ninjette.org - View Single Post - Lots of questions

DannoXYZ · June 5th, 2023, 04:50 PM

Engine-building isn't so much about swapping parts as it is about getting numbers right, which is 99% of effort. Trick is "blueprinting" steps, picking numbers that's most optimal given available production tolerances.

1. To remove deposits (burnt carbon from using non-synthetic oil), you'll want to use some kind of chemical that doesn't affect metal cylinders, such as B12/PB-blaster with 3M green scotch-brite pad. Cylinder-clearances should be at minimal end of range at top. I prefer taper-bore with mid-range clearances at bottom to relax stress on rings. Right now, most likely you've got too-large clearances between piston & bore. Leading to excessive piston-rocking with prevents rings from sealing. You can get replacement cylinders here (no boring, just minimum plateau-honing with brush/ball flex-hone to create cross-hatch, 5-10s max, angle between 28-35 degrees): https://www.ronayers.com/oemparts/a/...inder-piston-s

2. What gaps did you measure? Ring-end gaps is primary difference between worn vs. new engine. Buying pre-gapped rings just gives you pre-worn engine. I find tigher-then-spec works best for power and longevity. I'll install multiple sets of rings to find optimum setting. Start 1st set at tight end of factory spec. Then pull engine out after couple hundred miles and install tighter set and repeat. After 4-5 sets, I may see fretting-marks at end of rings, that set is too tight and I'll re-install previous set, done! Typically ends up being about 1/2-3/4 of minimum amount specified in manual.

4. Valve-seat sealing is all about pressure. Valve-springs provide fixed amount of clamping-force. As seats wear, their contact-width increases and you have less pressure per unit area (PSI). Mistake most people make is lapping their valves when rebuilding. They are "pre-wearing" their valve-seats by increasing width of contact and lowering clamping-pressure per unit area. This is most likely where you're losing 67-75% of your sealing. Every single Ninjette engine I've had apart have had worn-out valve-seats with too-large contact ring. Worse on pre-gens due to less-durable valve-train and more years of abuse. This engine has contact-width of 2,5mm on intake and 3,0mm on exhaust, way, way worn!!!

Specs from manual is 0,5-1,0mm contact seat width. Lapping does not improve sealing because it spreads out spring-force, leading to less pressure!

Proper procedure is to grind 32 and 67,5-degree upper & lower cuts to reduce 45-degree seat-area back to 0,5mm width. Then you've increased clamping-pressure from same valve-springs and seal is much, much better.

Water's not good for testing because it has surface-tension (it pulls itself together). Alcohol's typically used to test, but even then, it's not accurate model of actual combustion-pressures. Best to use vacuum or pressurised air since it has lowest viscosity. On high +12:1 engines, you'll see combustion pressures in 1000-1500psi range, depending upon RPM & load.

Not easy to model and test that on bench. Best to follow manual and cut valve-seats to minimum width. Old grinding-stones method is not longer needed. Modern Sunnen/Serdi machines can do all 3 angles in single pass (along with valve unshrouding):

Link to original page on YouTube.

June 5th, 2023, 04:50 PM	#16
DannoXYZ ninjette.org certified postwhore Name: AKA JacRyann Location: Mesa, AZ Join Date: Dec 2011 Motorcycle(s): CB125T CBR250R-MC19 CBR250RR-MC22 NSR350R-MC21 VF500F CBR600RR SFV650 VFR750F R1M ST1300PA Valkyrie-F6C Posts: A lot. MOTY - 2018, MOTM - Nov '17	Engine-building isn't so much about swapping parts as it is about getting numbers right, which is 99% of effort. Trick is "blueprinting" steps, picking numbers that's most optimal given available production tolerances. 1. To remove deposits (burnt carbon from using non-synthetic oil), you'll want to use some kind of chemical that doesn't affect metal cylinders, such as B12/PB-blaster with 3M green scotch-brite pad. Cylinder-clearances should be at minimal end of range at top. I prefer taper-bore with mid-range clearances at bottom to relax stress on rings. Right now, most likely you've got too-large clearances between piston & bore. Leading to excessive piston-rocking with prevents rings from sealing. You can get replacement cylinders here (no boring, just minimum plateau-honing with brush/ball flex-hone to create cross-hatch, 5-10s max, angle between 28-35 degrees): https://www.ronayers.com/oemparts/a/...inder-piston-s 2. What gaps did you measure? Ring-end gaps is primary difference between worn vs. new engine. Buying pre-gapped rings just gives you pre-worn engine. I find tigher-then-spec works best for power and longevity. I'll install multiple sets of rings to find optimum setting. Start 1st set at tight end of factory spec. Then pull engine out after couple hundred miles and install tighter set and repeat. After 4-5 sets, I may see fretting-marks at end of rings, that set is too tight and I'll re-install previous set, done! Typically ends up being about 1/2-3/4 of minimum amount specified in manual. 4. Valve-seat sealing is all about pressure. Valve-springs provide fixed amount of clamping-force. As seats wear, their contact-width increases and you have less pressure per unit area (PSI). Mistake most people make is lapping their valves when rebuilding. They are "pre-wearing" their valve-seats by increasing width of contact and lowering clamping-pressure per unit area. This is most likely where you're losing 67-75% of your sealing. Every single Ninjette engine I've had apart have had worn-out valve-seats with too-large contact ring. Worse on pre-gens due to less-durable valve-train and more years of abuse. This engine has contact-width of 2,5mm on intake and 3,0mm on exhaust, way, way worn!!! Specs from manual is 0,5-1,0mm contact seat width. Lapping does not improve sealing because it spreads out spring-force, leading to less pressure! Proper procedure is to grind 32 and 67,5-degree upper & lower cuts to reduce 45-degree seat-area back to 0,5mm width. Then you've increased clamping-pressure from same valve-springs and seal is much, much better. Water's not good for testing because it has surface-tension (it pulls itself together). Alcohol's typically used to test, but even then, it's not accurate model of actual combustion-pressures. Best to use vacuum or pressurised air since it has lowest viscosity. On high +12:1 engines, you'll see combustion pressures in 1000-1500psi range, depending upon RPM & load. Not easy to model and test that on bench. Best to follow manual and cut valve-seats to minimum width. Old grinding-stones method is not longer needed. Modern Sunnen/Serdi machines can do all 3 angles in single pass (along with valve unshrouding): Link to original page on YouTube. Link to original page on YouTube. Last futzed with by DannoXYZ; June 5th, 2023 at 06:02 PM.