Performance change after cam belt replacement?

[Julian Edgar]

They should line up IAW whatever the manual says. It will be quite specific & there will be pictures for them to look at.

This any help?

Thanks very much.

[Julian Edgar]

It's going back to the workshop this Friday. It will be interesting to see what they say.

[Julian Edgar]

Workshop that did the cam belt change says the marks line up exactly.

Perhaps the original cambelt had stretched a little and the custom dyno reflash (done at around 90,000km) was matched to that (presumably retarded) state of cam timing?

I might have a go at moving cam timing a little within the range provided by the slotted holes and see what happens.

Performance and fuel economy are just unacceptable - considering what it was like prior to cam belt change.

[Preen59]

It shouldn't have made that much difference mate. Altering the cam time by a couple of degrees moves the torque curve a few hundred RPM at most.. There's got to be something else wrong.

[gldgti]

OK, so I see the new engines have done away with the sprocket on a taper for factory adjustable cam gear.... same effect however.

Because of any belt stretch, unless the position of the camshaft with respect to the sprocket is checked to be correct (the "torsion" value in that writeup) then it may not necessarily be in the right place.... the thing to ask is if they adjusted the cam sprocket or not.

[Julian Edgar]

Because of any belt stretch, unless the position of the camshaft with respect to the sprocket is checked to be correct (the "torsion" value in that writeup) then it may not necessarily be in the right place.... the thing to ask is if they adjusted the cam sprocket or not.

They didn't adjust the cam sprocket. "We never touch those bolts", he said. "We've never had any problems, no one else has ever complained [etc]."

Altering the cam time by a couple of degrees moves the torque curve a few hundred RPM at most.. There's got to be something else wrong.

As I understand it, the cam has lobes that pressurise the injectors - it seems to me that altereed cam timing may change the amount of fuel that is available to be injected when the injector is electronically opened. In turn perhaps this has altered the shape of the torque curve.

To summarise: power has been moved up by 1000 rpm - at full power, the car used to wheelspin in first gear at 2000 rpm; now it does so at 3000 rpm. (A big diffeernce in revs when your redline is just 4500 rpm!) Highway fuel economy is 0.5 - 1 litre/100km poorer.

[Julian Edgar]

Problem fixed. I adjusted the cam timing within the slotted adjustment range.

[Preen59]

After re-thinking how these engines actually work, i'm not surprised that's all the problem was.

Good to see you've got it sorted, Julian.

[gldgti]

Problem fixed. I adjusted the cam timing within the slotted adjustment range.

Hazaar!

Good result!

[Julian Edgar]

Interesting development.

Yesterday I retarded the cam timing until, when I went for a test drive, the car had the same performance characteristics as prior to the cam belt change. So, change timing a tiny bit, go for a drive. Change it a bit more, etc.

Too much retard resulted in the car not starting, so I then advanced it a fraction from that point until it started sweetly. Car felt to have performance the same as prior to cam belt change.

However: today, from cold, car would not start.

Retarded timing a fraction until it started sweetly from dead cold.

(With the slotted holes and easy access, it's really fast to do this - 1 minute job for each cam timing change.)

Went for a drive tonight to test some new driving lights and fuel economy was outstanding - better than ever achieved in these cold conditions. Performance is good - pretty close to how it was before cam belt change... strong power comes in maybe just a fraction higher than before (eg at 2200 rpm rather than around 2000 rpm).

I'll check fuel economy over the next few weeks but the outcome is very interesting.

[Jarred]

Interesting indeed!

Glad you've got it sorted, and learnt something new too. (and shared it )