35 posts in this topic

Your usual great photos, Forman...No "major" damage evident, some wear visible but nothing serious.  The piston measurement was revealing.  Is there piston skirt aluminum sloughing or any skirt damage to the cylinder bore?  I recall severe glazing, but is the bore out of shape?  Were the piston skirts dragging the wall?

 

If not, this is as you say, an engine with accumulated debris.  Flushing passageways would be worthwhile if you decide to rebuild completely.  What kind of piston-to-wall clearance were you experiencing here?

 

Moses

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I'll have an inside micrometer available to me later this week.  I do want to finish this rebuild knowing that most likely it will take a overbore kit.  If you remember we started this thread after I bought a lower mileage engine with a cracked case.  I should have photos of that damage tonight, I'll post on the engine case thread started earlier

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Great, Forman!  After measuring the piston and cylinder, we'll outline the findings and factory recommendations from your shop manual...As a wrap-up for the "inspection" phase, it would be good to show piston to wall clearance and the ring end gaps in this loose cylinder.

 

We can start a new topic as you "rebuild" the upper end of this engine and perform related work: "Kawasaki KLR 650 Engine Rebuild" would be a good working title for the topic, you have the entire engine apart now...Your photo/video documentation has been valuable.  It's time consuming and appreciated.  

 

This is valuable to KLR owners and others...some consolation despite the work and cost involved!  Once done right, you'll have a reliable motorcycle that is quite desirable, the KLR has a strong following.

 

Thanks!

 

Moses  

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I've acquired a good inside micrometer, and was able to measure the inside diameter of this cylinder. I was also able to measure the ring end gap, and the piston outside diameter.  Keep in mind this cylinder and piston were bought off of craigslist and I can't explain why these measurements  seem odd. I'll refer to this cylinder as the '98 cylinder.   

 

Cylinder inside diameter  3.936     factory specifications (3.937-3.9374)  service limit 3.9409   I measured this cylinder in 20 different places I never got a measurement over 3.936.

 

Piston outside diameter   3.924     factory spec               (3.9347-3.9353)  service limit 3.9291  The piston has exceeded its service limit by .005"

 

Piston to cylinder               .012     factory spec               (.0017-,0028)   Its easy to see why I was burning so much oil  but I can't explain the power I felt.

 

Ring thickness                N  .0455     2N .0455                 (.0461-.0469)  service limit  .0430

 

Ring end gap                  N  .018       2N .016                   (.008-.016)  

 

Why the piston is so far gone and the cylinder has room for wear is beyond me I suspect some used parts were exchanged before I bought the engine.  The piston and rings will need to be replaced but the cylinder might be repaired by honing.   

 

Moses you had asked previously what jets were in the carburetor :  Stock main jet below 4000' elevation is a 148 mine is a 150 we are at 2000 feet.  Pilot jet and needle jet are stock and rated for my elevation.  My exhaust is a straight open pipe I don't know the brand name but it is not stock.

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I have the luxury of having another piston and cylinder, This is off of the '02 engine with the cracked crankcase.  The previous owner said it used oil and the piston had a thick layer of carbon build up.  

 

Cylinder inside diameter    3.937     (3.937-3.9374)              service limit  3.9409

 

Piston outside diameter     3.934     (3.9347-3.9353)            service limit   3.9291

 

Piston to cylinder                .003     (.0017-.0028)

 

Ring thickness                   N   .046   2N  .046     (.0461-.0469)

 

Ring end gap                    N   .012    2N  .013    (.008-.016)

 

I know my problem can be solved by installing an overbore kit, one I'm looking at will run about $450 with new forged piston, rings, gaskets,machine work and shipping.  I would like to save some money and hone the cylinder myself but I really don't know what tools, parts and technique that would require.

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Hi, Forman...Good work here...The piston is shot, that's clear, and the piston to wall gap is extreme, the cause, as you note, for the loss of oil control.  That and the cylinder not having a good cross-hatch pattern led to lack of cylinder seal.  A cylinder leakdown test would confirm.  (See my leakdown test video at the magazine site.)  These motorcycle engines have high compression ratios, and the compromised performance from poor cylinder seal is not always that noticeable, perhaps the reason the engine "felt strong".

 

I am puzzled about one reading:  ring end gap.  If those rings (#1 engine) were new, the gap should be less than the 0.018".  Your cylinder bore diameter is normal from your readings, yet the ring gaps are out of range.  When you do the ring gap check, make sure the ring is perpendicular to the wall and level.  This will keep the measurement accurate.  Measure below and above the "ridge".  Likewise, when you measure bore diameter with an inside micrometer, try to keep the mic level and also at the widest point in the diameter (typically right below the ridge).  This can be tricky to do, but you will get a more accurate read.

 

So, you're considering a big bore kit with a forged piston.  Be aware that a forged piston, though optimal for racing, does call for more piston-to-wall clearance.  On my XR650R Honda beast, I am staying with a cast piston (OE type) and quality rings.  The new cylinder sleeve from L.A. Sleeve is an iron/alloy (chrome/moly) that is spot on for bore diameter and piston-to-wall clearance.  The liner has a very nice machine cross-hatch, which I will be highlighting soon in an HD video during assembly...Forged pistons can be a bit noisier when the engine is cold.  Also, I stayed with a stock 10:1 compression ratio on the XR, while most forged pistons bump up the compression; this makes power but also impacts engine life and can be a cause of detonation (ping) unless you run spendy, high-octane fuel...Just some thoughts.  We can kick this around...

 

Your jetting may be rich enough for the open exhaust (uncorked), especially at your altitude.  Try to confirm the exhaust maker and research their jetting recommendations for the "uncorking".  On the XR650R, uncorking (intake manifold and air box improvements plus exhaust) requires a change from the 125 main jet (ultra-lean stock) to a 175 main at sea level.  This is a huge bump, but the XR650R OE jet is way too lean for openers...a U.S. EPA concession on Honda's part while the overseas carburetors are 175 main jet in stock form!  We're based at 4400 feet elevation, I ride to 6000 feet or higher often, and I'll first try a 172 main jet with the open exhaust and freer flowing induction.

 

Moses

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Lets just say the first cylinder piston is a wash and a great candidate for the overbore I spoke of.  

 

What about freshening up the cylinder and re ringing the '02 cylinder?  I have never done this or seen it done so I'll have many questions

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If the cylinders are interchangeable, that's a clear option.  I would spend the relatively small amount of money to have the cylinder power honed at an automotive machine shop to get a precision cross-hatch for oil control and compression seal.  If the '02 piston is on spec, that's a possibility, a new cast piston is not terribly expensive.  (There are new cast pistons in slight oversize, too, if honing goes wide.) 

 

Get the piston first for fitting while the machinist hones.  Ask his opinion about the right piston to order.  Do this once, I'll gladly walk you through this process to a successful end...

 

Moses

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Finding that machine shop might be the most difficult part...

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Forman, you're looking for a traditional automotive machine shop that does cylinder boring and honing.  In rural and semi-rural communities, these shops were often associated with NAPA stores and other retail parts outlets.  At your area, try the Yellow Pages under "Automotive—Machine Shops".  Also, some larger motorcycle shops have boring and honing equipment, a Honda, Kawasaki, Yamaha or Harley-Davidson shop might be helpful here.

 

You're looking for a shop that has a CK10 Sunnen or similar boring and honing machine.  This is the classic tooling for automotive block work.  There are some smaller machines for lighter engines. 

 

I can describe in detail how to use a "glaze buster" silicone honing brush or a three-stone hone, I have used these tools for years.  They are for light honing and glaze removal and can leave a decent cross-hatch pattern if used precisely.  You run these tools from a common 3/8" or 1/2" drill motor, or a drill press if set up properly.  If your cylinder is true and not measurably tapered, you can get by with a home honing job when done correctly.

 

See what you find for a local machine shop.  If you'd like to hone the cylinder yourself, let me know.

 

Moses

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