Given how ugly things could get if the jack bolt came loose, the lock cap must be secured.  Safety wire is mandatory.

Time to make a decision.

I can take the engine back out, disassemble, and machine a pocket in the top of the piston to lower the compression.  That’s a lot of work.

But there’s only a small amount of work remaining to put the bike back in operating condition.  Why not try it and see what it does?  If it detonates, stop and add fuel and/or pull out ignition timing.  If it still detonates, remove the engine and machine the piston.  At least I can find out if it will run with the new cam chain tensioner system.

It started right up.  No problem cranking it over.

I did a 500-mile break-in with 10W-40 mineral based oil.  The first 100 miles was total kid gloves.  Never took it past 4K.  Never gave it more than ¼ throttle.  The next 200 miles was a bit more aggressive.  Maybe as much as ½ throttle.  Kept it below 5K.  The last 200 miles was normal driving except for no WOT.   Throughout the break-in I continually accelerated and decelerated.  Tried not to run at a steady speed.

It ran just fine.  Absolutely no hint of the dreaded spark-knock, ping, rattle, etc.  I was mystified.

It felt frisky.  The increased compression and .060” quench really cleaned up the carburetion.  It idles better.  Throttle response is very quick.  It really raps when you blip it in neutral.  It’s way torquier.  It’s a blast to pass on two-lane roads.  Clearly more powerful.
 
There’s noise, not loud noise, not necessarily bad noise, different noise.  It’s hard to explain.  The tappets sound about the same, click, click, clicking away, but there’s also an unusual resonance, whir, hum sort of sound.  It doesn’t sound like anything is eating itself up.  No grinding or scraping sound.  But it is different.

After logging 500 easy miles it was time for an oil change and visual inspection.  I dumped the dino oil and popped off the clutch cover.
The oil looked fine.  No chunks of rubber or metal.  I poured it through a fine mesh wire strainer.  All I caught were a few pieces of hardened Loctite.  I stirred it up with my shop magnet.  Just picked up a few small bits of metal typical of what you would expect from an engine that shares oil with a crash-box transmission.

The tensioner plunger was at 19mm extension.  Not too bad.  I figure there had to be a fair amount of bedding in since new areas of the rear guide are bearing on the chain.  I can live with 1mm increased extension for now.

I pulled the rear chain guide.  It had a few areas where it showed impressions and rub marks from the chain.  It looked like a typical cam chain guide.  No evidence of failure.

The spark plug showed no signs of detonation.

This is what the wire strainer caught.

It was good to go WOT.

I strapped on the GoPro and headed out.  It ran great on my way to the test area.  I gave it WOT every chance I got and there was still no hint of detonation.  Rolling it on in 5th gear felt amazing.  It simply has torque everywhere, and acceleration is strong.

Got to the test area and started doing 2nd gear WOT pulls, recording each pull on the GoPro.  On the 4th pull I thought I might have heard a rattle.  On the 5th pull I heard it again as the tach flew past 5K.  It seemed to be detonating so I discontinued the test.

On the way home it ran just fine.  

I pulled the spark plug and there was no evidence of detonation.  I inspected the piston through the spark plug hole using a flexible camera.  The piston looked fine.

Review of the videos confirmed my seat-o-da-pants impression.  This thing is a lot faster.  The 2nd gear 4K to 7K time is now 2.89 seconds.  That’s .73 seconds faster than the baseline I established with the Stage II head and stock carburetor, and .56 seconds faster than the stage II head with Super E carburetor.  Consider that the .56 second improvement is only for second gear.  There are five gears.  There is an improvement in every gear so a WOT trip through the full gearset is gratifying.  Just need to address the detonation issue.

If what I think I’m hearing is in fact detonation, I must eliminate it.  If it’s something else, or my imagination, I have to figure it out and put the issue to bed.  IMO, if it was detonating it should have left some telltale indicators on the spark plug or piston, but those components look fine.  I also figure, that it should rattle when I load it up in 5th gear, but it doesn’t.  I couldn’t hear any rattling when I reviewed the vids.  I went through them with the volume at max.  No rattle.

First order of business was to add more fuel.  I upped the main jet two sizes from a 62 to a 66.  Took it for a short ride to see how it ran.  It felt good, but I could swear I heard a rattle when I took it WOT in 1st gear.  It was getting late, so I put it to bed for the evening.  I was going to take it for a vid run in the morning.

In the meantime, I plan on installing a wide band Air Fuel meter system and pulling 2° to 4° out of the ignition timing.  Any of you play with that ignition pickup?  How did you do it and how did it work?

Once I’m back on the road, I will continue testing, add fuel as indicated, and see how it goes.

The BIG question: is it really detonation or is it paranoia?  If I can’t find any concrete signs of detonation like balls of metal on the plug, cracked plug insulator, or sand blast texture on the piston, I’m not so sure its detonation.  The contraption has always been a bit of a rattletrap.  Maybe it’s just the normal Savage cacophony.  The 245-psi cranking pressure has me freaked out.  I might have target fixation.

For now, I have learned a few things.

It looks like the problems associated with dropping the head .130” can be managed.  You may end up with an engine with reduced life expectancy, but hotrods have never been models of economy.  If you wanna play you gotta pay.  Only way to answer this question is to keep runnin it and see how it holds up.

10.4:1 compression ratio makes some real good power, and that 245-psi cranking pressure seems to work out reasonably well with the Savage combustion chamber and .060” quench.  Under normal everyday driving conditions, it’s superb.  WOT is killer fast (hopefully not in the literal sense).  Dave has mentioned a number of times that the S40 responds well to an increase in compression.  That is an understatement.  This thing loves more squeeze.  I am amazed that it can handle 245 psi on 92 octane.

The little starter can still whip the motor over smartly, even with over-the-top cranking pressure and no flywheel.

Looks to me like there’s a lot of potential in a flat top Wiseco with .130” additional compression height.  If it turns out that I do have a detonation issue, the Wiseco could always be manufactured with a slight dish in the top to bring the cranking pressure down 20 to 30 psi.  Still need to find out if skirt thrust will be a problem if the compression height is raised about 3mm.

More to come.  I’ll keep testing and adjusting as necessary, and periodically post updates.

DragBikeMike wrote on 08/30/19 at 15:53:24:


Ed L. wrote on 11/25/08 at 12:25:42:

Years ago when my engine died due to a puncture on the bottom of the case, I had the original Stage 1 cam made/installed and also had the head shaved 25 thou. (.025") and the cylinder shaved 15 thou. (.015")  The numbers may have been reversed, 15 thou (.015") head and 25 thou (.025") cylinder, memory is a bit foggy.
Also required was a slight bore of 94.5mm due to  some scraping, and it received the silicone carbide treatment.  It ran great, no issues at all.  I don’t remember the cylinder cranking pressure but it seems like it was about 185-190.
Everything else within the engine remained stock.
Can you offer a general comparison between what you have done and the little I did back then ?
You are taking a whole lot more off than I did.

Regarding Versy's comment: "Yes, but you'll only get 2 small quench areas due to the 4 valve configuration."

I would like more quench area, but it is what it is.  IMO, if you combine the quench area on the intake side and the quench area on the exhaust side, it looks about equivalent to a Harley Evolution cylinder head's quench area.  It's certainly better than no quench at all.

I've been looking at a lot of sport bike engines at my buddy's independent shop.  They all seem to be set up with zero deck and .028" head gaskets.  They all also have pentroof combustion chambers.  Seems to me the factory did that for a reason.

I don't know if I will ever figure out whether or not the improvement in performance was worth all the effort, but I certainly am learning a lot.  From the learning perspective, its worth it.

BTW, thanks for the info on the pickup Versy.

Here's a pic of the quench area.  Its the area marked in red.