Engine Build Specs
Ring gap by bore size, ring order, valve lash, cam timing, and the three mistakes behind most post bore kit knocking. Plus every TBparts install PDF in one place.
Ring End Gap
By Bore
Piston rings
Four thousandths per inch
Four thousandths of an inch (0.004 inch) per inch of bore is the standard TBparts uses on every piston ring kit it sells. Square the ring in the bore with the piston, measure the gap with a feeler gauge, and check it against the chart.
- Too tight and the ring can seize in the bore as it expands with heat, which is catastrophic piston failure.
- Too loose and you lose compression, which is horsepower, and the engine burns oil.
- Stagger the gaps. End gaps must not line up with each other. Space them evenly around the piston.
| Bore | Inches | Target gap | Safe range | TBparts kits at this bore |
|---|---|---|---|---|
| 39mm | 1.535" | 0.006" | 0.0055 to 0.0065" | Stock bore, Z50, XR50, CRF50 (49cc) |
| 47mm | 1.85" | 0.0074" | 0.007 to 0.008" | Stock bore, CT70, XR70, CRF70 (72cc) |
| 50mm | 1.97" | 0.0078" | 0.0075 to 0.0085" | Stock bore, CRF110 (109cc) |
| 52mm | 2.05" | 0.008" | 0.007 to 0.009" | TB 88cc kits, Z50, CT70, XR50/70, CRF50/70 |
| 55mm | 2.165" | 0.0086" | 0.007 to 0.009" | TB 132cc kit, CRF110; TB 138cc kit, CRF125 |
| 55.5mm | 2.185" | 0.0087" | 0.007 to 0.009" | TB 130cc kit, TTR110 |
| 58mm | 2.28" | 0.009" | 0.008 to 0.010" | TB 147cc kit, CRF110; stock bore, KLX140 |
| 60mm | 2.36" | 0.0095" | 0.008 to 0.0115" | TB 143cc kit and 155cc stroker kit, KLX110 |
| 62mm | 2.44" | 0.0097" | 0.009 to 0.012" | Daytona 190 four valve, stock bore |
| 63mm | 2.48" | 0.0099" | 0.009 to 0.012" | TB 170cc kit, KLX140 |
| 64mm | 2.52" | 0.010" | 0.009 to 0.012" | See your kit listing for the bore size |
| 67mm | 2.637" | 0.010" | 0.009 to 0.012" | TB 178cc kit, KLX110 (55mm stroker crank) |
Five Rings.
One Order.
Ring installation
Bottom groove first
Every TBparts ring set installs the same way, bottom groove first. Rings installed in the wrong order or upside down is one of the three installation errors TBparts sees most, and it shows up as smoke and low compression on a brand new top end.
Before they go on
Gap each ring in the bore first (chart above), then install. Once the rings are on, rotate them so no two end gaps line up.
1
Expander ring
The wavy one. It goes in the lower groove first, by itself.
2
Lower oil ring
Thin flat rail. It sits below the expander in the lower groove.
3
Upper oil ring
Second thin flat rail. It sits above the expander in the lower groove. The expander is now sandwiched between the two rails.
4
Second ring
The black one. It goes in the center groove.
5
Top ring
The silver one. It goes in the top groove, with the markings on the ring facing up toward the piston crown.
Two Numbers,
One Direction
Cylinder head and cam
Valve lash, all TBparts heads and cams
0.003 in
Intake and exhaust, engine cold
Some valve tick is normal. That gap is the clearance the valve train needs once the engine reaches operating temperature. Recheck lash after the first session on a new top end; tight valves after break in look exactly like a jetting problem.
Cam timing, every TBparts application
Lobes down
Toward the piston, marks aligned
Line up the 0 on the cam sprocket with the mark on the head, and confirm the lobes face down toward the piston at that moment. Combined with the crank timing mark, that is the whole procedure. A cam installed lobes up runs, and knocks loudly, until it does not.
The Three Mistakes
We See Most
Before you call
TBparts lists these three as the most common installation errors on its bore kits and clutch kits. None of them is a parts problem, and all three show up as noise or smoke that gets blamed on the carb.
Cam in upside down
What you hear: loud knocking right after the cam went in. Runs, but sounds like a hammer.
Fix: when the 0 on the sprocket meets the head mark, the lobes must face down toward the piston. Pull the cam cover and look.
Clutch nut not torqued
What you hear: knocking that gets worse, then spline damage. Often after an oil pump or clutch job.
Fix: it gets tightened after the oil pump goes on, with a clutch nut socket. Not a hammer and a screwdriver. Ever.
Rings on wrong
What you see: smoke, oil use and soft compression on a brand new top end.
Fix: follow the five ring order above, markings up on the top ring, and stagger every gap.
Stroker cranks install exactly like a stock crank. Use a Clymer or Honda shop manual for the case split; the TBparts PDFs below cover the top end and clutch.
Every TBparts
Install PDF
Install guide library
These are the notes and photo sheets TBparts has written for its own kits. They are a help, not a substitute for a Clymer or factory shop manual, which every builder should have on the bench.
Honda 50 and 70 engines
PDFHonda 50/70 Bore Kit Installation InstructionsThe core top end procedure for every TBparts Honda bore kit.
PDFHonda 50/70 Engine Tear Down InstructionsGetting the top end and side covers off in the right order.
PDFHonda 50/70 Manual Clutch InstallationConverting the automatic clutch to a TBparts manual clutch.
PDFHonda 50/70 High Volume Oil Pump InstallationThe oil pump goes in before the clutch nut is torqued.
PDFV2 Cylinder Head Notes, Honda and ImportSetup notes for the V2 race head on Honda and import cases.
PDFBillet Quarter Turn Throttle, Cable InstallRouting and fitting the cable on the billet throttle.
PDFTBW1369 Oil Cooler KitOil cooler plumbing and mounting.
PDFTBW1370 Oil Cooler KitOil cooler plumbing and mounting.
PDFTBW1604 Oil Cooler KitOil cooler plumbing and mounting.
CRF110, CRF100 and other Honda
PDFCRF110 HD Clutch Assembly, TBW1599Stage 1 heavy duty clutch install.
PDFTBW1599 Diagram BreakdownExploded view of the TBW1599 clutch.
PDFStage 2 Clutch Kit, TBW1663Stage 2 clutch install.
PDFTBW1761 Install SheetInstall reference with photos.
PDFXR/CRF100 Rear Shock InstallationShock fitment notes for the XR100 and CRF100.
PDFCRF100 Carb Kit and Mud Flap InstallPhotos of the carb kit fitted.
PDFTBW1619 Shock Installation NotesShock install notes.
Kawasaki and Yamaha
PDFKLX110 Manual Clutch InstallationManual clutch kit with spacer, all KLX110.
PDFKLX140 VM26 Carb Kit InstallMikuni VM26 kit fitted on the KLX140.
PDFTBW1849 KLX140 Shifter InstallationShifter install notes.
PDFRoller Rockers TBW1710 and TBW9526Adding TBparts roller rockers.
PDFTBW1482 Installed ImagesPhoto reference.
PDFZ125 Engine Temp Sensor RelocationRelocating the temp sensor on the Z125.
PDFTTR110 TBW1826 Kit InstallationKit fitted on the TTR110.
PDFTTR110 with TBW0316 InstallationKit fitted on the TTR110.
PDFTBW1367 Oil Cooler KitOil cooler plumbing and mounting.
Engine Build
Questions
Get some answers
What ring gap should I run on a 143cc KLX110 kit?
The TB 143cc kit uses a 60mm bore. At 0.004 inch per inch of bore that is 0.0095 inch, with a safe range of 0.008 to 0.0115. Measure each ring squared in the bore with a feeler gauge.
What is the valve lash on a TBparts head or cam?
0.003 inch on both intake and exhaust, set with the engine cold. Some valve tick at that setting is normal. Recheck after the first ride on a new top end.
Which way does the cam go in?
Lobes down, toward the piston, at the moment the 0 on the cam sprocket lines up with the mark on the head. If the lobes are up at that point, the cam is 180 degrees out and the engine will knock.
My engine knocks after installing a big bore kit. What did I do wrong?
Almost always one of two things: the cam went in with the lobes up, or the clutch nut was not torqued after the oil pump went on. Neither is a jetting problem. Check both before touching the carb.
What order do the piston rings go on?
Bottom groove first: expander (the wavy ring), then the lower oil rail below it, then the upper oil rail above it. Black ring in the center groove. Silver ring in the top groove with the markings facing up. Then stagger the end gaps.
Do I need a special tool for the clutch nut?
Yes, a clutch nut socket. Tightening it with a hammer and screwdriver is the fastest way to damage the splines, and an under torqued clutch nut knocks and eventually strips.
Do stroker cranks install differently?
No. Every TBparts stroker crank installs exactly like the stock crank. Use a Clymer or Honda shop manual for the bottom end; the TBparts PDFs cover the top end and clutch.
What is the ring gap rule?
Four thousandths of an inch of end gap per inch of bore diameter. A 2 inch bore wants about 0.008 inch. The chart on this page has it worked out for every TBparts bore size.
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