The drz400s rebuild, stronger...faster...somthinger!

[955616846]

Originally Posted by HighwayChile

ceramic coating internals might be worth checking into as well if you are keeping it long term
I"ve heard of aftermarket gear sets, plenty of $ Im sure is it the entire set or just an OD 5th?

Ceramics? These engines are not normally that stressed.

A bit spendy... First is the same, the rest change. They're not for everyone.

[Spacelord]

I have 4K on my big bore, no issues.
I expect it will easily do 12K.

[DR650SEDDY]

After ur done rebuilding ur engine you'll have a blast. I know many who've done the big bore kit and they're happy with the results, i was gonna do this SUZUKI JE DRZ400 DRZ 400 BIG BORE 434CC CYLINDER KIT just for the heck of it. Keep up the good work focallength.

[focallength]

Im just concerned about the reliability of a BB, I dont want to tear the engine down every 6k miles.

[One Less Harley]

might as well do the 434 BB, as it doesn't cost anymore.

[955616846]

Originally Posted by focallength

Really?! You mean the engine dosent just magically create its own oil and coolant? Im shocked...shocked I tell you.



A new head is the expensive part, top and bottom rebuild kits run roughly $500 total.


One thing I did notice, the front lower engine mount bolt gets pretty coroded. Being as these bolts have no seals, liberal waterproof grease is in order when I reinstall them.

Swing arm does that too... In fact it kinda surprises me that you had a problem with the front bolt and no mention of the swing arm bolt. Some people use an anti-seize compound, but a good greasing does the job.

I am not sure how you define a "top and bottom rebuild" I've got about $1000 in the crank, main bearings, piston, cylinder, gaskets, seals etc. That is still cheap when I compare it to my Huskies (bare crank is ~$1200), BMWs or KTM.

The head that I have built is worth about $1100 in parts (no core purchase) to initially build and about $200 to rebuild later, but that head is built for a stroker which tends to blow out the top end cost. You could probably get it done for a heck of a lot less with a set of Hotcams and reusing many of the parts that I have discarded.

[955616846]

Originally Posted by focallength

Im just concerned about the reliability of a BB, I dont want to tear the engine down every 6k miles.

Don't be... There is no problem with the longevity of these pistons and cylinders

Maybe you have spent too much time listening to the kids on TT.

[focallength]

I havent heard any negative on a BB kit, however the very nature reduces longevity. Im slightly concerned with the head bolts. I had a xr600 with a 660 BB kit (10% over bore same as a 400 to 440) and it pulled the head off.

The big suck with my bike is I need a new head, thats $600 for a blank head. Im not reusing any parts from the seized head.

By rebuild I mean the kits they sell on line, theyre mostly bearings and gaskets, top end comes with a new piston...I dont think I need to go hog wild on a head, nothing fancy just stock parts aside from cams.

[955616846]

Originally Posted by focallength

I havent heard any negative on a BB kit, however the very nature reduces longevity. Im slightly concerned with the head bolts. I had a xr600 with a 660 BB kit (10% over bore same as a 400 to 440) and it pulled the head off.

The big suck with my bike is I need a new head, thats $600 for a blank head. Im not reusing any parts from the seized head.

By rebuild I mean the kits they sell on line, theyre mostly bearings and gaskets, top end comes with a new piston...I dont think I need to go hog wild on a head, nothing fancy just stock parts aside from cams.

I assume that you're looking at a brand new core. The only other OEM internal parts that you'll need are cotters and tappets which will cost about $240. Ferrea valves are about $120 and springs with retainers about $100 (Ferrea, APE or Kibblewhite)... That covers the bulk of it. The OEM stuff is about the same total price so is not unreasonably priced, but you can do better. I'd use at least Ferrea valves.

The head is bolted through the cylinder to the crankcase...Lifting the head due to the cylinder is improbably.
One point in favour of the stock bore is that the OEM piston skirts are longer and wider than the non genuine parts including those for the standard bore and there might be a longevity advantage using an OEM piston.
I don't think that there is a problem with using a 94mm bore, but if using the stock bits makes you comfortable then go for it. The S motor only needs cams, carb, compression and exhaust to go from asthmatic to a nice motor. Big bores are optional.

BTW, I'd definitely want to check the crank and transmission very carefully because it seems from the cylinder that the damage may not have been limited to just the head.

[Kawidad]

I would also suggest pulling apart the oil pump and look for wear/scoring. Then replace if necessary.

I rebuilt a blown up Yammie once and the oil pump had sucked some material and was surprised at the noticeable wear on the internal parts.

[Luke]

Originally Posted by focallength

....I have to check the oil and water pump and inspect bearings.....

I was helping a friend with a DRZ that had a chronic overheating problem. Repeated blown headgaskets, warped head, etc. It turned out that the waterpump impeller had unglued itself from the shaft and would turn on the shaft with only a little resistance. Or, not turn when the bike was running. It looked good, though.

Doesn't sound like your problem, but it's easy to check when you're in there.

[focallength]

So im slowly going over the frame as well, looking for damage. I have noticed 3-4 spots where the paint has chipped away revealing some surface rust. Need to take care of that, just need to find a similar color spray paint...

Im srarting to think a yearly engine pull is in order, theres alot of nooks and crannies that harbor dirt/mud. Plus engine mounts need greasing. Pulled the frame drain plug to check the filter, looked clean aside from a lone long hair?!

Plan on splitting the case tomorrow and seeing what parts I need to start ordering.

Stay tuned...

[TipsyMcStagger]

Originally Posted by focallength

... I have noticed 3-4 spots where the paint has chipped away revealing some surface rust. Need to take care of that, just need to find a similar color spray paint...

Bookmarked this post a few years back.

Tipsy

[focallength]

Originally Posted by TipsyMcStagger

Bookmarked this post a few years back.

Tipsy

Nice ill go pick some up, ty.

[focallength]

so here is the score so , far. Im waiting for a puller for the fly wheel then Ill split the case. Initial inspection shows some slight play in the rod, which means shes shot. I ordered a complete hot rods lower parts kit, to rebuild the bottom end. The gears arent blue, but I wont know until I can split the case. So far no definitive causes, the cylinder does show signs of previous wear and oil could have slipped passed the rings. The cylinder is nice and flat, but the head is pretty well warped.

Ill have the case honed just in case, so that both parts fit together perfectly.

Now the cylinder is salvagable, Ill prob. send it off to cylinder works or millenium and have them hone and replate it. Still not sure if I wabt to go with a BB or not.

The head is just a big paper weight, however there are signs of dirt being sucked into the valves, which is not that uncommon with a dirt bike. Just means Ill have to really check my air intake when I re install it. Most likely it happened over time, however I did notice that the FCR-MX carb dosent fit quite so well, so Im going to have to do something about that. Maybe find a airboot from another bike thats a little bit longer.

So lower parts kit should be here tomorrow as well as the puller, in addition Ill replace the countershaft bearings. Heres hoping the gears are good. Stay tuned, sorry no pics, nothing new to show...

I may pick up a kick starter kit though, should be easy to install with the engine in pieces...