Camshaft Timing

[jono]

My engine is fitted with QED 360 cams and adjustable pulleys. The cam timing was originally set up by the engine builder 15k miles ago and I've never considered fiddling with it as the engine goes well.

However I have carefully measured the timing since I have the engine out and find that the the inlet cam is advanced 4 degrees - MOP 101 ATDC v QED spec which is 105 and exhaust 6 degrees - MOP 116 BTDC v QED spec of 110.

Is it worth putting it to the correct spec, what am I likely to gain and lose?

Cheers,

Jon

[jono]

Well I decided to put it to the QED recommended timing so it will be interesting to see what difference it makes

[nmauduit]

Well I decided to put it to the QED recommended timing so it will be interesting to see what difference it makes

that would have been my first thought, too.

nb: would there be a typo in the initial post (ATDC/BTDC interverted vs inlet/exhaust)? I would tend to think from your measurements that both cams are late, that is adjusting the exhaust side would fix most of the lag for both with respect to the manufacturer setting.

If you then readjust the inlet (+2?) after setting exhaust 6 degrees back, you will set a tiny bit more overlap, but that would be difficult to feel in itself (my bet is that most of the improvement would come from the earlier inlet opening, but Rohan would have a more in depth prospective view of such settings).

Or you could just try -5? on the exhaust and check if you're within 1? for both - quick, and close enough for a street car...

[jono]

got me worried now

My methodology:

The cams were opening early (I hope!) - 6 degrees on the exhaust and 4 on the inlet. Did the measurement with a DTI allowing for dwell and established max lift on each cam then checked on the degree wheel when max lift was reached. This established that they were fully opened, early, by 6 and 4 degrees

To set them to QED spec I set the degree wheel at the recommended max lift point and them moved the cams via the adjustable pulleys until I got max lift on the DTI on the cam bucket.

Did this for exhaust then inlet and re checked everything on completion which showed the cams to now be bang on spec.

Jon

[rgh0]

Hi Jon

I would start with the QED recommended timings and then adjust if you have time to play around those settings.

I normally always rotate the engine and measure lift either side of maximum lift at say 40 thou below maximum and then divide the degree wheel readings to get the midpoint of the cam timing. Due to the dwell at full lift its hard to get a reading of actual full lift centre of lobe timing by measuring full lift itself. If you do it without rotating the engine you also risk the cam chain going slack as you try to measure it.

cheers
Rohan

[nmauduit]

got me worried now

My methodology:

The cams were opening early (I hope!) - 6 degrees on the exhaust and 4 on the inlet. Did the measurement with a DTI allowing for dwell and established max lift on each cam then checked on the degree wheel when max lift was reached. This established that they were fully opened, early, by 6 and 4 degrees

To set them to QED spec I set the degree wheel at the recommended max lift point and them moved the cams via the adjustable pulleys until I got max lift on the DTI on the cam bucket.

Did this for exhaust then inlet and re checked everything on completion which showed the cams to now be bang on spec.

Jon

what I meant is that inlet is before TDC and exhaust after TDC in my mind, then assumed you switched ATDC and BTDC, everything else being correct.

The lag I mention is with respect to the specs which was my take on your inital question (what if I restore timing to manufacturer specs), 101 vs. 105 for inlet being late 4? (i.e. not advanced by enough with respect to TDC), 116 vs 110 being late 6?. The key being reseting timing to the stock values, vocabulary can vary with personnal preferences. A drawing I find useful for these reflexions is the 2 hump sketch, which I draw with inlet to the left as if the time was on the X axis, but many draw it in reverse - in any case TDC is the reference.

[jono]

Cheers chaps

Rohan; for as installed lift I turned engine a full revolution and then measured on the bucket just before the lobe was on its peak, zero'd DTI then continued over the peak and back to zero. I took degree wheel readings at each of the lift measurements and took the mid point of those readings as being max lift.

When I made the adjustments I simply relied on max lift as observed on the DTI when the cams were slackened and moved and the degree wheel was at the required MOP. I then checked this using the original method and allowing for dwell and both were spot on to the nearest half degree.

I thought there may be a better way of doing the adjustements but I'm not experienced enough and this made sense to me and ultimately checked out when I re measured.

No grinding noises so I think I've managed it

Jon

[rgh0]

sounds like you should be accurate.

cheers
Rohan