I'm assembling my B16 motor (GSR head) at the moment and i'm only getting around .030 piston to head clearance (with OEM HG). From what i understand, for steel rods a clearance of .040 is recommended at the minimum.

What do you guys think about this ? and what piston to head clearances are you running on your FI setups ?

Thanks for your time

 

The d15/y8 combo is .030" and I'm building a d16 with .027"

I'm not sure how that relates to a b16, but it is what it is.

 

Im at .035" p2h with oem .026" HG and I thought that was close! Your block must be zero decked or close to it?
Are you measuring this with clay? Make sure you are only turning the crank counter clockwise as piston wobble will affect your measurement.

 

Yeah i think it is zero decked. I have replied to you in my build thread BTW. I checked the piston to deck clearance with a height micrometer. I'm not sure which way i turned the crank now though, i'll be rechecking tomorrow....

 

Just recheck with the height micrometer and i'm getting 0 clearance (not that .003 mean't anything) they almost look like they stick out the bores.

I don't know if you can tell by these pictures...

 

So it looks like i need a thicker HG then. I'm thinking this Cometic will land me in the safe zone... http://www.ebay.co.uk/itm/3208633292...9#ht_735wt_949

What do you think ?

 

Zero deck is not a problem in itself. And what is the "minimum" p2h clearance you are working towards? Ive never really found a solid answer but have heard .030 many times.

My pistons looked zero deck too but they turned out to be .008 to .009" in the hole. I clayed everything bc I had to measure v2p and v2v too. I ended up with around .035" p2h. I dont think you will have a problem with .030". I say that bc aftermarket steel rods arent going to stretch like aluminum or stock rods would. And unlike valvetrain you dont have the tbelt slop and additional parts stretching and thermal expanding. Plus keep in mind .030 to .045 is ideal quench for our engines.

Im not a professional engine builder. Id still like to hear what a pro has to say about this.

 

I only have the gasket thickness though, so I'm at less than. 030 . Ideally i wanted at least .040 to stay on the safe side of things.

I tell you what I'm going to do... when i get back from work I'm going to call Mahle and Crower and see what they recommend and why. I'll let know what they say.

 

I spoke to Mahle and Crower a few hours ago now. Mahle recommended at least .040 clearance but did really give me much info why. Crower on the other hand said at least .040 but it is fine BUT i could go down to .035 if i wanted as there rods are pretty good when it come to high rpm.

I've ordered a .051 Cometic HG which should keep me sweet. I have a question though, i am correct in saying once a head gasket has been compressed it can't be reused right ? In other words, i can't torque everthing down to and check with clay or solder and reuse the gasket ?? or can i ??

Thanks

 

Wondering if anyone has ran around .035 p2h clearence without issue? Muckman do plan on keeping your .035?

I'm putting together a 84x89 benson sleeved GSR block(GSR head) with Manley h beams, and I'm getting .0105 p2d clearence. That puts me about .036 with the oem gasket. With the .005 p2w I'm running, I'm wondering if I should get a thicker gasket? I already have a GE 84mm I would like to use, but I've read .040 min for steel rods. Any input? TIA

 

Yes sir. I ended up with .035" p2h with an OEM Honda .026 head gasket. My p2d was also about .010" so we have similar clearances. The thing to be mindful of with thicker head gaskets is they ruin your quench. Above .040" is the dead air zone. Quench gets more sensative with big dome pistons and right now youre in the sweet spot. Tight quench fights detonation and causes better combustion in the chamber.

 

I know it goes against my originally plan, but I'm at .035 myself now.

 

okay thanks, I think I'll give it shot. I'm also curious as to how you guys are measuring your p2d height. I have pretty good piston rock so i went with the average of both sides..

 

Piston tilt will F up your readings. Measure on both the intake and exhaust sides of the quench. Only turn the crank counter clockwise. Do not turn it clockwise at all (this reverses the tilt and will mess up your reading). Take which ever side is tighter (usually Int) as your P2H. If you cant get consistent measurements the repeat the test until you do.

 

see this is where it becomes debatable, If I did it the way you are describing then I am getting .001 out of the hole., but what happens when the motor becomes warm and the p2w clearence in much tighter, I will have less p2d height compared to cold measurements.

I have read a few posts that say to rotate the motor in the direction it spins, and average the extereme's of both the intake and exhaust... Have also herd pro engine builders will tape the piston to center them in the bore to get a more accurate clearence.

 

This is from another site: (speedtalk) and how I got my p2d clearence

"The proper way to check for the distance between the piston and the cylinder head deck surface is to do the following, but do remember that this method and the only method to actually check would be staticly and not dynamically. When an engine gets built the clearences are set statically with an understanding of what it will be at when in operation.

You first need to establish the absolute top dead center of the crankshafts stroke. You do this by taking a dial indicator and placing it on the piston area that is furthest from the center towards the intake side, lets say at the 12 o clock position on the quench side. You then apply finger pressure onto that side of the piston that will load (rock) that side of that piston downward and turn the crankshaft (bringing the piston up in the bore) until the dial indicator reads the pistons highest point. You then zero that indicator while still holding pressure. Using your fingers rock the piston on the other side of the piston so that the side with the indicator moves upwards towards the deck surface. Add the two numbers and divide by 2. Example: if the piston shows .000 (which you just set) rocked down and when rocked up it shows .040 than half the findings would be .020. Now drag that indicator base with dial indicator, so that the point of the indicator is now on the deck surface. The distance dragged should only be about .250 to reach the deck. Do this while holding the top of the indicator up so it is off the piston and doesn't crash into the side of the cylinder when moving/sliding the base. Make a note of the findings. The first proceedure as spoken about gives baseline and is needed prior to moving to the second step which would be the measurement read when the pointer is sitting now on the deck. Lets say half the rocking motion is .020 (.000 + .040 divided by 2 = .020). Now after you reference the new reading on the dial indicator, when on the deck surface, you can figure the difference out. Lets say for example the indicator on the deck now reads .050. Your piston to deck would be .030.

Now add your gasket thickness to that number and you have the answer to your question in regards to this topic.

* The above assumes that your deck is true to the mains and your engine builder decked the block properly.



Okay' lets assume I have a .041 gasket for below. Examples:

1. (Checking piston rock): One side is .020" in when rocked, rock it the other direction and I have a measurement of .006". So should I use the .006" reading and say that is closest to the deck?


- From #1 above if I use the .006" figure, the piston to head clearance would be .047"



Assuming you set the indicator on .000 when on the deck (opposite way of my description above but sill still outcome the same). .006 + .020 = .026 divided by 2 = .013. Your gasket is .041.

.041 gasket + .013 in the h o l e = .054

The number .054 is also reffered to as the "quench distance"

 

That is the most ridiculous way I have ever heard of. The biggest part being "if your piston rocks this much, divide that in half". The second largest being the fact that it says the drag the base and take another measurement. What an absolute joke.

There are a couple things that can cause a piston to rock in a bore, the biggest being detonation. If you have a slight problem and the piston comes into contact with the head big bad things can happen. Also, a 0.040" rock in the cylinder, that is some interesting piston to wall clearance. So the one asking the question is now telling us how it's done?

 

No not at all, maybe I misinterpreted the last post. I'm just wanting opinions which way would be more accurate/correct, and why. Depending on how I measure the p2d I can get .001 out of the hole, or .010 in the hole which is alittle bit of a difference.

 

When the crank turns counter clockwise and the piston travels up, the rod is angled towards the exhaust. The piston drags on the exhaust side and the intake side will tilt up. The intake side should be closest to the head at TDC. The exhaust side will never be higher than the intake. (unless the engine spins clockwise)

Two underlying points 1.) measure natural crank movement. 2.) only the closest natural tilt clearance matters. no averaging.

 

okay thanks for your input... I guess the real question is how much tilt is going to happen when the motor is warm vs cold? I guess that depends on the p2w clearence, and piston used... Weather I center the piston or tilt it and rotate the crank(counter-clockwise) and it doesn't move much from the orginal position before rotating the crank.

 

The amount of tilt depends on the p2w, the piston diameter, the piston skirt. I would think as the piston heats up and expands it will tilt less. So the tilt you are measuring now is worst case.