I had a chance to replace my stator this weekend. Last weekend I replaced my Spark Plugs
and tested the stator since my charging system
was acting funky. I was able to buy a used stator (with side cover and gasket) for $50 from an old SV racer who had a whole cabinet full of SV side cases with stators. I took the pick of the litter but I was hoping to kill two birds with one stone and find a clean side cover to replace mine as it has the dreaded paint rot but, as could be expected, all the SV covers were race rashed.
If you have seen my past posts you'd know that I can't just work on my bike as is, I like to find simple and cheap ways to improve the design of the components that I work on. As we all know the stator is a weak point on this bike so I considered that a challenge to address when I opened it up for service. Its seems clear that these stators run hot, breaking down the wire insulation and eventually shorts out. The first thing I noticed was how little metal there is on the stator mount built into the crankcase cover. That was a big red flag for me immediately.
While these stators are oil-splash cooled a significant amount of heat is conducted through that mount but it just doesn't have enough meat to draw the heat out of the stator core and coils. If the mount was filled in at the areas marked by the red arrows and silver lines then I think the stators would probably last a lot longer. Since Suzuki won't be recasting the side cases any time soon I thought of a plan-B.
In my business we use thermal grease for mating computer CPUs (that run hot) to a heat sink so I thought a little (okay, maybe a lot) thermal grease can improve the conduction of heat to the case cover and lower the heat load on the stator. Step one was to make sure that the mating surfaces were smooth and mated properly which is important for a good thermal connection. Here is a picture of my new stator, the back side that faces the cover (sorry for the blurry image).
The yellow circle highlights an area where I sanded down some bumps that would have kept the stator core from sitting flush on the mounting surface thus impeding heat flow. When I pulled my old stator I inspected it and found what look like resin gobs and weld splatter in the area where the wires are attached (circled in red). These defects would have definitely interfered with a proper mating of the stator to the mount and increased the thermal resistance in that area so I have to wonder if this is a factor in stator failures. Fortunately, my new stator was clean and smooth in this area. The surface that the rotor mates with on the side case is machined so it was smooth enough for a good thermal connection so I didn't have to do anything to prep that other than clean it with rubbing alcohol. BTW, I used rubbing alcohol to clean all the surfaces of oil before I started.
The second issue I addressed was the mounting bolts. These bolts are M6-1.0x30mm but fully threaded which I didn't like. I thought that a bolt with a shank would be better for conducting heat out of the stator core.
The bolt on the left is an M6-1.0x45mm which has a shank of 20mm which is a tad longer than the thickness of the stator core so I had to add a washer. I eyeballed the clearance of the cap head + washer and it was below coil wires so there should be no interference issue with the back of the rotor. I did have have to file down the washers diameters a bit to fit under the cap so they didn't hang over the edge of the stator ring. I stacked an OEM bolt on top of a washer and used that to mark the place to cut the 45mm bolt. Before cutting it I put on a nut so that after cutting I could remove it and it would chase the threads, then I filed down any cutting burrs and I had a 30mm bolt with a shank. Here is everything ready for assembly.
On the left (yellow circle) I coated the crankcase cover stator mount with thermal grease. I also put a small dab at the bottom of the screw holes to conduct heat from the ends of the bolts but left the threads clean. I used MG Chemicals Silicone Heat Tranfer Compound 860 which seemed to have the right properties, including temps over 200C/400F (the jar, which was $9, is circled in black but you can't read it as I intended. Also, its enough to do about 10,000 stators so I am set for a while... if anyone one wants some PM me). I greased the back of the stator (green circle) that mates with it's mount and put a liberal amount of grease in the through holes (I used Q-Tips). I also greased up the shanks of my custom bolts shown in the purple circle and put a dab on the ends of the bolts, keeping the threads clean. Before assembly I put a tiny dab of blue loctite on the mounting threads just to be sure nothing comes loose. Here it is all assembled and (almost) ready to be installed.
This is after a bit of cleaning with rubbing alcohol to remove the thermal grease that oozed out from all the contact areas when I assembled it and tightened the bolts. In retrospect I think I used too much thermal grease and Q-Tips are probably not the best applicator but I couldn't think of anything else. Also, the final step was to run a bead of black, oil-resistant sealant around the gap between the stator and the case cover. Its circled in green and that gap is not a pressure fit so I was afraid that oil would wash out the thermal grease which does not set like sealant.
Okay, there you go that is my new and improved stator install. As always, use at your own risk, YMMV, benefits may only exist in my mind.