In July of 2024, I tore down my engine for a 20,000-mile inspection.  I was testing the modified lube oil system, and it was time for a look inside the engine.  At that time, my odometer was reading just a little over 67,000 miles.  All the components affected by the lube oil system mods looked great.  No problems with gears, bearings, cam, rockers, or valve stems.  The lube oil system mods seemed to be a success.  But the piston was another story.  It had significant detonation damage.

I was running a 97mm Wiseco Pop-top piston.  It was set up with extra-high compression.  The cylinder was shortened to achieve a higher compression ratio (10.8:1 vs 9.5:1).

To keep my test program going, I restored the engine with a Wiseco 97mm Flat-top piston.  To reduce the compression ratio, I milled out the top of the piston to achieve a deeper pocket.  The deeper pocket increased the volume from 5cc to 10cc (the Deep-Dish Piston mod).  I used a standard-length cylinder and set up the quench at .038”.  Those changes lowered the compression ratio to 10.6:1. I was hoping that the slight reduction in squeeze along with the tight quench would solve the detonation problem.

This old post provides details on the failure, my evaluation, and recovery.

https://suzukisavage.com/cgi-bin/YaBB.pl?num=1720767228

It’s time to put this problem to bed.  The 97mm pistons seem to be prone to detonation when you jack up the compression over 10:1. The 94mm pistons don’t seem to mind, but the 97mm pistons aren’t happy with cranking pressure above 195 psi.  I decided to make three changes to my engine; seriously reduce compression, install a cam that closes the intake valves later, and take out two-degrees of ignition advance.  I anticipate a slight increase in cylinder head temperature resulting from the decrease in compression and retarding the ignition timing.  This post will document the changes.

Let’s start by figuring out how to reduce compression.

OK, so no tight quench.  I can’t use tight quench to mitigate the detonation issue, but I can easily reduce compression.  I used the compression calculator on the Wiseco website to figure out how much negative piston deck I would need to bring the compression ratio (CR) down to 9.8:1.  If the piston is situated .012” below the cylinder deck at TDC, and I install a .062” head gasket, I should have 9.8:1 CR.   A .036” base gasket combined with a stock length cylinder results in -.012” piston deck.

BTW, that calculator on the Wiseco website is sweet.  This is the data you will need if you use the tool.  The values will vary depending on your build.

The cylinder deck needed a kiss to make it flat.  I always find these things with an irregular head gasket surface when I check them on the surface plate.  That small area by the right-rear corner will be ok (I plug the oil passage).   I wanna keep the material removal to a minimum, and you can see the tool bit was just touching, so it can’t be more than a few ten-thousandths low.

The rigid hone saved my bacon.  I ended up with a great surface finish, and the cylinder was round and straight within .0002”.  I was very happy.  The Wiseco Website has some excellent guidance on honing.  I followed that guidance using three grades of stones and it turned out great.

The rigid hone has a micrometer feed, two abrassive stones, and two felt wipers.  The wipers help wipe and wash away debri.  The wipers also stabalize the hone.  This Lisle hone is a bargain.  It will do a great job if you are patient and meticulous.

I used 80 grit stones to bring the bore diameter within .003” of finished size.  Then 180 grit stones to bring it within .001” of finished size.  Then 280 grit stones to hit the mark.  The surface finish and cross hatch turned out great.

I always do a second check with feeler gages to verify that I didn’t screw up.  It’s a quick & dirty way to check piston clearance.  The feeler reading agreed with my micrometer readings (.0025” on the money).  I am confident I got the piston clearance right.

Then I make a threaded plug from an M6 x 1.0 bolt or screw.  Just cut off the head of the fastener and slot the end with a hacksaw.