drag) Supra today, we had a big discussion about cam gears

 

too much information

can i have more pictures

 

Sounds like a ball tearer!!

My brain just fried reading it!

 

lol

imagine writing it!

basically, it means "if there's nothing abnormal with your car, just line up the factory marks"

 

Sounds good!!

But dont post that where Rifledriver/Helms and a few others will see it!