OzGemini.com

Hi all,

I'm having a few issues dialing in my camshaft on my new motor, This is a first for me so I want to get it right and not have that soso feeling when I first start up the motor...

The cam is a Crow Cams 782507ohc
Engine is G180z with a heavily decked head and block, hence the adjustable cam gear.


So the issue I am having is working out is what reading to check when I am adjusting the cam. I have the motor set at TDC with a dial indicator and pointer, then as per the instructions, then put the dial indicator on the inlet valve and check that the cam is lifting 0.077 (1.95mm) at crank TDC.

-I have done this and set the gear in position and rotated the motor (all good) but when I have checked piston to valve clearance with playdoh the inlet valve well and truely interferes with the playdoh on the fly cuts leaving around 040 or 1mm clearance between valve and piston, which seems a little to close for a mild cam. Also the original TDC mark on the cam seems to be a little too advanced when the crank is at TDC?? (photo's tomorrow)

1. Is is possible that when the cam was reground that the mark is out of wack compared to the new grind?

2. Also is it normal to have to adjust a cam that much to get it to the correct setting?

3. what's the difference between 050 valve timing and advertised valve timing??

some questions
how deep are the flycuts
what size valves are in the head
how much have you had to adjust the cam timming

from reading your post it sounds like you have done it correct

If you've decked the head and the block a fair bit, then you're going to get interferance. Thats the smallest crow cam profile, and it's only got a bit more lift than a stock cam, but if you take say 3mm off everything from decking, then there goes your valve to piston clearances.

Your cam has a bit more duration as well as lift, so you'll obviously need flycuts, and you've got 1mm clearance, which may be just enough as long as you don't over rev and valve bounce, but it sounds like your doing the dialing in right.

If you're cluey enough to get this far, and know how to use a dial gauge, you'll work it out.

You asked about having to adjust a cam that much to get it to the correct setting, but didn't say how much you adjusted it.

From memory, advertised duration is like total duration, whereas cam companies will usually quote duration at 0.050" as it's a more real world figure ( I think because it's difficult to pick exactly where the lobe of the cam starts), but with OHC, Crows duration is at 0.075".

Hope that helps.

-Flycuts are 3mm deep
-Valves are standard (flycuts are 1mm larger than the valve diameter)
-The cam timing has been adjusted 1 tooth to advanve the cam.

I took some photo's :

-First one is the crank marker on top dead center (locks it in place)
-Cam gear adjusted to the crow specs sheet
-Showing how far the cam has been advanced (about 5 degrees out?????)to get the correct inlet lift at Crank TDC
-Dial guage showing 1.9mm (0.077 thou) lift on inlet valve at Crank TDC (ignore the reading as it was set at 5.0mm then the guage drops to 3.1mm)
-Fly cuts (3mm deep)
-Showing interferance with playdoh (leaving about 1 to 1.5mm gap)

So that's the process I went through to time the cam gear to the crank, as far as I can tell it's right. ---
If I had timed the cam with a standard gear and put it back in to factory specs I would presume that the car would NOT run as well as it should right? which would explain a few gems that make much less power than they should considering the carby and cam combinations that they run.?

Any more info would be appreciated, as this is still my first engine built that I have attempted to do everything with out guess work.

All your work looks good. I would say better than a lot of engine places. one question what was the valve clearness when you checked lift at TDC. I think it shoud be zero.

It dose seam to have tight piston to valve for the size of the cam. you did say it had been decked a bit (lot lol).
1mm pistion to valve is tight and dose not leave a lot of room for the odd over rev. the exhaust side is the most critical as the piston is come up as the valve is open.

Have you checked the total lift and duratiuon to check you have the right cam grind.

you have the alloy rockers

how much was that cam gear to get made up???

I am using the alloy rockers for a couple of reasons
-They are heaps lighter than the steel items (less valve train weight is good)
-the cam I am using only has a little more lift than standard
-it's not going to rev more than 6500-7000, they were fine on my last motor that reved to 6500

the cam gear was free.... coz I made it : D
-there are easier ways to adjust the cam (re-dowel the holes on a mill with a rotating table thingo)

your reasons are well justified

would you be willing to make another?? Seriously

I would love to make up cam gears but it's not really worth my time, that took around 6 or so hours @ $30hr (cheap rate) to turn up on a lathe and mill out the slots, that said when I buy a lathe 4 home (soon) I might look at making some or al least re-doweling standard gears so they can be adjusted.

Craig watson from what used to be Fourplus performance is a wealth of knowledge. I can get you in contact if needed.