I've seen many a question asked on how to modify a cylinder head at home, is it possible to get worthwhile results ? what are the important areas etc etc... so I thought I'd share my recent project with you, with a few words and lots of picks. It may inspire some of you to have a go yourselves, or at the very least, understand some of the work involved in a modified head and what to look for when buying one. It'll take a while to load everthing up while I shuffle pics etc so bear with me. This head is going on a friends 2ltr conversion for road use in his early MK2 GTi on K-jet. The head has standard valve sizes and is being used with a 280+ degree cam (more details as I get to the relivant part of the project) and competition valve springs. I thought I'd kick off with a few basics before we go into the main grinding work... You'll need the following as a minimum really to achieve a similar result... Health and safety plus some tools of the trade. Always wear protection (Ooh err), you "dont" want aluminium swarf in your eyes or up your nose. A pair of cheap gardening gloves are also handy (no pun intended), it'll save washing yr hands every five mins and having to pick ally dist from your nails. You cant really do this sort of work with a black "n" decker or a dremill, you'll need a high speed die grinder. The model I used for most of the work is a Makita 906, about 120 quid new (80 quid when I bought mine 8+ years ago !), or worth a look on good o'l e-bay. You also cant cut aluminium successfully without these... Carbide burrs.. available via the net or local compitant tool supplier (be prepaired for blank looks when you ask for carbide burrs!). Dont let your nice new burrs roll around the bench and fall on the floor, a simple stand will do and makes life easier when working with them. You'll also find one of these handy, a long shank burr (more blank looks from behind the tool counter), if you want to carry out more than the basic mods you'll need one (or a couple of different shapes) to reach down the port. And now the good bits... I'll try and put this in some sort of order, so to start with the minimum of work to achieve a result, we'll start with the inlet throat/seat area. Sticking a cutter or flap wheel down the first couple of inches of the inlet port will achieve nothing (apart from a waste of your electricity), so if you only want to, or feel confident doing the minimum amount of work, this is the area you need to start with... The bit with the rust spots on is the valve seat, the pics not great but you can probably see all the lumps and bumps below the seat that need to go, or be re-shaped. Here's a slightly better angle.. see the ridge below the seat, where the seat insert joins the head, that needs grinding down to something like this... Sorry the pics arnt very sharp, but i'm sure you can see the idea. Basically, your straightening the area down from the seat, down into the throat (although dead straight is'nt always the best shape, but more of that later). A bit of work on the short side turn wont hurt now... Again, not a great pic (note to self..must do better!), but if you look at where the colour changes (and if you have a cylinder head in front of you) you'll see a ridge that carries around into the throat... this nees re-shaping to look more like this... I did'nt use any at this stage (hence the finish), but a better finish can be achieved by spraying a little WD40 in the area that your working on... it reduces clogging of the burr and gives a better finish, though what it look like at this stage is'nt important, it's the shape that counts. The port floor already has a leading edge sweeping into the throat area, its the sharp(ish) edge that you need to cut back and blend-in.. you 'll see this much better on an actual head. The next area of worthwhile gain is the valve guide boss, shown here in yet another fuzzy picture (they do get better, honest). The idea is to thin down the guide boss, and widen the area between the boss and the wall of the throat... And looking at the same area from another (fuzzy) angle... If followed from above, this is the sort of stage you will/should be at... And from a different angle, you can see the shamfer on the guide boss... Something you can obviously see thats missing are the valve guides. They really need removing (pressing out) by your local machine shop before you start for a couple of reasons.. They'll get in the way when your trying to get the tool in the throat (easy !).. They'll no doubt need replacing due to wear.. And before the new ones are fitted they can be re-shaped for a little extra flow (more of that later). You can probably see at this stage that the roof of the port/throat area has been raised around the guide boss, and blended back into the roof of the port. You can also see at this stage that no material has been removed from the port runner itself. If you felt this was as far as you wanted to go, you could indeed tidy/smooth up the work so far with a flap wheel or some emery tape on a split rod, have the new guides fitted and seats cut, blend the lower part of the new 3 angle seat (a must) into the throat, lap your valves in, clean and assemble. You'd then have a basic stage 1 (if you must call it that) type inlet which would work much better than some "ported and polished" effort from a dubious source. But as power hungry enthusiasts we can do much better than that... For the next round of mods you'll need a pair of these... And one of these... The genarally accepted rule of thumb, is to open the throat area below the valve seat insert to around 0.95 of the valve diameter. For those without a Casio to hand, based on the standard 40mm GTi inlet valve, the throat needs opening to 38mm. Between the throat area and the bottom of the seat insert, a venturi type effect is desirable, though not easy to achive. The size here is generally 0.85-0.88 of the valve diameter, so in the case of the 40mm inlet, the diameter directly below the seat insert should be 34-35mm, opening out to the 38mm of the throat. Now get measuring with you calipers and see how small the standard throat area is... yep, theres a fair bit of material to come out.. The bulk of the work still needs to be done in the throat area, but at this stage, we can start looking at some inlet port runner mods. So we'll start here... Yep, it is what it looks like, an old valve. More accepted wisdom sizes the inlet port at around 0.82 of the valve diameter.. save your Casio's battery's.. it works out at approx 33mm based on our 40mm inlet. Now take a close look at the above pic, looks like the edge of the valve has been ground (machined) down.. yep, you've guessed it, to 33mm. This is our guide to sizeing and shapeing the inlet port, like so... Now an important bit.. "DO NOT" grind any material from the floor of the port. You need to open the roof and the sides of the port equally to start with so you can fit the head of the valve in. Bear in mind the floor is at the bottom of the port and the roof at the top (bear with me) as you would look at the head the correct way up... when working on the head, a lot of the time the head will need to be upside down so you can see what your doing.
Theres not much to tell at this stage except, be brave, and keep grinding, and checking, and grinding, etc. Most ports have a bias.. as you look down the port you'll see it curve slightly one way. If you then turn the head over and look at the combustion chamber you'll see the the bias sweeps toward the middle of the chamber (its very subtle), try and keep this bias by grinding more on the outside of the port wall than on the inside.. dont get confused with the head upside down though. Keep going until you get to this stage... By now, if you only have short burrs.. your stuffed ! You need to stop work (you'll be glad of the break, trust me !) and go out and order yourself a long shank burr or two so you can reach the rest of the port (i'll go through the types later). When your nice new burr(s) arrive and you feel like going back to the shed (workshop !) to be deafened by the die grinder some more (!), this is what you want to achieve... Along the way it's an exercise in finding where the dummy valve jam's in the port, grinding the restriction away then carrying on until you breakthrough into the throat area. Be careful not to go OTT whilst doing this, as you want to keep the port as round as possible, and not end up with dips everywhere where you've gone too deep with the burr. Use a flap wheel to help with the size and shape as you go. Remember, "DONT" take any material off of the floor of the port. When you've done the first inlet port, if you hav'nt thought "why did I start this !"... you've got another 3 to go ! During each stage, it helps with the shaping (as well as the enthusiasm to carry on) if you clean up the rough cutting work with some flap wheels, they also take off some material so you'll need to do this to keep the size correct.
You can actually take the guide support right out, then machine/taper the new guide where it comes through into the port. Doing it this way you won't reduce the life of the guide as it's still the original length, you'll only reduce it's life when you start reducing it's length. I tend to take the whole lot of my own heads. I'm in the position that I can whip the head of and change the guides quite easily when needed. If you're not prepared to do it though leave the guides the original length Nice post mate, keep it coming.
After some thought as to what way to go with the guide boss, and as Martin correctly points out above (nice mind reading act ! ) I decided to cut away the guide boss, for a couple of reasons... It's a pain in the ar%e to work around (though I still see many a fast road head with them still in).. It helps with flow.. It's a dam site easier to finish in around the whole throat area without it. So here goes... Going... Gone ! I came accross the next problem at this stage... the finish. With emery tape mounted in a split rod, the die grinder is far too fast and aggresive and with not enough control (remember those days!). Ah, the good o'l electric drill... nope too slow, bol*%ks. To get the decent finish I wanted to achieve, you'll need a speed somewhere between the two. A few phone calls to find no stock of the vairiable speed die grinder I now wanted lead me to a good friend of mine with an air grinder... absolutely brilliant, it gives all the control you need to get a good finish and allows better shaping around the roof where the guide boss used to be, and also around the short side turns. Like so... When all the final finishing and shaping is done through the port & throat/bowl area, the new guides can be fitted. Make sure you get the shape work done first, as once the guides are in you can no longer get in that area without damaging your nice new guides. With the guides fitted (I had these bullet nosed to help increase the flow a little) the new 3 angle seats can be cut. If you look close at the pics, the narrow rim around the top of the 60 degree bottom cut is the new valve seat (compair with the start pics). The lower (wide) bottom cut now needs cutting back and blending in to open the throat out some more and make the most of the valve area. The top cut that you can see around the edge of the valves now needs a little blending into the chamber. I'll post up the exhaust port details later, followed by the final seat finishing in the head and valves themselves when I finish it later in the week.
are you going to do any work to the combustion chamber area? to improve 'squelch' or whatever it is? nice post- you realise people are going to ask 'how much' for you to do their head now!
this needs to be 'stickied' once it's finished. Best DIY head thread i've seen in ages. do you do your own valve seats?
Too late... Nothing much in the chamber itself, apart from blending the top seat cut in a little and maybe opening out the chamber a little on the inlet side to de-shroud the valve a bit (I have a bit more scope with it going on a 2ltr bore), though i need to measure up to see what/if it needs it.
I've got a fair bit on for the next couple of months (a hillclimb engine, road engine and maybe a 16v road head), oh and a freshen up of my own engine, but a PM would'nt hurt.
Thanks.. The idea of it was to help those that fancied a go but did'nt know where to start, though some equipment is needed that most wont have, though it could be bought cheap second hand. Though I'll have to stick a few extra hours in at work for the flow bench !... [:^(] No the seats & guides were done by Pete Willis (PWE) at Tavistock. He's an old school, ex Brian Hart engineer (and a clever b%?*tard) with a huge amount of experiance (he's straightened bent conrods and valves for me which I still use in anger !), I trust his engineering 100%.
thats cool. With the combustion chamber bit i was thinking along the lines of de-shrouding (as you mentioned) and just the general polishing of that area, which seems to be popular with the usual suspects of head work. Damn good finish on those valve bowls
Top thread there Jason Probably just worth a mention on the carbide burrs, and where to find the damn things - I'd never seen these until I started trawling the car restoration circuit via the NEC Classic Car Show and the Beaulieu Autojumble. Then you're in amongst it: LB Restorations, based somewhere down in the South West, sell these, as do many others (Frosts? Car Builder Solutions?). NEC Classic is this weekend at the NEC, so draw up the shopping list. Assume the seats were cut after 100% of the porting?
Quick mention to anyone who hasn't used a 'gazooter' and a carbide bit. THEY REMOVE LOTS OF MATERIAL IN 1 GO! You've been warned
It is worth noting that you can make a head flow worse by porting it badly than when it was standard if you dont know what you are doing....so be careful, I have seen 'works' head guys throwing heads in the bin after taking a fraction too much out in the wrong place and ending up with less flow than when they started. Size isn't everything as my wife keeps telling me.
Cheers Chris. That was coming towards the end, but in view of the show at the weekend and in case any of you want to go "shopping" here's what your looking for to start with... http://bhinone.farnell.com/jsp/bespoke/bespoke3.jsp?bespokepage=bh/en_BH/new_content/roebuck.jsp The above are the suppliers for the short burrs, though I bought mine from a local tool supplier who would have got them from here. The part numbers are... 222689b - flame 222635 - cylinder 222645 - cone 222682 - tree 222672 - ball The long shank burr came from here http://www.merlinabrasives.com/ They're very helpfull, and supplied the flap wheels as well which are 13x15x6 in 40 & 60 grit.. and the emery tape is on a roll, 1 inch wide 80grit. The burr is a flame head made by HM-Frasstift, though Roebuck (above) maybe able to supply. All the burrs are 6mm shank. If anyone google's the above though they should be able to find them from various suppliers. The best price I've found to date for my next upgrade is here...http://www.powertoolsuk.co.uk/webcat/details.asp?ProductCode=GD0800C&ID=2857 It's a Makita GD0800 vairiable speed die grinder, it's needed for the control in the last stages of finishing as the fixed speed (Makita 906) is a great unit but too fast for the emery tape, though ok for the flap wheels. And yes, the seats were done after the last major shaping/finishing work, though the seat's now need blending into the throat, but as I dont need to go near the guide it wont be a problem at this stage... plus you obviously need the guides in the cut the seats, so it has to be done in that order.
