AM6 Vavle Body cover oil leak. Gasket sealing issues.

[EDC5]

Bit of a long post but here goes.

Recently I've noticed a few drops of oil under the gearbox when parked for a few days, the leak was traced to the valve block cover, specifically the section between the cover and the oil cooler.

With the help of Marc, the appropriate gasket was found and I got hold of some 'Hylomar Universal Blue jointing compound' and set about removing the valve cover:

The oil leak:



After removing the 11 T40 bolts the cover came off with ease, exposing the valve body:



To my surprise, the original cover did not use a gasket, relying only on the orange compound (Silicone based I believe):



After removing the old stuff, I added the Hylomar and gasket and refitted. This is where the problems started. Even with moderate tightening, the gasket tore. So, off with the cover to remove the bust gasket and clean the mating face again.

After that disappointment, I decided to try again using just Hylomar, applying a bead like so and bolting it up:


Unfortunately, as I was refilling the gearbox with oil it started leaking heavily from the join. So, off with the cover again and I repeated the application of hylomar, this time allowing it to dry before bolting it up (as per the instructions, I should have done it first time). The torque wrench I had only went down to 20NM so 5 more than the official book value:


The past two days I've checked the gearbox and all seemed well until this morning where after running my finger along the bottom of the valve body cover, I could see red ATF running down my finger. Needless to say, I was a bit miffed.

I rang the firm that sold me the first gasket and they recommended the Three Bond 1215 (https://www.techsil.co.uk/media/pdf/TDS ... 40-tds.pdf) It seems to be a bit more suitable from reading the datasheet. I've also ordered another gasket and a few more litres of ATF.

Basically, I'm after any experiences people have had with sealing gaskets:

Is the torque value critical?

Are gaskets essential?

What is the best jointing compound to use?

[Gibbo2286]

With pressed steel pans like that you need to be sure there are no distortions of the mating surface, use a straight edge on all the facings and file off or hammer down any high spots, forget the gasket, use the stuff originally used, RTV Silicone, you can buy it from most motor factors, Wynnes do it in a pump container.

[lexi]

Been there with this a lot. Apart from distortion, I found that RTV can work using this method. Do what you have done previous. However, don't squish it together in one go. Gentle finger tight, then leave to cure. Tighten next day. Try that.
3 bond was used on Honda iirc, probably good stuff but you may not need it.

[EDC5]

Thanks for the replies, I should have asked here first!

So I'm better off not using a gasket and just using the RTV silicone then?

I'll do my best with making sure the mating faces are flat, I did notice slight raised areas around the screw holes. When the silicone arrives I'll give it another go and file down the pan to get it as flat as possible.

[xantia_v6]

If using silicone, flatness is not such an issue, as the silicone will conform to the shape better than a gasket.

Degrease the pan, but have a thin film of oil on the transmission mating face when assembled, so that it will come apart again later.

Do up the screws leaving about 1mm extra gap until the silicone has cured.

I always use Loctite 5910 (still available at Halfords?), but others are probably as good.

I don't really trust Hylomar Blue to be oil-tight. Jaguar used it from 1970 on the V12 cam blocks, and they always leaked after a few years. The story was that the Hylomar is slightly soluble in oil and it just washes away.

[EDC5]

Thanks for the insight. I've got hold of some Loctite 5980 which I'm assured is designed for flanges in constant contact with oil.

I'll be repeating the job tomorrow morning. When it comes to the pressed metal cover I'll do my best to flatten it.

I've found a youtube video that explains a method for applying the silicone. If there are any details the video misses I'd be grateful for the headsup



Cheers.

[lexi]

That vid is about it. You are giving it time to form and shape a gasket with some body and thickness.
I used to get two longer set screws of the same thread and dia as your sump pan items. Cut off the heads and finger them on a few threads at 2 adjacent points. It gives you a good guide to slip the pan cover on first time, without smudging your bead of RTV. Screw a few of the real studs in and take your dummy ones out.

[Sloppysod]

I have always thought of "Hylomar Blue" being a non-permanent jointing compound, the last time I used was to put a smear between the rear calipers and the mounting plate to stop dis-similar metal corrosion. I seem to remember another sealant called, "Instant Gasket" either Orange (Temporary joints) or Red (for virtually permanent joints). And yes a little bit of oil on one surface help future dismantling.
EDC When you tighten the cover, slowly tighten opposite bolts, bit by bit, finger tight first then 2 or 3 steps to the full torque (1,5 daNm), The sequence below I would follow is only a guide, but it may help keeping things flat.
I have just watched the video you included and it says the same - doh! should have watched it first!!

[Gibbo2286]

Hylomar was a Rolls Royce invention back in the fifties, it was intended to seal metal to metal surfaces with tolerances of up to 10 thousands of an inch, used by Rolls on their gasket free cylinder heads, it was so successful they licenced it out for general use.

[EDC5]

Thanks for all of your help guys. As we speak I'm waiting to add the oil back into the gearbox. I followed the video and advice on here and hopefully we'll have a good seal

The pan was hammered slightly to give it a flatter surface, it was a bit lumpy before; now it's flat.

I hand tightened the bolts first, left it an hour or so and have now torqued them up (following Stu's tightening order diagram, thanks for that )

I think I'll leave it as long as possible before adding the oil to give the silicone the best chance of going off.

Updates to follow.....

[EDC5]

It's been about a month or so since the last reply and I'm just confirming that the RTV is holding well. No oil leaks to speak of

Cheers again for the help

[Sloppysod]

Good news, I do like a happy ending
Post bookmarked, just in case