Alright. I have been having oil leaking troubles, and have had a lot of blue smoke exiting from my tail pipes. This is a recently rebuilt engine, and I have been going throug it to see what could be causing this. I was thinking it was the rings until earlier this week, when I went to do a compression test on it, every single one of the plugs had oil on them. Well, I didn't get to finish the compression test, and was going to finish it today, but I was wondering if I had a different problem. Now, I am thinking that the oil is being sucked up into the runners of my intake manifold from the lifter valley. This would explain why all the plugs are coated with oil.

When I rebuilt this motor, we took .030" off of the block, and we also took about .008" off of the heads. Would this change the geometry enough as to create a gap at the bottom of the heads and the intake. I have been trying to go through this in my head, and I think, that I need to change the angles of intake to make is sit correctly on the heads. Does anyone know of a site where I can calculate this, or does anyone have the dimensions of a stock 350 block. I can probably sit down and figure out the angle I need, and how much I need to change the manifold.

 

83,

When you "cut 0.030" off the block", where exactly did you cut it? Off the deck surface?

Same question for the heads...

Typically, when changing the block deck and milling the heads, the intake has to be cut to match, or gaps can be created. The 0.008" off the heads isn't that big a concern, but 0.030 off the deck in conjunction with it means you have moved the heads considerably.

 

If in fact you have decked the block and the heads a combined total of .038", then you have moved the intake flange of the heads downward and inward roughly .7 (the actual number would be the square root of 2) of that distance, each.

You need to take your intake to the machine shop, and have them mill about .027" off of each flange where it bolts to the head, and the same amount or slightly more (maybe as much as .035") off of the bottom of it where it meets the block at the front and rear. Personally I prefer to have that surface of the heads milled, because if the gap between the intake and block shrinks, it doesn't hurt anything; and if you mill the heads, then you can use any intake at all, whereas if you mill the intake, you now have a custom intake that won't fit on top of unmilled heads & blocks. Likewise, if I have a block decked, I like to get them to lop the appropriate amount off of the intake mating surface of it, so that it doesn't cause intake troubles. Maybe your machinist isn't quite so detail-oriented?

I doubt that it would cause an oil leak, but I suppose it might. Usually what happens is, the bolt holes won't line up, because the intake is too wide to jam far enough down in between the heads to get both sides to line up at the same time. Did you have a hassle getting the intake to bolt up?

Actually I'd be more inclined to think that you have no valve seals. While you're dealing with the already-identified problem, since you'll have at least one valve cover off anyway, take off a spring and see if you have any umbrella or "positive" seals. If you don't, put some Teflon positive ones on if your guides are already milled to .500" or .530" outer diameter (the 2 sizes of those that they make) or put some umbrellas on if the guides are uncircumsized.

 

Okay, I've thought about this several times, thinking I should be able to do this math; spent the last hour diagraming, folding pieces of paper, calculating, etc. I think I've figured it out.

It's actually the sine of 45 degrees, .707 roughly, or 1/2 the square root of 2. For the intake port faces, multiply the amount shaved from the decks by .707 (the .027" figure you gave) for the amount to take off each face. For the amount you move the manifold down, divide the amount shaved by .707, or about .054" in this case. Remember the distributor has to stay in the same place, so the gasket should be shimmed by that much. (Sure hope I figured that right - somebody's GOT to have a "Hot Rodders Book of Engine Formulas" laying around that they can look in and verify this stuff.)

Where you take it off - up to the individual. No matter which you do, you're going to have a part (intake manifold) or parts (heads) that is/are now unique to that block.

I've never significantly decked an engine, but I have had a manifold suck oil in from the valley. I got a manifold that looked like it should have been scrapped - instead it was boxed. It sucked oil into the cylinders to the tune of about a 1/2 quart in 50 miles. I only figured out what was wrong after I removed the manifold, cleaned off all the gasket material, and set it back on the engine. It wasn't much of a gap.

 

Thanks guys for all of your help, especially five7kid, you have been really helpful with the last few posts I've had. I was trying to figure it out yesterday in class, but couldn't quite figure it out.

Vader, I did take the .030" off of the deck surface, and the .008" off of the head surface.

RB83L69, actually, I work at the machine shop where we did the work on the engine. I know the heads are good, cause I recently assembled them myslef. New guides, valves, seats, and seals. Can't see an oil problem happening from there, but I guess you never know. The intake was a real pain to bolt up, but this was mainly because the heads are the gen I vortec style, and the center bolt holes are at a different angle then the rest.

 

Just opened the box of my summit order that I recieved yesterday, and was flipping through the catalog that came with. Page 145 of the March-April catalog, the How 2 page has a chart showing this same topic. Just thought that was kinda funny. Thanks again though.

 

Hate to rain on your parade but those aren't vortec heads. Vortecs only use 4 intake bolts per head and all 4 are angled. The heads you have are 87 and up non vortec heads with the two center bolts angled. I am currently runnin these heads on my car and they work well but there not as good as the vortec.

 

I've been 1500 miles away from home since Monday, but I just happen to have that catalog with me.

Not so funny, actually. Their numbers are quite a bit bigger than mine, and the ratios are different. Now that I think about it, I made an assumption that probably isn't true (never thought about it before, actually) - that is, that the intake port mounting face is perpendicular to the deck. I'll take that plate of crow now.

Even they say to consult the machinist rather than using their numbers (why 76cc SBC heads wouldn't need the bottomer ends cut is beyond me). Hummmm....