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Max Welton
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Joined: May 19, 2003
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Location: Black Forest, CO
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modok
Samba Member
Joined: October 30, 2009
Posts: 26790
Location: Colorado Springs
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 Posted: Thu Aug 16, 2012 10:13 pm Post subject: |
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| yes that is what I assume. As you can see there are four places to put a feeler gauge, in the middle or on the ends |
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Max Welton
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Joined: May 19, 2003
Posts: 10697
Location: Black Forest, CO
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| Posted: Thu Aug 16, 2012 10:25 pm Post subject: |
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Right. If the straight edge is truly straight, and the cylinder tops are level and square, it will be in contact at all for points. No .001" spaces.
If there's any difference at all, the head can't sit flat on both cylinders. One of two things must happen. Either the head must deform under the clamping pressure (at operating temps) to conform to the cylinder tops or there will be a leak between the head and cylinder. Any leak there results in erosion of the softer metal of the head.
And if the head moves around a bit, it can loosen up. Ever wonder why some people need to re-torque the heads every 10k or so? This is one of the reasons.
Max
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1967 Type-3 Fastback
Under the Knife https://shoptalkforums.com/viewtopic.php?f=24&t=151582
Home Stretch https://www.thesamba.com/vw/forum/viewtopic.php?t=767836 |
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damicotile
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Joined: September 16, 2004
Posts: 1069
Location: WOODLAND CA.
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| Posted: Thu Aug 16, 2012 10:59 pm Post subject: |
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| Max Welton wrote: |
I think this is what he's talking about. The only parts that effect this are the case half and the two cylinders.
Max |
You are both right. In your picture you show laying a straight edge across the tops of the same side I am talking about.
The #1 barrel is about level in the middle next to #2 and less than .001 on the end of barrel #1 closest to the flywheel side.
I am quite sure it is the cheap ass barrel shims which are available here in Sacramento plus the bad job Brothers Machine did on this case as both registers were of different decks by .005.
Now, I know it isn't ideal and Max you're right about being perfectly flat is where it is at but being that the outer side of the head being just under .001 but the middle closest to #2 barrel being like almost level, wouldn't the head deform ever so slight as to seal but not be a problem at operating temp since the torque on the head would increase to about 60 lbs or so?
Am I just hoping everything will work out?
I do plan on checking the head torque after the first run the day after when all is cold.
I have been stressing on this for 3 days now. Some might call this anal and that I am splitting hairs.
I understand perfect is perfect but I am sure many an engine has been built with some discrepancy and have turned out fine, no?
I guess what I am asking is that if it isn't absolutely dead flat will it fail?
_________________
'73 SB
82x94
W-120 w/ CB light weight lifters
Silicon bronze sleeves
Scat 1.25:1
CB H-Beams
Straight cuts
42x37 Steve Tims
44 IDF's
9.2:1
A-1 Sidewinder coated
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Boolean
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Joined: January 19, 2012
Posts: 1712
Location: Stockholm
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| Posted: Fri Aug 17, 2012 12:05 am Post subject: |
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| Probably not. People get away with all sorts of stuff - but I wouldn't leave something I knew was wrong without fixing it. |
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modok
Samba Member
Joined: October 30, 2009
Posts: 26790
Location: Colorado Springs
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| Posted: Fri Aug 17, 2012 1:43 am Post subject: |
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The thing about perfect is it is only an imaginary idea. Even a straghtedge is probably not perfectly flat. I doubt max'd ruler is flat within .001" 
I can take a ruler like that and compare with an actual straghtedge, hmmm, it would be lucky to be within .001, then take that straghtedge and see how flat it is on my optical table........and actually that thing is not perfectly flat either.......if I really investigate it. Gotta draw the line somewhere.
If it within the specs I listed it will work, I have much experience in this area
Used vw heads are often off by as much as .005, and they still seal, metal is flexible, all things are flexible to some degree
the closer you look the more things like this you will find, like I was saying about the bearings throwing it off, it's there if you look close enough |
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miniman82
Samba Swamp Donkey
Joined: March 22, 2005
Posts: 9515
Location: Southern Maryland
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| Posted: Fri Aug 17, 2012 8:58 am Post subject: |
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That's why there are tolerances, perfect is a pipe dream and it doesn't matter that much in the end. In my experience, close is good enough.
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Build thread: http://www.thesamba.com/vw/forum/viewtopic.php?t=212747
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| satterley_sr wrote: |
I just wanted to bitch but I'm getting no sympathy. |
Welcome to the Samba. |
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mxracer
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Joined: April 09, 2011
Posts: 568
Location: NC
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| Posted: Fri Aug 17, 2012 9:31 am Post subject: |
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| Max Welton wrote: |
I think this is what he's talking about. The only parts that effect this are the case half and the two cylinders.
Max |
You could literally have a piece of shop rag fuzz between the cyl and case in that pic and be .001 off and when torqued would be .0005 or .000 I'm sure.
Point is that measuring across like that without torquing the cylinders to spec is only getting an idea of things. If we are talking about getting under .001 tolerance... a deck tool, things torqued to spec, and a depth gauge are what's needed, or better yet measuring the cylinder height with a height gauge and the case deck surface using a surface plate and depth mic. |
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Max Welton
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Joined: May 19, 2003
Posts: 10697
Location: Black Forest, CO
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| Posted: Fri Aug 17, 2012 11:28 am Post subject: |
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| damicotile wrote: |
| I guess what I am asking is that if it isn't absolutely dead flat will it fail? |
There's only one way to find out for sure.
Just be aware that the effects may not show up for a while. If you pull the head at 10k miles and there is no errosion, you're probably OK. If the head gets loose before that, there will be some doubt.
Me? I take as much doubt out of the equation up front as I can.
There are plenty of things that show up later in the engine's service life. When a problem shows up after 10-20 thousand miles, it's really hard to trace it back to one root cause.
Maybe I'm just being a little AR. If I did this for a living, that would be a problem. But my only customer is me. And I'm a tough guy to build an engine for.
Max
_________________
1967 Type-3 Fastback
Under the Knife https://shoptalkforums.com/viewtopic.php?f=24&t=151582
Home Stretch https://www.thesamba.com/vw/forum/viewtopic.php?t=767836 |
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damicotile
Samba Member
Joined: September 16, 2004
Posts: 1069
Location: WOODLAND CA.
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| Posted: Fri Aug 17, 2012 9:06 pm Post subject: |
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| Max Welton wrote: |
| damicotile wrote: |
| I guess what I am asking is that if it isn't absolutely dead flat will it fail? |
Maybe I'm just being a little AR. If I did this for a living, that would be a problem. But my only customer is me. And I'm a tough guy to build an engine for.
Max |
I appreciate it Max.
I'm a bit AR too. That is why I was asking all these questions.
I have all the right measuring tools, Mic's, calipers, depth gauges, bore gauges, all Mitutoyo, Starrett.
I figure crush into the equation and distortion during torque down too.
All my other engines were always right on but this time around it wasn't that right on so I had to ask.
Thank Glenn for your input. I value your expertise as a machinist.
I didn't want to cause a rift between you to, sorry if I did.
It's all bolted together. I left the long block out in the sun in the 106 degree heat all day to simulate a heat cycle and then re torqued the heads when it cooled the next morning. Not sure if it did any good but thought it couldn't hurt.
Anyway, thanx all for the input everyone.
Not to get it back on the road for Bugorama this Sept 1st.
_________________
'73 SB
82x94
W-120 w/ CB light weight lifters
Silicon bronze sleeves
Scat 1.25:1
CB H-Beams
Straight cuts
42x37 Steve Tims
44 IDF's
9.2:1
A-1 Sidewinder coated
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