DR350 Adventure Bike Build

Discussion in 'Some Assembly Required' started by hellotimmutton, Sep 9, 2019.

  1. hellotimmutton

    hellotimmutton Been here awhile

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    One day whilst having a beer with a motorcyclist buddy, he told me I should watch "Long Way Round". After binge watching it one quiet weekend, followed not long after by long way down, I had decided I must also do some long distance adventure riding. I had the hardest time deciding what bike I wanted, until I discovered Mondo Enduro and fell in love with the DR350.

    After a while of searching (theyre rare in the south east corner of Aus) I found a 95 model that had seen a lot better days. The airbox was cut open, a crappy pipe that did bugger all was practically glued on and the battery was way under spec. I got the bike legal, then thumped around on it for a bit, getting in way over my head in the mountains. Had a shop swap on an eiger cylinder, weld the balancer pin and swap in the 5th & 6th gear from a '91 dr350s transmission I scored cheap, which took forever because I'd been given the wrong piston rings and had to wait for the right ones to ship from o/s, and then thumped around it some more.

    Now Im in the process of tearing down the bike. Ive decided to swap the full DR250s transmission as the gap between 4th and 5th is horrendous (dont know why I didnt just do that originally) and want to get the piston flattened to reduce the compression ratio down from 10.5:1 so I can take it places with crappier fuel. Also considering an early model clutch basket with a late model 1st gear to make it a true wide ratio. And a new exhaust, since the current one is trash.

    Once I'm done with the engine, the plan is to upgrade the suspension and give it a larger tank and luggage rack, as well as some other odds and ends.

    This is how it sits currently. Feeling a bit in over my head, hoping I dont royally screw it up

    [​IMG]

    [​IMG]
    #1
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  2. mADVta

    mADVta Adventurer

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    Looks like mine DR just few months ago :) Though, I didn't do so many swaps and upgrades. Made just enough to bring her back to life and make her more suitable for long distance travels.

    Will be lurking around, looks like I can learn something new 8)
    #2
  3. AntónioPereira

    AntónioPereira Adventurer

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    I'm in for this one! ;)
    #3
  4. brownvv

    brownvv Been here awhile

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    Seems like most people just instal the 5th and 6th from the 250. I did the whole 250 transmission and the spacing feels perfect. I even used a later model 350 first gear to widen the transmission a tad more
    #4
  5. hellotimmutton

    hellotimmutton Been here awhile

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    After reading a couple build threads and the main owners thread, I had a massive list of things that could be done, and then had to go through and ask myself what was practical and what would be overkill. I'm hoping I settled somewhere in the middle

    Good to hear someone else has done it with success, there was a part of me that was worried that taller 2nd - 4th would negatively affect off-road performance. I'm hoping that this will make highway riding more comfortable while retaining my ability to ride trails, at the expense of racing performance (not an issue for me)
    #5
  6. brownvv

    brownvv Been here awhile

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    1st and 2nd are not taller. 3rd-6th are.
    I have a 441 kit in mine. I do highway and trail without changing sprockets most days
    #6
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  7. NorthernTraveler

    NorthernTraveler Long time Adventurer

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    Couple things for the suspension -

    Try to get a set of 1987 RM 125/250 forks. The are still 43mm, but are cartridge forks. The front axle is 17mm, you can swap the bearings in the stock DR front wheel but you'll have to make a new spacer. The stock brake caliper works. Get a set of Honda XR650L stock fork springs, they fit perfectly and are stiffer - .44kg, which is about right with a larger tank.

    For the rear end, get a dirt model shock. The dirt model is both compression and rebound adjustable. Add a Race tech gold valve if you like.

    I have a 450 cylinder kit and I don't use it. It pulled like a tractor on the bottom end but didn't want to rev out. The 380 or 400 is about right.
    I have 3 DR350s right now - 2 1990's dirt models and a '96 SE. The '96 has the above suspension, Acerbis 4 gallon tank, and stock rear luggage rack.

    Have fun!
    #7
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  8. hellotimmutton

    hellotimmutton Been here awhile

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    Engine disassembly is going slow. Got the magneto off but need to get my hands on a puller for the flywheel. Waiting for a socket to be delivered for the spark plug. Got the bolts for the head cover off, but the head itself won't budge. Tried gently pursuading it with a bit of wood and no joy, don't want to go to hard and damage the metal
    Good point, I'd forgotten that. Do you recall what sprocket sizes you're running?

    I've actually been accumulating parts for a while now, so I have a dirt model shock as suggested and the frontend of a drz400. Bit more work but should be a nice upgrade.
    #8
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  9. MotoPolo

    MotoPolo So many places, so little time Supporter

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    That kind of drinking will drive you mad with ambition - sent me on a two year quest - subscribed:clap
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  10. MiteyF

    MiteyF Long timer

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    I've owned 2 DR350's, awesome bikes. Looks like this should be a good one!
    #10
  11. hellotimmutton

    hellotimmutton Been here awhile

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    Made some good progress today. Managed to finally get the head cover off by placing a flat bit of wood against it and whacking it with a hammer. After that, the cam and sprocket came out pretty easily. Not the best picture, but the cam journals are looking pretty good. seems like the kind of thing that should have bearings

    [​IMG]
    #11
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  12. hellotimmutton

    hellotimmutton Been here awhile

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    [​IMG]

    Head, cylinder and piston now removed. Learning a lot as I'm going. The circlip took a bit of effort to get out, as the gap in the circlip on both ends lined up with the gap to remove it. I used a thin flathead screwdriver to rotate them a bit and then needle nose pliers to pull them out.

    I'm planning to have the dome machined off to make it a flat top piston so that the engine can run lower quality fuel if needed. The problem is, I know the engine acts up if you run non-premium with the 10.5:1 ratio piston, but I dont know what machining it to a flat top will reduce the compression ratio too, or whether that will be enough (stock is 9.5:1, aftermarket options are 10.5:1, AFAIK no one has done anything in-between)
    #12
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  13. adventure95004

    adventure95004 Adventurer

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    Instead of Machining the Piston what about running an extra base gasket or getting a thicker copper base gasket made up.
    That way you don't affect any balance issues with the crank and piston and you can always reverse it later if you want to.
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  14. hellotimmutton

    hellotimmutton Been here awhile

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    I hadnt considered needing to re-balance the crank, thats a good point. From what I understand, a flat top piston performs better than a domed when you dont need the compression boost. The other consideration is how that would effect the cam chain
    #14
  15. villageidiot

    villageidiot Long timer Supporter

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    there are calculations to be done to figure out your compression ratio.

    I'm sure taking the dome completely off the piston will make it much lower than stock compression.
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  16. hellotimmutton

    hellotimmutton Been here awhile

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    Using an online calculator I've calculated that it would drop the compression ratio to 9.86:1, not accounting for the volume of the valve reliefs or how much the gaskets get compressed, based on information from distech's rebuild thread, so it's quite possible that number is wildly inaccurate
    #16
  17. yokesman

    yokesman Long timer

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    fill the chamber at tdc , then fill it at bdc n do the calculations. usually use atf. calibrated container or syringe.
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  18. hellotimmutton

    hellotimmutton Been here awhile

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    Unfortunately my engine is now too dissembled to do that, however I dont trust myself to do it accurately anyway. I did however squirt some oil into the valve reliefs to get an idea of what the volume would be when machined "flat" and it was roughly 2cc. Plug that into the online calculators and one says that will result in a CR of 9.47:1 and two others say 9.6:1. If anyone knows how much the gaskets would compress when used I can recalculate for a more accurate number, but for now it appears it wont be dropping the CR below the stock 9.5:1

    On an unrelated note, does a rotor puller need to be a particular length? the common after market option (motion pro) isnt available in Aus. Theres other options here, but theyre quite a bit shorter so I dont know if that would be a problem
    #18
  19. hellotimmutton

    hellotimmutton Been here awhile

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    Not a lot of progress while im waiting on the flywheel puller and clutch holder to be delivered, however I have confirmed that the mechanic swapped all of the clutch springs with heavy duty ones rather than half of them. Gonna go half/half when I reassemble, hopefully that still takes care of the clutch drag otherwise I'll go all HD again
    #19
  20. brownvv

    brownvv Been here awhile

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    Heavy duty springs don't have anything to do with clutch drag. Its your thrust washers. There are tons of conversations about that on The 350 thread. New washers, possibly sand the back of your gear on your basket, then don't over torque it putting it back on
    #20
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