Re-assembling the XR’s engine top end

I let the paint cure for a few days and then took the left and right engine covers off as well as the camshaft cover, cylinder head and cylinder.  Then installed the rotor, stator, front sprocket (15 teeth in replacement of the original 14), and various small parts before screwing both side covers back on, this time for good. 

Now we’re ready to get the top end mounted on the engine.  The work is straight forward as Honda engineered everything rather superbly for the XR500 engine.  Let’s animate the steps through a slide show and see how everything is coming together:

All main parts are here, we’re ready to get started…


The cylinder is bored 1mm over to fit the 90mm Wiseco piston (see previous post for details on this piston). I’ve ordered a new set of corresponding piston rings — let’s verify that they fit.  The end gap should be between 0.30mm and 0.50mm and not exceed 0.65mm.  The measured end gap is 0.60mm, so we’re borderline.  I inherited this piston and cylinder and unfortunately I don’t know who machined it.  It was bored in the upper limit, but within tolerances.  Crossing my fingers that we’ll not have too much piston rattle (!).


Let’s mount the piston rings.  I’ve had a few unfortunate accidents in the past and now am hyper cautious during this operation and always use the help of a piston ring installer.


Piston is mounted in the engine.  The new Wiseco pin fits too tightly so I have to make a few adjustments to make it slide in properly.  The ring ends are positioned according to the chart provided by Wiseco.


Piston and cylinder are in place.  Sliding the piston in the cylinder while compressing the rings is another operation where I am very cautious not to damage a ring.  I’m breathing again.


The next step is to mount the valves back into the cylinder head.  Over the years I’ve used all sorts of valve compressors which were for the most part designed for large engines and thus were incredibly frustrating when applied to smaller valves and cylinder heads.  This time around though I got myself a new tool, and this one is killer, making the job a real joy (Genius Tools valve spring compressor).


Each of the four valves is mounted back in place.  The Genius valve compressor has me smiling all the way.


Valves are back on, cylinder head is ready to go.


Valve side of the cylinder head.  The camshaft bearing journals in the XR500 engine are known to easily get scored and show signs of seizure.  This cylinder head bearing journals though are in great shape.


Cylinder head is mounted.  Next step is to install the camshaft.


Camshaft is in place.  Here again, Honda engineering designed everything very well and the camshaft timing adjustment is straight forward.


Starting to look like an engine.  Final step is to adjust the cam rocker clearance and then manually rotate the engine to make sure that the 10.5:1 Wiseco piston offers enough clearance for the valves.  Everything is good.



Tadahhh!  The engine is ready to be mounted in the frame.

This was fun!  Next step is to clean and paint the exhaust and then we’ll start focusing on the frame and suspension components.

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14 Responses to Re-assembling the XR’s engine top end

  1. H. Fritzer says:

    Avec un peu de patience, nous avons traduit (pour les expressions techniques ce fût
    Papi:-)) le chemin de la restauration de ton engin. Je dois dire que nous l’avons fait avec beaucoup de plaisir, admiration pour ton travail et aussi un peu de fierté pour notre fils. Ca nous a également rappelé ta première passion pour la Puch 2 vitesses. Félicitations!

  2. Roland linder says:

    Salut, this looks just perfect maybe even better than at the factory!
    You should have put together our Porsche race engine too !!!!
    Now, let’s hope for the paint to survive the first heat wave.
    You better have a frame is a semilar shape too.
    Keep up the good work, this is great to see coming together
    Bonne semaine

  3. James says:

    Hi Mike,
    I was wondering if you could offer some technical advice. I’m working on the same engine and managed to strip the top cam tensioner bolt. The acorn bolt is nice and tight, but somehow the top bolt stripped out.

    I’m aware of the cam shaft issues in these engines, so I’m obviously concerned but wouldn’t mind not having to tear down the top end again…haha

    Thoughts on what to do?

    • Mike says:

      Hello James — my recollection is that the top screw holds one end of the tensioner in place while the lower acorn bolt is attached to the tensioner sliding mechanism and is responsible for maintaining the tensioner position. So both are needed to assure proper tension. If you don’t want to take the cylinder head off, which would mean taking the engine off of the bike’s frame, then you can try rebuilding a thread with something like Loctite Fixmaster Steel Liquid ( Not ideal but it could work. Once the top screw is back in place you really won’t need to unscrew it again to set the tensioner — untightening the lower one should suffice. Hope this helps.

      • James says:

        Hi Mike,

        Thanks for your reply. Do you think I could re-tap to a bigger bolt? The bike isn’t far from being apart, so pulling the engine won’t be a huge issue at this point.


      • Mike says:

        The challenge with fitting to a bigger bolt is that the tip of the larger bolt will need to enter the hole in the top part of the tensioner and this would not work with a bigger bolt — unless you machine it a bit.

      • James says:

        I decided to pull the engine and avoid the possibility of any metal shavings falling inside the engine. Thanks for the input.

      • Mike says:

        The right decision. Good luck!

  4. Forrest says:

    I wonder why it is difficult the lower cylinder block after I have dismantled the head. I broke one cooling fin in the process. I thought maybe the cylinder liner have embed so tight on the upper crankcase, pulling it out would need a little of heat to move the metals.

    • Mike says:

      Can you turn the crankshaft and move the piston in the cylinder? If not, then the piston is seized, which would explain the difficulty of removing the cylinder. If this is the case, don’t pull on the cylinder as it won’t move before you “free” the piston. To “free” the piston, spray lots of penetrating oil (WD-40, etc), let it take for a while then use a piece of soft wood and tap the piston down. Now if the piston is already at bottom dead center it won’t be able to move. This process can take a lot of time, like days of spraying, taping, spraying some more and tapping some more. Cursing helps at times. If a seized piston is the situation you have, understand that in all likelihood the piston will be shut and the cylinder will need to be re-bored, or at least honed.

  5. Gary A says:

    Hi Mike, you rebuild has definatey helped me. I noticed when you fitted your cam the lobes were in the down position.Was this with your piston at TDC? I just fitted my can with the lobes in the top position at TDC and am worried its 180 degrees out.Luckily the motor is still on the bench so can change it if need be??

    • Mike says:

      Hello Gary – The engine generates a spark on every rotation so even if you’re 360 degrees off (180 with the cams) your engine will fire up and run. That said, the marks on the flywheel are here to help with a TDC where both valves are closed so you may want to align the cams accordingly. It was a while when I rebuilt the engine and don’t recall exactly what I did at the time. But look it up in the maintenance manual, I’m sure that cam alignment is detailed. Hope this helps.

  6. fstar says:

    Hi – bought an xr500 project bike in Jan – dont have all the bits there, but do have a new 1mm oversize piston kit i bought from japan for cheap – i decided not to go dome because of the ping issues with these bike, esp at low rpms..

    interesting info here.. did u get here going? is there a vid? How id that header paint work out, ive tried tht stuff before.. but it doesnt stay that great for too long – might just powder coat mine and be done with it – even tho the VHT is good stuff.. not as good as a proper layer –


    • Mike says:

      The paint stayed on, no chipping or bubbling. Possibly because I took a lot of time to make sure that the parts would be completely clean and free of oil before applying the paint.

      The project bike is being driven in Colorado, with a base altitude of 5,400 feet (1,645 m). This means that the maximum intake pressure is reduced by about 15% (compared to sea level) and thus compression can be increased materially to compensate without promoting ping conditions.

      The bike has been in storage for the last 2 years as I had other projects underway but I’m about to get it out and make some additional transformations (this Fall). I’ll make sure to document it and post new pictures then.

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