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Looking for tips on removing a baked-on cylinder gasket

OUberLord

Member
Joined
Mar 13, 2023
Total Posts
24
Total likes
11
Location
Omaha, Nebraska, USA
Howdy all,

I wanted to get some advice before I strike off on my own with removing a quite stuck cylinder gasket. This gasket is the one that sits on the base of the cylinder on my 1981 CB400T, and sits between it and the crankcase. I do have both a set of traditional scrapers as well as a couple sizes of carbide scrapers, but this gasket material is very strongly baked into place. My chief concern of course is I don't want to scratch or mar the underlying surface, but I'm having a bit of trouble even getting started on the bulk of the gasket removal. Picture for reference, and you can see I've started to remove some of the gasket material in the bottom right:

20240309_182849.jpg

What steps can I take to make my life the easiest when it comes to removing this gasket? I've been told that brake cleaner / carb cleaner can be used to spray it on the gasket, let it soak for 10-15 minutes, and then try again. I also know that CRC makes a gasket remover. However I also want to protect the painted finish, and while I can certainly mask off those areas I also want to first make sure those ideas are valid ones and are worth the effort.

As before, I genuinely appreciate the guidance you guys offer. I haven't done this kind of work before, so I really want to take my time to learn and do it right.
 
I'd think brake and carb cleaners would evaporate too quickly but the "soften with a liquid" suggestion is on the right track, especially since I think that gasket is a fibrous paper...
Heck, begin the softening with plain water. And I'd suggest a penetrant that will not harm paint if there is one.
Surely, someone else who's already done this will chime in soon.
All of my experience/past gasket removals involved those on water-cooled engines where the gaskets scraped off easily from coolant and water absorption/saturation...
 
I use a 1/4" wide sharpened wood chisel on these kind of gaskets and would soak the gasket with WD40 for a couple days before if possible. I do have some nasty gasket removers and a paint stripper banned in many countries but even they are no magic bullet.
 
I have uesed a sprecial sealand remover, it's about $10 a can. That works much beter than diesael or brake cleaner. But you have to be careful with painted surfaces.
 
Man, this gasket is a fighter, I'll give it that.

I bought some of the CRC Gasket Remover, and applied it to the gasket with a brush to prevent it from getting onto the painted surfaces. I coated it, then coated it again 15 minutes later, and then let that sit overnight. It's barely made a difference.

The big issue is that I can get a little bit of the edge removed, but then it flakes away and ends up leaving an uneven slope. Given how little room anywhere I have to get it started and the resulting uneven patches, I'm real concerned about scratching the surface by being unable to keep the tool edge parallel to the surface.

I might try drowning it in WD-40 next and letting that sit for a couple days, and/or the idea of soaking it in a basin of diesel. At least the cleanup of the crankcase surface is going comparatively well, but there wasn't much of the gasket left on there.

Out of curiousity and looking ahead, for the three gaskets involved (below the cylinder, between the cylinder/head, and the head cover) which ones should I also use a thin film of hondabond with?
 
OUberLord said:
Man, this gasket is a fighter, I'll give it that.

I bought some of the CRC Gasket Remover, and applied it to the gasket with a brush to prevent it from getting onto the painted surfaces. I coated it, then coated it again 15 minutes later, and then let that sit overnight. It's barely made a difference.

The big issue is that I can get a little bit of the edge removed, but then it flakes away and ends up leaving an uneven slope. Given how little room anywhere I have to get it started and the resulting uneven patches, I'm real concerned about scratching the surface by being unable to keep the tool edge parallel to the surface.

I might try drowning it in WD-40 next and letting that sit for a couple days, and/or the idea of soaking it in a basin of diesel. At least the cleanup of the crankcase surface is going comparatively well, but there wasn't much of the gasket left on there.

Out of curiousity and looking ahead, for the three gaskets involved (below the cylinder, between the cylinder/head, and the head cover) which ones should I also use a thin film of hondabond with?
Click to expand...
Ah, the horror stories I can tell you about that gasket. Can't say I didn't tell you.
The only place you're going to use Honda Bond is sealing the case halves and then only a thin smear. All other gaskets are installed dry.
 
LongDistanceRider said:
Ah, the horror stories I can tell you about that gasket. Can't say I didn't tell you.
The only place you're going to use Honda Bond is sealing the case halves and then only a thin smear. All other gaskets are installed dry.
Click to expand...
Haha yeah, I figured it was going to be the worst part of the whole process. It lived up to that expectation.

That's good to know about the Honda Bond. Since I'm not splitting the case halves, it sounds like I really have no use for it for any of these gaskets then. It's use wasn't referenced in anything I've read, but I figured it was worth confirming.

ballbearian said:
I'm impatient. I used a small wire wheel to grind them down real thin (not all the way to the aluminum) then switch to the small abrasive (scotchbrite like) wheels for rotary tools (dremel).
Click to expand...
I'm pretty patient, but also man if I wasn't having an absolute hell of a time making progress. A buddy of mine reached out so I just spent a few hours over in his shop. I originally didn't like the idea of those 3M pads, as even though they're plastic I figured they would be too abrasive. He's done similar work before though, and we tested things out before ramping up it's use. Turns out, with some brake cleaner we were able to soften the top layer to make it easier to remove with just a plain flat razor, and that removed a bulk of it. We used that pad in combination with a lot of brake cleaner and a deft touch, and we got the surface very clean. It's smooth to the touch and you can't catch a fingernail anywhere, so I feel like this turned out about as well as one could reasonably expect. Certainly better than if I'd have kept trying with just my scrapers, as it already looked like I was risking some more-than-superficial scratches.

I have learned a LOT in the last few hours.

20240312_003632.jpg
 
Good place to learn your chops. The head itself and top of cylinders is the most critical to not gouge or scratch. Got new Orings for that base?
 
Yep, the gasket kit I bought came with those, everything else I know I need, and then a few gaskets I can't identify but I assume would be for the lower. I'm going to degrease and really clean the cylinder and then replace those o-rings.

I got the top surface of the cylinder cleaned up pretty similar to how the bottom looks there. Haven't done anything to clean either of the heads surfaces, but with how easily those gasket were removed that'll probably take little more than a clean cloth and some goo gone.

Though on the topic of cleaning surfaces, what if anything should I consider regarding the pistons? The surface of them does have some carbonized deposits, but I'm not sure to what extent I should care there.
 
Welcome to the wonderful world of Honda gaskets.
OEM are heat activated and designed to glue themselves in position.
Removing base gaskets is the worst job in shop, it's like punishment, plus, rarely do apprentices do it because it's so easy to gouge surface.
(you have to stand over them and check, boss gets very upset, 'I pay you too much to do that')
Turns out it's even more expensive for a new block (back in the day, it was 'fun')
 
I've used a plumbers propane torch to heat and bubble-up the old hard and stuck gaskets. I can't seem to get the hang of the Mapp gas fuel but propane is slightly less intense and those old gaskets bubble nicely and allow an easy scrape after.
 
Great job cleaning (y) Clean enough for your mother to eat off.
The danger of powered brushes/discs/wheels is they eat aluminum extremely quick creating low spots. They're fine on steel and hard gaskets but very dangerous around aluminum.
 
I saw someone else in a YouTube video using a torch right before I went to my buddies shop, but never tried that method out.

I was *deeply* concerned about using any rotary tool given the aluminum. I was pretty careful to never linger in one spot for long, even with the plastic bristle pad. Any time something didn't really come off, we figured it was time to hit it with brake cleaner and let that do some chemical work before going back to the physical.

For what's left on the crankcase side I'm probably going to use straight razors and brake cleaner (obviously after covering the holes). What steps should I take to prevent debris from going into the bolt holes?
 
OUberLord said:
For what's left on the crankcase side I'm probably going to use straight razors and brake cleaner (obviously after covering the holes). What steps should I take to prevent debris from going into the bolt holes?
Click to expand...
The bolt holes will need to be cleaned out and a tap run thru the treads anyway so covering them isn't terribly needed.
I used a 1x2x8" piece of hard wood with wet/dry sandpaper and oil to finish that surface running a figure 8 pattern.
 
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