How to set cam timing on a VVTI engine?

[RomanV]

Hi folks.

I'm trying to set the cam timing on my engine.

I set it up, and gave the crank a spin with a power bar, to make sure everything was alright.

When it gets almost to TDC, it cant turn any further.

Does anyone know if the late model (gen 4 & 5) VVTI engines are non interference? I am thinking that perhaps the valves are hitting into the pistons. I dont want to try and turn it over any further, as I dont want to risk bending the valves, or anything like that.
If it isnt an interference engine, then I need to find out what else could be stopping it.

If it IS an interference engine, how the hell do you set the timing?

Because the cam shaft can rotate independantly to the cam wheel.
Obviously it will set itself up once it gets oil pressure, but what if the valves are intefering before this time.

[Mr Revhead]

when rebuilding an engine with maching such as you have done you should use plasticine

vvt or vvti doesnt affect it when timing a rebuilt engine.
the "off" position is where you set the timing

[RomanV]

Okay, well I just tried something.

I took the cambelt back off, and set all of the pistons to half height.

I then spun the intake cam, no worries.

Then I set the crank to TDC, and tried it again. It didnt budge.

The valves are definitely touching the pistons.

Obviously I didnt turn it very hard, I dont want to bend the valves etc.

so it's obviously an interference engine.

Or, perhaps it is due to the machining work that has been done to the head. I doubt it though.

Perhaps I had the cam belt setup wrong, but there's a lot of movement range in the VVTI pulley.... more than 45 degrees.
(When there's no oil in it, the VVTI pulley can move independantly to the camshaft... meaning that even if I have the cambelt setup right, the cam angle could still be way out!)

[Mr Revhead]

how easy is that pulley to move?
iirc the 20v 4age ones arent that easy to move by hand.....
they default to the correct position for timing.
is the pulley moving while your working on it?

i strongly recomend you dummy assemble with plastincine.....
last thing you want is for it to bend valvles etc on start up...

[RomanV]

The VVTI mechanism is completely different to the VVT one, IIRC VVT uses some kind of helical spring arrangement or some such thing, whereas the VVTI works with oil pressure pushing little pistons, or something.

When I rotate the crank, the cambelt pulls on the cam gears, and the intake cam gear moves as far as it can, before the camshaft moves with it.

[RomanV]

And yeah, I definitely dont want bent valves.

[RomanV]

After some discussion with Celica_RA45 AKA Glenn, he suggested that one of the shims may have dislodged itself.... as there should be 3mm clearance between the valves and the pistons. And if a shim had moved, this would be enough to do it.

So I pulled out all of the shims, checked them, put them back in, reassembled everything.....

He was right! it turns fine now.

One of the shims must have dislodged itself, when I took the intake cam out to put in the head bolts.

Problem solved.

[85AW20v]

Also make sure that you are using the right marks on the cam wheels. The silvertop VVT pulley has 2 marks on it and its easy to get the wrong one. The motor will turn over but it won't start.

[matt dunn]

One of the shims must have dislodged itself, when I took the intake cam out to put in the head bolts.

My car did that at 7000rpm, TWICE, on different valves,
when the place that did the head stuffed up the shim clearances.

luckily it's a non interferance engine.

[dodgy]

romanV, these are non-interference engines with normally about 2.5mm clearance. there is some adjustment with the vvti cam, but only about 1-2degrees (on the outer cup/body the bolt holes are slotted). just dont pull your vvti cam unit apart! i did just to see how it works and took me 5hrs to put it back together!