Cam Timing

[Ahl 4]

Hey folks,

 

I'm shortly putting back together a mi16 with a new catcams inlet. I'm hopefully getting some adjustable pulleys shortly, and was wondering if anyone can tell me how to time it all up?

 

Its not a job I've ever done, and frankly, I've forgotten the advice and teachings I gleaned here and from Graeme Jeram many moons ago.

 

I should be able to find the information I need regarding lift at TDC, but how do you get them timed up?

 

Head on / head off?

Dial gauges, and a rod down the spark plug hole...?

How do you work out the valve lift?

 

I vaguely remember all these things, but don't remember exactly how its done!

 

Cheers,

Ahl

[Anthony 1,003]

You'll want the engine assembled and built up, with cambelt fitted and cam in approximately the right place (use a standard pulley for this)

 

Find TDC and mark it - Petert's website has a section about easily locating TDC on an Mi.

 

Use a dial gauge mounted so that it's measuring lift on the bucket of the inlet on #1 (cam cover off, obviously)

 

Turn the engine round to TDC and check lift, adjusting on the vernier as required and re-checking until it's correct.

[Ahl 4]

Thanks Anthony, that makes complete sense!

[Ahl 4]

Just had a thought, I'll be advancing the inlet cam to adjust for the block decking/head skimming and to get the cam in the right place as specified.

Should I also be advancing the exhaust cam? And if so, by how much?

 

I think I should be, but don't overly understand the theory to be honest (or mostly that I've forgotten it!)

 

Ahl

[DamirGTI 342]

http://www.guy-croft.com/viewtopic.php?f=3&t=213

 

Have fun !

 

Damir

[Ahl 4]

Thanks Damir, I forgot about Guy Crofts advice.

Both methods are good, and I'm quite confident to do this myself now.

 

A couple of (silly?) questions though:

1. Does the hydraulic lifter affect the measured lift?

2. Is it a good idea to advance the exhaust cam also, and if so, by how much?

 

Cheers,

Ahl

[DamirGTI 342]

Thanks Damir, I forgot about Guy Crofts advice.

 

Cheers,

Ahl

 

Shame on you Ahl ! cos you've been said to me back in the days , when i started to mess around with engine tuning/porting , about Mr. Guy and hes website ... and hes helped me allot with advices infos and various other stuff till today ... myself and Mr. Guy are good friends now

 

Can't help with regards to your questions though , i don't have experience with 16v cam timing adjusting .. The boys will know , or , can ask Mr. Guy about that as well ..

 

Damir

[Ahl 4]

I know I know, all good stuff on Guy's website.

 

I've been looking into this more and still not sure what I should be advancing the timing to:

 

My inlet cam is: Catcams 4900526, not sure which revision but specs are:

237° duration at 1mm

10.80mm valve lift

112° peak angle

Thankfully it clears the lifter bores on turning - just!

 

Exhaust cam is standard.

 

I realise now that the inlet cam is pretty rorty really, and will be rather interesting on standard management, at least to start with.

From what I read I should advance it to about 106° (or maybe slightly less) to get the greatest gain, but occuring in the mid range.

 

Not sure if I should advance the exhaust cam or not, but I think I understand doing this will also help midrange torque and thus drivability, at the expense of top end. (Restoring/increasing dynamic compression, but lessening exhaust scavanging?)

 

What has anyone else with a 16v advanced their cams to, and how does it work with your driving style?

And am I talking bollocks?

[Anthony 1,003]

526 is just the usual mild inlet cam that people run on standard management isn't it? If so, it runs fine - just a touch lumpy at idle.

 

The figures that you've listed are fractionally different to the ones on the Catcam's website though.

 

Personally, assuming you've got a vernier I'd time the cam up as per the Camcam figures (ie 1.45mm @ TDC) and go from there, advancing or retarding the cam slightly to suit your preferences regarding power delivery. If you don't have a vernier, then from memory a #4 pulley is in the right ballpark.

[Ahl 4]

Anthony,

 

That's right, 526 is the first sports cam that Catcams offer.

The figures I gave are direct from the catcam sheet that came with the cam (from 2006!) - I noticed too that they are different, but I remember Mattsav saying that catcams had revised their specs slightly.

 

Just going by the increase in lift and duration (and especially compared to petert's cams) it would seem to be quite an increase over standard cams. Its good to hear that it works ok though - a lumpy idle would be quite nice actually...

 

Thanks for the information on the timing. How would you set up the exhaust, personally?

[Anthony 1,003]

I've always just left the exhaust cam timing as standard (ie #2 pulley) when doing an inlet-only swap, although that's not to say that's ideal.

[petert 588]

I've always just left the exhaust cam timing as standard (ie #2 pulley) when doing an inlet-only swap, although that's not to say that's ideal.

 

I retard the exhaust cam so it has approx. 0.050-0.060" lift at TDC by either fitting an offset key in reverse or using a vernier pulley.

 

Also, a lobe centre line of 112 (1.45mm @ TDC) is probably not advanced enough and 106 will be too far. With that cam you should be aiming for approx. 108-109 deg. which should equate to approx. 0.065-0.070" @ TDC or maybe even a touch more.

Edited April 30, 2011 by petert