what sealant to use on chain housing reinstall?

rrichar · 12-30-2010, 01:54 PM

I intended to fixed the leak in my chain housing this weekend and started to make sure I had what I needed. I have new gaskets for everything from the cam to the housing cover. What I didn't expect was my old DOW 730 to be hard as a rock. After a quick look I didn't find any local. What are some recommended sealants for the appropriate spots? Would Curil-T or Loctite 518 work in any of these spots?

cam flange/thrust washer and gasket
chain housing to engine case
chain housing cover

David · David's Garage

If all the surfaces are clean, flat, and free of scratches no sealant is needed on new gaskets.

rrichar · 12-30-2010, 02:14 PM

David,

That is a pretty big if. I thought when I put it together the parts met all those requirements. However, I have this constant leak that appears to come from the cam flange and related parts. I can't see up between the housing and the cylinders but I have cleaned and waited for it to reappear several times trying to locate the exact cause. I get a constant leak that appears to come from up between the housing and the cylinders/cam housing. So I was hoping a removal and reassembly might help me eliminate the leaks. I was hoping to add a little extra protection this time around.

David · David's Garage

The chain housing covers should seal well without sealant. If I was to put some sealant on the cam flange, I'd probably use Curil-T.

Quicksilver · 12-30-2010, 02:29 PM

Dow 730, Curel-T, and Loctite 518 is kind of an apples, oranges, and kumquat kind of thing.

Dow 730 just plain rocks as a sealant.
Curel-T is a really good non-hardening sealant for o-rings and gaskets.
Loctite 518 is a anaerobic sealant to be used on thin-gap machined surfaces instead of a gasket. It is marketed as a "Gasket eliminator"

As mentioned above pretty much all modern gaskets are designed to be installed dry...
... but if you want 0% leaks you will find that any high end engine builder uses sealants.

For your app Dow 730 and Curel-T are the good choices but the Dow 730 is really the best of the best. It is a little bit pricey and a bit difficult to find but you will happy you took the trouble.
The important detail is to use as little as possible. Anything that squeezes out of the parting line has to go somewhere. We have all pulled apart motors that some monkey has glopped silicone sealant into and fluorosilicone can do the same thing, causing all sorts of trouble.

rrichar · 12-30-2010, 02:34 PM

I ageee with the housing covers: I have never had a leak there. I wasn't that familiar with Curil-T until I started looking into this today. That is one of the products that looks right for that location/application. When I rebuilt the engine it was recommended by a well known Porsche engine rebuilder that I use the DOW 730 and NO gasket on the housing to engine case seal. It seemed to have worked well with no leaks there. However I think I would feel better using a gasket this time. Would you supplement that with Curil-T as well?

rrichar · 12-30-2010, 02:40 PM

Quicksilver,

Your reply came in as I was typing another response to David. Would you use/recommend DOW 730 on the cam flange gasket seal? Sparingly of course; would a thin layer on both sides of the gasket be the only place around the flange?

lindy 911 · lindy 911's Garage

The cam flange gasket can move VERY easily during the assembly process. Mine would not seal without a sealant here. I used Permatex aviation gasket maker on both sides which drys semi-hard but still flexible. The chain boxes to the case need 574 as do the covers. Thin, even and on both sides, 574 will seal them for a long time. Unless you need to remove the chain box covers for chain adjustment (solid adjusters) seal 'um up tight.

Curel-T is no good for the joint between the box and case, the box and the cover or the flange gasket. I have not found a good use for it anywhere honestly.

Lindy