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A brief tour of how to check clearances in your motor

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56K views 66 replies 33 participants last post by  DC5SR  
#1 ·
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.
Image

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. :p
Image

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

The exhaust valves at full lift.
Image

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.
Image

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

Now we re-check at 0 lash.
Image

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.
Image


Tomorrow, I should have pictures up from claying the motor. :up:
 
#2 ·
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.
Image

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.
Image

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

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.
Image

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.
Image


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.
Image


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.
Image


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.
Image


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.
Image


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.
Image


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


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. :)
 
#55 · (Edited)
chunky` said:
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.
Image

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.
Image

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

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.
Image

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.
Image


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.
Image


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.
Image


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.
Image


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.
Image


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.
Image


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


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. :)
Click to expand...
Chunky, sir this is some interesting and valuable information to say the least! Even 15+ years later, To this day I've never seen or heard of online, You Tube, tv shows and what have you... Anyone go over some of this kind of information. Hats off and I'm sure this will help fellow K20'ers for another decade or two or 3! Not sure if you or anyone else on this thread are still on the forum but I have to say thank you!

How I came about finding and running into this was I just swapped my cams and springs. Toda A3 cams, valve springs, put in new valve seals while at it, dropped a valve by accident and had a blast fishing it out but that's besides the point LOL.

So I am 99% sure I successfully got everything back together without skpping a tooth. I am confident that I was careful enough and held tension to the chain throughout the entire process, even at times having multiple contraptions pulling the chain tought
While doing my valve backlash clearance adjusting, the though entered my mind to check piston 1 and 4 top dead center in comparison with my cranks/cam gear tdc marks. What I found was interesting and I so wish I thought about . checking this before starting the job but unfortunately I did not which is what brought me here, I found that I am at true top dead center before the cam gear marks align and piston begins down travel a hair before the marks align.

My first thought was, dammit! I must have skpped a tooth on the crank gear & was mentally preparing to either remove my engine, down my car for a while and do some work while I have it out, send head out maybe do some bottom end work etc etc. OR try to pull the chain cover off on the car and getting replacing chain and some other stuff while I get it back on timing.

After running into this thread I have some hope that in fact I possibly did not skip a tooth and the cam gear marks are just for initial build reference and not necessarily means timing is off just because piston isnt at tdc exactly when the marks align?? I am so hoping so. Chunky mentioned his True TDC occured before the cam gear marks aligned which makes me feel even better as that's exactly what I'm experiencing. TDC occuring before cam gears aligning. i'm hoping this is the case!

Chunky or others, any enlightening encouragment as to just "send it" ?? haha. I'm still weary of finishing up and buttoning everything up only to find out I have to tear everything down again and then some. However as they say "only one way to find out" LOL. Just hopefully it's not "fak around and found out" I will be sensible about it , let er idle for a while first and slowly add rpm, if anything out of ordinary or of course if cel is on I'll prep to remove chain cover and whatever comes along with it.

I guess if I don't hear from anyone as being this thread is ancient is probably going ot be the case. I'll just "send it" fire er up and see how it goes, of course if no cel and no signs of being out of time, I'll slowly check higher rpm and then Vtec if all seems normal.

I'll report back as well just to possibly help others in the future with added info and feedback which never hurts. I'm hoping to do that tomorrow. Keeping fingers crossed!!

PS:
this reminds me of when i installed my LSD with other trans work, Honda calls for 0-.004 thrust clearance or something like that , plz dont quote me on that. Anyway it was at zero and I almost left it but something told me to try getting some shims and checking. I had to order some after measuring the stock one, I ordered a few since they were cheap and I wanted to have what i needed on hand so I ordered a few, the increments were in a way where one of them was 5 or 6 thousandths thicker which is higher than even what the max spec is but I added that increment anyway just in case. It turned out I needed the thickest one! I ended at I believe .0015 of thrust clearance with a shim that was approx 5 thousandths thicker than the existing one meaning if I wouldve left it as it was (zero) which on paper is in spec it would have been .003-.004" overly compressed cold, even worse warmed up! Could have possibly cracked my trans case or cause other issues So it goes to show as the lesson here Chunky addresses to check even if on paper things seem ok. Real world can throw many different circumstances at you no matter what others may have said worked for them etc.
 
#3 ·
nice job chunky...

If you get some time maybe do a quick list of tools/parts needed for each process...
 
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#5 ·
Chunky, I'm confused. How where you able to take picture of the bottom of the head while rotating the chain? How where you also able to check clearance with a feeler gauge while rotating the chain?
 
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#12 ·
In my case I'd have two options.

1) have the valve reliefs on the piston deepened.
2) run a modded cam gear to limit travel to 45deg.

My bottom end is assembled and is not coming apart for this. Plus, I wouldn't want to lose compression just to gain 5deg of cam timing. My engine hits TDC "sooner" relative to the markings, so the extra 5deg of travel probably wouldn't afford me much power. 50deg is only utilized in the lower RPM anyhow.

Since I already have cam gears made that can limit VTC travel to whatever I want (with the option to easily change in the future) that's the route I will use.
 
M
#17 ·
If we retard the exhaust cam at 10deg. with the use of an adjustable cam gear, that will equate to 20deg at the crank. Now does that mean that if your VTC was set at 50deg that would actually mean that k-pro will actually set it at 30 deg since we played with the exhaust side by 20deg?

Does that mean that the max degrees the VTC can now see is 30deg and not 50deg?
 
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#24 ·
As it was explained to me by Hondata, when the exhaust cam is moved it changes the electronic center for VTC the same amount untill the VTC hits the mechanical limits. Basically maintaining the same cam to cam timing.

The ECU reads the cam positions and moves the intake cam to maintain the exact same amount of degree seperation useing the VTC.

But I could have misunderstood that.
 
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#25 ·
Are you replying to my question Talon? Because I don't think your reply answered my question. :p

Any V2P contact for the k2 at 50 VTC is what I'm after. Chunky did state the 50 VTEC maps were not tuned due to clearance concerns in the k2vsS2 thread, and there are people who said the k2 is fine at 50 degree. Granted all of them are using different pistons for their setup. But for a stage 2 cam like K2, I would reckon any 12ish:1 piston out there should work fine with it at 50VTC? Or am I wrong?
 
#35 ·
Only two ways to find valve to piston contact is, clay it, or start it. And it wouldn't be fun taking a motor apart to replace new parts because of skipping a simple test.

Very good info on this, thanks chunky. I take that you measure the smashed clay to find the distance from the valve to piston? Is there a minimum?

Also how do you guys fix the high cam in for testing? Move the pins around?
 
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