: N* Head Milling Machining



jwaynes
05-03-04, 12:32 AM
Is it necessary to always machine the head when replacing the head gasket?

zonie77
05-03-04, 12:59 AM
Do you mean the valves or the gasket surface?

I'd say no if the engine was running well except for the coolant leaking and the gasket surface looks good and checks straight. (Use the best straightedge you can get to check it and check in multiple directions.)

Lawrence
05-03-04, 11:52 AM
You've got a .002 limit on the cylinder head.

BeelzeBob
05-03-04, 12:23 PM
It is not necessary to remachine the head deck surface when replacing a head gasket. It would be very rare to find a "warped" head or anything...so rare as to not even worry about that. The valve seats and such are usually fine at well over 100K so I would not even worry about those either. Just replace the head gasket and go. Use the OEM gaskets.

ttown
05-03-04, 12:29 PM
I would at least have the heads examined by a reputable machine shop. Preventitive medicine.

I personally have all my heads decked if I have to remove them for any reason, auto manuf. have a tolerance that is not acceptable to my machine shops standards.

BeelzeBob
05-03-04, 01:00 PM
I would at least have the heads examined by a reputable machine shop. Preventitive medicine.

I personally have all my heads decked if I have to remove them for any reason, auto manuf. have a tolerance that is not acceptable to my machine shops standards.


Not acceptable tolerances, huh....????.....to tight for you....LOL got to get them remachined by the corner shop to sloppen them up a bit....LOL

Most all automotive machine shops do not have the measuring capability to determine what the "tolerances" are much less meet the factory's level of machining capability.

ttown
05-03-04, 01:15 PM
Not acceptable tolerances, huh....????.....to tight for you....LOL got to get them remachined by the corner shop to sloppen them up a bit....LOL

Most all automotive machine shops do not have the measuring capability to determine what the "tolerances" are much less meet the factory's level of machining capability.
Tell ya what big boy, My shop builds racing engines for people all over the country. Racing specs are much tighter than standard specs. As cheap as it is to have heads decked, it is worth it to me, especially if you have blown a head gasket. Chances are, from my experience (and I have built many an engine) if you blow a head gasket it is possible that the head is warped.

You need to stay on the porch with the pups fella.:shhh:

Lawrence
05-03-04, 01:25 PM
Not acceptable tolerances, huh....????.....to tight for you....LOL got to get them remachined by the corner shop to sloppen them up a bit....LOL

Most all automotive machine shops do not have the measuring capability to determine what the "tolerances" are much less meet the factory's level of machining capability.

Bill, having a bad day? :)

You've aroused my curiousity though. A machinist straight edge is not accurate enough the check warpage limits? Personally I would check with a straight edge and if it out, take it to my machine shop for them to remeasure and machine if needed, hmmm...... Now, my personal experience tells me it is more important "where" and "why" the head is out .002 rather than "simply out .002") and the service manual doesn't really go into that. But beyond that,

Can you tell me what is the proper procedeure/equipment for field checking straightness?

ttown
05-03-04, 01:28 PM
Bill, having a bad day? :)

You've aroused my curiousity though. A machinist straight edge is not accurate enough the check warpage limits? Personally I would check with a straight edge and if it out, take it to my machine shop for them to remeasure and machine if needed, hmmm...... Now, my personal experience tells me it is more important "where" and "why" the head is out .002 rather than "simply out .002") and the service manual doesn't really go into that. But beyond that,

Can you tell me what is the proper procedeure/equipment for field checking straightness?
I use a machinest straight edge and feeler guages.

Lawrence
05-03-04, 01:35 PM
I use a machinest straight edge and feeler guages.

ttown..........in defense of bbobynski, he is a GM powertrain engineer and helps out alot on this forum. He gets a lot of really rediculously simple (Edit: No offense intended, any question is valid if you don't know the answer) questions here and does his best to answer them. I think it just wears him out sometimes and he gets a bit wired.

ttown
05-03-04, 01:40 PM
ttown..........in defense of bbobynski, he is a GM powertrain engineer and helps out alot on this forum. He gets a lot of really rediculously simple questions here and does his best to answer them. I think it just wears him out sometimes and he gets a bit wired.

I am interested to read his response/clarification.
Sometimes I loose my temper, but I think that his response was completely uncalled for.

Opinions were asked for and that is all I offered. I did not say it was the only way to go, just what I would do.

Lawrence
05-03-04, 01:47 PM
Agreed, as I'm sure bbobynski would too.

ShadowLvr400
05-03-04, 02:25 PM
Both of you two know what your doing, relax a bit. Bob, there are shops outside of GM that could do things well. His local shop could be Coates Intl, or Ligenfelter's. You might be surprised by the expertise of some backyard builders anyways.
Ttown, Bob does have the point in that a lot of small town shops wouldn't have the skill and expertise to do work on the Northstar. I know plenty of shops in town that I wouldn't let touch my mower, let alone my car.

As for the person who asked about milling the head during a headgasket replacement, I'd say do it if you know your machine shop is good at what they do. If it's just Joe Blow with a ruler out there doing the work, I'd probably advise against it. The key is, know your shop.

BeelzeBob
05-03-04, 02:59 PM
Sorry to start a flamer there. Really, just kidding. If you read my post and review the frequent "LOL" I tried to lighten it up. Besides, what is "so uncalled for" in my comments. Consider my viewpoint.....

Considering that the plant checks the head deck machining flatness with electronic equipment that can detect variences of one micron I am always doubtful of ANYONE that says that they can do it better. The diamond faced cutter alone that does the head deck probably costs more than the total equipment in many "machine shops"...LOL.

Besides, checking the flatness with a machinist straightedge and a feeler gauge and then talking about the "factory tolerances" being "too loose" are create a funny picture in my mind....when we are specing the thing in microns....and then someone is going to check it with a straightedge and feeler gauge and do it "better"....LOL

BTW....for what is required for the head gasket to seal the surface finish is more important than the absolute flatness. I have never seen a Northstar head not "flat" or "warped" too badly to seal. Even when studies are done regarding flatness the head has to be pretty off to not seal with the production gaskets.

I am fully aware of the capability of the aftermarket shops....we work with them on many projects quit often. Many have good equipment and can do excellent work. It is easier for them to do custom work, obviously, but in terms or tolerance or accuracy....I will put the factory equipment up against any of their stuff anyday.

Outside engine builders and shops are run by people and the machines only do as good ajob as the machines do. I have seen MANY MANY out of spec, mismachined, and ruined parts come back from some of the BEST names in the aftermarket. Not knocking their capability or knowlege....just realizing that they are humans too and can make mistakes....more mistakes than we see from our plants, actually, given that the plants make thousands and thousands of engines for every one that they do.

In our particular group we work with a lot of the aftermarket engine builders and parts suppliers so I have a lot of first hand experience with the work that they do. Most of it is very very good. They occasionally make mistakes....big ones. And their equipment and people cannot hold any closer "tolerances" than the factory can. I see the process capability of the machining centers and equipement that we use and it is based on running thousands of parts. The statistics and tracking that is used proves that the equipment is extremely capable. Outside engine builders do not machine enough parts usually for us to even get a representative sample of their process capability so most of them have no idea how much of a "tolerance" they can hold.

Understand that we often build hundreds of development and test engines during a development program....and those parts are quit often machined outside at one of the larger specialty machine shops ..... so we/I have just a little experience with this sort of thing....just a little.


The other thing to consider is that performance machine shops are looking at one end of the specs for performance. The factory sets the specs considering performance/noise/longevity/reliability/etc.... Just because the factory specs do not fit the pre-conceived notion of an engine builder does not mean that they are "wrong" or that the factory "didn't do it right" or "hold the right tolerances"..... It simply means that the shop wants a differend clearance or spec on that part for performance....ignoring noise/reliability/etc....

Some examples to clearify: piston fits....the factory is "good enough" that we run single size pistons and single size bores and control fits to within about .0005 tolerance on the piston walls once the two parts are mated. Outside shops "fit" each piston to each cylinder bore...and when we go back and check them they are rarely within .001 tolerance. Even when custom fitting each piston to each bore. The difference...???....the factory controls the temperature of the block and the piston when machining and measuring....just changing the temp of the piston can change the "tolerance" .0005 or more.

Talking piston fits again....the factory will set piston clearance at .0005-.001 wall clearance. Tight for long life/quietness/oil control/etc. A shop will "open that up" when "blueprinting" an engine to about .003-.004 to reduce friction and make more power. Neither is "right" or "wrong"....just different criteria when making the decision about what is wanted from the engine.

"Blueprinting" and engine is NOT making it "perfect" the blueprints..i.e...correcting the factory mistakes. Blueprinting in an aftermarket engine shop is changing all the tolerances and clearances as far as possible to the factory limits for performance. Any "blueprinted" engine is not going to be in the middle of the factory tolerances...it will be on the absolute limit of the tolerances in the desireable direction for performance...unfortunately what is forgotten is that this is not necessarily the most desireable direction for quietness/durability/etc.

Building racing engine is relatively easy. Cost is no object. They just have to do one thing (make power) for a very short period of time (4 seconds in a top fueler...LOL). Production engines are machined adn built to a completely different criteria. A good racing engine builder does not necessarily build a good passenger car engine by the thousands.


So.....if I didn't piss you off and you are still reading. ... LOL... I appreciate the skill and knowlege of the various engine builders out there. They make some excellent racing engines and do really good work on average. I just don't think that they have any greater capability to machine parts accurately. Neither their equipment nor skill nor knowlege is better than that of the factory engineers and equipment. That is all that my comments reflected.



As far as me staying on the porch....NOT A CHANCE.

Lawrence
05-03-04, 03:11 PM
I think I see whats happened here. I think ??? ttown was referring to the .002 service limit on a used warped part, rather than new production specs.

bbobynski...is the machineist straight edge the best method for determining straightness on a used part in the field? If there is another way I would like to know, if only to see that my machine shop uses it.

Lawrence
05-03-04, 03:12 PM
As far as me staying on the porch....NOT A CHANCE.

:)

Lawrence
05-03-04, 03:29 PM
Is it necessary to always machine the head when replacing the head gasket?

jwaynes, in case your answer got lost in all the comotion, in the case of the Northstar your answer is;



It is not necessary to remachine the head deck surface when replacing a head gasket. It would be very rare to find a "warped" head or anything...so rare as to not even worry about that. The valve seats and such are usually fine at well over 100K so I would not even worry about those either. Just replace the head gasket and go. Use the OEM gaskets.

ttown
05-03-04, 03:30 PM
:worship: In the war of words and first hand knowledge, I have been defeated.

Yet I would like to say that my stand on "used" parts remains the same.

It is quite obvious you have a vast knowledge of new car industry standards, which if the need ever arises I hope you may be helpful.

As far as staying on the porch, you are welcome in my yard any day.

BeelzeBob
05-03-04, 04:10 PM
No win or defeat...just conversation and understanding. I think that we both understand the same thing...just from different view points.


Checking flatness with a straightedge and feeler gauge is fine. That is the first thing that anyone grabs when there is a question of flatness. The million dollar coordinate measuring machines come later ..... LOL.

ttown
05-03-04, 04:27 PM
No win or defeat...just conversation and understanding. I think that we both understand the same thing...just from different view points.


Checking flatness with a straightedge and feeler gauge is fine. That is the first thing that anyone grabs when there is a question of flatness. The million dollar coordinate measuring machines come later ..... LOL.
I agree.;)

dloch
05-03-04, 06:00 PM
Wow... this was fun..

jwaynes
05-04-04, 02:53 AM
:hide: Thanks for the response, guys. I am now comfortable with just replacing the head gaskets.

ILL LD
05-04-04, 04:10 AM
Experience, Knowledge, discussion, consideration. You guys are great. We could use minds like yours in Washington.