Hello!

Quick dumb general question (actualyl not even pertaining to my 123, but with the OD board closed, this is probably the best place to ask).

I know that RTV (at least the stuff I have) is supposed to fully cure in 24 hours. Now, I know that it'll dry at a somewhat earlier time than that.

So, my question is...what is the minimum safe time to put pressure on RTV?

I'm trying to seal something up with externally-applied RTV (dumb, I know, but I don't really have a choice ) and am getting tired of waiting a full day between applying another layer of RTV and pressure-testing the cooling system...and have practically wasted over a week and a half on this process already.

Thanks!

Tim, you already know the deal with this.

It may be dry to the touch in six hours or so. But, you are trying to make it do something that it was not really designed for: hold pressure on its own. It may not work if you wait the full 24 hours. Trying to shorten this time will only lead to a "do-over" IMHO.

Tell us what you are trying to seal.

Okay, this is on the truck.

I replaced the timing gear cover because the probe mount on the original broke off. The water pump goes in top of the timing gear cover (the four center bolts actually bolt to the cover itself; the other bolts holding the water pump on go through the timing gear cover to the engine block, and actually also help hold the timing gear cover on). Bad design on an otherwise good engine IMHO.

So, I put the water pump on the timing gear cover, and found a water leak coming from the bottom of the water pump. Assuming I had either not installed the gasket properly or it had slipped, I pulled the water pump again and put on another gasket, this time putting a 1/8" bead of RTV on both sides of the gasket. Put the water pump back on, and the leak went away...until I applied pressure on the system (wiht a cooling system pressure tester I'm loaning form Autozone). At about 5 psi, I started getting a slow drip.

Given that this has happened to other people, I came to the conclusion at this point that the timing gear cover's warped slightly, and that re-replacing the water pump gasket would be a waste of time and $$. Finding another timing gear cover for this engine in decent shape is an iffy proposition at best, so I decided that the only feasible option would be to try to get at the leak externally (and no, I don't like this idea any more than I imagine you would). The first couple of coats missed spots where water wound up coming out (this time, it at least waited 'till I got the system to 10 psi). A third coat actually got the leak, and even held pressure up to 15 psi (two psi more than the system's designed to hold)...but the part that covered it up was thin enough that it started bubbling up. At that point, I removed what I had put on and started anew, and there are 4 or 5 coats of "new" RTV on there now, the last of which I put on about a half hour ago (the coat before it had been in place 2 days, and I actually didn't test it before putting the last coat on, although the system is full and not leaking).

Brian, you're probably right *sigh*...I'm just getting a bit impatient as this is the only thing stopping me from putting the crank pulley on and getting the accessories installed and actually seeing if the truck will run after everything I've done to her. I know that patience is a virtue, and especially with all I have done, I should be patient and wanting this to be done right...but, I'm sure you understand that human emotion has to come into play, especially after 3 months (and a month and a half since the engine should have been finished)...

I probably shouldn't even have asked this question, but I was hoping that maybe there was something I didn't know and maybe I could cut the "lag" time somewhat, particularly because, with the way my schedule has been, that "24 hour period" has usually turned into 2 days at a minimum, and more like 2 weeks...and with everyone in school now, I need a third vehicle PDQ...

Tim, I feel your pain. But, every time that I have rushed a job, to try to get done sooner, I have regretted it.

The most recent time was with one of the large turbines that I balance every so often. We loaded the arbor into the turbine and started to tighten the (14) 1"-8 socket head cap screws. The first pass is only 120 in.-lbs. But, after tightening the set, we checked the first one and found it to be loose. Well, instead of doing the right thing and finding the problem, this genius decides to save time and retighten the first bolt and make sure all the rest are tightened to spec and then start the sequence over at 700 in.-lbs.

Well, the fact that the #1 screw was loose told me that the arbor was not seated properly. This means that it had to come back out and the issue resolved before going on. I just went on.

The result was a bad seat. The arbor moved .0015 inches from the original position (.0001 is max) and we lost 8 hours of work.

I always say: never again.

But, I still do it. I'm advising you to wait even though it is painful.

Tim, I know you know Brian is correct...
That 'warpage' would probably not show up as a leak if you will use cork gaskets.... coat them the day before with RTV as thin as you can... then put a thin coal on them as you install them... and then wait as long as you can to put pressure on them.... when I started doing this.... after having to take a bunch of stuff back off when my Dodge 318 water pump leaked..... I have had no leaks on any gaskets for 25 years....
When you do try to close a leak from the outside... don't let the RTV be working on its own.... use it to put brass shim stock over the area... this makes it " one" patch....and the amount of pressure it will withstand is multiplied by the strength of the RTV or epoxy times the surface area of the shim stock.

Greg, yes, you and Brian are both correct...and I spent this afternoon cleaning stuff up instead. I'll test the system tomorrow, although with no pressure in the system, it looks to be holding up. I had put water in the system before putting this last coat on (the last coat was an impulse decision after I saw a spot that looked like it might leak with pressure); the entire surface was dry and I didn't put any pressure on it, so I think it's okay...since everything was dry, any RTV that's touching water at the moment is at least 72 hours old...

I hadn't thought about a cork gasket...question there is, who sells them? Both Ford's and Fel-Pro's gaskets are paper...

If this doesn't work, that may be worth trying...heck, maybe I can find one for the timing gear cover as well?

Hardware stores, tool trucks, and even Sears sell thin sheets of cork for the purpose of lining tool box drawers. Works great.

Does high humidity make it cure faster?

Hi warden,
what kinda rtv are ya using? an a sheet of cork tis good idea, used ta make my own gaskets with sheets of cork... at the time all I could afford while still in school. got pretty good at it. I don't know for sure, but looks like the front-end of my 6.9, all they used is the orange hi-temp rtv to seal the covers. I 've used it on my jeep to seal the bango's and water outlet with no problems. take care .

chip

Tim, you know that Greg is right about this. The RTV is not designed to work in the way you need it to work. If it does work for a decent period of time, you will be a very lucky man. If it does not work, the cork idea is an excellent one to take up the error due to the lack of flatness in the face. I think that the combination of RTV and the cork, during assembly, is unbeatable. The only way this will not work is if the mating surfaces are a mile (.015 or more) out of flat. This is unlikely.

Tirebiter, you make a good point, although I was hoping that someone might make pre-cut cork gaskets for these. The gasket design for this water pump is pretty intricate...can't be done, but would probably prove to be a PITA.

Knotman, I imagine that high humidity would actually make it take longer to cure...although I can't say that with authority.

Chip, I started with Blue RTV, and switched to Red high-temp RTV when the blue stuff ran out. I should have started with the red; makes it easier to see spots that I missed. I actually didn't post this on TDS 'cause I figure I'm bugging everyone and this is a general question, and I'm also 1 post away from the 6K mark and am wanting to save that post for when I get the truck lit off. If I get too close, I may have to start deleting old posts in the Bilge or something

Brian, I understand...as said, I really dislike doing it this way in the first place, and would be quick to join in on chewing someone else out for doing this. The main goal is to see if I can actually get the engine to light off, so even if this holds for only a month, I'm okay with that. The other side of this is that the leak from the gasket looks to be a baby leak to begin with, and the leak may seal itself as the engine heats up. I know that that's not something I can count on, but it wouldn't be the first time it's happened with a 6.9l...

*fingers crossed* if pressure holds tomorrow morning, I may be able to light off tomorrow...

We'll all be rooting for you................!!

If you will follow our advise you will not need ' crossed fingers'.....
We have already made these mistakes in our pasts...
This is the purpose of a written langauge.... each generation does not have to RE-Invent the WHEEL....

Greg, unless he strips off five days of RTV and starts over, he needs crossed fingers.