Gti6 Cam Timing Question

[VTS_Tibi 0]

Hi Guys,

 

I have a Xsara VTS fitted with a Peter Taylor stg.1 inlet camshaft.

 

It was fitted a few years ago, and it was timed up with a dial gauge, but now I'm not really sure the timing is spot on.

 

Torque is just AWSOME low down the rev range (I can accelerate out of corners in 3rd. gear from 15km/h without any kind of judder! - bit weird for a petrol engine... even my HDI don't like that!), but higher up it just flattens without any pulling power!? It pulls to around 5400-5500 and the pull goes away.

 

So first I would like to check the timing of the camshafts.

 

How do you check the lift @ TDC? This is how I done, and I would like to ask for comfirmation to see if it's OK:

 

I turned the 1st. piston to TDC (checking the true TDC with a dial gauge) while checking the lift with an other dial gauge which was pointed on the top of a tappet.

 

 

Is this method correct?

 

 

Could anyone tell me the original exhaust cam's lift @ TDC so I can check it's timing aswell? (I think it was adjusted in the past, so there's a chance it's timing is not spot on now!)

 

 

Additionally, I have an XU10J4R stg.1 inlet cam grind in an XU10J4RS engine. Would it be a wise move to swap that out for a stg.1 regrind for the XU10J4RS?

 

 

 

Regards,

 

Tibi

[petert 588]

As there is piston dwell at TDC, you need to verify your TDC mark by measuring say 20 deg. either side of your mark, and make sure you get the same measurement. Alternatively, set up a marker on the motronic flywheel teeth as per my website.

 

With TDC firmly established, put a dial indicator on an intake bucket (cyl #1) and measure the lift (amount of opening, bucket dropping) as you rotate the engine from 90 deg BTDC to TDC. For your cam, anything from 0.060-0.065" will be ideal. Certainly nothing more, or you'll risk valve-piston contact. You can experiment with the exhaust, but something in the range 0.020" to 0.050" max.

 

Your cam is bigger than the Stage I grinds I now offer for RS engines. There are other alternatives for the exhaust.

[VTS_Tibi 0]

As there is piston dwell at TDC, you need to verify your TDC mark by measuring say 20 deg. either side of your mark, and make sure you get the same measurement. Alternatively, set up a marker on the motronic flywheel teeth as per my website.

 

With TDC firmly established, put a dial indicator on an intake bucket (cyl #1) and measure the lift (amount of opening, bucket dropping) as you rotate the engine from 90 deg BTDC to TDC. For your cam, anything from 0.060-0.065" will be ideal. Certainly nothing more, or you'll risk valve-piston contact. You can experiment with the exhaust, but something in the range 0.020" to 0.050" max.

 

Your cam is bigger than the Stage I grinds I now offer for RS engines. There are other alternatives for the exhaust.

 

Thanks for the reply Peter!

 

 

I've followed this guide in the past:

 

 

Make a pointer using a bit of wire and attach it to a bolt somewhere convenient. Next set the timing disc to indicate zero on the pointer when the crank is at TDC. The trick to finding true TDC, lift is dwell. This is a period (about 10°) either side of TDC when the piston ‘hovers’ at the top of its stroke. What this means is that you don’t try to find the exact position of TDC using one reading on the dial gauge. To find ‘true’ TDC : Set up your dial gauge indicator so that it is touching the top of the piston, if the head is still on you will have to make up an extension to reach through the spark plug hole. Turn the crank until the piston is at the top of its stroke and set the timing disc to zero. You will find that there is a dwell period of approx. 10 degrees where the piston is at its maximum height. True TDC position is at the centre of this dwell period. Rotate the crankshaft and stop at a figure just before TDC, approx. 0.2mm on the dial gauge. Record the figure on the timing disc from the pointer. Now rotate the crankshaft and stop at the same figure (0.2mm) after TDC. Record the figure on the timing disc again. True TDC is positioned in the middle of these two figures. The TDC position can be calculated by adding the two figures together and dividing by two. Adjust the timing disc pointer so that it reads zero at true TDC.

 

 

So it seems like I was more or less correct with this. Problem could have been a bad dial gauge (which as far as I remember was not spot on). I'll check the timing again anyway!

 

It would be better to make marks on the fly, like your guide states - being a bigger diameter -, but it's quite hard to reach that area with the engine and gearbox still in the car.

 

 

What is the exact original timing figure of the exhaust cam? Or nothing like that existed? So they were within the range you wrote above?

Edited March 14, 2011 by VTS_Tibi

[petert 588]

 

What is the exact original timing figure of the exhaust cam? Or nothing like that existed? So they were within the range you wrote above?

 

I've got no idea what the exact timing is, but given the size of the cam it will be around 0.030" @ TDC. Keep in mind that advancing the exhaust cam will decrease this number and decrease overlap. I'd experiment by retarding and advancing. With an Mi16 exhaust cam and your inlet grind, I normally run around 0.060" @ TDC (too much for yours). However, given the GTi6 has a more efficient exhaust, results will differ.