Head / Block Skimming

[Kai]

I know that the ideal thing to do, is to take off as little as possible - but i'm thinking - should that be 2 thou/5 thou/10 thou ?

Same goes for the block - should i just get 2 thou taken off and finished at 15-20 RA?

 

[IJ.]

Whatever it takes to get a smooth flat finish Kai.

 

[Kai]

Fair do's, but i've heard horror stories about those that have taken too much off and buggered the cam journals up - so i want to take off as little as possible :/

2 thou ought to be enough for an otherwise good head though, shouldn't it?

 

[IJ.]

Fair do's, but i've heard horror stories about those that have taken too much off and buggered the cam journals up - so i want to take off as little as possible :/

2 thou ought to be enough for an otherwise good head though, shouldn't it?

Drugs?

You don't go anywhere near the cam journals when surfacing a head (they're on the other side)

It takes whatever it takes to get a smooth flat surface....

There is no set amount, constantly amazed when people start buying parts before the machine work is done.

I went through 5 blocks trying to find one usable when I built my 7M, they were all junk in one way or another after inspection so I ebded up dropping the coin on a new one.

 

[4U2QUIK]

make sure the shop that doing the head knows the difference between negative and positive cutters. Otherwise they'll have fun trying to hit less than 20 ra.
http://www.supramania.com/forums/showthread.php?t=90018
and if they have the correct cutter they can easily get it around 10 or less as seen in this link.

 

[Zumtizzle]

Find a shop with a CBN Cutter and a can do attitude.

 

[Kai]

IJ - it apparrently goes; if the head isnt flat when you start doing the machining, and you're trying to make it flat from being banana'ed, even slightly, you'll bugger the journals when you put the cam back in, because several of them will be out of true.

Of course i guess line boring them would be an option then, but ideally you don't want to be doing that in the first place!

I'll be going to pretty much the only machine shop in the south of england - SERDI: http://www.serdi.co.uk/

Sorry if these sound like dumb questions, but its better to ask those that KNOW and have done it before, than relying on second hand information that seems dubious.

 

[4U2QUIK]

Find a shop with a CBN Cutter and a can do attitude.

cbn is a negative cutter. not for use with aluminum. that's what the N in cbn stands for.
that's the problem with 99% of automotive machine shops out there. None of them even understand what the names of the inserts stand for!!!!
If you want to know the skinny on machine tools and inserts I'm the guy to ask.

kai. you're partially right about the bananna heads.
it's because they take a warped head and machine it in a semi restrained condition without straightening it first. so them when it's released the cam journals are jacked.

 

[suprarich]

Kai - If the head is not warped out of spec, a cut of about .0012 to .0018 is usually enough to do the job provided the fire rings from the previous gasket did not indent too much. The problem is that many machine shops will go over kill on the amount cut just to save themselves the set up time. They would rather cut out a lot of material then take the time to really set up the head to provide for the least amount of material to be removed. If the head is warped out of spec, and it passes a hardness test, you can have it straightened in an oven prior to skimming, or you can have the cam journals aline honed to fix the run-out created by milling one side of a bent rectangle.

 

[IJ.]

IJ - it apparrently goes; if the head isnt flat when you start doing the machining, and you're trying to make it flat from being banana'ed, even slightly, you'll bugger the journals when you put the cam back in, because several of them will be out of true.

Of course i guess line boring them would be an option then, but ideally you don't want to be doing that in the first place!

I'll be going to pretty much the only machine shop in the south of england - SERDI: http://www.serdi.co.uk/

Sorry if these sound like dumb questions, but its better to ask those that KNOW and have done it before, than relying on second hand information that seems dubious.

Any machinist with a clue isn't going to skim a warped head.... :nono:

 

[gaboonviper85]

cbn is a negative cutter. not for use with aluminum. that's what the N in cbn stands for.
that's the problem with 99% of automotive machine shops out there. None of them even understand what the names of the inserts stand for!!!!
If you want to know the skinny on machine tools and inserts I'm the guy to ask.

kai. you're partially right about the bananna heads.
it's because they take a warped head and machine it in a semi restrained condition without straightening it first. so them when it's released the cam journals are jacked.

about time someone points this out...Cbn is for iron....should be using carbide or even better diamond for cutting aluminum!

 

[suprarich]

cbn is a negative cutter. not for use with aluminum. that's what the N in cbn stands for.
that's the problem with 99% of automotive machine shops out there. None of them even understand what the names of the inserts stand for!!!!
If you want to know the skinny on machine tools and inserts I'm the guy to ask.

Cubic Boron Not for 7m head. LOL

CBN insert has worked perfect for me.?.

This is a single pass without lifting the cutter on the return. Single CBN cutter on a dual cutter head. RA of under 50 everytime..

 

[gaboonviper85]

For shits and giggles try diamond inserts...you'll be amazed I promise! If you look in kenmetal catalogs you'll notice that cbn's are a purpose built insert (usually for cast iron)...sure you can cut aluminum with them but in a machine shop it's considered using the wrong tool for the job when aluminum generally uses a positive rake.

 

[suprarich]

For shits and giggles try diamond inserts...you'll be amazed I promise! If you look in kenmetal catalogs you'll notice that cbn's are a purpose built insert (usually for cast iron)...sure you can cut aluminum with them but in a machine shop it's considered using the wrong tool for the job when aluminum generally uses a positive rake.

I have used pcd inserts before in the past, was not much better. In all the machine shops I have worked in, it is only the wrong tool if it does not work.

 

[4U2QUIK]

For shits and giggles try diamond inserts...you'll be amazed I promise! If you look in kenmetal catalogs you'll notice that cbn's are a purpose built insert (usually for cast iron)...sure you can cut aluminum with them but in a machine shop it's considered using the wrong tool for the job when aluminum generally uses a positive rake.

yep. and in a real machine shop it's the wrong tool if it takes 10X longer to do the job. I can use my prefered positive cutter and get a Ra of less than 10 using a feedrate of 50ipm!!!! If I used the cutter You mentioned it would use a ipm of about 10-30 depending on the rigidity and HP of the machine used, and you would never ever come close to an RA of 10.

 

[gaboonviper85]

I have used pcd inserts before in the past, was not much better. In all the machine shops I have worked in, it is only the wrong tool if it does not work.

Legit machine shop or motor building shop....In my personal opinion motor shops are far from being considered "machine shops" as generally they lack the education of tooling and general operation of machines:-/

this is not an attack on you as I'm sure you're an awesome motor builder and what you do works...but there are other ways (technically proper) ways of machining....here at my shop " http://www.efgroup.com/ " we deck crotchrocket heads with diamond and the ra is 3-5...although we mill the valve seats down a bit cause if the diamond hit one it will break.

 

[4U2QUIK]

couldn't have said it better myself.
btw. I'm the inspector at www.esprecision.com
and rest assured rich, I have no doubts in your ability either.

 

[suprarich]

I worked at Ajax manufacturing which is a giant machine shop/tool and die shop around here, a mold shop, and a aluminum foundry, prior to turning to motor shops. Could not find anyone to properly machine our nitromethane motors, so started doing it myself years ago.

 

[gaboonviper85]

I worked at Ajax manufacturing which is a giant machine shop/tool and die shop around here, a mold shop, and a aluminum foundry, prior to turning to motor shops. Could not find anyone to properly machine our nitromethane motors, so started doing it myself years ago.

I have the same thoughts! After being let down by two motor shops all I've thought about is how I could do better:-(

 

[4U2QUIK]

From what I hear from a couple of guys I know that do nitro boats, a lot of the nitro stuff is done by specialty shops. Which makes sense because running nitro, and or blown nitro like my friends do it's a whole different ballgame. Most of what you know about engines goes right out the door.