20 replies to this topic

[Easyrock]

Hi, I was just wondering whether anyone on here had done any porting/polishing on there own cylinder heads at home? I ask because i've got a few spare heads and i'd like to give it a go myself and was just wondering whether or not it's worth having a go? I wouldn't want to try and do any extensive work, just a little smoothing out of the ports and chambers. Any advice is very much appreciated :)

[Sam Walters]

You could try with a flexi drill drive thing and some carbide burrs.

However, the issue if the valve guides. You need to remove these to do a good job of it.

Putting them back in is a professional job and needs the valve seats to be recut.

[CMXCVIII]

The 1960s Clive Trickey book, "Tuning a Mini" has whole chapters on where to file - and where not to file!

There are usually cheap copies available on Amazon if that helps.

[Pigeonto]

google Des Hammill. His is one of the few that the publishers havent blocked viewing on line to try to make you buy it. Only comment I would make tho is he is an out and out racer so you would end up taking ports out bigger than you want for road use ( you will get a crap idle and horrible low speed issues due to lack of air speed).All the valve throat,chambers and guide boss stuff is there tho. Defo do some research.

[Cooperman]

With the A-series heads a little basic work does make a big difference. Just smoothing out the 'steps' around the edges of the valve seats, de-shrouding around the inlet valves and removing most of the valve guide boss intrusions in the inlet & exhaust tracts makes a real improvement.
Always remove the valve guides and fit new ones and have the valve seats lightly re-cut.
When grinding in the chambers fit old scrap valves to prevent the cutter slipping acrtoss the valve seat.
Once ground on smoothed you need to se-set the compression ratio so first of all fit the valves and ensure that all chambers are the same volume to around +/- 0.3 cc, then do the calculations and have the head skimmed to bring the C.R. up to what you want - normally around 10:1 is OK.

[dklawson]

Vizard also covers porting in his books should you not be able to find the others mentioned above.

As a footnote to the good advice above, don't polish too much. Smooth, blend, and enlarge the ports where the texts say it is beneficial and then go for a decent, ground finish. Do not go after shiny, smooth, glossy polish in the ports. A bit of roughness there can be desirable. However, polishing combustion chambers does help some to slow carbon deposit buildup.

[Easyrock]

Cheers for the advice guys :) definitely gonna give those books a look. Probably have a go on one of my heads in a few weeks, I'll let you know how it goes :)

[Turbo Phil]

The trouble with an ordinary drill is they run far to slow to drive a carbide burr properly. The burrs soon lose their edge & material removal is slow. If you have a decent compressor a cheap die grinder is a far better option.
The Viizard book, Tuning The A-Series Engine covers head work extensively & is well worth a read. You definately need to have some guidance on what to do, as simply enlarging the main body of the ports is what most amatures/first timers do, but is not what's required for good performance.

Good luck !

[Cooperman]

The trouble with an ordinary drill is they run far to slow to drive a carbide burr properly. The burrs soon lose their edge & material removal is slow. If you have a decent compressor a cheap die grinder is a far better option.
The Viizard book, Tuning The A-Series Engine covers head work extensively & is well worth a read. You definately need to have some guidance on what to do, as simply enlarging the main body of the ports is what most amatures/first timers do, but is not what's required for good performance.

Good luck !

Absolutely right. Don't be too adventurous on your first attempt. Just take most of the valve guide bosses away, clean up the surface of the combustion chambers and de-shroud the valves a bit as explained in David Vizard's 'Yellow Bible'. Then get the compression ratio right.

[bmcecosse]

But - it's really really not worth doing any of this on a standard 998 head. Get hold of a better basic head (202/295/940 in order of usefulness) and a LOT of the work is already done for you....... The 940 head being best by far - but it also benefits from simple improvements as described above. Basic work can be done with little grind stones (mounted points) and an electric drill - but it WILL ruin the drill. And always wear a dust mask - and use an old HEPA filtered vacuum cleaner to suck away the dust as you grind away.......

[Easyrock]

I work at a garage every weekend so I can get hold of a compressor and what not no problem.

I was gonna give it a go on one of my 940 heads instead of a 998 head as like you say it's a better starting point. The plan is to get a 998 block pocketed to take the head and rebuild my twin hs2's over the next month or two to give me something to play around with whilst the minis at the bodyshop, hopefully i'll end up with a nice little engine

[bmcecosse]

You don't need to do much to the 940 head - for use on a 998. The main restriction is in the exhaust valve throats - where the gases have to turn the corner past the valve guide boss - it's very tight in there! Don't pocket the block - just sink the exhaust valves into the head until you have 320 thou clearance to the head surface (assumes standard lift cam). And a big single carb is much better than the tiny twins........

[Merryck]

This is all very very confusing!

[tiger99]

If in doubt, you could just just polish and remove bumps and rough spots for your first attempt. If you don't really remove much metal, you will only need a very light skim, if any. It will make a difference, but not a dramatic difference, but it will give you a good feel for using the grinder, and the head and ports will stay clear of carbon for longer.

Some engines, such as 998 A+, were prone to running on, and a basic clean and polish seems to relieve it for a long time.

[Turbo Phil]

Whatever you do don't polish the inlet ports ! If you "must" polish do the chambers.