I need help ;-)

[Porny]

My TD5 is still 'in the build' process....

It will be fine

...  :roll:

Matt, what do you think the effects of a high compression ratio (i.e. you skim too much of the head) would be???  



Ian

[mud-club-matty]

if the head has not been skimed and it dont look like it has because when a head is skimed the edges are sharp but the head he has gont the eadges are not sharp so it might not of been skimed the only way to solve it it take both heads off

[Porny]

if the head has not been skimed and it dont look like it has because when a head is skimed the edges are sharp but the head he has gont the eadges are not sharp so it might not of been skimed the only way to solve it it take both heads off

Depends if it's properly finished.....

I know of some one who used to sell recon engines....  They were freshly painted, so must have been rebuilt.

Not.  All he did was repaint them, never stripped them down or rebuilt them.


Ian

[mud-club-matty]

yer true so whats they way to do it then

[Porny]

Properly...

Take both heads off, and meaure the volumes of the head and the cylinder/piston.

Do the calcs and compare the two results.





Ian

[mud-club-matty]

and if on is bigger get the biggest one skimed

[Porny]

and if on is bigger get the biggest one skimed

You'd skim the one with the lowest compression ratio (so both became even) which is actually the one that has the largest volume measurement.

[Range Rover Blues]

you can check how much has been skimmed, on the front of that head is a square lug with a hole in the end, if it's closer to the gasket surface than the outside edge it's been skimed by the difference in the 2 apparently. .

[gtomo2]

you can check how much has been skimmed, on the front of that head is a square lug with a hole in the end, if it's closer to the gasket surface than the outside edge it's been skimed by the difference in the 2 apparently. .

Cant find that lug or more likly i just could not see it. :roll:  will have to have a good look and feel of the head today and have a think about which route to take. weather to put the new head on or get the orignal one drilled out and re threaded

[Range Rover Blues]

It's a small square lug, obviously on the finished surface of the head, less than an inch square with a hole in the front (or rear) face.  You should be able to see it in-situ on the driver's side head, though not get the callipers on it to measure.

[Porny]

It's a small square lug, obviously on the finished surface of the head, less than an inch square with a hole in the front (or rear) face.  You should be able to see it in-situ on the driver's side head, though not get the callipers on it to measure.

I doubt you'd really tell much if you can't measure it... even then you would need to be very accurate with the measuring.

What you could do is get the old head off...
Measure the volume, and meaure the volume of the new head...

If they are the same, just bolt the new head on... if different skim the new head to match.  Unless the new head is already skimmed too far.


Ian

[gtomo2]

I just knew this would not be a ten min job. Thanks everyone for the help so far. Sorry if sound thick just never done this sort of job before. changed heads on old cast blocks (talbot sunbeams etc). just not had any experance with alloy heads and dont fancy having to do it twice when i muck it up the first time.  :roll:

[Porny]

Do you need the Disco everyday???

The other option, is to keep your existing head.

If you can get the head off and over to me, I can get it repaired at work.
Means you can keep your existing head and not worry about CR problems etc etc.


Regards

Ian

[Range Rover Blues]

I'd be very tempted to take that offer up, provided you get the head off without it twisting then put it back as you found it.  Trust me, if the first time you do the job it all goes relatively smoothly, you'll not think twice about tackling it again some time.

[Range Rover Blues]

What you could do is get the old head off...
Measure the volume, and measure the volume of the new head...

Ian

I think you need to explain how we would go about this though.  One of the problems with measuring the combustion chamber in the head is that the head is often skimmed because it has warped, so it can be skimmed more at the ends than in the middle (they even get made this way) so whilst it's very accurate (provided you are dilegent in the measuring) because you can work out exact figures for each cylinder, the information alone isn't always enough.

[karlo]

If you can get the head off and over to me, I can get it repaired at work.
Means you can keep your existing head and not worry about CR problems etc etc.


Regards

Ian

If you need a lift over with it mate just give a shout!

[gtomo2]

If you can get the head off and over to me, I can get it repaired at work.
Means you can keep your existing head and not worry about CR problems etc etc.


Regards

Ian

If you need a lift over with it mate just give a shout!

Thanks for that just may be taking the head off and giving it to Ian as it may be safer than me drilling throught the head and out the other side. Will let everybody know over the weekend. it will depand on me geting the works van for a few days

[Porny]

Just to add another spanner in the works...

This cylinder head…. been doing a bit more thinking – and I've probably just been a bit pedantic:

 
First off, a warped head will not directly affect the CR.  All you are doing is measuring (with liquid) the volume of one (or more – see below) of the head chambers.
When you measure the CR, unless you're building a blue printed race spec affair, you'd only measure one head chamber and one piston/cylinder (so a warped head wouldn't show up)
Only if you wanted everything to be absolutely perfect you'd bother measuring every head camber and every cylinder –and then calculating the average.
 
Before you even started this though, you'd check that the head wasn't warped (well, more than an acceptable tolerance) by having it slightly skimmed, or just with a flat edge and a set of feeler gauges.  And then, even if you did measure every head chamber, you'd still only be taking an average.  
Though, if we are talking race spec engines, and thus you wanted every chamber to be the same you'd just do a bit of machining   ...  the main thing is that the head face it flat (well within tolerence)

 
If we take your engine to be completely standard and running standard CR then….
 
Then unless the new head is massively skimmed, or from some super low compression ratio engine, then you shouldn't really have any issues.
 
If your engine was brand new (and hadn't done 'x' amount of miles) then it would be worth checking, but in this application and usage if the CR differs between banks it really isn't going to make that much difference.  Not when you consider loses that already affect a 'used' engine.
 
As mentioned before, you could just measure the height of the head itself… although not the most accurate method; it would give you a basic idea.
 
When the head is off (easier access) just measure it's height, and then measure (in the same place) on the new head.  You do need to fairly accurate to do this though (well to get a reading that's even worth taking) – we are not talking cm and inches here!!
 

In saying that, I will still happily repair your current head... will even give it a wash and crack test if needed!!!  


Ian