How to tell - skimmed or not?

[F 447]

Hello everybody, can you tell me how you tell whether a head has already been skimmed or not? Is it the Head gasket? Is there markings on it? Sorry novice asking. Thanks:confused: :confused:

[E_T_V]

Most likely you'll not be able to tell and it doesn't really matter either so long as there is enough head left to skim again.

[BIGLAD]

Originally posted by F 447
Hello everybody, can you tell me how you tell whether a head has already been skimmed or not? Is it the Head gasket? Is there markings on it? Sorry novice asking. Thanks:confused: :confused:

Hi,
No- you cannot determine how "thick" the head is by looking at the gasket.
I know Ford and Peugeot/Citroen use a different thickness of gasket depending on how much has been machined off the head face.
e.g. the more that is removed from the head the "thicker" the new gasket needs to be.
This is usually indicated by how many "notches" are on the gaskets.
If you know how thick the Prima/Mdi head is to start with (from new), i suppose you could measure it with a digital vernier and see if there is much difference.
Remember that the "official" line is that you are not to supposed to skim these heads too much.
If my memory serves me right i think it is in the region of 12-15 thousands of an inch- whatever that is in new money?
I cannot be 100% on that at the moment without looking at the workshop manual- and its too cold/dark to go looking in the shed!!
You can usually tell if its distorted by giving it a good clean and holding a straight edge across it.
Also check for pitting/corrosion around the water jacket area's.
Biglad.

[F 447]

Thank ETV & Biglad for your replies. The main reason I ask is, I was asked if the head had been skimmed, when I ordered a Head gasket. I said I don't think so. My cars says it has done 86000 miles, previous owner said mileage was right. Someone at work said I might need a thicker gasket. What are your thoughts please. Steve.

[BIGLAD]

Originally posted by F 447
Thank ETV & Biglad for your replies. The main reason I ask is, I was asked if the head had been skimmed, when I ordered a Head gasket. I said I don't think so. My cars says it has done 86000 miles, previous owner said mileage was right. Someone at work said I might need a thicker gasket. What are your thoughts please. Steve.

As far as i know there is only one thickness/part number for a Monty TD Head gasket.?
Biglad

[J199 HHG]

You do need to be careful with the diesel head - I have heard 12thou as being the max you can take off.

The problem is that the valves are only 40-60 thou away from the piston at TDC, so shaving the head erodes that margin.

On a petrol engine however, you've got much more scope. I took 4mm from my old land rover head, and am presently running a rover V8 with 2mm taken off.

[BIGLAD]

Hi,
You can get around the problem of the valves being too proud after skimming
You have to have the valve seats re-cut further back into the head. (if there is enough "meat" left on them. If there is not then new seats maybe required ).
And then alter the valve clearances by changing the tappet shims to the correct clearance as stated in the W.shop manual(the proper way.
I have known people just reduce the tappet thickness by the same amount that has been machined off the head/and the same distance that the seats have been "moved" back/recessed.
I think the real problem is going to be that the more you machine/skim off the head face the closer you are going to bring the injector nozzle and glow plug toward the piston crown.- i dont know how close these are to start with.
But yes, i thought it was around 12 thou.
Biglad

[F 447]

;) Thanks for the info, just waitng for my locking kit to come before I can take the haed off to see how it is .

[Andy]

I a a compleat novis to engines and was wondering whot exactly does this do does it improve bhp or performance

[E_T_V]

in petrol engines you can skim the head to increase the compression ratio, but in this instance it simply removes corrosion, slight warping and very small cracks and pitts.

[MGTurbo]

Originally posted by Andy
I a a compleat novis to engines and was wondering whot exactly does this do does it improve bhp or performance

Seems your spelling is also due some attention :rolleyes: Can barely figure out your post!

This topic has nothing to do with performance, simply a case of making sure the cylinder head surface is flat for the new head gasket, if warped, the gasket will soon blow again and could cause more damage.

As it happens, skimming the head on a Prima wont increase the compression ratio (although the valves are recessed into the head and thus have a very tiny amount of volume there, but not enough to increase the CR to any measurable amount) The O series is the same, compression is determined by the dish in the piston, and also the actual cylinder bore, as the pistons do not sit flush with the block surface.

1.3's and 1.6's are different though, increasing the CR will help performance so long as the octane rating of the fuel you use is sufficent and ignition timing is not too far advanced.

Gareth

[Andy]

Ive allreddy said befor my spelling is :censored: lol

Thanks for the replys just i have seen skimmed head on list of engine upgrades for tuned cars in mag's etc