gear-driven DOHC on older Toyota

[Number_35]

My friend is doing a water pump/timing belt change-out on his mid-90s Corolla, and showed me some photos of his prep work.

I was really surprised to see that the TB drives just the one camshaft pulley. That camshaft drives the other one with a fixed gear.

This will make the TB change much easier, as he won't have to worry about the cams getting out of time with each other. I guess the only downside is that variable valve-timing would be harder to implement.

 

[AKhan87]

Originally Posted By: Number_35
My friend is doing a water pump/timing belt change-out on his mid-90s Corolla, and showed me some photos of his prep work.

I was really surprised to see that the TB drives just the one camshaft pulley. That camshaft drives the other one with a fixed gear.

This will make the TB change much easier, as he won't have to worry about the cams getting out of time with each other. I guess the only downside is that variable valve-timing would be harder to implement.
that engine had variable valve timing? I highly doubt that.

2000 Corolla was the first time it was introduced in that specific model.

 

[Blinker]

I think what the OP meant was that it would be hard to design an engine with this style camshaft gears and incorporate VVT at the same time.

 

[Ducked]

Originally Posted By: stower17
I think what the OP meant was that it would be hard to design an engine with this style camshaft gears and incorporate VVT at the same time.


That's what he said, as well.

 

[AKhan87]

Originally Posted By: Ducked
Originally Posted By: stower17
I think what the OP meant was that it would be hard to design an engine with this style camshaft gears and incorporate VVT at the same time.


That's what he said, as well.
oh shoot, I didn't read the last part...

 

[440Magnum]

It could still be done. IIRC, there are dual-VVT engines out there that slave one of the cams off the other with a short chain, but there's a cam phaser between the driven sprocket on the "slave" sprocket and the camshaft itself. You could do the same with a geared cam setup by having the driven gear have its own cam phaser between the gear and the shaft. The "master" shaft would also have its own phaser- both driving and driven gears would be locked to the crank and the cams would be controlled by their respective phasers.

You could even do the same with a vertical quill shaft drive (no chain) to the overhead such as old Allison and Rolls-Royce aircraft engines had. In that hypothetical case, all the gears would be rigidly timed to the crank, but a phaser between each cam gear and its camshaft would allow for variable timing.

Problem is- its big, heavy, and expensive compared to a shared chain.

 

[HerrStig]

Originally Posted By: 01_celica_gt
Originally Posted By: Ducked
Originally Posted By: stower17
I think what the OP meant was that it would be hard to design an engine with this style camshaft gears and incorporate VVT at the same time.


That's what he said, as well.
oh shoot, I didn't read the last part...
Jumped right on the guy though...

 

[kschachn]

Yeah, the 1MZ-FE in my old Sienna is not VVT-i but later ones were.

This is a random Internet picture that shows both (the VVT-i not looking so good):

 

[AKhan87]

Originally Posted By: HerrStig
Jumped right on the guy though...
highly doubting is "jumping right on" someone?

 

[artificialist]

VW does something similar. On the 1.8T 20V and some 30V V6 engines, there is a miniature timing chain where Toyota uses miniature timing gears.