325i head...what can I do with it?

[yoda634]

I've got a 325i head that I pulled at the junkyard a while back, and am looking to use it as a learning experience, and ultimately use it as the top of a 2.7i. Essentially, I'd like to do anything possible to it performance-wise, primarily for the experience, and also to have a sweet motor at the end.

So far, I've got it mostly stripped down. I've still got to figure out how to remove the valve guides and stem seals, but everything else is out.

Current plans are: check the valves for straightness, check the casting, regrind the valves, new stem seals and guides, port/polish. Possibly add a Schrick cam, but I'm looking to do this fairly cheaply.

What else is there to be done in the way of modifications to this head? I'm open to anything. I've never done a port and polish before -- any good how to guides out there?

Another issue -- I discovered that the rocker shaft journal nearest the firewall on one side is cracked. Any way to repair this? Or will I have to junk this and get a different casting?

[Snowmann]

in terms of a port match BMW isn't like your typical small block chevy where the ports leave a ton of material to be removed.

The polish is about 5% of the job and the porting the other 95%


Some of the best articles come from the hot rod magazines and just do a search for some pdf articles from reputable hot rod magazines.

Head work and "cheap" do not mix. I'm not your mom and I won't baby you and also won't call you a moron for thinking it can be done cheap - but just so we have that clear.

The valve guides would be worth having a machine shop do - they could throw on the seals for little to nothing extra - otherwise a 11mm iirc deep well craftsman socket is the PERFECT tool for install. Find the correct size so that the socket walls are on the metal walls of the seals - but I would still have a shop do the guides.

If you are going to do any port work leave the old guides in until completed! then swap over the new guides - you will knick the old guides while you're in there.

The main work to be done is the un-shrouding of the valves and the sparkplug.

One can see gains from do-it-yourself head work on the m20 head however don't think you are going to set the world on fire - BMW engines - even ones this old are far advanced and with out a flowbench and extensive experience in head flow work you won't see much.

However if you are like me and looking to tinker - have fun mess around - these things are cheap in the big spectrum of things and if you wanted to do another one you wouldn't be out a ton.

[yoda634]

Not cheap? I'm thinking this is going to cost me all of $60 for guides and $20 for stem seals, plus a bunch of dremel attachments.

I've got a moderately-well equipped machine shop at work that I'm using to do all this, this isn't happening in my basement or anything. Good tip on leaving the old guides in for now, makes perfect sense.

What do you mean by un-shrouding?

And like I said, I'm not focused on super huge gains here, just on putting some work into it, getting some experience, and having a decent finished product that I've got something personally invested in.

[vr2jetta]

The only way to learn how to port is to do it. Thats how I started. This is the attachment I use:

http://www.dremel.com/en-us/AttachmentsAndAccessories/Pages/AttachmentsDetail.aspx?pid=115

It eats through the aluminum like butter!! Be sure to keep it doused in PB Blaster and it wont clog. You should only need one, maybe 2. Be sure to keep the runners even. I have done 3 different heads and a few intakes and they all came out good. Take your time, take measurements and pay attention to any openings you may cut into, like coolant passages and oil return galleys. Good luck!

[a_thomasmr23]

Unshrouding the valve will increase airflow but not by a ton and it has a huge effect on knock resistance (shrouding produces swirl which reduces knock). Just something to keep in mind when you are doing this. BMW put together a pretty great design for the late 70's early 80's when they where doing the work on these heads. The best thing to do is clean up production flaws like casting marks and roughness.

Edit

Shrouding is when the side of the head come close to the valve opening. This leaves a large opening on one side and about .25 to .33 of valve diameter of space on the other side