Generation IV Internal Engine - Oil pan alignment - *HOW CRITICAL* is it???

OK guys, I've run into something that has me a bit nervous, & could use a bit of help real quick... :rolleyes:

I'm bolting my oil pan back on, while trying to follow the instructions below (taken from a GMHTP article (http://www.gmhightechperformance.com/tech/0609htp_stroker_build/photo_51.html) that I found online)...

http://images.gmhightechperformance.com/tech/0609htp_51_z+stroker_engine_build+straight_edge.jp g

After tightening all of the oil pan bolts, check your work with a straight edge; the J 41480 works well as it's steel and super-flat by design. The bellhousing-mounting surfaces at the rear of the engine block oil pan need to be within--get this--a quarter of a millimeter! Any extension of the pan surface past the block is unacceptable: that is, the pan can sit back from the block as much as 0.25mm, but can't protrude from the block at all.

Now what I've done is to place a thin layer of black RTV around the sealing surface (between the gasket & the block), let it tack up for a few minutes & then set the (new Fel-Pro) oil pan gasket onto the block. Then I've carefully aligned the pan, set it gently down onto the gasket & threaded all of the bolts in with my fingers.

Once the bolts were all in finger-tight, I tried to push the pan toward the front of the block as much as it would go. When it didn't really appear to go flush with the back of the block, I gave it a few "love taps" with a rubber mallet - no luck. As it stands right now, both the gasket AND the rear of the oil pan are extending "behind" the rear face of the block by approx. a quarter of an inch (which is a HUGE amount if the article above is to be believed).

I'm tempted to say "screw it" & just push on ahead, except that the pan has a warning stating 'Oil pan alignment & torque are critical' cast into the bottom surface. I don't know if this is because I'm trying to use an F-body pan on a truck engine block, or what but I'm just not comfortable with barging on ahead until I get some more information. (For what it's worth, both the pan & the gasket extend past the block & both have the same contour/shape, even though the pan is from an F-body & the gasket is for the L92 engine...) :confused:

Guys, I'd sure appreciate some feedback here...

Thanks.

If the oil pan sticks out too much, you may have clearance problems with the flexplate or flywheel. There really isn't alot of room for clearance there. Maybe the L92 is different; but the LS2 block is the same.

Per the GM F-body service manual:"The alignment of the structural oil pan is critical. The rear bolt hole locations of the oil pan provide mounting points for the transmission housing. To ensure the rigidity of the powertrain and correct transmission alignment, it is important that the rear of the block and the rear of the oil pan are flush or even. The rear of the oil pan must NEVER protrude beyond the engine block and transmission housing plane."


You're only supposed to put the sealant in each corner of the front and rear cover; not the entire surface of the oil pan gasket.

Here's a pic of the oil pan alignment:

Well, HELL. I'm not sure what I can do about it, other than to remove the pan & "oval out" the bolt holes so that it'll mount forward a little bit - but that sounds like a recipe for disaster. :bang:

Being aluminum, I'm sure that I could use my die grinder to trim the rear portion of the pan also, but again - that's "redneck engineering", addressing the symptom rather than fixing the actual problem. :eyes:

I guess I'll leave it alone for a bit, there are other parts of the swap that I can work on, & maybe a solution will present itself. The thing that really gets me is that the (F-body) pan has the same contour as the (Escalade) gasket, they're both extending out past the rear face of the block... It just doesn't make any sense to me... :bang:

Ah well, thanks for the reply, you likely saved me from a mistake.

The back of the oil pan isn't totally machined flat. What you're trying to make flush with the back of the block is the area on the oil pan that bolts to the transmission. You want the mounting surface on the pan to be flush with the mounting surface on the block so that the transmission mounts up square.

There will be a part of the oil pan that extends past the back of the block, (probably only about an 1/8" though) but not the mounting surface. I don't even see how a 1/4" could be possible. I've installed f-body pans on Iron truck blocks and LS2's with no problems.

Im glad I read this

OK, thanks :thumb: for that info Jonathan, that makes me feel a bit better. I'll get a picture up tonight, & maybe someone can tell me how it looks...

OK, here are the pics that I just shot - no editing, no resizing, no nada. I hope that they're good enough, if not I'll take some in the morning w/ my wife's camera (which is, at least theoretically, a better camera...).

DIAL-UP WARNING - All of these thumbnails lead to full-size pictures that are fairly large. If you don't have a broadband connection, you might have to wait a couple of minutes each...

http://www.postimage.org/aVCoE2S.jpg (http://www.postimage.org/image.php?v=aVCoE2S)

http://www.postimage.org/gxJ1OSS.jpg (http://www.postimage.org/image.php?v=gxJ1OSS)

You can see in the picture below, that the rear surfaces are basically flush at the right-hand side (where the bolt is) - but that's the only place on the rear where that is true:
http://www.postimage.org/gxJ1Wmi.jpg (http://www.postimage.org/image.php?v=gxJ1Wmi)

Here are just a couple of "overview" pictures, so that you can judge the overall fit... (Like I said, all of the bolts are threaded in, but only finger-tight...)
http://www.postimage.org/Pq1iIcar.jpg (http://www.postimage.org/image.php?v=Pq1iIcar)

http://www.postimage.org/aVCok5J.jpg (http://www.postimage.org/image.php?v=aVCok5J)

Thanks for any help you can give me guys... :)

I Just put my ls7 stroker together not too long ago and had the same problem. You just need to make sure the pan is aligned with the bellhousing flange. Then put the two long bolts in to hold the pan in the right spot. Then go ahead and put all the smaller bolts in. Its just the extra material on the oil pan gasket around the small bolt holes causing the problem. You can do alot of damage if the pan is not aligned with the bellhousing flange.

OK, thanks again guys.

I think that what I'll do is to bolt up the bellhousing (fairly tight) to the back-side of the engine, then cinch down the oil pan so that it's basically "sitting back" flush against the bellhousing (but not completely tightened down), then remove the bellhousing & inspect/measure. Does that sound reasonable??

I spent some more time looking at it again a couple of days ago, & I suspect that I may have been measuring the wrong location - if I were to measure it at the same location as shown in the magazine photo in the original post, it's really close to being flush. But confirming that will have to wait until next week, when I have the time...

Thanks again. :nod:

im in the same boat... and i think im gonna do the same thing. bolt up the tranny and use it for the oil pan alignment.

has anyone ever done this?

Take plenty of pics LOL, my swap seems to have been neglected in this area and now I have an unidentifiable leak. Make sure all the stuff on the pass. side is cinched up good. I would also appreciate if you could get a pic of that side while you have it out.

You look to be in better shape than me so far though, my pan even has a nice half moon shaped chunk taken out of it...

Great info :nod:

Laso, if it is not flush, or torqued wrong you can get a small crack through the bolt holes. I had two small cracks at the front bolt holes and it would push oil at high rpms.