Dimentional drawing for engine blocks/heads

[Carby131]

Hi all

Anyone know where i can get proper engineering drawings?
i was wondering how to determine how much if it all one of the gasket faced had been skimmed.
this is only hypothetical at this moment in time so i dont have a specific engine to had but one in mind

thanks guys

[davepoth]

You will be after the blueprints then. The manufacturer won't let you have them, but often the workshop manual will have the info you are after to aid in skimming.

[rev-erend]

Seems a pointless paper exercise.

Surely you should measure the CC of the chamber and cc of the area above piston
work out the cr then with the bore size you can work out the new cr for any head or block skimming..

[K87]

rev-erend said:

Seems a pointless paper exercise.

Surely you should measure the CC of the chamber and cc of the area above piston
work out the cr then with the bore size you can work out the new cr for any head or block skimming..

Yer agree with this. CC measuring is pretty straightforward with a syringe and a piece of clear plastic.

Would you include the thickness of the head gasket when working out the CR?

[rev-erend]

Oops .. forgot the gasket .. composite often 1mm or there abouts.

[K87]

rev-erend said:

Oops .. forgot the gasket .. composite often 1mm or there abouts.

Cool I did when we did it but wasn't sure how thin they go once torqued up so wasn't sure if it was relevant.

[Carby131]

im used to haveing to be very acurate in my job so it kind of rubs off here too, all it was for was to check that any block or head that i got hadnt been skimmed to within a thou of its life

thanks all guess im being too picky :P

[rev-erend]

Troble with drawings - they do not allow for core shifts in the foundry .. etc

[stevieturbo]

Only way to know, is to measure before and after.

[Yuxi]

rev-erend said:

Troble with drawings - they do not allow for core shifts in the foundry .. etc

Core shift doesnt come into it.

Normal gasoline production aluminium heads are gravity die or low pressure die cast, either way the combustion face and chambers are a metal part of the tool. Some tools have chambers that can be individualy adjusted up and down, some dont.

Normaly there will be 3 pads on the combustion face and a flat area or pip in each combustion chamber. The head is set up for machining by creating a plane (Z plane) through the 3 pads then probing each combustion chamber and calculating the position of another plane (W plane) parralel to Z and through the average of the combustion chambers. The combustion face is then machined at a drawing dimension from plane W and parralel to Z. The tolerance on the combustion face is normaly profile 0.1 to W. This method is used to ensure the correct compression ratio and a best fit ratio across the head. Part of the logic used to work out the average height of the chambers also rejects any head where there is a big difference in chamber height, normaly more than 0.3 is rejected.

The top of the head is then dimensioned from the combustion face, normaly with a tolerance of something like profile 0.2 to the comb. face.

Any shift of sand cores, which make the water jacket, ports, oil core etc will not change the position of the machining relative to the casting datums or the thickness of the head.

The only way to know for sure if a head has been skimed is to know the drawing dimension between the top and bottom faces and compare it to what you measure. On the example above if your head is more than 0.1mm thinner than the drawing it has been skimmed. On some heads the section of the chamber probed to work out the average height of each chamber dissapears when the spark plug hole is machined so there is no way to check it after machining.

Diesel heads are different as they dont have combustion chambers, these are set just from the 3 pads or sometimes from features inside the ports.

[stevesingo]

Carby131 said:

Hi all

Anyone know where i can get proper engineering drawings?
i was wondering how to determine how much if it all one of the gasket faced had been skimmed.
this is only hypothetical at this moment in time so i dont have a specific engine to had but one in mind

thanks guys

What engine? Someone may know what you need to know?

Steve

[rev-erend]

Yuxi said:

Core shift doesnt come into it.

Normal gasoline production aluminium heads are gravity die or low pressure die cast, either way the combustion face and chambers are a metal part of the tool. Some tools have chambers that can be individualy adjusted up and down, some dont.

Normaly there will be 3 pads on the combustion face and a flat area or pip in each combustion chamber. The head is set up for machining by creating a plane (Z plane) through the 3 pads then probing each combustion chamber and calculating the position of another plane (W plane) parralel to Z and through the average of the combustion chambers. The combustion face is then machined at a drawing dimension from plane W and parralel to Z. The tolerance on the combustion face is normaly profile 0.1 to W. This method is used to ensure the correct compression ratio and a best fit ratio across the head. Part of the logic used to work out the average height of the chambers also rejects any head where there is a big difference in chamber height, normaly more than 0.3 is rejected.

The top of the head is then dimensioned from the combustion face, normaly with a tolerance of something like profile 0.2 to the comb. face.

Any shift of sand cores, which make the water jacket, ports, oil core etc will not change the position of the machining relative to the casting datums or the thickness of the head.

The only way to know for sure if a head has been skimed is to know the drawing dimension between the top and bottom faces and compare it to what you measure. On the example above if your head is more than 0.1mm thinner than the drawing it has been skimmed. On some heads the section of the chamber probed to work out the average height of each chamber dissapears when the spark plug hole is machined so there is no way to check it after machining.

Diesel heads are different as they dont have combustion chambers, these are set just from the 3 pads or sometimes from features inside the ports.

Great post .. very informative

[Carby131]

Yuxi said:

rev-erend said:

Troble with drawings - they do not allow for core shifts in the foundry .. etc

Core shift doesnt come into it.

Normal gasoline production aluminium heads are gravity die or low pressure die cast, either way the combustion face and chambers are a metal part of the tool. Some tools have chambers that can be individualy adjusted up and down, some dont.

Normaly there will be 3 pads on the combustion face and a flat area or pip in each combustion chamber. The head is set up for machining by creating a plane (Z plane) through the 3 pads then probing each combustion chamber and calculating the position of another plane (W plane) parralel to Z and through the average of the combustion chambers. The combustion face is then machined at a drawing dimension from plane W and parralel to Z. The tolerance on the combustion face is normaly profile 0.1 to W. This method is used to ensure the correct compression ratio and a best fit ratio across the head. Part of the logic used to work out the average height of the chambers also rejects any head where there is a big difference in chamber height, normaly more than 0.3 is rejected.

The top of the head is then dimensioned from the combustion face, normaly with a tolerance of something like profile 0.2 to the comb. face.

Any shift of sand cores, which make the water jacket, ports, oil core etc will not change the position of the machining relative to the casting datums or the thickness of the head.

The only way to know for sure if a head has been skimed is to know the drawing dimension between the top and bottom faces and compare it to what you measure. On the example above if your head is more than 0.1mm thinner than the drawing it has been skimmed. On some heads the section of the chamber probed to work out the average height of each chamber dissapears when the spark plug hole is machined so there is no way to check it after machining.

Diesel heads are different as they dont have combustion chambers, these are set just from the 3 pads or sometimes from features inside the ports.

wow thats not even copied and pasted! your like god