1973 intake manifold not fitting

[cadman56]

Here's a puzzler for all:
I am rebuilding a 73 472 engine.  It is an unkown entity in that I know it has been rebuilt a couple of times by others but I don't know exactly what was done..

I had to have the block decked to true it to the main bearing bore after having the block align bored.  The heads had been shaved or trued up but I don't know how much.

The intake bolts will not go into the heads unless I remove the front/rear rubber seals.  With no end seals or gasket on, I can get all the intake bolts started but they are at the bottom of the holes in the intake.

How much do I have to mill the intake gasket surfaces & at what angle?  Without having AutoCad I am not able to determine the answers.

Thank you in advance,
Larry

[Bobby B]

Larry,
Hi. The machine shop that did the block/heads should have taken care of this when the machine work was being performed.  It must have fit up until the last time you had any work done, unless you acquired it in boxes. Go back to the shop and they should take care of this for you. They know the exact amount that needs to be shaved to compensate for a tighter valley area. If you know how much was milled off the block deck and the heads, all you need to do is measure the angle of the heads with a protractor and you can arrive at the exact amount that needs to be shaved for correct port/ bolt alignment. I have a chart for this if you need to know how much  material needs to be surfaced to make it fit. As long as the bottom of the manifold is not used as a valley cover, it's that much easier.  Don't attempt this yourself unless you have the correct milling equipment. If it's not accurate, it'll leak. Good Luck!
                                 Bobby

[savemy67]

Hello Larry,

Without knowing how much metal was removed from the block and heads, you may want to consider the issues discussed in the attached link.

http://www.practicalmachinist.com/vb/general/v8-chevy-intake-manifold-milling-166909/

Christopher Winter

[Scot Minesinger]

Understanding your question, the heads have been milled down to increase compression ratio, and so the intake manifold bolt holes in the head are now lower.  Otherwise the intake manifold fits, it is just that the holes in the intake manifold are just a little too high is that right?

It seems if this is so, the only solution is to elongate the holes in the intake manifold so that the bolt holes in the intake manifold will meet the threaded holes in the heads.  This should be accomplished with a rat tail file.  If you mill the intake manifold because the heads have been milled down, the intake manifold will not fit (and be too small), although the bolt holes may align.  If you buy a rat-tail file attachment for a reciprocating saw (saws all), you may make quick work of this problem.

Since the bolts align just barely without seals, guessing just an 1/8" or so of filing the holes should do the trick.  I would use some washers on the intake manifold bolts to hit more surface of the intake manifold, as some is filed away.  If you do this, the manifold can still be used on stock engines.  You could try it on one bolt hole to see if it works.

Good luck on your 472 project, and we hope it becomes a strong running Cadillac!

[Jeff Rosansky CLC #28373]

Put a magnet next to the hole you are filing. You don't want all that metal dust in the engine.
Jeff

[Bobby B]

Understanding your question, the heads have been milled down to increase compression ratio, and so the intake manifold bolt holes in the head are now lower.  Otherwise the intake manifold fits, it is just that the holes in the intake manifold are just a little too high is that right?

It seems if this is so, the only solution is to elongate the holes in the intake manifold so that the bolt holes in the intake manifold will meet the threaded holes in the heads.  This should be accomplished with a rat tail file.  If you mill the intake manifold because the heads have been milled down, the intake manifold will not fit (and be too small), although the bolt holes may align.  If you buy a rat-tail file attachment for a reciprocating saw (saws all), you may make quick work of this problem.

Since the bolts align just barely without seals, guessing just an 1/8" or so of filing the holes should do the trick.  I would use some washers on the intake manifold bolts to hit more surface of the intake manifold, as some is filed away.  If you do this, the manifold can still be used on stock engines.  You could try it on one bolt hole to see if it works.

Good luck on your 472 project, and we hope it becomes a strong running Cadillac!

Scot,
  That really isn't a good idea. Anything over .030 requires machining. You'll be dealing with port mis-match doing it that way, because all you're accomplishing is elongating a hole, not correcting the problem.

Larry,
If you have the heads off the block, the better way is to have the metal removed from the intake side of the head for two reasons. Heads are far easier to set up in the surfacing machine, and all replacement manifolds will fit without having to be resurfaced. The calculations are easy if you know how much metal was removed in the first place.
                                                                                                               Bobby

[76eldo]

If the machine shop is cooperative I'd have them shave about 20 thousandths off of the manifold and try it and maybe have to repeat that once or twice.
Once they remove too much it's too late.

The shaved deck and milled heads drops everything down and changes the fit but hopefully not the angle.

Brian

[Scot Minesinger]

All,

Any filing of the intake manifold would be done with intake removed from the engine and on the work bench.

Understanding is that if the heads have been milled down to increase compression ratio, the width of the heads remains the same, intake manifold female threaded bolt holes are lower.  The intake fits in all respects except that now the intake manifold has bolt holes that are too high.  No machining of any part save the elongation of the bolt holes will solve the problem (and the dowels might be too low too).  The alignment of the intake manifold be determined by the angle of heads and where it stops on block, not location of bolt holes where the clamping force is provided.  I really don't see the problem in filing the holes in the intake manifold. 

The intake manifold valley pan gasket accounts for the holes and you need to check it to be sure it can still work if holes are elongated down slightly.

This trikes as a fairly common problem for 1971 thru 1976 472/500 blocks (and many other V-8 engines of the era) when engine compression ration is desired to be increased by milling down heads.  Maybe a better way to do this is to change the pistons.

Further to that let's hope the machine shop that performed the work is known and the employee who performed the work remains and is knowledgeable about that engine.  Then perhaps this problem can be remedied by a single source.  Sounds unlikely given the post.  Plus this type of project is often constrained by funds and a rat tail file sure is economical.

I'm just assuming heads have been milled down based on post, if not all I wrote is for not.

Again, the way I read the post, machining the manifold will make it too small.  The width of the intake manifold side to side of engine would need to remain the same and only get smaller if the width of the heads was increased, which is near impossible.

[Bobby B]

The angle of the block-to-head relationship never changes , no matter how much you take off of either. There's nothing wrong with cleaning up heads or block decks. I actually prefer doing this with any engine I rebuild, and it also allows you to get the correct RA finish for any type of modern gasket. Not dropping the manifold down to the correct level will cause the intake ports to be mis-matched between the head and manifold. there's no guessing involved here, it's simple math.
                                                               Bobby

[cadman56]

Well, thanks to you Bobby.  It appears I will have to spend some time to measure the angle then compute the amount I have to have machined.  I forgot about having to cut the guide slots out a bit, that would account for some of the problems.
I will keep the thread posted on the outcome.  Thank you for the chart, I will try to figure out how to get it printed.
Larry

[Scot Minesinger]

Boy,

Your way is better.  Looks like the amount to be removed is going to in the 1/8 inch range.  Need to be sure that the front and back sides determine height.

[SixDucks]

Larry,

With all of the decking and milling that has been done to the block and heads, it would certainly be a good idea to check for pushrod length. Your  build may require shorter than stock pushrods. You may also want to check for port alignment and do a gasket match if necessary. It seems likely that a gasket match to align the ports is going to be a requirement.
Hope this helps.

Terry

[Bobby B]

Larry,
Hi. Here's your answer….
                       Bobby

[cadman56]

Terry
I did notice the lifter plungers seemed to be a bit deeper than I expected, thanks, I will look into it after I determine how much the head has been cut.  Hopefully I can find an OAL of one of my uncut heads & compare to the heads in question.  That has to be my first step-ugh.
Bobby
Yep I have to find a protractor like one pictured.
Thanks to all, it may be a couple of weeks before I can get it all figured out but will let you know.
Larry

[Bobby B]

Larry,
Hi.
                            Bobby
http://www.ebay.com/itm/12-Inch-SS-Combination-Tri-Square-Ruler-Level-Protractor-Gauge-metric-english-/110969902801?hash=item19d65256d1:m:mUrYk_5YybXIO3VbSv-GTeA

http://www.ebay.com/itm/12-Combination-Tri-Square-Set-Angle-Finder-Protractor-Level-SAE-Metric-/151457134143?hash=item23438c763f:g:xkkAAOSwY45UUDTc

http://www.all-spec.com/products/GT828.html?gclid=CIaQjvrPwcsCFUw6gQodNzsNAw

[Jeff Rosansky CLC #28373]

My kid is having a little trouble with Geometry class this semester. I'd have to put him on Prozac if I brought that protractor home to him.
Jeff

[Bobby B]

Jeff,
  Better watch out or we'll really fluster him with the "Slide Ruler'….
                                                                                               Bobby

[cadman56]

An update:
I located a local machinist who knew just what to do & he told me just how to measure everything.
Now all I have to do is remove & disassemble the heads (UGH!!!) & take them to him with the measurements I recorded.  A cool way to burn $40 on head gaskets? 
They do not machine the manifold, too complicated & time intensive to set up.  Instead the intake ports get machined.  I have determined the block has been decked .027".  I still question the heads whether they have been cut but am not sure until I get them off again.
Wonder what the compression ratio will be with this much cut off & a + .040 bore?  Silvolite says +10% at +.030 bore so I figure at least 9.5:1, now probably closer to 10:1.  With my dual profile cam & dual exhaust I bet I will eventually have a great running car.
Bet it will launch pretty good with the 3.21:1 differential & 4L60 OD trans?
Will keep you all posted.
BTW, I forgot how to use a slide rule. :-)
Larry

[Scot Minesinger]

If the intake ports get machined to align with head intake ports, then the original fit issue does not seem like it will be resolved.  Intake bolt holes may still not line up, and elongating the holes may be required. 

The 472 stroke on a 1970 engine is 4.06, and compression ratio is about 10 to 1.  That would mean that the remaining travel is about 0.406 inches.  if it was an 8.5 to one compression ratio the clearance might be 4.06/8.5 or 0.478 inches, a 0.072 difference.  With 0.027 removed the 0.478 is reduced to 0.451; 4.06/.451 = 9.0.  These numbers are likely close, so on a 4.3 bore engine with a 4.06 stroke, a 0.027 head reduction results in about 0.5 improvement in compression ratio I'm estimating.  Very nice.

Even stock a 472 with std TH400 in good mechanical condition launches real well.  Your improved drive train should be super nice.  I have that 4L60 on my 2007 Chevy truck with 117k miles all original except fluid.  Did you change over to get a 4th gear and have less rpm at highway speeds.  The std diff is 2.93 on a 1973 Cadillac RWD DeVille, how did you get it to 3.23 is that what came on a Fleetwood?

Exciting stuff.     

[Bobby B]

If the intake ports get machined to align with head intake ports, then the original fit issue does not seem like it will be resolved.  Intake bolt holes may still not line up, and elongating the holes may be required. 



 

Scot,
  That is the correct way to do it as I stated above. The Stars will Align if it's done correctly.  It's a very common problem that's easily resolved. If Larry actually knew what was removed, he would've been done by now. Unfortunately, he has to deal with the "X" factor.  Just curious as to why you still think that the intake bolts will not line up? The idea is to move all components in the same plane…...
                                                Bobby