Base gasket sealer

[MS260 Fan]

Hey guys,

I've read lots of posts over the years about the use of yamabond, motoseal and the like for sealing the cylinder to the crankcase at the base. I always assumed people were using it in place of a base gasket. I'm working on a project saw. I can't get the base gasket to seal. It leaks at the crank case gasket on the exhaust side.

I've had the saw apart 3 times. At first I thought I didn't clean up the case gasket enough before putting the cylinder on. I cleaned it up and it looked great. It still leaked.

I took it apart again. There was a bit of a step were the case halves came together at the exhaust side. I shaved a little off one side with a utility knife blade. It worked well. Now it's flat across the joint but it still leaks a bit. Am I missing something??? Should I be using Yamabond with the base gasket?? When people use Yamabond and the like, are they using with a gasket or only without?

 

[z71mike]

I've seen people use a gasket and sure it up with sealer. As long as the squish is good, I don't see a problem with that.

 

[RiverRocket]

I always use a thin film of Hylomer on the base gasket.

 

[Flintknapper]

I'm sure there are other comparable products, but I've used Yahabond 4 with the best success.

 

[w8ye]

Some available sealers for the cylinder to crankcase . . .

Specialty Gasket Makers : Permatex® MotoSeal® 1 Ultimate Gasket Maker Grey

Gasket Makers : Permatex® Ultra Grey® Rigid High-Torque RTV Silicone Gasket Maker

Anaerobic Gasket Makers & Flange Sealants : Permatex® Anaerobic Gasket Maker

Yamaha Motor Corporation, USA - Adhesives & Loctite® Yamabond® 4 Motorsports

There are others like:

Honda Bond 4
Threebond 1211 (Evenrude)
Stihl Dirko

 

[MS260 Fan]

Sound like great products. Thanks. Anyone surprised that I can't get perfect seal with the use of a base gasket??

 

[redunshee]

Yea, I'm surprised as I simply use a good sealer w/o a base gasket and haven't had a leak. Something is wrong if you still get a leak.

 

[MS260 Fan]

Redunshee - I was talking about a leak with a base gasket only. I have to look at the cylinder better. I focused on the joint between the case halves. The saw holds vacuum pretty good but leaks at the cylinder base under pressure...

 

[towingace]

If you already haven't, I would take a small metal machinist rule to use as a straight edge and check both surfaces from several angles to determine if there are any low spots. If you see anything questionable you can check the area with a feeler gauge between the straight edge and the surface.

Because the surface area is rather small in spots it can be difficult to get an accurate reading with this method in which case you might consider trying positioning a small light in the cylinder (without the piston) and install the cylinder, without gasket, on to the case. If you see any light shining through (I bet you do), you've located the culprit.

The best kind of light to use is a 12 volt turn signal bulb and socket. Make sure it's the style with a separate ground wire (not self grounding) and feed the wires through the spark plug hole before you install the cylinder. If you get a socket from a parts store you will probably need to add on to the wires so you don't have the battery in your way and you will be able to move the saw around freely. You can use the wires as a handle to move the light around.

This is just a non-scientific home-brewed idea that should help you out.

 

[redunshee]

Redunshee - I was talking about a leak with a base gasket only. I have to look at the cylinder better. I focused on the joint between the case halves. The saw holds vacuum pretty good but leaks at the cylinder base under pressure...

Ok. Sealer will cover up small areas that are uneven. You may want to try it w/o a base gasket and see if it holds pressure.

 

[olyman]

as redr said,,hylomar is the schnitz!!!! they put the merlin engines together with the stuff....

 

[elanjoe]

threebond 1194

 

[glock37]

when using the sealer let it set for 24 hrs before putting pressure to it !

 

[redunshee]

when using the sealer let it set for 24 hrs before putting pressure to it !

Agree with something like permatex Motoseal No 1 which has a long handling time. Dirko HT however has a very short working time and can be pressure tested almost immediately. Waiting never hurts however.
Bob

 

[blsnelling]

It sounds to me like someone replaced one case half, and it didn't line up perfectly. Unless that is addressed, the cylinder may be setting at an angle.

 

[glock37]

Just making sure you don't have to tear it back down because the sealer wasn't fully curd

or to think it is and cause a air leak that cause a lean condition !

better to give it time !

 

[wyk]

Are any of the loctites worth a damn for 2-strokes?

 

[nmurph]

Some available sealers for the cylinder to crankcase . . .

Specialty Gasket Makers : Permatex® MotoSeal® 1 Ultimate Gasket Maker Grey

Gasket Makers : Permatex® Ultra Grey® Rigid High-Torque RTV Silicone Gasket Maker

Anaerobic Gasket Makers & Flange Sealants : Permatex® Anaerobic Gasket Maker

Yamaha Motor Corporation, USA - Adhesives & Loctite® Yamabond® 4 Motorsports

There are others like:

Honda Bond 4
Threebond 1211 (Evenrude)
Stihl Dirko

The equivalent Honda product is Hondabond 5.

when using the sealer let it set for 24 hrs before putting pressure to it !

I regularly assemble saw with Yamabond 4 and run them as soon as I can get the cylinder, carb, and associated parts together. I don't worry and haven't had any problems doing so.

It sounds to me like someone replaced one case half, and it didn't line up perfectly. Unless that is addressed, the cylinder may be setting at an angle.

Yes, it (according to JJ) is much more of a problem with Stihl's than Husky's.

 

[machinisttx]

If you already haven't, I would take a small metal machinist rule to use as a straight edge and check both surfaces from several angles to determine if there are any low spots. If you see anything questionable you can check the area with a feeler gauge between the straight edge and the surface.

Because the surface area is rather small in spots it can be difficult to get an accurate reading with this method in which case you might consider trying positioning a small light in the cylinder (without the piston) and install the cylinder, without gasket, on to the case. If you see any light shining through (I bet you do), you've located the culprit.

The best kind of light to use is a 12 volt turn signal bulb and socket. Make sure it's the style with a separate ground wire (not self grounding) and feed the wires through the spark plug hole before you install the cylinder. If you get a socket from a parts store you will probably need to add on to the wires so you don't have the battery in your way and you will be able to move the saw around freely. You can use the wires as a handle to move the light around.

This is just a non-scientific home-brewed idea that should help you out.

Something like this is a lot easier to use for that. Greenlee Flexible LED Flashlight - Tools - Electricians Tools - Electrician Accessories

 

[MS260 Fan]

It sounds to me like someone replaced one case half, and it didn't line up perfectly. Unless that is addressed, the cylinder may be setting at an angle.

Thanks Brad. I can't believe I didn't think of this. The saw came to me in pieces as one side of the crank case was broken. It had a new case half with. When I started going through it and replacing worn out components I lost track of the real reason this saw ended up on my bench. I took it for granted all the parts would mate together. Anyway, looking back there was more slop in the alignment pins than I expected. It was really easy to align the halves. No struggle at all.

When I checked it like towingace recommended I could see one side slightly higher than the other. I loosened the crank case screws a bit and gave the high side a little tap with a rubber mallet. Nothing as the gasket held tight. I tightened the cylinder down to see if it would push the high side down. I couldn't tell so torqued the case together and checked it again. It holds pressure and vacuum. The alignment pins either allowed a little misalignment in the initial reassembly or I just bent them to make the cylinder sit flat...If that's the case the crank is slightly off square to the cylinder.

If there was something out with the replacement, what's the fix? Do you trust the pin locations and have the mating surface to the cylinder machined flat? Or do you doubt the pin locations?