Head Surfacing For 25/30

[psi]

Ok, The long and the short of this little tale is that the head I have has a bit of a bow in it..

My machinest can straighten this, and re-cut the valves and all that other stuff,

But the question that I really need to know the answer to is how much can I safely shave off the face after all the other work is done?

its a stock RB30 bottem end, stock 25det head. Stock head gasget, stock valves, stock cams (Planning on pon cams during the year!)

I would like to raise the compression if possable, can you guys help?

[Spoolup]

Your best bet is too get another head.

As to straighten a warped aluminium head PROPERLY will cost you more or nearly as much as to buy another. The process involves heating the head to the point where it straightens itself, or levels itself out so to speak. This in itself isnt the expensive part. You will then require to have the camsaft tunnels line bored to make sure they are straight, and more than likely the majority of valve seats replaced ( new ones pressed in ) , as they come loose due to the different expansion rates between the two different materials.

If your machinist just plans to surface it - then you consider all your optins first.

[psi]

yea , I am aware of all you said. They sometimes 'pull' the lifter bores out of round and valve guides can fall out as well!

All of which I am aware of.. thanks for the heads up. Yes, he is doing all that plus a cc check, pressure check and crack test before any machining takes place..

The old owner must have had an issue, cos the deck face is flat as, but the cam journals are a bit out. We are thinking that the old engine had an issue and he just skimmed the head and away he went without checking anything else..

So the question still remains, after i get all the other stuff fixed, how much can be shaved off the face? has somebody done a valve to piston check? does someone know the answer I am after?

[psi]

c'mon guys.. surely somebody has done a head shave and checked all the clearances?

[R34GTFOUR]

if it was me, i would just get one of those engine CR calulators on the net and spend an hour punching in numbers, until you get a combo that comes up with a good CR, somewhere around the 8.2-9.0 mark.

When you say stock bottom end, std pistons/rods or rebuilt? stock 86mm bore?

I'm not sure what the stock hg thickness is, but you'll need to work that out, im sure someone here will tell you.

I would just take off as little as possible from the head, just untill its level, then definately cc the head so you know how much to take off the block to get your target CR. You have much more to work with, with the block since the stock pistons sit below the top of the bore, so if any decent shaving is to be done i would be looking there, not the head.

So basically, if you want to keep this head, get it sorted with the lest possible taken off, find out how many cc's there are in each chamber, determine the hg thickness, then get on the calculator and work out how much you need to deck the block to get you CR, you might even zero deck the block..

[psi]

the block has completly stock everything atm (226 000km on it! not going to refresh it), going to just run it to see how well it goes, if it works as well as I hope, I will start on 'built' engine. But this mongrel head is being a pain in the butt. If its not sorted in a few weeks I will buy another head and go nuts on it!

Thanks for the input. Got any links to a compression calculator? cheers

[R34GTFOUR]

google.com.au

or spoolup, the person that answered in this thread has one on his website which is in his signature.

By the sounds of things, if the head has been that badly warped it would be cheaper and easier to just get another head. Goodluck with it

Edited December 27, 2008 by R34GTFOUR