400 SM rebuild (Ryan’s old bike).

I picked up a pair of DRZs at the start of June. Ryan’s black SM and a blue S (Shane’s). I thought I’d use this (long) post to cover the story of the SM rebuild.

I’d heard about the bike at least a year earlier from Karl. “DRZ SM with a knock”. Ryan and I had exchanged messages, but I figured I’d likely need to replace the crankshaft at least some of the bearings, rings, and get a valve job done. The numbers didn’t look great. A year later, mention of the bike came up, and the price had dropped.

James legitimately gave me heck for buying project bikes at the start of the summer. Consequently it’s been 3.5 months before I got it done, and even that was after skipping most of the normal valve work.

Back together.

The build was pretty much the normal thing. I do have some video of the bike running before I took it apart. It was “knock under load”… it sounded like hell and I was sure it was the crankshaft.

August 3rd, I finally got around to the SM.
Aug 6th. Well that sucks. Not really a surprise though. The kind of slack and play that causes a bad knock is likely to push the piston around.
This may be worth remembering too. The stator side main bearing (that’s the one which should have the tighter fit, the one that you normally use the crank puller to pull the crankshaft into) looked a bit odd on the inside. Matching stains here on the crankshaft.

So, what to do for a new cylinder/piston? I already donated the one out of my spare motor to one of the motors I’ve worked on… probably the 400S (I think it was a bit scored up, Scott’s summary was “it’ll smoke a bit”.)

Then came the big summer ride. 10 days including the 2020 WANDR event. I came back with a bike that wasn’t very happy, and a few other high priority home/house/family tasks.

And I still hadn’t decided what to do for a cylinder. Cylinder works kit? Repairing the cylinder would be slow and $400, and I’d still need to chase up either a piston kit or $$ for OEM. I ended up getting the cylinder works big bore kit as it was $80 cheaper than the stock kit ($670 vs $750 … old inventory?)

Interesting, I don’t think there were valve seals in this gasket kit. I stole those out of my pro-x top-end gasket kit that I didn’t need/use.
In case you don’t remember, the BBK in my (yellow) bike came to me because they messed up at manufacturing, and left a big gusset/chamfer in this corner. They fixed it in this version… although I ran into a different problem with the oil jet.
Shiny new vertex piston
Base gasket. I always get me units mixed up. I was thinking it was 30 thou for the E gasket and 90 for the S, but maybe that hundreths of a millimeter? .70 would be midrange, slightly higher compression than stock.
Vertex ring set, in case anyone needs to re-order.
These were the “new” valves I bought to put into the head that came out of Shanes bike. They were supposed to be new, but the look to me like they’ve been in an engine (and run). But they’re in far newer shape than the valves out of that head… which is the head I used in this build. The 400S got my spare head which had a fresh valve seat grind and all new valves.

Tear down went smoothly enough. Crankcases got warmed in the toaster oven both for removal of the old bearings and insertion of the new. Main bearings were replaced with the Hot Rods kit (K049). I believe I used an NTN and an SKF bearing for the counter balancer in this motor, and the Hot Rods BBK0018 kit in the other (400S) motor. Both got the Hot Rods TBK0090 transmission bearings.

Then it was time for the new Hot Rods crankshaft.

New bearings, new crankshaft. The next step gave me grief until I “warmed” the right side crankcase. Turns out the bearing was just tight on the shaft and either needed to be pressed down (a tube up against the inside race and hit it), or warmed to expand it. The symptom was that when the cases were screwed togther, the crankshaft didn’t want to turn. Never had trouble with that before, not sure if the Hot Rods crank was a tiny bit bigger, or the bearings were smaller, or ??
Sept 7th. Bottem end ready to be covered up.
Lost a day or so working on the TrailBlazer as the gasket and filter for the automatic transmission finally arrived. I really didn’t expect all this cool stuff to be sitting in what I thought was a pan full of ATF fluid. Looks like a mini-terminator to me.
Sept 9th.

I may have been stuck here. We had almost exactly the same problem that Quentin had with the last Cylinder Works BBK. It turned out that the recess they cut for the oil jet that pokes up from the right crankcase is either too narrow our slightly out of place. I filed down the side of the oil jet and touched the recess with a dremel. After that the cylinder did not seem to “rock” anymore.

lousy pic, filed jet sitting on the jug which has also been filed. When the filed part of the jet lines up with the filed part of the recess, things seemed to fit ok.

Somewhere around here, the guy that caused Ryan’s bike to pop back onto my radar posted that he was back to looking for a bike, and he had more $$ this time. I’d been running numbers through my head and his max price was about what I was going to have to ask. So we got to talking, and consequently I boosted the priority on getting the SM back together…

Fortunately I had a new chain slider on hand…. unfortunately, it doesn’t match the color scheme. It was sort of an experiment, and expected to go on my bike. This is the cheap chinese one… vs the $40 US hotfoot moto one that’s about $80 CDN by the time it gets here.
Old chain slider. No point putting that back on. And yes, the swing arm is a bit scored.
Starting point Sunday. Motor’s in the frame, and the mounts are on, but little else.
3.5 hours later it is running. Still a few pieces left to re-assemble.
We’re dealing with wildfire smoke. This was supposed to be the apocalyptic shot… but that big red sun is just a bright spot just above the headlight…. oops.

This was an interesting bike to work on. I believe Ryan took very good care of it. The bike has almost 40k km on it… and it has sat for the last 4 years, but for a bike that was supposed to have been trail ridden, it is in amazingly good shape. Even more surprising is that all the rear suspension linkages seem to be in good shape. Those usually dry out and rust away… but these were all nicely greased.

Ryan said he had some significant work done on the wheels. I believe they were re-spoked shortly before the knock problem. I didn’t have the front wheel off the bike, but the rear bearings feel good.

I did check the starter motor brushes, they are worn, but not about to start causing missed starts.

I hadn’t realized how low the tire pressure had fallen, and knew the bike felt wierd when I ran it to the gas station. After boosting the tire pressure to 20 psi front and back, the bike was much more predictable. I did run it through my normal gravel parking lot with those concrete things that tell you were to park and which make good lifters. It seemed to move just fine. Front suspension might be set a little soft (the clickers). Rear brake feels soft, but does grab. Didn’t check the pads, meant to bleed some fresh fluid into the brakes but didn’t get to it. Rear pads are good, bled the system, pushed the piston in a couple times trying to flush air back up (reverse bleed) but it didn’t firm up.

Throttle response seems pretty good, bike is loud (which is why I won’t buy a powercore exhaust), and does gurgle quite a bit on decel, with the occassional backfire. I suspect it is running rich … As I expect Ryan put a jet kit in it (almost had to with that header/muffler), and those tend to run rich … and the change to a BBK would also incline it to being rich.

In retrospect, I almost certainly should have parted this bike out… rebuilding it was not a productive use of my time. If I make noises about repairing (for sale) more DRZs, someone slap me.

Footnotes.

Right, there were a few other things to note. The nut holding the front sprocket was on backwards. Turns out that the nut was pretty messed up and there was no way to start the threads on the other side. Threw it in the “parts replaced” box. Newer nut doesn’t want to go on either. Yikes not sure what happened, but somehow the threads on the end of the countershaft are somewhat damaged. Put a grindstone on the dremel and chamfered the end of the shaft to take off that damaged line of thread. Easy enough with the chain on and bike in the air… just spin the rear wheel and hold the dremel against the shaft as it turns.

Oil filter bolts. Trivial tidying up. Two of the acorn nuts had apparently jammed, causing the studs to come out… one of which had been lost and replaced with a normal bolt. Using a pair of nuts jammed against each other I freed up the jammed acorn nut, and stole a stud from a spare cover of mine. Back to looking and behaving like it should. Oh, and that damn O-ring at the base of the oil filter? It was missing, stole the one from the same spare cover, but probably could have used one from any o-ring kit.

Footnote two: Took the bike up Flatty after picking up the steering lock key from Ryan’s place. Bike needs some sorting out for off-road. Bike did not inspire confidence standing… some of that may be that I’m used to bars with more sweep (e.g. higher). Some of that definitely was the wide tires, which I did not air down. Motor and clutch were awesome though, great low end torque easily put to the tire (which wouldn’t stick. Front brake is opposite of rear… grabby. Rear shock may need a pressure boost, and clickers should be checked all-round. (And duh, the tires are 4+ years old, older and harder instead of soft and sticky.)