I got a 1983 xr80. What are the piston/cylinder clearance specs.. stock? And how much can I hone/bore out?

Rebore size/piston clearance will depend on the piston diameter and engine type. A split skirt piston tends to have less clearance. An air cooled engine tends to have more clearance.

It is important the boring operation leaves the bore one or two hundredths of a mm undersize and final finishing is done with a micrometer hone passed rapidly up and down the bore in order to leave a 120 degree crosshatched pattern, proven to be the most efficient for oil retention.

It takes at least 1000 miles for steel piston rings to properly bed in but 500 miles is sufficient for cast iron rings and it is important to use a low spec oil for the bedding in process - straight 30 or a proprietary running in oil.

Using a high spec oil from the start is likely to result in the piston rings taking an extraordinary amount of time to bed in - if ever!

As an engine wears the ring lands on the pistons wear also. In addition to ring land wearing on the piston, the bore in the cylinder develops a wear pattern. Has the engine been rebuilt?
If the pistons have worn ring lands and were re-used it may allow the rings (new or old) to twist in the grooves and catch on any ridge in the cylinder, thus breaking them.

When the engine is apart you must check for proper ring land wear. You need to consult the piston manufacturer for proper wear specs, typically around 0.006in.

If you're getting a visible amount of smoke/oil from the breather after the rebuild something is not right. The rings are not seating. I would definitely recommend boring/honing the cylinders and going with a new set of pistons/rings so you don't have to pull it apart again. A little more now can save a lot in the long-run.

General Specifications Item Specification
Displacement L (CID) 4.6 (281)
Number of Cylinders 8
Bore and Stroke mm 90.2 x 90.0
Firing Order 1-3-7-2-6-5-4-8
Oil Pressure (HOT @ 1500 rpm) kPa 138-310
Drive Belt Tension a
Cylinder Head and Valve Train
Combustion Chamber Volume cm 52?±.5
Valve Seats Width?€"Intake mm 1.9-2.1
Valve Seats Width?€"Exhaust mm 1.9-2.1
Valve Seats Angle 44.51-45.01 degrees
Valve Seats Runout (T.I.R.) Max mm 0.025
Valve Arrangement (Front-to-Rear) (Left Hand) E-I-E-I-E-I-E-I
(Right Hand)
I-E-I-E-I-E-I-E
Valve Stem to Guide Clearance?€"Intake mm (Inch) 0.020-0.069
(0.00078-0.00272)
Valve Stem to Guide Clearance?€"Exhaust mm (Inch) 0.045-0.095 (0.0018-0.0037)
Valve Head Diameter?€"Intake mm (Inch) 44.5- (1.75)
Valve Head Diameter?€"Exhaust mm (Inch) 34.0 (1.34)
Valve Head Diameter?€"Gauge Diameters mm (Inch) 42.5- and 32.0
(1.67 and 1.26)
Valve Face Runout Limit mm (Inch) 0.05 (0.002)
Valve Face Angle 45.25-45.75 degrees
Valve Stem Diameter (STD)
?€"Intake mm (Inch) 6.995-6.975 (0.275-0.2746)
Valve Stem Diameter (Std)
?€"Exhaust mm (Inch) 6.970-6.949 (0.274-0.2736)
Valve Springs?€"
Compression Pressure N @
Spec. Length?€"Intake 587.14 N @ 28.02 mm
Valve Springs?€"
Compression Pressure N @
Spec. Length?€"Exhaust 587.14 N @
28.02 mm
Valve Springs?€"Free
Length ( Approximate)?€"
Intake mm (Inch) 49.55 (1.951)
Valve Springs?€"Free
Length (Approximate)?€"
Exhaust mm (Inch) 49.55 (1.951)
Valve Springs?€"Installed
Pressure N @ Spec. Length
?€"Intake 244.64 N @ 40.0 mm
Valve Spring?€"Installed
Pressure N @ Spec. Length
?€"Exhaust 244.64 N @ 40.0 mm
Valve Springs?€"Installed
Pressure N @ Spec. Length
?€"Service Limit 10 % Pressure Less @ 28.02 mm
Valve Springs?€"Installed
Pressure N @ Spec. Length
?€"Out of Square Limit 2 degrees
Valve Guide Inner
Diameter mm (Inch) 7.015-7.044 (0.2761-0.2773)
Rocker Arm?€"Ratio 1.75:1
Valve Tappet?€"Diameter
(STD) mm (Inch) 16.000-15.988 (0.66-0.629)
Valve Tappet?€"Clearance
to Bore mm (Inch) 0.018-0.069
(0.00071-0.00272)
Valve Tappet?€"Service
Limit mm (Inch) 0.016 (0.00063)
Valve Tappet?€"Hydraulic
Leakdown Rate b 5-25 seconds
Valve Tappet?€"Collapsed
Valve Tappet Gap?€"
Desired mm (Inch) 0.085-0.45 (0.0033-0.0177)
Camshaft
Lobe Lift?€"Intake
mm (Inch) 6.58939 (0.2594)
Lobe Lift?€"Exhaust
mm (Inch) 6.58939 (0.2594)
Lobe Lift?€"Allowable
Lobe Lift Loss mm (Inch) 0 (0)
Theoretical Valve Lift @
Zero Lash?€"Intake
mm (Inch) 12.0 (0.472)
Theoretical Valve Lift @
Zero Lash?€"Exhaust
mm (Inch) 12.0 (0.472)
End Play mm (Inch) 0.025-0.165
(0.00098-0.0065)
Journal to Bearing
Clearance mm (Inch) 0.025-0.076
(0.00098-0.003
Journal to Bearing
Clearance?€"Service Limit
mm (Inch) 0.021 (0.0048)
Journal Diameter (All)
mm (Inch) 26.962-26.936
(1.061-1.060)
Journal Diameter (All)?€"
Bearing Inside Diameter
(All) mm (Inch) 27.012-26.987
(1.063-1.0625)
Camshaft Runout
mm (Inch) 0.05 (0.002)
Cylinder Bore
Diameter?€"Surface Finish
(RMS) 0.2-0.6 Microns
Diameter?€"Out-of-Round
Limit mm (Inch) 0.015 (0.0006)
Diameter?€"Out-of-Round
Service Limit mm (Inch) 0.020 (0.00079)
Diameter?€"Taper Service
Limit mm (Inch) 0.006 (0.00023)
Piston
Piston?€"Diameter?€"
Coded Red 1 mm (Inch) 90.177-90.197
(3.550-3.551)
Piston?€"Diameter?€"
Coded Blue 2 mm (Inch) 90.190-90.210
(3.5507-3.5515)
Piston?€"Diameter?€"
Coded Yellow 3 mm (Inch) 90.203-90.223
(3.513-3.5521)
Piston-to-Bore-Clearance
mm (Inch) -0.015 + 0.031 (0.0005-0.0012)
Pin Bore Diameter
mm (Inch) 22.0015-22.004
(0.866-0.8663)
Ring Groove Width?€"
Compression (Top)
mm (Inch) 1.520-1.550 (0.06-0.610)
Ring Groove Width?€"
Compression (Bottom)
mm (Inch) 1.520-1.530 (0.060-0.0602)
Ring Groove Width?€"Oil
Ring mm (Inch) 6.996-7.224 (0.275-0.2844)
Piston Pin?€"Length
mm (Inch) 61.93-62.05 (2.44-2.443)
Diameter mm (Inch) 21.994-21.999
(0.866-0.8661)
Pin to Piston Clearance
mm (Inch) 0.005-0.010
(0.0002-0.0004)
Pin to Rod Clearance
mm (Inch) 0.015-0.040
(0.0006-0.00157)
Piston Rings?€"Ring Gap
?€"Compression (Top)
mm (Inch) 1.0 MAX (0.0394)
Piston Rings?€"Ring Gap
?€"Compression (Top)
mm (Inch) 1.0 MAX (0.0394)
Oil Ring?€"Side Clearance
mm (Inch) 1.25 MAX (0.05)
Oil Ring?€"Compression
(Top) mm (Inch) 0.040-0.090
(0.0016-0.0031)
Oil Ring?€"Compression
(Top) mm (Inch) 0.030-0.080
(0.0012-0.00031)
Oil Ring Snug Fit
Oil Ring?€"Service Limit
mm (Inch) 0.015 MAX (0.0006)
Ring Gap?€"Compression
(Top) mm (Inch) 0.23-0.49
(0.01-0.02)
Ring Gap?€"Compression
(Bottom) mm (Inch) 0.23-0.49
(0.01-0.02)
Ring Gap?€"Oil Ring (Steel
Rail) mm (Inch) 0.05-0.66 (0.006-0.026)
Lubrication System
Oil Capacity?€"Automatic
Transmission (Quarts U.S.) 6.675?±0.125
Oil Capacity?€"Manual
Transmission (Quarts U.S.) 6.425?±0.125
Cylinder Block
Main Bearing Bore
Diameter mm (Inch) 72.401-72.422 (2.85-2.851)
Crankshaft and Flywheel
Main Bearing Journal
Diameter mm (Inch) 67.483-67-503 (2.65-2.657)
Connecting Rod Journal?€"
Diameter mm (Inch) 52.988-53.003
(2.0861-2.0867)
Crankshaft Free End Play
mm (Inch) 0.130-0.301 (0.0051-0.012)
Crankshaft Runout to Rear
Face of Block mm (Inch) 0.050 MAX (0.002)
Connecting Rod Bearings
Clearance to Crankshaft?€"
Desired mm (Inch) 0.027-0.069 (0.001-0.0027)
Clearance to Crankshaft?€"
Allowable mm (Inch) 0.027-0/069 (0.001-0.0027)
Bearing Wall Thickness
(STD) mm (Inch) 2.44-2.452 (0.096-0.0965)
Main Bearings
Clearance to Crankshaft?€"
Desired mm (Inch) 0027-0.065
(0.0011-0.0026)
Clearance to Crankshaft?€"
Allowable mm (Inch) 0.027-0.065
(0.0011-0.0026)
Bearing Wall Thickness
(STD) mm (Inch) 1.920-1.928 (0.075-0.076)
Connecting Rod, Piston and Rings
Connecting Rod?€"Piston
Pin Bore Diameter
mm (Inch) 21.959-21.979
(0.864-0.865)
Connecting Rod?€"
Crankshaft Bearing Bore
Diameter mm (Inch) 56.756-56.876 (2.234-2.24)
Connecting Rod?€"Length
(Center-to-Center)
mm (Inch) 150.7 (5.93)
Alignment (Bore-to-Bore
Max. Diff.) c ?€"Twist
mm (Inch) 0.050 per 25 (0.0015-0.984)
Alignment (Bore-to-Bore
Max. Diff.)?€"Bend
mm (Inch) 0.038 per 25 (0.0015-0.984)
Side Clearance (Assembled
to Crank)?€"Standard
mm (Inch) 0.015-0.45 (0.0006-0.0177)
Side Clearance (Assembled
to Crank)?€"Service Limit
mm (Inch) 0.05 MAX (0.02)
Crankshaft Main Bearing
Journal Taper mm (Inch) 0.020 (0.0007)
Crankshaft Main Bearing
Journal Runout mm (Inch) 0.05 (0.002)
Crankshaft Connecting Rod
Journal Taper mm (Inch) 0.015 (0.0006)

Sounds like worn piston rings,oil passing rings(blow by),have to check piston to wall claerance to make sure its within spec,usually .002 to .004,if more, next size piston and bore,but if its within spec replace rings and hone cylinder to deglaze.

Hi,
Most late modle MX & enduro (from about 1990 on plus some even earlier)
have what is called an electrofusion bore.
This is a very thin plating on the alloy cylinder. They use this so as to allow heat to dissipate quicker & can run tighter piston cylinder tolerances for improved performance.
To answer your questions,
No, they can't be re-bored(like the older style steel sleeved bore bikes could)
Yes, they can be honed but it requires a special type of hone(finger type bottle brush style hone).
Pistons are available increasing in size by much smaller incriments than the old style & are usually marked A,B,C,D(as the coating is much thinner than steel sleeve).
If it is scored very badly & you can see alluminum spots/scores anywhere on the cylinder surface there are several ways to deal with this.
Here in Australia there is a company(electrocill) that can re-cote the cylinder which is much cheaper(plus thicker & stronger) than replacing the barrel
If you have a cylinder re-coated It has to have all studs, seals & power valve assemblys removed.
You would also need to supply(or have them supply) a new piston in order for them to set the correct clearance.
Also here in Australia you can have most of the common models fitted with a sleeve & this gives you the abillity to rebore in the future.
In the U.S this company is known as Wisco(serco in Aust.)
It is worthy of noting that the piston rings are not interchangable between an electrofusion & steel type cylinder.(so if you opt for a re-sleeveing any spare rings from your spares kit ar of no use).
If you need a lead on how & if these services are available in your country(if your not in Australia) I suggest taking a look in the classified section of your local dirt bike magazine.
The trick is to undertake regular srevicing of your air filter(this is A MUST),oiling it properly with propper foam filter oil, useing a top quality 2stroke oil(motul,syn-lube for eg)
& regularly inspect & replace rings/piston as needed to get the best life from electrofusion or steel type bores
Hope this explains it all for you
Regards Andrew Porrelli

Do not hone anything. It its just light rust, dont wory about it. If the rust is heavy take stel wool and some penetrating oil (blaster) and try to clean it up.. Just oil the cylinders down when ready to put the head on.

Yes.

excessive piston clearance.really needed bore job with oversized piston,not just honed and rings.measure piston to cylinder clearance,check spcifications and verify

If your going to do do that much work , I would invest in a Chilton's or Haynes manual