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Rebuilding the Honda XR650R Motorcycle Upper Engine

dirt motorcycle dirt motorcycle forum off-road motorcycle dual-sport motorcycle dirt bike discussion dirt bike how-to dirt motorcycle how-to Honda XR

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#1 Moses Ludel

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Posted 28 December 2013 - 04:54 PM

The magazine's Honda XR650R performs remote field work as an HD video filming platform.  Reliability is essential.  After purchasing the bike in non-running condition, I ran a compression test when the engine refused to start.  I moved from the simple compression test to a full-fledged cylinder leak down test, the pinpoint diagnostic tool of choice.  Want to know more about a leak down test? Click here for the 4WD Mechanix HD Video Network feature and details on the leak down test!

 

High cylinder leakage called for a top end inspection and repairs.  That tear down for inspection can be found at the magazine as the HD video how-tohttp://www.4wdmechanix.com/Honda-XR650R-Motorcycle-Upper-Engine-Rebuild-Part-1-Tear-Down-How-to.html.

 

Attached File  Cylinder Leak Down Test-8.JPG   96.97KB   0 downloads Attached File  Honda XR650R Engine Teardown-8.JPG   92.29KB   0 downloads

At left is the cylinder leak down test covered in the HD video how-to. At right is the actual top engine tear down, part of the current rebuild. See both HD videos at the magazine for details! 

 

The step-by-step teardown, rebuild and assembly are now a single HD video streaming rental at Vimeo On Demand.  Included in this rental is a bonus feature on valve adjustment (which is also available as a separate streaming rental). You will find this 54-minute feature at: http://www.vimeo.com...and/hondaxr650r.

 

Here is a review of that rental video:

 

     "Coming across this video couldn't have been more fortuitous - both in timing and content. I happened to inherit a motorcycle of the exact same type and with the exact same problems as the one starring in the clip. The author/producer treats the subject thoroughly and with close-ups giving great detail of the matter at hand. Not only that, he has an online magazine with a forum through which he is eminently available for input and feedback. Having watched this gave me the confidence to embark on the solution on my own - saving loads of money and learning in the process."—David E.



#2 DavidEasum

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Posted 02 July 2014 - 06:34 PM

Question for you, Moses:

 

Is there a difference between the compression stroke and the exhaust stroke on the XR when the cam is out? I’m worried that if I’m 360 degrees off on reassembly, I’ll put it back together with the ignition firing on the wrong stroke. Or does the ignition simply fire every time the crank goes around so that it doesn't matter? 

 

D.



#3 Moses Ludel

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Posted 29 July 2014 - 07:17 AM

David, for the Honda XR650R, the ignition fires on each TDC of the piston, two times during the four strokes.  Specifically, the ignition fires at the top of the compression stroke and top of the exhaust stroke.  The exhaust stroke firing keeps the spark plug cleaner and otherwise will not affect performance. 

 

Simply put, for valve timing, as long as the piston is at top-dead-center (TDC) on the Honda XR650R, you can align the camshaft sprocket properly.  Your only concern is to have the camshaft and its sprocket tensioned on the pull side.  To accomplish this, always bring the piston to TDC without going too far and needing to back up.  This way, there is pull tension on the camshaft sprocket and no chain slack.  This prevents a valve timing error due to chain slack.

 

Following the camshaft and sprocket installation, I always recheck the valve timing after installing the chain tensioner.  After installing the tensioner, rotate the crankshaft in its normal direction of rotation, orienting the cam sprocket marks properly.  Bring the piston slowly to TDC and stop there.  Tension applied at the backside of the chain, the cam sprocket timing marks should be exactly where you want them with the engine running.

 

Moses



#4 DavidEasum

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Posted 09 August 2014 - 07:32 AM

Thanks for confirming! That's what I thought.

 

But then if I was wrong, I would feel pretty stupid once everything was together but wouldn't run!

 

D



#5 Moses Ludel

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Posted 10 August 2014 - 11:33 PM

Very sensible to be clear here.  As you note, valve timing is a big thing with a four-stroke, especially an engine with an overhead camshaft, long chain, a tensioner and a timing sprocket that must align properly.  Glad you confirmed!

 

Looking forward to your success story with this engine.  You'll really like the renewed performance, David!

 

Moses



#6 DavidEasum

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Posted 11 September 2014 - 12:48 AM

Hi Moses,

 

I reassembled the cylinder, piston and head last night - taking little "computer breaks" along the way to confirm what I was doing by looking at your video of the rebuild. What a great resource to have in this backwoods! (I mean the internet - but your video as well!)  :D

 

I still have work to do (valve adjustment among other tasks), but I'll give a few insights from my experience so far:

 

  1. For people sticking with the original cam: When reinstalling the retainer clip for the auto-decompress plunger, note that the clip can seem like it's properly installed, but in fact, it's possible that it is riding in the space below the groove provided. If so, this will prevent the plunger from rising to its intended height. It pays to double check with a good flashlight and your reading glasses. 
  2. When reinstalling the camshaft (I suppose this applies no matter what version of cam you use), you should insert the 8x17.5 cam-end retainer dowel in the head before dropping the cam in. Once the cam is in and the sprocket on, the dowel can no longer be inserted (actually, it probably can, but it would involve some force that I hesitated to apply). As you can gather, I had to remove the freshly torqued cam sprocket bolts, slide the sprocket off the shoulder on the cam, move the cam, insert the dowel, put the cam back in place with the sprocket, re-time the sprocket (I marked it so at least it was easy), reinstall and retorque the sprocket bolts, risk dropping stuff in the engine because now you lost patience, bla bla.. You get the picture.
  3. I suspect that the long 6 mm bolts that go in the right side of the valve cover down into the cylinder are prone to stretching - I've not torqued one of them to full spec.as it feels a little "iffy."

Overall, things have gone smooth as butter - in large part thanks to the video. Not only is it "directions" on how to do things, but it's also a photographic record. I found myself going back, not always to listen to you, but to find an angle showing where that little doohickey lying on the floor is supposed to go!  

 

I'm surprised by how much resistance there is to turning the engine now, but I don't suspect there's anything wrong. It's just that it seems there's way more compression now than before - yet I haven't even installed the spark plug!!!

 

Now off to try to find some motor oil! That's another thing that we suffer here - no fancy selection of oils. 

 

D.



#7 DavidEasum

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Posted 11 September 2014 - 12:36 PM

Pfffttt... Seems I have something strange going on with the autodecompressor despite my efforts to ensure that the moving parts were rotating the right way. I even removed the magneto cover to ensure counter-clockwise rotation and proper TDC-C (had not done this before as I felt comfortable with just looking at the mark through the peep hole).

 

Despite all of this, the right side exhaust valve is asking for a huge amount of backing off the adjuster screw. I tried to include a photo, but the computer is not cooperating. And then when I turn the engine over, I notice that the right side valve has a distinct timing delay over the left for opening and a similar amount of timing advance for closing (though I think I understand the exhaust valves are supposed to open in concert).

 

Time to do some more sleuthing. Unfortunately, the fridge is dry, so there's no more fuel to keep me going (I mean beer - and jetting is not critical in this matter), so the investigation will have to wait....



#8 DavidEasum

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Posted 11 September 2014 - 12:48 PM

On the plus side, I have found a place to get "good" oil. It's a South African outfit called Engen; and they sell synthetic 10W40 full-synth in half liter bottles for about $5 a pop. I hope it mixes well with the 1/10th liter of Lucas break-in oil that was mentioned as "de rigueur" by Moses. 

 

I suspect that the "with zinc" additive is more "break-in important" for cams (of which mine is not new - though it was for Moses) than for rings and pistons (which have indeed been changed in my case). In any event, this lube will only stay in there for the first few hundred kilometers of break-in before getting swapped out with 100% full-synth. I hope there's a market for the Lucas stuff among my buddies since I brought back 2 pints/liters and I only need about 1/10th of that for the XR!

 

Whatever the case, having "good" lube of any kind will surely work wonders for this motor that has apparently been starved of TLC in its previous life.

 

More later!

D.



#9 Moses Ludel

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Posted 11 September 2014 - 05:55 PM

You're making very good progress, David!  Yes, the camshaft bearing set pin should be in place before installing the camshaft and sprocket.  This is shown in the video, but I'll add a footnote.  Will also emphasize the importance of seating the oil plunger circlip in its groove.  If the valve clearance and valve timing are correct, the resistance that you're feeling without the spark plug in place should be the tension from the valve springs.

 

Exhaust valve unseating is part of the auto-decompression system.  When adjusting the valves, you must bring the rockers and valves into position without passing TDC on the compression stroke.  If you do pass TDC, continue rotating the crankshaft two more turns to bring the piston once again to TDC on the compression stroke.  If you do go too far, the auto-decompressor will unseat the exhaust valve to relieve compression.  This is what you're experiencing, making you want to loosen the adjuster.  The gap closure and valve opening is actually the auto-decompressor working. 

 

Try just bringing the piston to TDC on the compression stroke while rotating the crankshaft in its normal direction of rotation.  Review the valve adjustment section of the video.  See 25:41-minutes.  You'll recall that the intake rocker arms open together, but the exhaust valve rockers are separated.  One exhaust valve rocker works with the auto-decompressor on the camshaft.  The other exhaust rocker works with the hand lever decompressor.

 

Note: As a precaution, check or adjust the hand lever decompressor free-play to make sure there is no interference when adjusting valves.

 

As for your break-in oil, the zinc additive will help.  Do not use the synthetic oil yet.  You want enough friction at the piston rings to seat the rings.  Your synthetic oil offers exceptional lubricity, which can prevent normal ring seating.  At your first oil change, you will remove the non-synthetic oil and zinc additive.  Now you can refill with your synthetic oil if the rings are seated.  I would go to 400 kilometers before this first oil change.  That way, the rings will surely be seated.  As a footnote, I installed a new oil filter after the first 50 miles and topped off the oil.  This gets rid of initial flushing and wear-in particles that may accumulate in the oil filter. 

 

Check the oil level immediately after shut-off, before the oil drains downward into the sump and engine.  Run the engine, idle down, shut off and immediately check the oil level.  If you wait, a false reading will lead to overfilling and possible damage to seals and crankcase sealing. 

 

Moses



#10 DavidEasum

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Posted 13 September 2014 - 02:46 AM

Sure enough, it was just too late at night for me to have the patience in getting the cam off the autodecompressor. Yesterday with a little more time on my hands, I rotated the crank a few more times (it actually took a whack at the kickstarter), and the decompressor clicked off, letting the right side exhaust valve lash go wide as expected. I've reset it now, and it would seem that all is good to go.

 

Carb, vacuum and breather hoses, and new cables are the next step of reassembly.

 

D.



#11 Moses Ludel

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Posted 13 September 2014 - 12:50 PM

David...In the video, you can see me lubing the camshaft bearings and sprocket/chain with LubeGuard.  The auto-decompressor mechanism could gain from a light lube in that process.  This is a busy mechanism with a one-way, spring loaded clutch.  It can get sticky.

 

On my XR650R, pre-rebuild, the motorcycle had set for a long period in storage (previous owner).  I attempted to kick over the engine and had the auto-decompressor jam several times with increased kicking effort and even a lock up of the kick starter, which did free itself without damaging parts, fortunately.  This was another incentive for my opting out of the auto-decompressor and installing the Hot Cams Stage 1 camshaft to eliminate the stock auto-decompressor. 

 

Again, there is nothing intrinsically wrong with the auto-decompressor or stock camshaft, many racers liked the feature.  In "Dust to Glory", it appears that the engines use an auto-decompressor with Stage 2 level camshafts, as the riders are kicking repeatedly and in rapid succession during restarts at the pits.  This is not possible with the manual decompressor, as it takes a few seconds to "find" TDC and tip over slightly before kicking the starter through.  Though this may sound time consuming, I can start a high compression thumper with just the hand lever decompressor in about the same time or less than an auto-decompressor. 

 

For high compression XR thumpers, Honda capitulated early on and added the auto-decompressor for kick starting.  My XR350R and XR500R each have cable actuated decompressor mechanisms.  The kick starter mechanism actuates an exhaust valve unseating lever via an external cable to the rocker box.  The auto de-compressor became incorporated with the camshaft on the XR600R, a feature that the XR650R inherited.

 

Note: Some members are having difficulty adding photos or illustrations to posts.  Simply click on "More Reply Options" next to the "Post" button.  Drop to the bottom of the full editor box, and you'll find the "Attach Files" button at the left.  That will open up your computer file browser, where you can pick the photo file or any other file (several at one time if you like), then add it/them to the attachments.  You'll see the photo(s) or file load.  Now place the curser at the point in the edit box where you want the photo to appear.  Click on the "Add" button next to the loaded file.  The bracketed file description will appear in the edit box.  When you "Post", the photo (thumb) or file (like the PDFs I like to toss out for folks) will appear in position at your post!

 

Moses





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