Sealing a cylinder head gasket

My beloved GMS .47 engine seems to have sprung a leak. I didn't notice that
the cylinder head screws had worked loose, and I either managed to get the
cylinder head gasget fouled, the cylinder head warped, or both.
I have a replacement cylinder head and gasket set on order from Tower for
about $8 plus s&h, so at least it's not an expensive problem. I'm just
wondering if I should add some type of adhesive sealant to the cylinder head
gasket when I replace it.
What would you engine experts out there recommend? Should I just replace
the cylinder head and gasket like it came originally and then just make sure
I check the bolts once in a while? Should I seal the gasket with a
modelling or automotive product? Should I leave the gasket alone but add
thread lock to the cylinder head screws?
As always, your expert advice is much appreciated.
Reply to
Ed Paasch
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I wouldn't use any type of sealant. Just install the new head and check it. If the head won't seal because the case is warped you could hand lap it. Shouldn't take very much lapping. Leave the gasket out when you lap and use the finest water mixed compound you can find. Go slow check often and be sure to remove all traces of lapping compound before you reassemble it.
Reply to
Frederick Witt
Dittos on what Fred said.
If you don't have any lapping compound on hand, you can even use a little Comet Cleanser or even toothpaste.
Reply to
Double Ace
I dont know about "expert" but I rebuilt a GMS .32 that had a nasty run-in with a boulder. Replaced the case, muffler, and cylinder head (hey, it was ginched and ugly) and just bolted it down. Main thing is to torque em in a "star" pattern. Thread em down finger tight, noon, 6, 3, 9,1, 7, 5, 11, so on then do the same with the hex driver. Just like torquing the lug nuts on your car. This may be self evident. My .32 runs like a champ and no head leakage. Same with my OS .46LA. On THAT one I had to use high temp silicone for the plastic back cover on the case but the head doesnt leak.
Reply to
Fubar of The HillPeople
Hi Ed, Absolutely *no* sealant! Here's Dub Jett's drill:
"TORQUING YOUR HEAD: If you have a torque wrench, be careful how you use it. It has been shown that many of these tools are not as consistent as you are with your fingers. Use a screwdriver handle type hexdriver, not a T-wrench.
Make sure all of you bolts are clean, and will screw completely down without sticking. If not, run them in a few times until they loosen up. Clean all the critical parts with a paper towel: The cylinder flange. The head surfaces. The gaskets. The head clamp where it touches the head button. The screw holes and head bolt seats. Next, seat the gaskets and head button on the cylinder and place the head clamp on top. Grasp the head clamp with two fingers and hold it down tightly while you spin the bolts down with the hex between your fingers--don't touch the handle yet--just your fingers on the small hex. When the bolts touch (you are still holding the head down with your fingers) go to the next one across, using a 1-4-2-5-3-6 crisscross until you have them all touching. Work the circle twice. Turn loose of the head clamp and tighten once again with your thumb and index finger on the handle. Always work the circle twice. Finally torque the head bolts to the desired amount with your torque wrench or by hand. About 16 inch-pounds for the .40-.50 and about 20 for the .60-120.
It is more important to do step one--seat the bolts--than any other. If you skip it you will find that you torque wrench will give you as much as 100% variation in torque, which can surely ruin your engine."
Reply to
Ed Forsythe
No, nothing on it. The annealed copper gasket will form a good seal. What happens when the screws get loose is the hot gasses heat and harden the gasket and it won't conform to the sealing surfaces anymore
Reply to
Paul McIntosh
Thanks to all who responded to my previous question. Tower Hobbies got the new cylinder head and gasket set right out and I installed them. The new gasket sealed just fine and I've gotten a couple of good flights in with the engine.
What's funny is that I feel like I'm breaking it in all over again. The engine feels tight at the top of turn again and I've been fidgeting with it quite a bit. The needle valve setting seems totally random from flight to flight so far.
I'll keep working on it and hopefully my GMS .47 will be just as powerful and reliable as it was last fall.
Reply to
Ed Paasch

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