Head gasket

[Gordon]

What do others use for head gasket material. I have an engine which I am having a problem getting to seal. I have tried .015 fibre gasket material and .030 material and also .33mm PTFE. The regular gasket material does not seal at all and the PTFE seals sometimes but not consistently. It may seal the first time but then never again. The design only has two head bolts and ath valves are off to one side in the head so not much sealing surface. Others have built this engine and have been successful. I have lapped the head and the cylinder on a flat plate with 1200 grit wet/dry sandpaper. So far no luck. The leak is significant.

 

[mayhugh1]

What do others use for head gasket material. I have an engine which I am having a problem getting to seal. I have tried .015 fibre gasket material and .030 material and also .33mm PTFE. The regular gasket material does not seal at all and the PTFE seals sometimes but not consistently. It may seal the first time but then never again. The design only has two head bolts and ath valves are off to one side in the head so not much sealing surface. Others have built this engine and have been successful. I have lapped the head and the cylinder on a flat plate with 1200 grit wet/dry sandpaper. So far no luck. The leak is significant.

A mirror finish for a head gasket sealing surface isn't always the best idea. I once finished a full-size aluminum head for an engine building friend, and he was adamant about using a faster feedrate for the surfacing cutter than I wanted to use. He said aluminum heads need a surface with a 'byte' in order to seal properly. I've been bead blasting those on my models ever since. I can't say whether it really made a difference or not.

I personally don't like using gasket sealers on model engines. Something I've lately been thinking about for stubborn cases to form a very fine gage (AWG 40 or finer) copper wire into a loop and lay it into a teflon head gasket around the combustion chamber before torquing down the head. I don't think the loop ends would need to be butt soldered, only overlapped just a bit. My theory is that the copper ring would embed into the teflon and give a gas tight seal against the opposing metal surface.

I got the idea from a Youtube video (no longer available) from an Australian full-size radial engine building company. I don't remember their name offhand, but they built engines for DIY home aircraft builders, and I swear they looked like full-size versions of Hodgson's 9 cylinder radial. Anyway, they showed off their step-by-step assembly process, and I was amazed to learn that a couple of their oil sealing gaskets were no more than a loop of silk thread laid between two metal surfaces.- Terry

 

[Jasonb]

I always use a liquid gasket from a car accessory shop

 

[minh-thanh]

I have lapped the head and the cylinder on a flat plate with 1200 grit wet/dry sandpaper. So far no luck. The leak is significant.

How I do:
I never use sandpaper with grit size smaller than 150 .
Start with 100 grit to remove deep scratches, then 120 grit - Finished - If the contact area is too small, I will use 150 grit for finishing
My rule: always stick sandpaper to the surface of the glass - stick it evenly and press it close to the glass
Head gasket : I use what I have on hand, usually I use paper
Hope this hepls

 

[xander janssen]

I use this material with great succes.

https://www.bengs-modellbau.de/material/dichtelemente/abil-dichtpapier
It is a material with a cellulose-base and a NBR-binder.

 

[Peter Twissell]

I make head gaskets from annealed copper.
I would echo the comments about having some surface roughness to 'bite' into the gasket.
I am concerned that with only to bolts holding the head down, you may be fighting a losing battle.
On drag racing motorcycle engines, I have previously made braces which fit under the head bolts and distribute the load across several areas of the head to prevent it from distorting and lifting off the gasket.

 

[Chiptosser]

Can you show some pictures?
Definitely need a textured surface, just like concrete. Slick and slide. I have never seen a two bolt head unless combined with some clamping accessory. Can you add extra head bolts?

 

[Gordon]

Can you show some pictures?
Definitely need a textured surface, just like concrete. Slick and slide. I have never seen a two bolt head unless combined with some clamping accessory. Can you add extra head bolts?

Not having much luck. Teflon seems to work the best but still not a complete seal. I refaced the head and the cylinder to be sure that the surface was flat. It leaks around the valve area off to the side. Not much sealing area at that point. FYI Bore is 3/4 and valve dia is 1/4. This is from a set of drawings that Ronald Reid posted on Model Engine Maker. His was successful.

 

[petertha]

I got the idea from a Youtube video (no longer available) from an Australian full-size radial engine building company. I don't remember their name offhand, but they built engines for DIY home aircraft builders, and I swear they looked like full-size versions of Hodgson's 9 cylinder radial.

Guessing probably Rotec?

https://www.rotecaerosport.com/

 

[minh-thanh]

In my opinion, there are too many large scratches due to machining and you will have a hard time getting the air tight

 

[Steamchick]

I agree with Minh Thanh about the rough machined face. I suggest you set it up in the lathe and give it another skim, but with a larger radiused tool than the sharp pointed tool you have used. Take the best care with the feed of the cross-slide. Check the rotational speed so you are not running too fast for correct cutting speed at the outside diameter, then depending on how you control the rotational speed (gears or Variable speed control?) You should increase the speed when the material is cutting too slow as you progress towards the centre. Actually, you need not re-surface the combustion face, but easier if you do.
I guess you'll only need to remove a few thou to clean-up the surface, but you should achieve a score-free surface with a large radiused cutter and slow feed and correct cutting speed, allied to a small cut of just a few thou. Then you'll find the head seals better.
K2

 

[Steamchick]

Another check: Before assembly, apply some Engineers' blue to your surface plate, put the cylinder face and cylinder head face on the blued surface plate and confirm the surfaces are not dished, distorted, and are really flat and smooth.
If your cross-slide or set-up is not truly perpendicular to the lathe axis, then you will have dished or domed surfaces.
K2

 

[Gordon]

I have tried a mirror finish with wet/dry sandpaper and three different gasket materials. Teflon works the best but not constantly. It is interesting that the advice is that I need a rougher surface and a smoother surface. In every case it leaks at the same place on both heads. It leaks out both sides of the side nub where the valves and the valve channel is located. I am sure that the fact that it only has two head bolts is the main problem. I am sure that adding a couple of head bolts closer to the side nub would solve the problem but since Ronald Reid got his running without the extra head bolts I wanted to try to get it running without the extra head bolts. I may have to just give up and add the extra head bolts but I am a stubborn old curmudgeon with more time than common sense.

 

[mayhugh1]

Guessing probably Rotec?

https://www.rotecaerosport.com/

That's it! At one time, just after I finished building one of my radials in fact, I came across one of their videos showing the step-by-step re-assembly process of one of their engines that had come back for a rebuild. I watched it many times, but one day it disappeared - probably for liability reasons. - Terry

 

[mayhugh1]

Consider Hylomar Blue as a hail Mary:

https://www.amazon.com/Valco-71255-...qid=1673816494&sprefix=hylomar,aps,121&sr=8-8
If you've blued the two surfaces and checked that they're truly flat with a 100 grit surface finish and still leaking, Hylomar Blue is a last resort. Use without a gasket on both surfaces per instructions. I don't like it for use with model engines myself, but Rolls Royce used it in place of gaskets on their Merlins, and shops use it today to solve nasty sealing problems on full-size heads. At least this stuff lets you disassemble without the need for scraping. (I still like my wire in a teflon gasket best.) - Terry

 

[ninefinger]

Speaking of the "side nub" that has the lower valve, how is it attached to the main cylinder body? There appears to be a straight line from one side to the other that indicates a mating part. This could be the source of the leak.

 

[Richard Hed]

I have tried a mirror finish with wet/dry sandpaper and three different gasket materials. Teflon works the best but not constantly. It is interesting that the advice is that I need a rougher surface and a smoother surface. In every case it leaks at the same place on both heads. It leaks out both sides of the side nub where the valves and the valve channel is located. I am sure that the fact that it only has two head bolts is the main problem. I am sure that adding a couple of head bolts closer to the side nub would solve the problem but since Ronald Reid got his running without the extra head bolts I wanted to try to get it running without the extra head bolts. I may have to just give up and add the extra head bolts but I am a stubborn old curmudgeon with more time than common sense.

LOL, you're also very funni

 

[minh-thanh]

I have tried a mirror finish with wet/dry sandpaper and three different gasket materials. Teflon works the best but not constantly.

Because teflon is relatively "soft" and it will be squeezed with the pressure of the bolt, and if it is thick enough it will temporarily seal - But if the time is long and especially when the engine can run (probably will no ) and with temperature it will be useless to that surface

In every case it leaks at the same place on both heads. It leaks out both sides of the side nub where the valves and the valve channel is located. I am sure that the fact that it only has two head bolts is the main problem. I am sure that adding a couple of head bolts closer to the side nub would solve the problem but since Ronald Reid got his running without the extra head bolts I wanted to try to get it running without the extra head bolts. I may have to just give up and add the extra head bolts but I am a stubborn old curmudgeon with more time than common sense.

Think simple: With valves and valve seats (especially ball valves) they have very little contact surface and if machined properly they will seal perfectly - Perfect means good enough. for sealing , good enough with homemade engine
To me , making an engine : most of the time and most importantly is surface treatment .
Surface of cylinder, valve, seat, piston, groove, ring, surface of block and cylinder head, surface of shaft.........
Polished or rough surface I don't know which is better. But if the surface rough is good enough and it's airtight then why should I waste time and effort polishing it ?!?

 

[Richard Hed]

Because teflon is relatively "soft" and it will be squeezed with the pressure of the bolt, and if it is thick enough it will temporarily seal - But if the time is long and especially when the engine can run (probably will no ) and with temperature it will be useless to that surface



Think simple: With valves and valve seats (especially ball valves) they have very little contact surface and if machined properly they will seal perfectly - Perfect means good enough. for sealing , good enough with homemade engine
To me , making an engine : most of the time and most importantly is surface treatment .
Surface of cylinder, valve, seat, piston, groove, ring, surface of block and cylinder head, surface of shaft.........
Polished or rough surface I don't know which is better. But if the surface rough is good enough and it's airtight then why should I waste time and effort polishing it ?!?

My thimpfking is that, as long as it is perfectly flat, and there is no deflection as Gordon says because of the bolt pattern, that too smooth a surface, that is, polished, is not good but too rough of a surface also is not good. But a certain roughness would be perfect. That perfect roughness might only be seen with a mag glass or even a microscope.

 

[minh-thanh]

that too smooth a surface, that is, polished, is not good but too rough of a surface also is not good. But a certain roughness would be perfect. That perfect roughness might only be seen with a mag glass or even a microscope.

I don't know... But I always use 120 grit sandpaper (and 150 with less surface contact) and it's always good. and I will certainly never assemble an engine with a surface like the in Gordon's picture