Sealant for Barrel to Crankcase Gasket?

I'm getting ready to install the barrell on my Mk IIA, and was wondering if anyone has any experience with using high-temp sealant on the gasket. I know that Mick Hemmings recommends not using any and just putting the paper gasket on dry. Is there a good reason for not using a thin coat of sealant? It seems like good insurance against oil misting out of this interface.

I tried the dry paper gasket and got a leak. Pulled it apart and used Loctite Plastic Gasket with no paper gasket and got no leak. Also ups compression a little. I'm sure Yamabond or Hylomar would work. Yamabond is what I used to seal the crankcase halves. No leak there, either.

I used Permatex Super Grey - it's Permatex's version of Yamabond (or is Yamabond Yahaha's version of Permatex Super Grey?)

In any case, it's great stuff for the same uses.

+1 on the Permatex Ultra Grey (which I generally refer to as Yamabond).

Do you guys use Yamabond/Permatex with or without the paper gasket. It seems to me that Yamabond should be applied by itself without a gasket.

Correct - no gasket. Mick Hemmings, forgive me!

Works a treat.

(I do use a light smear of Yamabond on gaskets all the time though - works great!)

No gasket on the earlyier 850, YAMABOND is good ,just make sure you keep the oil way clear and don't get any oil on the sealing faces, quite tricky, fit pistons, the support barrel above crankcaes, degrease, apply sealant, sealant is more recomendable than the gasket on 850 application.

I use "Ford" brand high temp RTV (grey) and it works good.

I used the permatex grey (no gasket) and inserted a long pipe cleaner in the cylinder oil passage, insuring the pipe cleaner protruded from the underside of the cyl about an inch. With the cyl held off the base by the pistons being at the top of the stroke and pistons just far enough into the bore for the rings to be engaged, smeared a THIN coat of the sealer onto the crankcase surface. Then I lowered the cyl, ensuring that the pipe cleaner entered the passage on the crankcase. After tightening the cyl down I removed the pipe cleaner, soaked a new one in lacquer thinner and inserted it in the passage until it bottomed and rotated it back/forth. I pulled it out and repeated that with a new pipe cleaner. I pulled that one out and then shot compressed air into the passage from the timing case side. This ensures the passage is totally clear of any sealant. When I pulled the cyl I found that a previous "mechanic" had managed to obstruct the passage almost 1/2 way with RTV. Since the passage is only 1/8", it is (IMO) too small anyway, any obstruction will create a big problem with oil filling the intake rocker box.

Here's a pic though later I realized I should have taken it earlier and from the side before I lowered the cyl to show the pipe cleaner protruding from the bottom and the oil passage it was going to be entering. Oh well...

When I pulled the cyl I found that a previous "mechanic" had managed to obstruct the passage almost 1/2 way with RTV. Since the passage is only 1/8", it is (IMO) too small anyway, any obstruction will create a big problem with oil filling the intake rocker box.

Click to expand...

Just another reason why I prefer anaerobic sealants like Loctite 518 rather than RTV silicone for this type of application!

That little oil passage is just ment to drian off the head right? I have that as well as an external hose to drain off the head........

That passage is the single drain for the intake rocker box. The exh rocker box drains initially from two small passages in the head but then to the pushrod tunnel so it has much better draining.

You have an external line that handles draining from the rocker box(es)? Could you post a pic of that?

I've already installed the barrel (with pistons installed of course) with a dry gasket but not torqued anything nor installed the head. Is it imperative to have sealant on this gasket? Prior to assembly I saw several comments saying this gasket is usually installed dry.

Base gasket goes in dry. If you use one at all. I think the received wisdom is that omitting the gasket (which nets you a 0.3 compression ratio increase, BTW) and just using a little Wellseal, Yamabond, Permatex Ultra Grey, or other sealer is preferable. That's what I just did on my 850 and it worked just fine. FWIW/YMMV.

I tend to stay away from any type of silicone RTV on four stroke engines in general. I've rebuilt too many engines with orange or grey blobs of silicone blocking the oil inlet screen.

I prefer lacquer based sealants like Threebond 1194 or the equivalent Yamabold liquid sealants. I apply a very thin layer with a solder flux brush on one side of the parts to be assembled, wait about 90 seconds then tighten the parts together. Leakage is rare.

When disassembly time comes, it all wipes off with a cloth soaked in lacquer thinner and never seems to clog things up.