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Discussion Starter #1
I am thinking about milling the head on my D, since I want to have higher compression, but I no longer have my PM7 pistons. It's also nice because I can acheive more ideal compression ratio (low 12s) with a stock headgasket, rather than going up to 12.7 or so with the pistons and lowering it using a thicker HG. Anyway, aside from the need for an adjustable cam gear (which I already have), what are the drawbacks to milling (say 0.050") vs finding some more pm7s?

I've been seriously thinking about putting the H22 swap off recently, at least until the summer when I'm out of school and have more time/money to work on it. With the money I'd put into it now (or less) I could continue my D project, and build the head, get some goodies for it, and also do some other things I need on the car. I'm a bit torn now about what to do... I'm starting to lean toward the D again.
 

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downest said:
I've been seriously thinking about putting the H22 swap off recently, at least until the summer when I'm out of school and have more time/money to work on it. With the money I'd put into it now (or less) I could continue my D project, and build the head, get some goodies for it, and also do some other things I need on the car. I'm a bit torn now about what to do... I'm starting to lean toward the D again.
I think with milling you may have to worry more about possible warping under extreme conditions, but I don't know how much you rag on your car (probably not much from what I've seen :).

I don't really know a lot about it, other than that I'm in the same general position. Not in school at the moment as I'm taking a year off, but I'm working full time and I'm between buying a 1991 Si with a B16A3 in it, and just trying to continue fixing up my DX instead. My goal is ultimately to have an Si in showroom condition with a B16, turbo, and A/C all while having a DX to daily drive.

Money sucks, why can't things be availible based upon enthusiasm?
 

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Discussion Starter #3
Why will it be more prone to warping? I do beat the motor pretty hard, at autocrosses it spends a long time up in the redline area.
 

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.0050?!! EEK..
I don't know Tom thats an aweful lot to remove.If you were to remove that much I'd start to worry about valve clearance issues.

So basically you want to do a non-vtec swap like I did? or am I reading this wrong?

I calculated my compression at 12.09:1 with what I did w/the p29 pistons,and my motor is mostly an A6.
 

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didn't he state 50 thousandths not 5 thousandths ollie? I wonder if he means 5.

What is a safe amount to go with?
 

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downest said:
Why will it be more prone to warping? I do beat the motor pretty hard, at autocrosses it spends a long time up in the redline area.
I would think at high temperatures with a reduced area for dissipation it could make a difference, in addition to taking it away from factory spec. It was more of a guess towards an issue than something I've seen, as I said, I'm new to the milling scene :p.
 

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Discussion Starter #7
ollie said:
.0050?!! EEK..
I don't know Tom thats an aweful lot to remove.If you were to remove that much I'd start to worry about valve clearance issues.

So basically you want to do a non-vtec swap like I did? or am I reading this wrong?

I calculated my compression at 12.09:1 with what I did w/the p29 pistons,and my motor is mostly an A6.
Well I sold my PM7 pistons, and my A6 bottom end is pretty good right now, it's fresh and has ARP hardware. I have another Y8 head sitting around, I'd be using that, and milling will allow lower compression than I would get using the PM7s with the Y8 head.

I know it seems like a lot to take off, that's why I was asking!
 

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Oh don't get me wrong I'm not yelling at ya Tom.
I just remember talking to my machine shop guy about milling my own block when it was in.
With the #'s we were talking .005 or 50 thousandths of an inch.It seemed like an aweful lot to be milling.
I know that when I milled .0006 off of my block we clayed my heads just to make sure the valves didnt contact.I was nervous... :lol:
If you get that much off and have no issues I'd like to hear about it.
GL on your build Tom.
 

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Ok forget what I said about .005...I was seriously not thinking correctly.
For some reson I had 50 thousandths on the brain..
Yeah .005 = 5 thousandths..

Oh and a 5 thou cut on a milled head is way acceptable.Sorry for the confusion.
Now on the other hand a .050 cut would be scary! :shock: :lol:
 

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Discussion Starter #13
I have a cam gear already. Can anyone tell me fo sho that 0.050" milled off isn't going to be too much, or that it is?
 

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Discussion Starter #14
I've been doing some reading... it seems that head milling isn't well liked. It's obviously a permanent thing, so there's no going back, and there are obvious issues with piston-to-valve clearances and cam timing. I didn't think these would be big problems, but I can't get any definite info. Cam timing isn't a problem to me, I can adjust the cam gear to tune that out. Piston to valve clearance is definitely a problem, I don't want to worry about them touching, especially if I'm running a bigger cam. I only have a Stage 2 now, but I want the ability to upgrade in the future.

I'm going to look into getting another A6 block, and build it with overbored PM7s. If I do this, I'll go over the bottom end as in the Endyn articles, open up the oil passages and stuff. I hate to get rid of the block I have now, it's got a fresh rebuild on it, so I don't want to take the pistons out (and replace the rings and bearings). Oh well... at least I could take my time with a second block that I don't need to drive around with.
 

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downest said:
Oh well... at least I could take my time with a second block that I don't need to drive around with.
Yes, two engines ARE better than one. :lol:
 

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5 thousands would be just to make it flat again ie. good bonding for the gaskets and such but .050 would be way to much to take off most any head. Even if it was a v-8 you would have to angle mill it to go that far. Buy different pistons and just take off enough to make it flat. :D
 

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Tom, I believe that the pistons could be milled also. You would use the pm7 pistons and mill down the dome to achieve a compression ratio in the desired range. I think that you could take some basic measurements on the pm7 pistons and calculate how for to vertically mill the tops of the piston domes in order to achieve the desired volume reduction per cylinder.
 

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Hmmm, on second thought, you would need to verify the thickness of the dome section by looking at the underside of the pm7 pistons. I can take a look at my pm7s this weekend to confirm.

I thought I researched piston milling at some point and found that it could be done
 

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The machine shop will check the thickness of the pistons to see how much can be fly cut from them but the engine builder would have to check the piston to valve clearance to see how much needed to be cut from the dome.
 

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Piston to valve clearance wouldn't change from pre to post fly cut on the mill. These pistons are already known to have adequate piston to valve clearance, he had them in the motor at one point.
 
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