My new AFR-head-LT4-intake combo has resulted in relatively huge gaps at the ends of the lifter valley, has anyone else seen this? Did a thick wad of RTV seal it up OK?

http://para.noid.org/~lj/AFRgap.jpg

The block was not decked recently, and this pic shows that the old GM casting-LT1-intake combo had a normal sized gap

http://para.noid.org/~lj/Fuel/images/Didn'tFit3.jpg

 

I had that happe a lot before..What id do is take a punch and punch a series of holes in the block face and intake face..Use good silicone and you will be fine..GM says to do that to cure the LT1 intake leaks..

Unless you have a blowby problem you should be fine..If you had the heads milled during the buildup then they should had done the intake face as well..That could be the problem..Every time ive had heads milled i had to bring the intake as well.

 

Thanks for the feedback! The scary thing is that the gap is a solid 0.300" with the gasket in place (but not torqued). http://para.noid.org/~lj/AFRgapmeasured.jpg I checked port alignment with a bent wire - it looks like I can afford to cut the cyl head mating surface a little. Now I need to do some geometry to figure out how much the intake port opening moves relative to the head port opening per .001" of cut.

 

You might try "the right stuff" sealant from the NAPA store, I had a problem with my vacuum pump sucking in the std RTV . After switching to this sealant problem was solved, only problem is its a PIA getting the intake off when needed.

 

yup! It comes from the way the heads ae cut on the intake side. most times if they are cut to a factory degree you are fine(But not always as in your case). if you used the 10*(i think) you get this

http://groups.msn.com/WashingtonFBod...to&PhotoID=538

http://groups.msn.com/WashingtonFBod...to&PhotoID=537


Next you will need to have that intake cut to fit the heads and that will take out alot of the problem I see in your pic

 

If I were going to try to fill a gap that large I'd probably try to adapt a trick I saw Tom Silva use on Ask This Old House, when he was repairing a plaster ceiling.

Squirt out a "half" layer of silicone, lay a strip of non-metalic window screen on top of it, then squirt out another "half" layer of silicone, so that when you put the intake on you get a sandwich with the screen captive inside it. You can trim up the part that shows after it's hardened.

My thinking here is that the screen material would provide some reinforcing in the same manner that the screen material Tom used on the show did with the new plaster, and help prevent the sort of small blowouts that you often get with larger gaps.



Of course, keep in mind that I just pulled this idea out of my *** on the spur of the moment and just because it sounds good in my head doesn't mean that it would work in real life.

In any case, make sure your PCV valve or breather is working well, because no matter what you do, you're still going to have a silicone seal that is taller than it is wide and it would be best if you minimized the pressure.

I suppose that something else you could do would be to fab up a could of pieces of aluminum that could be welded or glued onto the bottom of the manifold in the front & rear and fill most of the gap, leaving only enough room for a normal silicone bead.

That would of course be more work than the sandwich idea, but it would be far more solid and permanent.

 

I second this stuff, It is by far the best RTV i have ever used. It is the ONLY stuff i will ever use. I had some on my block when it went in to get tanked at the machine shop. The block came back clean as the day it was cast, but it didn't take off the Right Stuff that was still on the intake surface.

Having the intake manifold machined is probably the better way though.

Bill

 

i had the same problem. rtv leaked bad so i welded alum spacers to the intake then machined them to fit without gaskets. seemed to cure the problem. i might even have an extra set of the spacers if you are interested.

 

I talked with the engine builder this evening - he said he had a few sets of spacers at the shop, so I'll check 'em out tomorrow. If that doesn't work I'll send you an email. Thanks for the offer!

 

Yes AFR's do that, I think mostly 210's & 220's, I don't think you can machine the intake to match cuz then your ports won't lign up. AFR knows this & they sell the fix, its a 3/16th spacer part number PN 5607, they mention it here:

http://www.airflowresearch.com/support/sbc_install.htm

very bottom there, but thats the part number PN 5607, they'll get you one if you need it

Matt

 

Thanks for the lead. I especially like this line:
"17) PORTING INSTRUCTIONS:
Be aware of water jacket locations between the two center exhaust ports and above the exhaust ports between the port and the spring pad before getting the bright idea to hog out material in these areas."

 

hehe yeah its pretty funny

 

My AFR 190 heads had a similar gap on my non-LT-1 (early style) SBC. I went the "big blob of RTV" route and have no problems to report.

I wonder if AFR makes the heads that way so they can raise the intake port just the tinyest little bit vs. a factory head yet still get the intake ports on a standard intake to line up properly.

The more I looked at my AFR heads the more I noticed the very very subtle ways they had moved stuff around in/on them vs. a stock head.

 

Yes they wanted a straighter shot so hey raised the intake or something, thats what the guy at AFR said.

 

yeah that is what brodix said about my ports

http://groups.msn.com/WashingtonFBod...to&PhotoID=537