Cometic Primary Gasket Review. – Knoble Moto May 2020
From when I first became interested in motorcycles, everyone told me Harleys leaked oil. As I advanced as a mechanic I have learned that is not true, with modern gaskets anyways.
I have an 05 FXD I use as a daily rider and traveler. Recently I was telling a Cometic rep about how my primary gasket kept leaking. He told me they have a new line of primary gaskets that will seal a gap up .060”. He said this was done by “Cometic’s proprietary AFM (Aluminum Foamette Material) gaskets feature an aluminum core with a chemically blown, compounded nitrile synthetic rubber bonded to the outside.” I was intrigued. Cometic has always been a friend to the grass roots guys, and they proved this again by sending me one to try and give it a review.
The gasket came well packed and in a solid box, so that wouldn’t likely get damaged in shipping. The kit came with good instructions, a primary gasket, shifter plate gasket, new o-rings for the shifter tube, and all the o-rings for the inner primary. It also included the metal tabs that lock in the inner primary bolts in place. The primary gasket has a metal backing plates, and small cellulose foam material that is on either side of the gasket. This foam is what seals against the mating surfaces. The instructions were straight forward with good info. It would be nice it the included the torque pattern in the instructions though.
The average mechanic can complete this repair in their garage with basic hand tools and a torque wrench. You will need an allen socket or torx socket to torque the bolts to spec. You can get these at most auto parts stores. *Buy the better torx socket, because the cheap ones twist easily.
First I drained the primary oil into a catch pan, then since I run mid controls, I removed the shifter and the left foot peg mount. Before I removed any cover bolts, I took the gasket box and I did a poorly drawn picture of the primary cover, then poked holes through it at the bolt location. This allowed me to place the bolts in the same location hole as I removed them. There are an assortment of different length bolts so it is important to keep them in order. Next I removed the shifter plate. From there I went around the cover and loosened each bolt slightly, before I fully removed them. This keeps the cover from cocking and jamming a bolt in before I was able to remove it. I then removed all the cover bolts and the outer cover itself.
Once it was removed I inspected the inside of the cover for damage or debris, and I also inspected the primary chain for wear and free play. There should be .5 to .75” free play in the primary chain, and I was on the high end of this measurement, so I did have to move the adjuster up one notch. At 52,000 miles I figure that is not that bad. I then cleaned the gasket surface with a razor blade then some solvent.
Next I replaced all the o-rings on the shifter tube, cleaned and lubed the shifter shaft, and installed it into the inner primary. Afterwards I installed the Cometic Primary gasket on the alignment studs, and then I put the primary cover onto the studs and I started the bolts in by a few threads. By only using a few threads at first, this allowed me to keep a small gap in between the primary and cover so I could see that each bolt went through the gasket hole and didn’t bind up the gasket. I subsequently ran each bolt into to finger tight, then checked again for alignment and binding.
Bolts are to be torques to 84-108 in-lbs according to the Mo-Co . This is one of the times that torque pattern and specs are extremely important. The shifter plate I torqued afterwards because it is easy to miss torque this plate, and cock it sideways, leading to a faint leak.
From there I reinstalled the shifter, and the foot peg mount. Next I refilled the oil, and then reinstalled the derby cover. I run 75w-140 with friction modifier for primary oil. You can fight amongst yourselves as to the appropriate weight for primary oil. After a 100 mile test ride there was a very faint amount of oil that had wheeped out of the main gasket. So I re-torqued everything and cleaned up the oil. After 500 more miles, nothing has leaked out.
I am very happy with the Cometic product and I would recommend it. 5 Stars! Plus they are located in the greater Cleveland area, so it is always great to keep my money local. Check them out at www.cometic.com The Part Number for this kit was: C9885. I also posted the how-to, install video of this on my Youtube channel www.youtube.com/c/knoblemoto
Knoble Moto is a partner of Skidmark Garage. We teach classes for the DIY crowd, on all aspects of motorcycle repair. Entry level maintenance, valve adjustments, carburetor cleaning and tuning, drive line service, suspensions, and even engine work. Our class subjects are updated regularly, so check back often. If there is a subject you do not see covered, shoot me an email at knoblemoto@gmail.com Find us on Facebook at www.facebook.com/knoblemoto, Instagram Knoble_Moto and www.KnobleMoto.com
