LT1 Intake still leaking

[lgoodson@pacbell.net]

I replaced the intake gasket about a 150 miles ago and it has started leaking again. I used the strongest RTV I could find and was very careful not the disturb the RTV when installing the intake, I carefully torqued the bolts to factory spec and pattern but still I get a leak. I read in a datsun racing engine building book that to seal oil pans, you should use "weather strip adhesive". Maybe that would work.

 

Anybody have any good ideas. I undestand that LT1's have a sealing problem, GM didn't design a rear seal, just use RTV so they leak.

 

Thanks, Larry

[deja]

I used Felco intake gaskets. I ran RTV along the front and rear block running it a little up onto the heads covering the end of the gaskets to make sure the seam between the head and block was sealed. Use a bead 1/8" to 3/16" high, you don't want any RTV to get indise the rngine. I used no sealer or adhesive on the gaskets themselves. I used Mike Mavrigian's "How to rebuild a LT1/LT4" along with the GM factory manual. Both said no sealant on the gaskets, only use RTV on the block. Did you use thread sealer on the bolts? They run into the oil galleries and need to be sealed. Torque the bolts in the proper sequence first pass to 71 in lbs and a final pass to 35 ft lbs. Make sure all mating surfaces are clean and dry before you put the gasket or RTV on. We used a lot of asitone to clean surfaces.

[lgoodson@pacbell.net]

Did all of that except the thread sealer but it looks like th oil is coming out along the back of the block. I cleaned it all off and I'll see what it looks like tomorrow.

thanks, Larry

[lgoodson@pacbell.net]

Well it's tomorrow and after driving 20 miles I rechecked and the leak is coming out the back on the right side of center of the engine, I looks like it is leaking from between the RTV and the intake manifold. Jody, on this site, says to install the manifold and let it set for an hour before tightening the bolts. Has anyone else done it this way? And also, don't trim the excess RTV off which I did trying to be neat. I did it days later though.

[deja]

I did not do that but Jody is the LT1 Guru so I would listen to anything he says. It certainly couldn't hurt. I did not wipe off any of the RTV. I've got 2600 miles on mine and I look at it all the time because the old engine leaked there and I know LT1's are know for that leak. So far all is well.

 

 

Well it's tomorrow and after driving 20 miles I rechecked and the leak is coming out the back on the right side of center of the engine, I looks like it is leaking from between the RTV and the intake manifold. Jody, on this site, says to install the manifold and let it set for an hour before tightening the bolts. Has anyone else done it this way? And also, don't trim the excess RTV off which I did trying to be neat. I did it days later though.

[lgoodson@pacbell.net]

Yes, he has been a lot of help so I listen and follow his directions closely.

He has not mentioned the bolt sealant though. Couldn't hurt.

 

He also has told me that difficulty shifting this T-56 into reverse could be a sign of a bad clutch. Does any one know what else could cause this problem. I have to slam the shift lever all the way to the right to get it to go in. I have a B&M Ripper shifter that I bought from Jody also. He said that he never had this problem when it was in his car so what else could it be. If the shift lever was not inserted into the trany correctly, I wouldn't think that I could shift at all but the other 6 gears shift fine.

[gvincent]

When looking at the rear of both of my LT1 engines from the factory there is a thick bead of exposed factory sealant about 5/16 in diameter along the back of the intake. I was thinking how sloppy and was going to trim this blob of excess sealant off to clean up the look before I painted but a mechanic friend of mine told me not to unless I wanted leaks. After reading about the LT1's on the other forums it is a common leak and generous beads of sealant are used at the rear when replacing the intake on these motors. I think Shobox has a write up on his site.

Greg

[lgoodson@pacbell.net]

Thanks Greg

[lgoodson@pacbell.net]

Greg. I now have replaced the intake gasket 2 times and I just drove the car for maybe 10 miles and back in the garage I poped the hood and guess what. Oil leak. A big oil leak.Comming from the rear of the intake. Now I did what you and everyone said to do. I cleaned the surfaces real good with brake cleaner. I applied a generous amount of RTV on the rear and front of the block running it up the sides sealing the intake gaskets. I placed the intake on the heads and finger tightened the bolts and let it sit for an hour exactly. I then torqued the bolts using the GM torque pattern and to the Shop manuals specs. Still I have a leak.

So I wonder if the Fel Pro intake gaskets are too thick and therefore holding the intake off the rear of the block, creating a gap. I don't know what it could be.

What does any one think about this. I think I will take a look at GM's gaskets and compare.

[rx8ss]

This is my take on the LT1 intake install. I have built many lt1's and have not had any problems. You have to clean all rtv off of the intake and engine. I use a air die grinder with a 3m pad (brown) to clean the complete intake and engine mating sufaces. Then once all material is cleaned, wipe off with carb cleaner to remove the oily residue that is left over. Do not take any metal off by pushing hard to clean, as this will cause problems with sealing. I use black rtv. First place a dab of rtv in the corners where the gasket meets with the head/eng on all four corners. Place gasket into the rtv. Now run a 1/4" bead on the front and rear block surfaces. Let is set for a few minutes. Now take the intake and hold above the block/heads and set it directly down on the engine not sliding it to the front or rear, this is what causes most leaks. Insert all the bolts and tighten in a circlular pattern starting from the center bolts in four steps to the recomended touque. Now let it set for 24hrs and no less. This will allow the rtv to set up fully. As a side note I have found that excessive crank case pressure (blow by) can cause leaks as well as a leaky oil pressure sending unit or added oil pressure lines. In one case The heads had been milled so much that the intake no longer set sqaure in the valley.

 

This how I do it, does not make right or wrong.

Good luck and LT1's rule

[dts300z]

Also, I have seen the above happen as well...very sound advice.

 

Good luck,

Dan

Edited February 24, 2010 by dts300z

[lgoodson@pacbell.net]

I do believe that when I last installed the intake that I moved it slightly to line up the bolts, I tried not to do that but I did. As far a pressure in the crank case. I have 2 seperate breathers on one valve cover. One at the PVC valve location and a breather oil cap. There should not be any crank case presure.

As far as cleaning goes. I know the importance of doing that. There is no sealant used on the heads and I made sure that the front and rear surfaces were clean and

de-oiled with break cleaner. Going to try again this week end but I just wonder if the intake sits all the way down on the block at the rear. It seems like the Fell Pro gaskets might not let the intake sit all the way so there would not be a good seal.

[80LS1T]

And I thought I was the only one with this problem! I did my intake 2 times before I finally got mine to seal up in the rear. I was at a local speed shop shooting the **** with the owner and I asked him if he had issues sealing them up and he said "nope not since I started using "Permatex Right Stuff sealant" He swears by this stuff. I didnt do anything special when installing it. Just layed a nice THICK bead on the block and a little under the intake gaskets and a little on top of them(where they meet the block) and torqued it down properly. My leak is 100% gone finally!

 

Permatex # 25229

 

 

I got it at fleet farm. It comes in a areosal can with a tip to direct the sealant like a caulk gun.

[lgoodson@pacbell.net]

Tkanks for that tip on the permatex. I will give it a try. In a Datsun competition engine rebuilding book that I bought at MSA, the autor sayss to use Weather strip adhesive to seal up oil pans so I was goin to give that a try I think but the "Right Stuff" may be ta better way to go. Thanks. Can't drive the car with this oil leaking out. Don't want the mess.

[PaulR]

I thought I had an oil leak at the back of my intake manifold that turned out to be a leak at the rear of one of the valve covers. Might want to check that, if you haven't already.

 

Paul

[piston]

rightstuff from permatex is awesome. clean all the oil, wipe dry, run a nice 1/4 bead on the block side and let sit for a minute or 2. put manifold on and slightly tighten it only until sealant squish out the sides nicely and redo the bolts tighter about 20 mins later. worked for my old lt1. never had a problem.

Edited February 26, 2010 by piston

[zgeezer]

Yes, he has been a lot of help so I listen and follow his directions closely.

He has not mentioned the bolt sealant though. Couldn't hurt.

 

He also has told me that difficulty shifting this T-56 into reverse could be a sign of a bad clutch. Does any one know what else could cause this problem. I have to slam the shift lever all the way to the right to get it to go in. I have a B&M Ripper shifter that I bought from Jody also. He said that he never had this problem when it was in his car so what else could it be. If the shift lever was not inserted into the trany correctly, I wouldn't think that I could shift at all but the other 6 gears shift fine.

 

If you are using a hydraulic clutch, the problem could be in master cylinder leak down. Pump the clutch: if the transmission then moves easily into gear, the problem is that the clutch is not disengaging completely.

 

This is a common problem for high mileage Cherokees.

 

g

[lgoodson@pacbell.net]

Just changed the valve covers and gasket. That's not the problem.

I pulled the intake today and saw a spot where my finger had disturbed the RTV when I last installed the intake.There is not much to grab hold of at the back of the intake so that's how that happened.

 

Check this out though. I sat the intake back into place using to old gaskets. I thought they would be compressed. I then checked to see if I could slide a buisness card under the intake, just to see if it was metal to metal. What I found was that there was a big space between the manifold and the block. I took a Autometer decal with the backing paper still on it and folded in half. I was able to slide the decal under the intake and it was still loose. This, to me, seems to be a problem. Maybe that is why the LT1's have a rear leak problem. What do you all think?? Could the stock gaskets be thinner?

 

I used the bolt sealant last time. I'm not sure if it is needed. That's not where the leaking is.

 

The T-56 reverse shifting problem turned out to be a bad ECM. Wasn't sending the lock out circut to ground. Put another computer in and the car shifts easliy ito reverse now finally.

 

I have the "right stuff" in hand and will give it a try tomorrow. I think I will bolt on something to the rear of the intake to hold onto.

[lgoodson@pacbell.net]

Just changed the valve covers and gasket. That's not the problem.

I pulled the intake today and saw a spot where my finger had disturbed the RTV when I last installed the intake.There is not much to grab hold of at the back of the intake so that's how that happened.

 

Check this out though. I sat the intake back into place using to old gaskets. I thought they would be compressed. I then checked to see if I could slide a buisness card under the intake, just to see if it was metal to metal. What I found was that there was a big space between the manifold and the block. I took a Autometer decal with the backing paper still on it and folded in half. I was able to slide the decal under the intake and it was still loose. This, to me, seems to be a problem. Maybe that is why the LT1's have a rear leak problem. What do you all think?? Could the stock gaskets be thinner?

 

I used the bolt sealant last time. I'm not sure if it is needed. That's not where the leaking is.

 

The T-56 reverse shifting problem turned out to be a bad ECM. Wasn't sending the lock out circut to ground. Put another computer in and the car shifts easliy ito reverse now finally.

 

I have the "right stuff" in hand and will give it a try tomorrow. I think I will bolt on something to the rear of the intake to hold onto.

 

Well here is the next day. Installed the intake using the "Right Stuff". Took the car out and put 20 miles on it, some at hight speed and I have "NO LEAKS" The stuff seems to have worked good. Hope it lasts.

 

Now it's on to changing the Dash. I have a 72 dash that is nearly perfect so I will try to get in. Need to repair th e glove box first though. Ther is a 2" hole in the corner of it that someone cut for who knows what reason.If I can't repair it, I will replace it.

Edited March 1, 2010 by lgoodson@pacbell.net