Ported head. Need to measure clearance with liquid

#1

Has anyone ever used this special liquid to pour down the bore to measure clearance when at TDC to gauge what the figure is keeping in mind the gasket thickness. I have just had my head ported and as my engine is still in the car with the pistons not being flat it’s not feasible to get an accurate measurement using a filler gauge

#2

I am going to venture a guess that by “ported” you mean “Milled” and you are worried about valve to piston clearance??

And with the engine still in the car I assume you did not deck the block? Knowing what the original thickness of the head and how much has been removed will tell you what thickness gasket you need. Unless you have cut more than what is allowed by factory specs you do not need to worry about this…

Are you building a spec e30 or something else?

Al

#3

The block hasnt been touched it standard hence why its in the car. I was refreshing the head and whilst its off to gain some HP i had it ported or milled as you mention. so yes i was referring to the piston to valve clearance. i was told that measuring this with liquid would result in a more accurate reading as even out a thou would affect the compression and result in possibly less HP

Would simply calculating the amount taken off the head to measuring the gasket thickness result in the same conclusion?

#4

I’m having problems understanding how this liquid would work but the normal solution is to “clay” the head. This involves putting some silly putty-like clay on a piston face, putting the head on, then turning the engine thru a couple revs being careful to stop if you feel resistance.

Then you pull the head off and inspect the indentations the valves made in the clay. That will show you how close the valves are getting to the pistons.

Do some reading on this before attempting because I’ve only done it once and there’s sure to be a bunch of tricks to doing it right and reducing the chance of bending a valve.

#5

Yall are talking about 2 separate test

Piston valve clearance checked by a thin layer of something on the piston to make sure they do not touch.

CC’ing a cyl head to make sure all the combustion chambers are the same…you pour liquid into the head chambers to make sure they are all the same size.

I would hope that you did not cut enough off the head to make the valves touch…it has happened, and I guess you could get a thicker head gasket…

Al

#6

Nothing has been taken off the head as yet. I have a new head gasket set (elring klinger).
Can you explain how it’s actually performed? I’m not doing it myself as I have no idea but im curios as I have not heard of this before

#7

PO, I don’t know what you’re asking about. Claying a head checks valve to piston clearance. CC’ing a head involves pulling out the cam so all valves close, flipping the head upside down, and then pouring a measured amount of liquid into each combustion chamber to ID the volume of each.

When you say “pour liquid” it sounds like you’re asking about CCing a head. When you say “measure clearance at TDC” it sounds like you’re asking about claying the head.

There’s lots of info and videos of each on the web.

#8

[quote=“Ranger” post=75830]PO, I don’t know what you’re asking about. Claying a head checks valve to piston clearance. CC’ing a head involves pulling out the cam so all valves close, flipping the head upside down, and then pouring a measured amount of liquid into each combustion chamber to ID the volume of each.

When you say “pour liquid” it sounds like you’re asking about CCing a head. When you say “measure clearance at TDC” it sounds like you’re asking about claying the head.

There’s lots of info and videos of each on the web.[/quote]

Hi Ranger,

So to clarify all this we are looking at CC’ing the top of the pistons to get the cc measurement as you would know the standard pistons in the E30 325i are shaved with a cut out. I’m told by my mechanic that if he performs CC’ing on the cylinder head then the final cc measurement he will get will change due to the shape of the pistons. So has anyone tried CC’ing the pistons?? If so I wouldn’t mind getting the measurement figure you got in cc. This will all have an effect on the end compression of the engine.
Sorry guys about the confusion I wasn’t entirely understanding myself whst was involved here. I hope that clears it up a little.

PS my bottom end block of stock and un-modified so using the standard size pistons

#9

hmmm

Not sure the difference in stock pistons is enough to make a difference, I have always heard of CC’ing a combustion chamber in the head or in the piston if it is a flat head design. more would be gained by taking the bottom end apart, balancing everything, decking the block etc…then maybe worrying abort the piston top differences…of course if there was a difference you would have to re-balance the pistons…when talking about a difference of a CC not sure you can measure in the cyl accurately enough, maybe with a degree wheel on the crank, what about differences in how the ring land/ring is…this is a used bottom end? Doubt you could get any useful info.

NOTE

I have never rebuilt a bottom end or really done any engine work other than taking a head to a machine shop and getting a basic valve job.

Al

#10

Maximum decking on a cherry picked head yields 9.3ish or so compression ratio. Tell me what your head volume in CCs is and I’ll calculate your ballpark compression. I’m not sure why you need this information though. If you haven’t taken much off the head, your CR is likely still around 8.8 or so. You can reliably take the head thickness down to 4.909" without concern for PV contact. You can go further if your measure PV clearances with clay. Stock head thickness is normally 4.922" or so…

#11

CC the pistons eh? Ok, well piston face shape is a big deal. A little change in piston face shape can dramatically change compression. I’ve not heard of piston faces being CC’d, but I don’t know hardly anything about custom pistons. Certainly techniques to CC piston face shapes have to be out there being discussed.

SpecE30 is prob not a great place to find out about things that are illegal in our class. There’s lot of folks here knowledgeable about an awful lot of stuff, but it’s pretty focused on stuff that we’re allowed to do.

E30tech.com might be a better place to ask.

Maybe remove a piston and dip it’s face into a full vessel of water. Measure water spilled out or measure increase in height of water, something like that. Dip piston to a water depth matching the depth of the contours of the face, 5mm maybe? That should tell you CC of face shape, except some air might get trapped in valve reliefs.

#12

.020" over piston volume (above deck height) is 3.7CC.

Procedure for measuring:

  1. locate a piston at TDC.
  2. Set dial indicator on top of piston and depress .3".
  3. seal pistons to cylinder with lithium grease.
  4. use graduated pipet to fill bore to block surface and record volume.
  5. calculate the volume of your cylinder using the measured bore diameter by .3" and record volume.
  6. subtract step 4 volume from step 5 volume.

The solution is your piston crown volume above deck height.

#13

Ok so with it not being possible to perform cc’ing on the pistons I have had the cylinder head done which resulted in a reading of 41cc. My model 325i is a euro so my standard CR is about 9.7:1 compared to the US models being lower. Im trying to get as close to 10.0:1 as possible. Im wondering if there is another way I can find out how much needs to be shaved off the cylinder head to achieve something around this figure??