Nick Jones

I know we are all petrol heads but still interesting......




Nick

This is a follow-on to
http://sideways-tech.../690-diy-heads/
and should be read in conjunction with it.

Didn't want to add this onto the bottom of Neils excellent thread, but make no mistake, I'm drawing heavily on Neils information. I've added some observations of my own too.

The victim is the head from my Mk2 2.5PI. FWIW the number is 218225 though for the purposes of this modification they are are pretty much the same apart from the 219016 head from the 2.5S which are quite different in the inlet valve throat area.

What will vary from head to head is the amount of core shift. What the hell this that? Well this head is quite bad, so I'll show you.......

When the heads are cast, after the main impression is made in the sand which form the basic shape, cores are laid in that will create the voids for the waterways, ports and the basic shape of the combustion chamber.

The port cores want to be positioned so that the centre of the section that forms the valve throat is concentric with the position the valve guide. That means that when the valve throat and seat are machined later you get a reasonable blend of shapes without any serious steps.

The pic below shows that the cores on this head were too far to the left so there's a pronounced step in the short side radius and an undercut below the seat area on the far side.



This one shows the undercut better. This is the bigger problem really as the SSR step can be cleaned up, but this really needs material added.



About all you can do with this is to chamfer the sharp edge. You are limited by the need to leave plenty of material under the valve seat. DO NOT undercut the seat!
This is my attempt


I don't know how big an effect on flow this actually has.

Another interesting thing noticed was the evidence for high and low flow areas in the valve throat.



Yellow arrows show the cleaner areas indicating higher flow,
Red arrows show heavier deposits indicating low flow. The section just next to the exhaust valve appears to have the lowest flow by some margin.
Green arrow shows what appears to be the "flow shadow" of the valve stem. Never seen this before and I think it's partly due to this being an injection engine. It's not equal on all cylinders, which may be telling me something about the state of my injectors.
Blue arrows show areas of heavy deposits that always seem to form in these corners indicating stagnant areas.
As a general comment, this head came from an engine which was a VERY heavy oil user. The flow patterns don't show through into the combustion chamber all that well. This may be because I wasn't using the engine hard before it was dismantled.

Have been doing a cylinder head for the PI this weekend. I've done the ports as per Neils instructions, done a tiny bit of chamber modding and was in the process of fitting new bronze guides.

I made to couple of tools to help press them in, then fitted the inlets, having first measured them to make sure they were correct. They were 12.71 - 12.73mm which is much the same as the cast iron ones which came out.

Then the exhaust ones......... first one measured at 12.71 and was duly fitted. However, the remaining 5 measure at 12.67 - 12.68 and almost install themselves....... one drops most of the way in under its own weight!



Was going to drop the head at the machine shop tomorrow to have inserts fitted....... not now. What really irritates is I actually bought these in 2009 so I can't really send them back!

Nick

A bit late now I know as most (if not all!) of the day has passed down under but hope you had a good one.

May your hangover be small but well deserved!

Cheers

Nick

I despair of the great British public. (No taz smiley - how can I rant properly without a taz smiley?)

There is a possibility that there MAY be a tanker drivers strike at some point. We KNOW it is at least 7 days away because they have to give 7 days notice. This hasn't happened yet and probably won't happen (if ever) before next week as they are still talking about talks. So there is no reason to think there will be a petrol shortage anytime soon is there?

Then some DICKHEAD politician stands up on his hind legs and suggests it might be wise to stock up. What a complete moron (ah yes Francis Maude, no surprise there then).

So today, driving round Somerset and north Dorset, the only petrol stations without huge queues were the ones that had sold out - in turn triggering more panic....... In Yeovil the queues were leading to general traffic chaos in places as well.

There IS now a petrol problem (around here at least) - but it's entirely the result of herd stupidity. Hopefully the seriously stupid now have petrol and issue won't repeat tomorrow or over the weekend (could make the HCR tricky!)

This was of especial irritation to me as I went out (in ignorance, I don't tend to watch the TV news as it just depresses/irritates the hell out of me and I've been driving the Vitesse all week so can't hear the radio) in the Vitesse, with less than half a tank of fuel and some miles to do. The tank isn't very big. I was unable to buy fuel without serious queuing (I loath queuing - bad Englishman) so came home on fumes (having done everything I planned to do) and then had to slink out later, after the great unwashed had gone home to the telly, to buy some, and most local stations were dry. So I had to buy a bit at stupid prices (bloody BP weren't sold out 'cause they are so damn expensive) just to wet the bottom of the tank and stop the pump going nuts.

Just goes to show how close to the edge "civilization" is these days. One of my colleagues observed a person (female) trying to fill 2L plastic milk bottles with petrol. She was prevented (with much screaming and shouting from her apparently) by the forecourt manager. Good thing as those bottle melt in petrol.......

Interesting observation I read somewhere earlier petrol sales 80% odd above normal but diesel only 38% read into that what you will. It gets me thinking about certain stereotypes and I'm sure I would be politically incorrect.....

We're all doomed I tell you......

Nick