JOG, thanks for the tip on the Stone Coat.  I'll look into it.  I doubt that I will switch from the JB Weld High Heat putty.  I'm having excellent results with it, and because it's a two-part log the consistency is perfect for the initial application into the port.  I would be very reluctant to put any sort of metallic reinforcement into the epoxy.  If piano wire or stainless mesh got loose and went through the valves it would be horrific.

Thanks for refreshing my memory Sneezy.  Sure wish you had told me that your gearset was installed in a maximum effort motor that had been run on a flat track for an entire race season.  

I spent a couple of hours putting around on the 4-speed this morning.  I'll get used to it.  It actually shifts better than the 5-speed.  But the absence of the extra gear keeps me wishin it was still there.  I guess I got spoiled.  One nice feature is I always know when I'm in top gear.  With the 5-speed, I was always checkin to make sure I was in top gear.

C'mon gang.  I know there must be some of you with engines on the deckplates all opened up.  Take a peek in there and see if ya gots any pits in them gears.

Aweseome posts and I will read through a few times.

I am pulling out my 87 engine today as I have some noise and aluminium in the filter.
I have decided not to sell it and keep it for another couple of years. I am going to buy Lancers stage 3 cam if the 2 way shipping cost isn't going to make it too expensive.
I am going to go up to a 97mm Wiseco as I have found a few people with them here in Australia for sale.
Will need to inspect the top end and valves for wear and decide what else I need to replace to freshen up this motor. It currently has the stock carb with 155 and 55 jets, straight pipe and a cone filter.

The rear side of the piston isn’t as bad as the front.  Only trace amounts of carbon accumulation below the 2nd ring groove.

I checked the ring free gap.  Both the top ring and the 2nd ring had free gaps right at 11mm.    The factory wear limit is 9mm & 11mm respectively (note: bigger is better), but that’s for factory rings.  Comparing the used Wiseco rings to new Wiseco rings seemed prudent.  I have a set of brand-new rings and the free gaps were 12mm & 13mm.  The old rings didn’t seem too far off the mark.

I had measured the piston and compared it to the detailed drawing.  The detailed drawing specifies 3.6985”, and the piston measured 3.6985”.  I slipped the piston into the cylinder and checked clearance with a feeler gage (quick & dirty).  It was .005”.  That seemed like a lot.

So, the rings looked good, and the valves checked out.  There was no evidence of a head gasket leak.  The only thing I can see that might be the cause of the reduced compression would be the bore and/or the skirt clearance.  Those linear marks probably result in some leakage.  Looks like debris off the gear teeth strikes again.  The piston rocking in the bore most likely results in some leakage too.

Another possibility could be my compression gage.  As of late, I seem to be seeing 200 to 205 psi an awful lot.  I have also noticed that it doesn’t seem to hold solid at the max achieved pressure.  It tends to bleed a bit and then holds.  I need to check out the gage.

This thing was runnin great when I tore it down.  Aside from a bit of oil consumption, all was good.  Power, noise, vibration, temps, pressure were all good.  I’m sure I could have continued to run it for a good long time.  I’ve been reading a lot about gear pitting.  Gears have a tendency to pit in areas where there is heavy contact, and then as the load gets redistributed across the tooth the pitting subsides.  The gear gurus refer to this as “initial pitting”, as opposed to “destructive pitting” (self-explanatory).  My pitting doesn’t look like initial pitting, but who knows.

I have the bottom end completely disassembled.  With the exception of 4th gear, all looks good.  I plan to figure out a way to provide more lubrication to the two top gears (4th & 5th on a 5-speed, or 3rd & 4th on a 4-speed).  That should prove challenging.  While I’m figuring that out, I will continue racking up the miles on the Big Bore 4-speed.  I have a way to monitor the gears for pitting.  If I don’t detect any pitting, I will run it at least 10,000 miles before I tamper with it.  I want to see if the heavier 4-speed gears hold up better than the 5-speed gears.

More to come.

So, this begs the question-what is your assembly/break in procedure for the piston/rings?
In the 70’s, when Udo Gietl was building F1 and then Superbike BMWs, he ran into all sorts of grief with ring seating. Big ass air-cooled motor.
After a ton of work, he came up with the following routine, which I still use:
After the cylinder is honed (bead hone), thoroughly wash the cylinder with hot soapy water, and dry. Do not put any oil on the cylinder walls, not even WD-40.
Assemble the rings on the pistons, install the piston in the cylinder just up to the bottom of the rings. Put one dot of oil on the piston skirt front and back. Complete assembly.
Use a break-in oil in the motor. Regular amount of oil. Non-synthetic, like the basic Honda oil or the Amsoil break-in oil. 10-40 or thinner.
Put a fan in front of the motor. Start the bike and hold he revs to about 2K. Run for 30 seconds or so until the smoke stops.
Hop on the bike and ride. Not lugging, not redlining. Varying throttle. Do this for at least 100 miles without excessive idling. Once the bike has 300 miles, dump the oil and use your regular oil.
I’ve pulled apart lots of motors that I’ve broken in this way, and always saw almost complete contact/wear on the middle ring, and no blow by past the middle ring. Minimal blow by past the top ring.

Lancer, thanks very much for taking the time to check the piston size.  I think maybe you measured in the wrong location or possibly are misinterpreting your thimble.  The reedings you provided would result in a clearance on the order of .020" (0.5 mm), which is astronomically big.

I measure my piston at a location 1/2" up from the bottom of the skirt, and 90 degrees from the wrist pin bore.  Like this.