Dave, do I remember correctly…you are replacing the 97mm piston with the 94mm flat top?

Is that right?  I can’t remember why you wanted to downsize from 97 to 94.  Was it compression ratio and/or lighter weight?

If I ever decide to try a higher performance piston, I’m trying to learn what I should be considering.  Wanting to understand why you are making the change.  Thanks.

badwolf wrote on 07/04/24 at 17:47:00:


My rides are mostly in the 3,000 - 4,000 rpm range.  Once I get beyond the populated areas the roads often go for 20 miles without any gear changes or intersections.  I seldom go through the gears with more than 1/2 throttle......these roads are more fun in the corners than they are on the straight parts.
I was able to get the rings off this morning.  The grooves look good with a minor amount of burned oil on the exhaust side of the oil grooves.  There is no deposits in the holes.

Higher compression definitely relates more power , even on reg fuel. It runs ok on reg but the higher the octane the crisper the throttle gets. Feed it good fuel. I prefer a tank full of high test with a 1 qt can of the lawnmower fuel you get at the hardware store. That combo wakes up the performance. No need for octane booster with the canned fuel. Crisp , all throttle , no coughs , hiccups or farts , just $hit n git ! Now for some red dot training.
Hope the new piston serves you well.

ThumperPaul wrote on 07/05/24 at 09:08:58:


Yep - I have a few sets of pistons and cylinders on the shelf.  

It is an addiction - I gathered up some spare parts and even a couple of engines just in case I blow something up!!!

The ring compressor is a little taller than I would like - but it worked.  Later on I will clamp it to a stock piston in my lathe and see if I can trim some metal off - it is stainless and trying to cut it with shears or a hacksaw or cut off wheel is likely just going to make a mess.

In addition to the ring compressor - I made a wood block to hold the piston up while I placed the cylinder down over the piston and rings.

Here is the bottom of the head.  I did not polish the aluminum combustion chamber this time - but I did coat the valves with the Cerakote thermal barrier (front and back)......and I also coated the exhaust port.

Dave, I just can't get enough of your cafe.  It is simply beautiful.  Did you have to humiliate me with those shots of the work area.  It's like open heart surgery.  I can't even detect a micron of dirt anywhere.  How in the world do you keep things so clean.

Your rocker arms and cam look great.  I have had poor luck with the welded cams.  I suspect that's a result of poor welds.  As I recall, you had a problem with your cam a few years back.  Web replaced it.  How many miles are on the cam shown in the current photos?  The Web cams I ran were used with heavy springs.  I wonder if the pitting was a result of the increased spring pressure.

After 17K you can still see the tool marks on your piston, only the bottom edge of the skirt is polished.  Pretty sweet.  I don't understand those scuff marks.  I always see those when I tear a project down for an inspection.  I can't feel them, can't snag a fingernail on them, but they are clearly a visual indication of something.  I wish I could figure out what's goin on with those scuff marks.

I feel for you with the oil weeps/seeps/leaks.  I just can't seem to solve my oil weep issues.  Seems like capillary action just draws the oil though all the crevices.  I just finished converting to an external oil feed.  No more pressurized oil goin up through the cylinder.  If I continue to struggle with the oil weeps, it will be coming from a drain, not a pressurized passage.

How do you like working on your engine in the frame?  I really like it.  To me, it's way less invasive and also comfortable.  I don't have to worry about tipping the engine over, or having it fall off the work bench.  Application of torque to the primary drive gear, clutch, flywheel nut, alternator rotor, and drive pulley nut can all be accomplished safely, without fear of dumping the whole shiteree on the deck.  It's the ideal engine stand.

You mentioned that you were able to easily remove your rings.  By any chance do you recall if your 2nd ring was a bit tight?  It would be very helpful to me if you happen to recall how tight that 2nd ring was on the back side of the piston (intake side).

Could you take a look at the butt faces of your old rings, the rings off the 95mm pop-top?  You run your butt gaps waaaaay smaller than I do.  I am interested to hear if there as any polish on the faces of the butts, any sort of indication that the butts are touching.

I agree, the 87 octane will no longer be an option with the flat-top piston.  You're gonna have a lot of squeeze with that flat-top.  Please do a compression check and let us know how much you pump.  It should be about 240 psi.  BTW, what is your quench clearance?

You make your own ring compressor???  I gotta hand it to you.  That's pretty resourceful.  I'm too lazy.  Looks to me like you did a really nice job on the tool.

Please keep the pics of your project comin.  It's an inspiration.  Very nice indeed.

In 2018 I removed the pawl from the cam chain tensioner and made a spacer to fit behind the plunger to limit the travel of the plunger back into the housing.  This has been working fine and I don't really believe there was much of a change (unfortunately I did not record the extension anywhere that I can find it).

My new method is to make a new plunger with a longer shaft so that there is more plunger contained in the housing - which both limits the backward travel but also has more plunger in the housing to prevent the bind that can happen when the stock plunger extends too far.

I first used my lathe to cut the plunger diameter, then a milling machine to cut the flats in a 5/8" bar.