2006 Suzuki DR-Z400 Project Bike Review Part 2

My DR-Z400 bored, stroked, and back together

I've been spinning wrenches for years, prodding a slew of derelicts back into motion since before I could legally drive. Somehow, in all that time, I've never rebuilt an engine. I've pulled them and swapped them, replaced heads, cams, and transmissions, but never broken one down to its hundreds of individual components and put it all back together. That changed when my newly acquired Suzuki DR-Z400SM sent a valve through its piston, launching shrapnel into the crankcase.

project bike in small shed
Tight quarters.Zach Bowman/Beth Bowman

To make matters worse, I didn’t have a garage or a shop. The bikes and my tools shared space in a tiny, unheated garden shed a short walk from the house. But there was a workbench, electricity, and enough room to scoot around the DR-Z’s now empty frame if I rolled two other machines outdoors. The miracle of the motorcycle is that it takes up no space, that you can stitch one together in the square footage of a queen-sized bed. I’d be joining the army of fools who’ve assembled bikes in kitchens and bedrooms, basements, and, yes, sheds.

Zach in prefabricated shed
I’ll never bad-mouth these prefab sheds again.Zach Bowman/Beth Bowman

I’d aimed to get the thing done for less than the cost of a new DR-Z, and maybe it would have been possible if I already owned the arsenal of specialty tools motorcycles require. I raided Rocky Mountain ATV for slide hammers, case splitters, crank pullers, and clutch pliers. And, because I’m an idiot who did not want his freshly rebuilt engine to look like it’d spent its life submerged in West Virginia mud, I ordered up all manner of fasteners and new case covers to replace the corroded factory bits, plus every bearing and seal. You’re not living until you’re on a first-name basis with your UPS driver.

bottom end debris
The bottom end was full of debris from the valve.Zach Bowman/Beth Bowman

The meat of the build arrived in one big box, courtesy of eBay: a Cylinder Works 469cc bottom end rebuild, complete with a stroker crank, a big-bore cylinder, head and base gaskets, and crank bearings. I also picked up a used head from a DR-Z400E, but the biggest hitch was waiting for my cams. There are off-the-shelf options available, but making reliable power here seems to hinge on a cam with enough duration. I sent my old bits off to Web Cam, and waited five weeks for my custom grind to come back.

There was plenty to do while I waited, disassembling every last bit of the engine and carefully cataloging it in labeled Ziplocs. Past experience had taught me to take as many photos as I could. No matter how good your service manual, there are always things hidden in the exploded diagrams, orders of operations, tiny springs, or check balls that show up as a smear on the page and get forgotten when it comes time to reassemble everything.

motorcycle engine
An engine is overwhelming when taken as a whole.Zach Bowman/Beth Bowman

When I finally separated the cases, it was clear just how much metal the valve had sent south. There were shavings and chunks in every bearing. If I’d just replaced the piston and head and hoped for the best, the bike would have been apart again in under a month. For the first time since I brought the bike home, it felt like I’d made a correct decision by going for the full teardown.

The cases were filthy, corroded, and oily from years of neglect. I gave them a good scrubbing with gasoline, then aluminum mag cleaner before bringing them to a buddy’s for soda blasting. They came out looking brand new.

empty bike frame
Nothing’s more heartbreaking than having to stare at an empty frame through most of riding season. I took the time to clean up a bit of rust and touch up the paint while waiting for parts.Zach Bowman/Beth Bowman

Meanwhile, another idea began scratching at the back of my skull. The gearbox on the DR-Z has always been a sore spot for me, with first being too long for technical trails and fifth too short for highway duty. The thing has always felt like it needed a sixth gear. There are no conversions that will add another cog to the mix, but ACT has been selling a wide-ratio kit for years. ACT is well regarded, with few, if any complaints. At $620, the swap isn’t cheap, and it requires a few modifications to both the case and the shift forks. Still, I could see a future where I went through all this effort to build a DR-Z with 20 more horsepower than factory only to be more frustrated by the bike’s gearing.

If I was going to experiment with a wide-ratio DR-Z, now was the time. Add “rebuilding a transmission” to the list of things I’ve never done before. There’s something that happens when you have every last piece of a machine apart and in your hands. You understand for the first time how impossible the thing seems. How fragile. How a thousand components must be assembled just so in order for the thing to function at all. The miracle of the machine.

tiny shed
The shed’s tiny, but it has enough space for what we need.Zach Bowman/Beth Bowman

Weirdly, it was the wide-ratio swap that gave me the most trouble. ACT will sell you pre-modified shift forks, but because I am an idiot who owns more grinders than dollars, I figured I could take care of the work on my own. That decision meant the gearbox was seized tight the first three times I assembled the cases. After a frustrating amount of grinding, cleaning, assembly, and disassembly, I had the cases glued and bolted back together with the transmission shifting as it should.

An engine is overwhelming when taken as a whole. There are so many pieces to potentially forget, so many systems within systems, that just getting started can be paralyzing. The good news is, you can’t come at it all at once. It won’t let you. It has to be taken bolt by bolt, just as a year must be taken minute by minute, day by day. There are no shortcuts.

reassembling bike engine
You don’t need much to rebuild a bike engine. A quality service manual and a clean workbench go a long way.Zach Bowman/Beth Bowman

It took three months of working off and on at night and over weekends to get the engine together and back in the bike. None of the dudes at the local shop should be worried about job security. It had been so long that I had forgotten how good the thing looked as something other than an empty frame.

I poured fresh gas in the tank, made sure the battery was charged, and hit the ignition. Want to experience the entire spectrum of human emotion in the span of a few revolutions? Try starting an engine you’ve just rebuilt in a shed. The big single-cylinder churned once, twice, and fired, blatting its resurrection at the neighbors. It would be days before I could ride the thing. I had to go through a punishing break-in procedure, complete with varied rpm and re-torquing the head bolts at specified intervals. An early oil change to swish out any bits of debris left in the engine. But it was done. Together. Complete, and, I hoped, better than it had ever been.

case reassembly
Reassembly means taking your time, and making sure nothing’s binding as you tighten the case bolts.Zach Bowman/Beth Bowman
Left-side case
Left-side case, clean and with fresh bearings.Zach Bowman/Beth Bowman
ACT wide-ratio gearset
ACT wide-ratio gearset.Zach Bowman/Beth Bowman
ACT wide-ratio gearset, installed
ACT wide-ratio gearset, installed.Zach Bowman/Beth Bowman
bags and labels
Bagging and labeling everything is crucial when it comes time to put it all back.Zach Bowman/Beth Bowman
clearance for new gearset
Making clearance for the new gearset took some trial and error, which meant assembling and disassembling the cases a few times.Zach Bowman/Beth Bowman
Reassembling the cases
Reassembling the cases is the most stressful part of the build. Go slow, tighten the bolts in stages, and make certain everything is torqued correctly.Zach Bowman/Beth Bowman
surface and sealant
Clean mating surfaces and a high-quality sealant are the best armor against unwanted leaks.Zach Bowman/Beth Bowman
reassembling the cases
Reassembling the cases.Zach Bowman/Beth Bowman
Suzuki DR Z400 project bike
Back in one piece.Zach Bowman/Beth Bowman
tusk tools
Tusk may be the best thing to happen to the hack mechanic. Cheap, quality tools, shipped quickly.Zach Bowman/Beth Bowman
470cc rebuild
The complete 470cc rebuild.Zach Bowman/Beth Bowman
engine in bike
After three months, just seeing the engine together and back in the frame was huge.Zach Bowman/Beth Bowman