I’ve been having trouble with my transmission.  The higher gears pit.  On my 97mm Flat-Top engine, 5th gear pitted and the debris from the gear-teeth got into my cylinder.  The cylinder was damaged.  No more rebores on a 97mm.  Then, on a smaller engine (94mm Flat-Top), 4th gear started pitting.  I caught that failure before any serious damage occurred to other components.  I suspect these gear failures are related to overload.  As Armen says, “You find your limits by exceeding them”.

To prevent another gear failure, I built a new engine using an old 4-speed gearset from a 1987 LS650.  The gears, for the most part, are wider than the 5-speed gears, and they appear to be beefier.   I’ll be doing a report on that engine soon.  It’s a bit different.  It makes a lot of power and should be a good test of the 4-speed gearset.  I also have plans to add a separate lubrication system for the gear teeth.  It’s ambitious, but no guts no glory.

I needed a way to inspect the gears without tearing the whole engine apart.  The only way I’m gonna learn anything is to keep trying, and an inspection routine is a must.  I already had a cheap borescope that I got at Walmart, but the camera is too big (9mm), it can’t capture a photograph, and the resolution sucks.

A good friend of mine turned me on to DEPSTech Endoscopes.  They make these cool endoscopes that connect to your smart phone or iPad via Wifi.  They take still pictures and videos.  The resolution is decent, but glare is a problem.  With a bit of effort, and a little patience, you can get a good idea of what’s goin on in your engine.

About $43 bucks on Amazon.

I had the new engine opened up for a clutch repair.  Like I said, it makes good power.  That gave me an opportunity to try out the endoscope.  This is a picture of 4th gear that I took with the endoscope.  Lots of hob marks but no pits yet.  The endoscope is inserted through the port just below the clutch, 4th gear is on the right, 2nd gear is on the left.  The gears are on the input shaft.  Haven’t figured out how to access the output gears yet, but the failures seem to be confined to the input gears.  I think this will work good.

To get consistent pictures of the transmission gears and make setup easy, I made some fixtures to hold the camera in just the right location.  You tape the camera to the fixture, insert the assembly into the appropriate hole in the case, and you are ready to go.  The gears on the input shaft rotate freely when you turn the rear wheel, so 360°inspections are easy.

Camshafts are another component prone to pitting.  Would be nice to be able to check the lobes for the emergence of pits.  I threw together a top end with an old, pitted cam.  This will give you an idea of what to expect.  I feel that I will be able to identify the onset of pitting using this tool.  This is a shot of the exhaust lobe.  Even though there’s a lot of glare (due to all the oil), it’s still easy to identify pits.

After practicing a bit, I was able to get some good pictures of the 97mm Big Bore 4-Speed DR650 cam.  I think these shots are a lot better.  Much easier than removing the head cover for inspection.

This is the DR650 intake lobe.  Still looks great.

One of the areas that interest me is the cylinder bore.  The front side of the bore starts developing vertical, linear, marks from the debris getting wedged between the piston and cylinder.  If left unchecked, the debris eventually wrecks the cylinder and the rings.  It’s not the clearest picture, but I can see the vertical lines in the front of the cylinder.  Access via the spark plug hole is easy.  The camera is only 3.9 mm, goes right in and allows you to form the flexible shaft to get the angle you need.  Don’t know why I couldn’t get a clear shot but it’s better than nothin.

Very cool!
I’ve been waiting for these gizmos to get small enough and cheap enough for me to justify. Sounds like it!
I’m not clear about which one to get. One is listed as 2 Megapixtels, one is 5 MP, and yours uses a different rating.
Obviously, 5 MP is better than 2, but how does yours fit into the ranking?
All else being equal (except the price) I’d like to buy the best one.
As always, thanks for your hard work and thorough documentation.
Hope all is well, and Happy Holidays!

Armen, I don't know much about mega-pixels.  The device I got (WF070) is rated at 1920*1080px.  I'm not sure exactly what that means but seems to be the same numbers used to define a laptop video display.  I got it primarily for the small camera.  The camera is 3.9mm diameter which is really small.  It has lights in the camera.  It's not the greatest resolution, but with a little practice you can get a decent picture.  I really like the feature that allows me to take still photos and videos.  You can also zoom in & out, and rotate the picture.  I'm sure the resolution is fairly low because the files are small.  This thing creates a file on the order of 200kb while my iPad files are usually at least 2mb.

Justin, I wish I knew exactly why my gears are failing.  I call the failure "pitting", but the correct term is "spalling".  Spalling is an extreme form of pitting and is defined as "destructive failure".  It's a fatigue failure associated with cyclic stress due to overload.  The obvious solution is "reduce the load" (not an option I am willing to accept, yet).

There are a few things I can do to try and prevent pitting/spalling.  Reduce the load (not on my list).  Provide more lubrication (I'm workin on that).  Increase quality and viscosity of the lubricant (I run Mobil 1 V-Twin 20W-50).  Increase the contact area (the 4-speed gear set does that).  Increase hardness of the contact surface (that's a tough one).  Improve surface finish of the contact area (New England Gear Polishing).  So far, the 4-speed gear set seems to be holdin up.  Have to see where things go.

This final comment will probably raise the fur on Armen's back.  I have a suspicion that the mini flywheel might be associated with the gear spalling.  I have noticed that the engine struggles to maintain high speeds in 4th & 5th gear.  It really struggles if an incline is involved.  When faced with a challenge like a 6% grade at 4500 rpm, I have a tendency to attempt to overcome the obstacle (twist the wrist).  Without the stored energy of the 6-pound flywheel, it doesn't wanna carry through the parasitic strokes (exhaust, intake & compression).  So, in order to maintain speed and/or accelerate, you have to develop a lot more BMEP than necessary.  In other words, the push you have to apply on the power stroke must be a lot greater without the flywheel.  The gears have to deliver that push.  

I'm currently runnin the big wheel.  It would be nice if I could test the theory, but my resources and energy are limited.  I would have to do long term tests with and without the mini-wheel.  So, for now, it's the shotgun approach.   The heavy flywheel was easy.  Wider gears were a bit harder.  More oil will be challenging but I have a plan.