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Harley Shovelhead Exhaust Leak Solution

Harley Shovelhead Exhaust Leak Solution
by Rudy Avizius
Posted September 1, 2019

Troublesome shovelhead exhaustAfter decades of enduring what may arguably be one of the weakest links in the design of the Harley Shovelhead engine, I believe that I may have a solution that most Shovelhead riders will appreciate.

I have found a solution to Shovelhead exhaust pipe leaks and I want to share this with the Shovelhead loving community. While I am targeting this article to Shovelheads, it is not limited to this and is a solution that could also be utilized for other motorcycle and automotive applications.

Due to there being only a single bolt to hold the exhaust flange, most Shovelhead riders have experienced the annoying exhaust leaks where the pipes connect to the heads. This results in exhaust blow collecting on pipes, frame, and other places, a muddled exhaust tone. However, the worst part is probably the very annoying popping and backfiring one gets when they let off the throttle.

I have tried double gaskets and that did not solve the problem. Then I tried using high temperature red silicon gasket paste, and that seems to work for a short while. However, but the temperatures at the pipe exceed the temperature capacity of the silicon and it eventually just turns to a soft sticky mess requiring resealing.

I tried the hardening exhaust sealers, but they quickly crack and are very difficult to scrape and clean up to prepare for new sealing attempts.

After researching different gasket materials and compounds used in industry, I came across 3 products that looked promising. I eventually settled on one product and it will be the focus of this article, but will cover the others later in this article. I wish to preface this that this article does sound like a commercial for these products, however I receive no financial benefits from anyone associated with the manufacture or distribution of this product. This is being done simply experiences with other riders.

Deacon 8875 sealantThe research uncovered a compound called Deacon 8875, which is a heat curing fibered paste for high-temperature flange sealing and gasket dressing applications. This is a sealant / refractory hybrid that does not become weak or brittle, and is not affected by the thermal cycling that would be associated with the heating and cooling of motorcycle exhaust pipes. It has temperature range: 500°F to 1800°F, which is well below the operating temperature of motorcycle exhaust pipes. This product comes with comprehensive information and safety handling sheets.

It can be be used on warped or pitted flanges, exhaust systems, turbines, ductwork, any metal-to-metal joints, gaskets, hot blast valve flanges, high temperature steam, hot air and gases, corrosive conditions, up-grade sealing capability of standard non-asbestos gaskets, good chemical resistance. This certainly sounded like all of the properties a good motorcycle exhaust sealant would have.

Deacon 8875 is a thick, fibrous thermal reactive paste sealant/refractory hybrid used in high temperature and high pressure applications. In the presence of heat , Deacon 8875 will expand and form a mechanical (“mechanical type”) seal that is not weak or brittle like ceramics. Very importantly, Deacon 8875 will not cement the flanges together, thus, it will not interfere with future repairs of metal
-to-metal joints.

This sealing material does not air dry, but cures when exposed to heat. It took approximately 1 hour of a normal riding for it to fully cure, and it still seals totally even before curing since there is little pressure in the flange area because the exhaust pipe itself is a large open port to release the exhaust gasses.

To install the sealing compound, I removed the exhaust pipe and cleaned up all carbon buildup around the flange surfaces of the pipe and the heads. I then applied the compound to the flange surface of the pipe using a butter knife I was willing to lose. Then the exhaust gasket was placed onto the pipe. Personally I prefer the copper based gaskets instead of the aluminum ones since copper can withstand more heat that aluminum can.

I then spread more of the sealing compound to the top of the gasket and carefully installed the pipe onto the motorcycle. Once the exhaust port bolt has been tightened, the sealing compound will be squeezed out, and you can carefully remove the excess compound and clean up around the joint.

(It may not be necessary to place any sealing compound below the gasket, and if anyone tries that any feedback would be appreciated by me and other readers as to how well or not well that works out. I am merely stating what I did and what worked for me).

locking bolt for shovelhead exhaustFor another quick tip: while I am on the tightening of the the exhaust bolts, if you are not using some sort of locking hardware on your exhaust bolt, you might want to consider purchasing a “Shovelhead Locking Hardware Exhaust Gasket Kit”. If you a google search you should find distributors for this kit. I purchased mine on eBay. In my earlier years of riding my Shovel, exhaust bolts working loose was a recurring problem until I started using these kits.

Once the excess sealant has been removed, you can take the bike out for a ride in order to apply heat so that the sealant will cure. Once it cures it will create a mess on the outside of the flange which can be cleaned up with a razor and some steel wool. I then masked off the pipes and applied a little high temperature touch up paint to the heads and the pipe seal looked really nice on the bike.

pipe well sealedNow for the best part, there were no exhaust leaks anywhere on either cylinder and without any leaks, the exhaust on my bike has never sounded so good. The best way to describe it is to say that it has a “crispness” that it never had before. There are no more annoying pops or backfires when the throttle is let off and the bike even seems to run better overall. The result were so impressive that this sealant was applied to my wife’s Shovelhead, with the same positive results.

Now, here is the big downside of this sealer. The smallest amount that I could find is a one quart can and it costs $130 which is probably more than most riders would want to spend. Perhaps if you are a motorcycle shop, this would make sense. The product has a 2 year shelf life if stored in a refrigerator.

I toyed with the idea of purchasing smaller containers and making a profit on selling small amounts over the Internet. I have decided not to do this since I only wish to share my experience and knowledge with the riding community. However for someone who may be unemployed or having financial difficulties, this could represent an economic opportunity for some extra income.

Deacon 8875 Thin sealantNow, there were other products that were considered that are available that may also accomplish the sealing of the exhaust pipes. One was Deacon 8875 Thin. This was considered since it comes in a tube that fits into a caulking gun and costs about $38 which is significantly cheaper than the quart can. I also liked how it would probably be easier to apply than the Deacon 8875. The reason it was rejected was because it lacked the fibrous filler material of the Deacon 8875. I was concerned the Thin version might not fill flange gaps as well.

Another product that was considered was Deacon 3300, which is an extruded product. In fact this was the first material considered, but it was even more expensive than the Deacon 8875, and had a lower temperature operating range, so I opted for the Deacon 8875.

I would be very interested in receiving feedback from people who try any of these products or products from other manufacturers that work (or do not work out) for you and share your experience with others in the riding community so we may all benefit. Please feel free to share your experiences in the comments section below.

Wishing everyone out there good and safe riding!