A brief tour of how to check clearances in your motor

[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. :p

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.

[KPowerEP3]

as always, some excellent info from chunky.

he's a smart dude and def. knows his stuff. He's not widely known here, but on EPhatch and some of the other k-series websites he's known as a very reputable source.

[Da_unknown]

good stuff chunky...

[speedminded]

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

ha! was just about to ask about claying it and what do you know, the last thing you say

[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.

[speedminded]

err, yeah that would be a lil bit too close...especially with a cold engine! How much has the head been shaved?

oh yeah, nice degree wheel

[chunky]

err, yeah that would be a lil bit too close...especially with a cold engine! How much has the head been shaved?

oh yeah, nice degree wheel

Well, on a hot engine, the clearances will increase since the hot lash is typically greater than the cold lash. The head has never been shaved. The mating surface has never even been resurfaced because it hasn't needed it as of yet.

I had a hell of a time finding a degree wheel that would mount to the crank pulley. ATI sells the fluidampr that is marked in 1 degree increments, but it's too rich for my blood. That's how I ended up making my own. :p

[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.

[speedminded]

I had a hell of a time finding a degree wheel that would mount to the crank pulley. ATI sells the fluidampr that is marked in 1 degree increments, but it's too rich for my blood. That's how I ended up making my own. :p

Summit sells the aluminum wheels for like $20 but like you said still need a good & reliable way to put it on the crank. Pretty sure the one i've always used was from Moroso.

Built an LS a few months ago, shaved the head 0.01 and the block 0.05 and the piston came up out of the block .015" haha Stock cams and crank but used GS-R pistons. Clayed it and had plenty of valve clearance but the piston was making contact with the head...grind the head or the piston? Flipped the head over, layed down the gasket, and enlarged the combustion chambers slightly. The piston then slid up inside it perfectly Remember, this was a budget build with basically only time involved using spare parts.

Used a degree wheel before and after and now both the exhaust and intake is retarded 5° and can't run adjustable cam shafts, lol. Rotational torque with rear main seal on was 6.8lbs...Running 100 octane only and aiming for 12:1.

[chunky]

Summit sells the aluminum wheels for like $20 but like you said still need a good & reliable way to put it on the crank. Pretty sure the one i've always used was from Moroso.

Built an LS a few months ago, shaved the head 0.01 and the block 0.05 and the piston came up out of the block .015" haha Stock cams and crank but used GS-R pistons. Clayed it and had plenty of valve clearance but the piston was making contact with the head...grind the head or the piston? Flipped the head over, layed down the gasket, and enlarged the combustion chambers slightly. The piston then slid up inside it perfectly Remember, this was a budget build with basically only time involved using spare parts.

Used a degree wheel before and after and now both the exhaust and intake is retarded 5° and can't run adjustable cam shafts, lol. Rotational torque with rear main seal on was 6.8lbs...Running 100 octane only and aiming for 12:1.

My problem with the degree wheel is that I needed something small, 6". Summit's smallest size was 8", which simply wouldn't work with the engine still in the car. Plus, all of their degree wheels are made to go on the flywheel side of the motor.

Sounds like you did your LS build right, might not have spent a whole lot, but the details like degreeing after shaving the block/head make all the difference.

[chunky]

All the previous pictures are down right now. My server will be back up later in the day. Sorry about that.

I just wanted to update with some preliminary results.



So in a nutshell, with the ported head and degreed exhaust cam, I'm making essentially the same peak numbers with a lot more midrange. Once I drop the VTEC down to 5000-5500, the midrange will really fill out. The a/f is all over the place, so there's some good gains to be had from just a/f tuning, not to mention the intake cam angles were untouched and will surely need to be tweaked. The final numbers are shown SAE corrected, with STD correction, it made 232. And remember, that's UNTUNED. :p

Thanks to MAINSTREAM for letting me hop on the dyno on Thurs. night before I left town.

[ash7]

Haynes ain't got nothin on this.

excellent write up - very informative

thankyou!
-jonathan

[StreetHazard]

I am a complete NOOB, I read this twice and hardly understood ANY of it!

WTF is lash?
Why is there fuggin clay everywhere?
how the fvck did you make that degree wheel?
how the fvck do you use a degree wheel?

I dont know chit compared to this guy! ima get back to being happy about my ability to change my own oil.

[speedminded]

I am a complete NOOB, I read this twice and hardly understood ANY of it!

WTF is lash?
Why is there fuggin clay everywhere?
how the fvck did you make that degree wheel?
how the fvck do you use a degree wheel?

I dont know chit compared to this guy! ima get back to being happy about my ability to change my own oil.

lol! Nice thread bump

[2.0lef_itbs]

so why do you want a 50 degree cam gear?is it to have both exhaust and intake at full lift while still keeping in time?

i am trying to do this on my b series its just a little harder cause of the needed room.
and i am running JUN 3's.

[chunky]

so why do you want a 50 degree cam gear?is it to have both exhaust and intake at full lift while still keeping in time?

i am trying to do this on my b series its just a little harder cause of the needed room.
and i am running JUN 3's.

Well, the K-series intake cam gear has a range of either 0-50deg or 0-25deg depending on which part # you have. The 50deg offers more advance, which typically allows you to get more power out of the engine if the cams are designed to use the full range of the VTC.

[nismo_92]

i saw this run to nite very fast

[chunky]

thanks man.

Damn. All my pics are down. Hopefully they'll be back up in a bit.

[2.0lef_itbs]

hey man soo i was putting my motor together my intake valve might as well be touching my piston
i puttied with no head gasket and no lash and had paper thin putty in my relief
whats a safe tolarence for P2V on a B series
.i am looking into fly cutting my pistons(intake relief).good idea?

[southside]

Head gasket might add a little clearance.What pistons and cams are you using?

[masonhenson]

nice!

[chunky]

hey man soo i was putting my motor together my intake valve might as well be touching my piston
i puttied with no head gasket and no lash and had paper thin putty in my relief
whats a safe tolarence for P2V on a B series
.i am looking into fly cutting my pistons(intake relief).good idea?

Well, this response is a few months late, but you need to check clearances WITH a head gasket and with the valve lash set to some reasonable value. Going from 0.008" lash to zero lash can take a clearance from safe to dangerous.

[BABY J]

http://www.preludepower.com/forums/s...d.php?t=242616