chunky

First, start by installing 4 valves into your test head with the lightest valve spring you have. In my case, I used the inner valve springs only from the Skunk2 Pro series valve springs. This keeps the amount of tension you have to keep in the chain to a minimum. Less tension in the chain makes things easier to turn.

Then, you need to rig up something like this to keep the cams in time relative to one another. With a little ingenuity, you can make it happen. Note that I have the intake cam gear pinned at 50deg. I have a custom cam gear that allows me to check clearances at individual cam angles, but that's currently for my eyes only.

Here's a shot of the intake valves at full lift.

The exhaust valves at full lift.

Now we start to measure valve to valve (v2v) clearance. I started with the lash set at .010". I didn't have feeler gauges thick enough, so I just stacked two together.

The v2v on my Skunk2 stage II cams, VTEC lobe @ 50deg intake advance and -5 marks on the exhaust cam gear.

Now we re-check at 0 lash.

As you can see, the v2v goes WAY down with valve lash. Let this be a warning to you people out there that like to lash things ultra tight on big cams.


Tomorrow, I should have pictures up from claying the motor.

WHTZ

KYSI

How much do you trust doubling up on feeler gauges?

chunky

doubling up on a feeler gauge won't be the most precise way to do it, but the error will be on the safe side, meaning it will tell me there is less room than there actually is.

In this case, those feeler gauges were brand new, so they were perfectly flush to one another. I doubt there was much error.

chunky

Just got back in from claying the motor. Came up with some interesting results. But first, I realized that yesterday I did not have my exhaust rocker assembly properly lashed. I used a new rocker assembly on the exhaust side. Therefore, I repeated the v2v measurements.

This time the v2v clearance was more in line with what I expected. This was at .010" lash. Quite a different result from last night.

Just for kicks, I checked the v2v at .011" lash. .001" of lash gained .002" of clearance.

Now, on to the claying. The process is very simple, cut out strips of clay, and lay it out on your piston in the following areas. Lock your rockers in VTEC and set your cams to the max settings you think you can get away with. Then assemble the head to the motor. Some people will spray down the combustion chamber roof with WD40 to keep the clay from sticking to the head, but I've found that it's a crapshoot on whether the clay will stick to the piston or the head no matter how much WD you spray on.

Once the head is on the motor, turn the engine over so that the valves make their impression on the clay. Then take it apart to inspect. As you can see below, there is plenty of clearance between the piston domes and the head. The exhaust v2p measured out to .125". I didn't even need to measure to know that the intake v2p is insufficient. The intake v2p measured out to .015". This is one reason why you use old valves when claying a motor. If things do touch, you don't want to trash a new valve.


The conclusion is that the Skunk2 stage II cams are NOT 50deg safe in my motor. I always suspected this. Back when I did the cam test, the skunk2 stage II's (and the IPS k2's) had an insane knock count anytime I'd advance to 50deg on the VTEC lobe, no matter what rpm. My suspicions that I'd have clearance issues at 50deg were cemented when the v2v clearances came up so small with the exhaust rocker lashed correctly. For reference, I have shelf stock CP 12.5:1 pistons with Eagle rods.

One curious note regarding my engine is that TDC occurs well before the factory mark on the crank pulley and cam gears. I've long suspected this, but was able to verify it with a travel gauge. Finding the true TDC point of your motor is a simple affair with the head off and a travel gauge. You setup the gauge perpendicular to the piston and turn the crank while watching the gauge. When the needle reverses directions, you've found your TDC. You can do the same thing with the head on the car, but you'll need a long extension for your travel gauge.


Typically, knowing the "true" TDC of the motor is not necessary, but in my case, I'm degreeing the cams in so I need to know exactly where my TDC occurs. Once I know where TDC is, I can set my exhaust cam centerline accordingly. Oh, and to degree cams, you need to be able to measure the angular travel of the crank. So I made this little thing.


The goal is to have my cams precisely dialed in relative to my "true" TDC. But that will be saved for another post.

KYSI

Lots of good info keep it up

chunky

The true TDC was found with the travel gauge and then marked using a pointer. In my case, a steel rule + magnet. It was tough to get the camera in at the right angle, but it was marking zero.


Now, the crank is turned to the desired centerline of 107 BTDC. So 360 - 107 = 253. Again, it looks off, but it's b/c I couldn't get the camera at the perfect angle in the fender well.


Once the crank is set to the desired centerline, setup a travel gauge on one of the rockers or retainers. Loosen the set screws on the cam gear and slowly advance/retard the cam and look for where the rocker arm reaches it's maximum travel. Lock the set screws. You can double check now by actually rotating the crank. If you assume a symmetric ramp rate, you can turn the crank to slightly before the location of the centerline, and zero out the travel gauge. Turn the crank, passing the centerline until the travel gauge hits zero again. Subtract the starting crank angle from the finishing crank angle, and divide by two. Then add to the starting crank angle. That is the location of your centerline. I verified my centerline about 3x over and found that I only needed to retard the exhaust cam 1.25 marks, or 5 crank degrees.


I aslo checked my pistons to see how far out of the hole they are. came out to be .009"


So the moral of the story here is, if you're building a motor with big cams like the skunk2 stage II's or IPS k2's and using an after market rod/piston setup, CHECK YOUR CLEARANCES!!!. It's best to KNOW what you're getting into. I've been told all sorts of things regarding what is safe for my motor and what kind of cam gear settings I should run etc. The reality of the situation was that my motor didn't follow the rules. Now I know my engine's mechanical limits and I can dial it in and hopefully make the most power that it is capable of.

Hope you guys enjoyed this brief tour.

HatchSpeeD

Good stuff

mar778c

iTrader: (1)

Very informative.

Old Renegade

good information.

EkJavi

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Old Renegade &raquo;</TD></TR><TR><TD CLASS="quote">good information.</TD></TR></TABLE>