RTV Silicone for head gasket

[Asallante]

Hello, my QB service manual states "For the head / cylinder barrel joint it is essential to use - on both faces - a high temperature RTV silicone compound". I was thinking that one of the V-tech range of products (available on Amazon) might do the job. What temperature should I be aiming for? Dumb question maybe but is the colour of RTV silicone important? Seems to be related to the chemical resistance and/or adhesive properties. The original silicone looked like it might have been red or orange at the the time it was applied. Many thanks!

[Horsley-Anarak]

Hi and welcome to the forum.

I use Loctite 5920 Premium Silicone Copper Gasket Maker/Sealant.

http://www.halfords.com/webapp/wcs/stor ... yId_255217

Never had a problem with it, do not use on carbs or fuel system.

https://tds.us.henkel.com//NA/UT/HNAUTT ... 920-EN.pdf

H-A

[Asallante]

Hello H-A,

Many thanks for the advice and warm welcome!

Loctite 5920 looks good. The surfaces are quite rough, especially on the water outlet side of the head so was wondering how much silicone I need to apply. When the surfaces come together some will find its way into the water channels which is not a problem I guess but how about the top of the combustion chamber - do I need to be careful not to apply too much here?

[Collector Inspector]

"When the surfaces come together some will find its way into the water channels"

What comes outside, goes inside.

Re configure your sealing and surface prep to avoid. Back to basics.

Fuel system is also combustion chamber so don't. Other post HA above.

RTV can NOT be torqued down as a head gasket should be firm.

RTV = No Firm ever.

B

[Horsley-Anarak]

I just put them back together the same way that Seagull did.

H-A

[david doyle]

I am pretty new to this BSF wrench turning but the 4 heads I have taken off showed no signs of any gasket cement. That copper gasket tourqed to 18 ft pounds forms a pretty good seal. I would be loathe to disagree with H-A but I do like to believe that Collector has a point.

[Asallante]

Hello, if RTV isn't really needed, I wonder why Seagull themselves explicitly call it essential. Is it just insurance? Not sure about other engines but the curlew head gasket is 3 layers of copper and has a very purposeful feel to it. The pitted surfaces around the outer water channel worry me a bit though. Also, there is a small crack in the head inner surface where the tell-tale screws in. Just another way for water to exit so I am not that worried but it would be nice to keep it all tight.

[Charles uk]

Were any of those heads QB's David?

[david doyle]

Nope not a one, guess seagull quality fell a long way over the years so maybe the later models require it per the service manual.

[Charles uk]

Or perhaps the design changed.

[Charles uk]

After Bruce's comments on the use of RTV I thought it time to check if there was any basis for his fears.

So using the RTV my local car parts supplier stocks (Pro Seal, Black RTV Silicone Instant Gasket 80046) I performed a high school type experiment.

I placed a swirl & a wipe of this RTV on one side of an English 2p piece (copper based) & left for 48 hours to cure & then weighted it,
8.1 grams.

I then placed the coin in a cleaned, screw top, pickled Jalapeno chillie jar, I then poured over it about 100 ml of unleaded none ethanol pump gas & placed the jar & contents after a mild shaking on the shelf above the cistern in the bathroom where I would see it every time I took a P.

The jar was shaken 2 or 3 times a day, after 7 days I remove the coin dried with loo paper left for 10 mins to make sure there was no petrol remaining & weighted, 8.1 grams. No colour change of petrol.

The coin was replaced in the same fuel for another week of the same treatment, The jar was shaken 2 or 3 times a day, after 7 days I remove the coin dried with loo paper left for 10 mins to make sure there was no petrol remaining & weighted, 8.1 grams. No colour change of petrol.


The coin was replaced in the same fuel for another week of the same treatment, the jar was shaken 2 or 3 times a day, after 7 days I removed the coin & dried it with loo paper only to notice that the RTV had increased in size & was spilling off the side of the coin & had lightened in colour a couple of shades & had a jelly like feel as opposed to the hard rubber feel it had after curing, at this point it weighted 10.3 grams.
I then left it on the scales for a couple of hours, while I did something usefull, on my next inspection (P) I observed that it had returned to it's original colour, texture & weight 8.1 grams but was no longer stuck 100% to the coin, more than half was just resting on the coin.

My conclusion from this Noble prize winning work of science, is that Bruces fears are partially justified, if your using RTV to repair a leak in your fuel tank, but if your using it to seal your crankcase halves together & to the cylinder base, you should be OK, I use it on my race motors & that's working it a lot harder than you will, with no problems yet! & use the high temperature version on the head gasket, I've broken just about everything else possible but haven't had a head gasket go yet.

Please send my Noble prize money to me c/o the Bedlam Mental Hospital, where they're so kind to me, must go medication time.

[Stelios_Rjk]

Nice experiment Charles

[Asallante]

Thanks for the comments everyone. Much appreciated.
I think this time around, I'll stick with what the manual says and use RTV.

[Stelios_Rjk]

Thin smear only on the cylinder. Applying RTV on the copper gasket will block the thermal exchange.

[Asallante]

Thanks for the tip... so its a thin smear on the cylinder block, just like your avatar? How about the head side? Would it be better to coat the gasket to avoid making a mess at the top of the chamber?