CMG Project: DR650 Update#3

It’sbeen two months since I last updated you on my DR650 project, but a lot has happened since then. It’s not quite all together, but it’s pretty close.

Last time, I talked about the changes I made to the bike’s bottom end. In the last few weeks, I’ve finished reassembly of the top end and installed the engine into the frame. Now, I’m just waiting for a weekend to hook up all the hoses and wires, install a new chain, bleed the brakes, wire in a new taillight, install the bodywork, and finish off a dozen other small chores that need to be finished before the bike is put back on the street.

Here’s how top end reassembly went:

Cleaning and painting

Just like the side cases, I had the cylinder and head soda blasted to strip off corroded paint. It didn’t do quite as good a job as I’d hoped, to be honest; I think the blasting shop had a hard time seeing what needed to be done, once the caked-on soda obscured the job at hand. If I was doing it again, I think I’d try a harsh chemical stripper on the paint first before dropping it off at the shop.

But, this was an experiment, and I’m mostly happy with the results. Clean-up from the soda blasting was easy; some soda did get into the inside of the head/cylinder assembly, despite carefully taping it, but it washed out easily enough, since soda is water-soluble. So far, the paint seems to be holding up well.

Here’s the old piston (L) beside the new (R). The differences are obvious; the older piston was undamaged, and could continue to serve if I cleaned it up.


One of the key aspects of this whole project was installation of the high compression piston sent to me by JE Pistons. The old one was in fine shape (I inspected it when I removed it), but since I had to take the head off anyway, I decided a new piston made sense.

Removal of the OEM piston was simple; installation of the new piston was relatively straightforward, but it was a little tricky getting the retaining circlips into place, as they are much stiffer than the OEM clips. My piston didn’t come with any markings indicating orientation in the bore, but I quickly figured that out.

All the measurement specs for the new piston checked out, and with an extra set of hands helping, I got the cylinder (freshly honed) slid down over the rings. Mission accomplished!

The JE piston is available for $175.58 US at the company’s website.

The new camshaft installed, and hopefully ready to go.


Along with the high compression piston, I also had my camshaft reground by Web Cam. Instead of the more radical 190 grind, aimed at boosting top end performance, I opted for the tamer 223 grind, which boosts low- and mid-range performance. I think this is more valuable for woods and backroad riding.

Installation of the camshaft isn’t that difficult once you know the tricks to making everything fit. And, I got to install it twice, because after installing the camshaft, you’re supposed to measure valve squish, to make sure there are no fitment issues with the combination of new cam and piston. You don’t want your valves smashing into your piston.

To do this, I purchased some modeling clay and placed it in the piston’s valve pockets before installing the head and assembling the camshaft. With camshaft installed, I put the valve follower assembly back together, set the valve clearances, and then turned the motor over by hand.

I then disassembled the top end and used calipers to measure the depth of the modeling clay, which had been squished by the descending valves. The depth of the modeling clay indicates the clearance between your piston and valves; I found the measurements within specifications, so reassembled everything.

The 223 grind Web Cam is available for $260 plus core at this website.

At every step along the way, the Clymer manual as well as the instruction sheets for the aftermarket parts urge you to carefully measure clearances to make sure everything is within spec.

General maintenance

Along with the aftermarket parts, I also did a fair bit of general maintenance on the motor; I had Thug Engine Works tidy up the valves seats, I bought a new camchain and I replaced several bolts and nuts in the top end, including the valve cover bolt that was the cause of this whole rebuild. I also painted several spots on the frame that had started to get a bit scabby.

What’s next?

With everything looking ready to go, I had a buddy help me muscle the engine into the frame, where it’s sitting now, waiting for everything to be hooked back up. That’ll be done by the next update, and I’ll have some details on the aftermarket bodywork I installed as well, along with a new Leo Vince exhaust system.

Summers are busy for me, as I have to cram a lot of riding and testing into a very small timeframe, but hopefully I’ll get the chance to not just finish this project, but also spend a bit of time riding it, to tell you how it all works out before the snow flies.

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