Use loctite glue

[minh-thanh]

Hi everyone !
I have never used loctite, so I have questions:
What kind of loctite do you use for valve seats?
How well should metal surfaces be handled to use loctite glue?
How much is the tolerance between 2 metal parts? Does it fit snugly?
With the temperature of the glue is about 150 degrees Celsius, is it durable when the engine heats up and runs for long time ?
Thanks !

 

[WOB]

You should go to the Loctite website and read some of the instructional and applications literature. All your questions will be answered accurately and completely.

WOB

 

[werowance]

Minh-Thanh, i used locktite 638 on the valve seats on the webster. my seats were a press fit but not an extremely tight press fit. i did use the small arbor press to put them in but didnt take much pressure. they are still holding up fine and have had the engine extremely hot.

now when im gluing say aluminum plates together so i can machine 2 parts in a single operation i have used the 638 but more often i use just the lock tight "red" high strength from the auto parts store. i believe its 262. i do still have to keep a clamp on it or they will pop appart during machining. but once im done if a whack on the corner doesnt break it appart then i use my butane pencil soldering torch and have to heat it pretty hot. hot enough to burn you quickly if you touched it to get it to break appart. 150 deg c is = to 302 deg f and i can say that i have put pieces in my little toaster oven i use in the garage to heat metals slow and for a long time and 350 deg f didnt break the locktight bond with the red

but long story short, the 638 i know works for valve guides and i learned that from looking at other users builds and what they used here so im not the only one using it and its holding up for me.

 

[minh-thanh]

You should go to the Loctite website and read some of the instructional and applications literature. All your questions will be answered accurately and completely.

WOB

WOB
Yes, I read quite a bit about the information of each type of glue loctile. but they don't say: "it's good for valve seats" (or maybe I missed it a bit) and more importantly the experience of people using will always be better than ads.

Minh-Thanh, i used locktite 638 on the valve seats on the webster. my seats were a press fit but not an extremely tight press fit. i did use the small arbor press to put them in but didnt take much pressure. they are still holding up fine and have had the engine extremely hot.

now when im gluing say aluminum plates together so i can machine 2 parts in a single operation i have used the 638 but more often i use just the lock tight "red" high strength from the auto parts store. i believe its 262. i do still have to keep a clamp on it or they will pop appart during machining. but once im done if a whack on the corner doesnt break it appart then i use my butane pencil soldering torch and have to heat it pretty hot. hot enough to burn you quickly if you touched it to get it to break appart. 150 deg c is = to 302 deg f and i can say that i have put pieces in my little toaster oven i use in the garage to heat metals slow and for a long time and 350 deg f didnt break the locktight bond with the red

but long story short, the 638 i know works for valve guides and i learned that from looking at other users builds and what they used here so im not the only one using it and its holding up for me.

werowance !

For me, who has never used loctite glue
That is great information !

Thanks All !

 

[minh-thanh]

Hi All !
One more question :
If the valve seat is broken (in the process ....), how do I remove it?
Drill or use heat?
And if you use heat, can you explain the process?
(I have not used glue loctile before, so there are many questions tupid )
Thanks !

 

[werowance]

I would recommend heat. a plumbers torch or butane pencil soldering torch works well for me. now one thing that I often notice is that after the heat if you let it cool completely the locktight will bond again. yes its a very weak bond after being torched but often still enough to make it stuck again. so once hot take a pick or something to pull it out while still hot. welding gloves are nice to have while doing this.

I usually will see the lock tight start smoking like oil burning. I can definitely smell it (try not to breathe the fumes) when its starting to burn and break down. you don't have to heat red hot or anything but by the time its hot enough it will definitely burn you very quickly.

 

[minh-thanh]

Hi All !
Today I bought loctite glue and reread this discussion, and realized that, I need to clarify a few things
so I will say it clearly:
The way I made the valve seat is different from the way people usually do, and it has the limitation of not being able to make two valve seats in parallel in a small cylinder engine, and there are a few other issues, so I want to learn more , one member said "Every method has benefits and drawbacks", I give this discussion the main purpose is to learn everybody have been successful with it , Because the two valve seats are parallel to each other, other details will be easier to do.
That is what I want .

 

[petertha]

I'm not sure I'm answering your question, but in my engine, the valve face is turned 45 degrees and the valve seat (of the valve cage) is also 45 degrees. So that makes them parallel to one another in cross section & mated to one another along the length of the seat assuming perfect geometry. I have followed others guidance & made the valve seat quite thin, about 0.010". It can be a bit challenging to achieve a good seal as evidenced by vacuum test because there are all kinds of little issues that can make the assembly leak. For example incomplete surface finish like 'record player' machining marks from turning. Or altering the surface by secondary lapping/polishing. Or introducing eccentricity/distortion if for example the valve cage takes on a different shape when inserted into the head. Or valve & seat are perfect but the valve stem sliding portion is off axis which then mis-aligns the valve to the seat. Etc. Etc.

Some people advocate making one of the faces a slightly different angle, for example valve at 45-deg & seat at 46-deg or 44-deg. The intent is to form a contact 'line' at least initially. Maybe after the engine runs in it is supposed to develop into something like a thin machined seat in-situ? I'm not too sure. I've read about it but don't see it being very prevalent among most model engine designs.

This is my first engine build so don't put too much weight on my opinion. I tried to follow Terry's procedures and valve seat length in particular.
https://www.homemodelenginemachinist.com/threads/another-knucklehead-build.27584/page-2

In terms of removing a cage or seat with heat which has been installed with high temperature Loctite, I heated some bronze tester cages from aluminum block just to see. Mostly I was interested in running conditions. My heat gun didn't provide enough heat with gentle tapping so that satisfied me for running conditions. I reverted to gentle butane torch heat. The cages were 544 bronze machined 0.001 - 0.002" diameter undersize to (6061 aluminum) head hole using Loctite 680. I'm going to do another test one day & attempt to accurately measure temperature. Anyways, I think it might be challenging to remove one cage & not adversely affect the other, so might be better off making a new head. That's why my 5-cylinder build pictures will usually show a 6th head LOL. Maybe others have some valve cage salvage stories.
Hope this helps!

 

[minh-thanh]

petertha !
For me, all information is useful, and moreover it is your experience !
Thank you very much !

 

[blockmanjohn]

I have a quick question concerning removing a loctited part with heat. After heating to the proper temperature, is the joint unglued forever, or will the loctite bond again after the parts cool?

Thanks, John.

 

[petertha]

The technical literature doesn't explicitly say, but I think its safe to say it has been permanently cooked. Here is the strength vs temp diagram for 680. The de-bonding temp is 250C. Even though it might appear to gum up after cooling, I don't think it is reversible & you climb back up the curve.

 

[werowance]

Hi Petertha, i know i said it would "bond again" but what i was meaning is it leaves a gunk behind that on an already tight fitting part is enough to keep you from being able to just pull it out. but yes just 2 plates glued together after heating will usually just fall apart. sometimes if you heat and let cool you do have to just tap it a little to get it fall apart but not much. much like flux residue left behind on a part that didnt actually take any solder. the burnt flux is sometimes enough to hold the part together to make you think its actually soldered.