TheSamba.com :: View topic

Fri Aug 04, 2023 7:58 am

THANK YOU BOTH .

I too know and love Hylomar but I'd never thought of using it there .

What is the current thinking of cleaning the mating surfaces ? .

TIA,

Fri Aug 04, 2023 8:33 am

Acetone

Fri Aug 04, 2023 12:27 pm

I use acetone too. Good solvent.

Before that, stone the surfaces with either a machinist stone or a lapping plate. Knock all the high spots down so the cases mate nice and even all the way around. Then clean the cases really well.

Fri Aug 04, 2023 5:26 pm

chrisflstf wrote: Acetone

Mmmmm...yes and no. It depends on what you are cleaning off of the case.

Acetone is a very strong solvent but it does not do well on certain things. It cannot dissolve certain greases cleanly….completely. I will explain why that’s an issue shortly.

It’s very specific chemistry wise. For instance, for cleaning up epoxy adhesives its perfect. The problem is not the oil in the grease. Acetone will dissolve most oils. It’s the base materials that it cannot dissolve and some of the additives that it may not get out because it flashes off so quickly.

Also, if there are dried sealants or adhesives...RTV's...acetone will not work well on them.

However, I do use a lot of acetone. If you know the two case halves are already very clean and all debris are gone and you just want to remove any skin oils or basic motor before applying sealant....then yes...acetone works very well for that.

Where it also does not work well is getting embedded stuff out of fine kerfs and cracks, usually because that kind of crud is made up of more than one material. I use something stronger when I have stuff like that....like lacquer thinner or MEK.

This is a really good thread. Lots of good information.

As Vanapplebomb notes...if you can dress the case halves with an stone to simply smooth the surfaces, you will seal better.
The big issue is it depends on what you are sealing with and relying on acetone only.

If you had any oils or greases that had sulfur in them….gear oil…assembly lubes….clean the surfaces with something like a mineral spirit like xylene. Or use MEK or lacquer thinner. Or even a strong detergent with a caustic and water and then dry. After that, acetone is perfect for the last wash up right before application of sealant. Methanol is good too.

Sulfur, even very small amounts of residual sulfur prevent virtually all moisture cured RTV’s from curing properly. In areas where gear oil is in heavy use….even too much in the air can spoil the cure.
There are too many times when some people swear that RTV just does not hold up in certain applications because it leaked. Too many of those times, when you inspect while tearing the equipment or engine down you find that the RTV is not cured in certain places. Still kind of gooey. Sulfur contamination usually.
The other issue with RTV failure on something like a case joint or flange is what we have talked about here at other times. Getting it applied thin enough.

Most RTV’s are very high density. Most are designed as “gasket makers” or “gap fillers”. When you apply it to a machined joint and do not start out thin enough….as the joint starts to close….and it starts squeezing the RTV along both surfaces, yes…some will squeeze out….but the big issue is that as the RTV squeezes along the surfaces and the gap is closing, the friction and surface tension increase exponentially. This increases the density of the RTV.

Eventually the already high density RTV starts to act like a solid and will lock up. The RTV layer will only get so thin if there is too much volume to start with.
As Modok noted I think…it can prop the two surfaces apart, And, as I noted In my last post….the thicker inner layer of RTV will be susceptible to tearing is there is any pressure operating on it.

You really only want the handful of microns needed….to fill the machining imperfections between the case halves. As Modok has said before....yes...on a good joint you can probably seal the case with ketchup if its properly applied. Ray

Sun Aug 06, 2023 7:28 am

Very much appreciate all the detailed answers .

Mon Oct 30, 2023 4:54 pm

txoval wrote: Always brave to post a video.

I made an entire playlist with my 1st engine build, hoping to be informative for others who can learn from my rights and wrongs

First start video is coming live next week or so !

Mon Oct 30, 2023 6:50 pm

O.K., first thing I hate to tell you but those are thin wall cylinders My son used a set to very good effect indeed, he installed "super cool" under cylinder sheet metal .

The comment was about the CASTING and clearly it's a minor issue here, I don't think I'd bother cleaning it up as more metal in the breeze means cooler running....

Listening to you reminds me of my first VW engine teardown and overhaul....

Mon Oct 30, 2023 6:54 pm

BTW : you need two 10MM 1.25MM fasteners on that engine support or you're going to have a terrible day in due time .

Are those stock twin port cylinder heads ? . they have clearly been re welded once, this cracking is endemic / normal .

Tue Sep 30, 2025 6:36 am

raygreenwood wrote: chrisflstf wrote: Acetone

Mmmmm...yes and no. It depends on what you are cleaning off of the case.

Acetone is a very strong solvent but it does not do well on certain things. It cannot dissolve certain greases cleanly….completely. I will explain why that’s an issue shortly.

It’s very specific chemistry wise. For instance, for cleaning up epoxy adhesives its perfect. The problem is not the oil in the grease. Acetone will dissolve most oils. It’s the base materials that it cannot dissolve and some of the additives that it may not get out because it flashes off so quickly.

Also, if there are dried sealants or adhesives...RTV's...acetone will not work well on them.

However, I do use a lot of acetone. If you know the two case halves are already very clean and all debris are gone and you just want to remove any skin oils or basic motor before applying sealant....then yes...acetone works very well for that.

Where it also does not work well is getting embedded stuff out of fine kerfs and cracks, usually because that kind of crud is made up of more than one material. I use something stronger when I have stuff like that....like lacquer thinner or MEK.

This is a really good thread. Lots of good information.

As Vanapplebomb notes...if you can dress the case halves with an stone to simply smooth the surfaces, you will seal better.
The big issue is it depends on what you are sealing with and relying on acetone only.

If you had any oils or greases that had sulfur in them….gear oil…assembly lubes….clean the surfaces with something like a mineral spirit like xylene. Or use MEK or lacquer thinner. Or even a strong detergent with a caustic and water and then dry. After that, acetone is perfect for the last wash up right before application of sealant. Methanol is good too.

Sulfur, even very small amounts of residual sulfur prevent virtually all moisture cured RTV’s from curing properly. In areas where gear oil is in heavy use….even too much in the air can spoil the cure.
There are too many times when some people swear that RTV just does not hold up in certain applications because it leaked. Too many of those times, when you inspect while tearing the equipment or engine down you find that the RTV is not cured in certain places. Still kind of gooey. Sulfur contamination usually.
The other issue with RTV failure on something like a case joint or flange is what we have talked about here at other times. Getting it applied thin enough.

Most RTV’s are very high density. Most are designed as “gasket makers” or “gap fillers”. When you apply it to a machined joint and do not start out thin enough….as the joint starts to close….and it starts squeezing the RTV along both surfaces, yes…some will squeeze out….but the big issue is that as the RTV squeezes along the surfaces and the gap is closing, the friction and surface tension increase exponentially. This increases the density of the RTV.

Eventually the already high density RTV starts to act like a solid and will lock up. The RTV layer will only get so thin if there is too much volume to start with.
As Modok noted I think…it can prop the two surfaces apart, And, as I noted In my last post….the thicker inner layer of RTV will be susceptible to tearing is there is any pressure operating on it.

You really only want the handful of microns needed….to fill the machining imperfections between the case halves. As Modok has said before....yes...on a good joint you can probably seal the case with ketchup if its properly applied. Ray

Hi Ray - thanks for all of the detail. I'm hoping to do this process this week. You mentioned that you like the Yamabond/Motoseal. Would you recommend that I go for one of those, or RTV?