Jawa / VVM [dieselmaster]

[vincentyeager]

Hi there!

here's another bike building thread.
a few weeks ago, Jeroen from VVM racing and yours sincerely decided to build a dieselbike.

First, a diesel engine was purchased. It appears to be a PTM 420D without the brand name sticker.
I got it pretty bare (no pull/start cord, muffler, electrics).

Then the base bike was hunted and found in the form of a Jawa 638 from 1996.
These bikes have amazing options like a quick shifter, and kickstarter/shifter in one etc.

All the right ingredients where there to start building (sunday 17 th April, made a 12 hour day right on).
First we stripped the bike to have a clean base. The diesel engine as well as the Jawa frame and engine had to cope with the hacksaw.
The idea was to have a majesty vario-matic on the bike, but since the diesel engine didn't have a starter we decided to use the transmission of the Jawa. A dieselbike with quickshift!

hey ho, away with that forced air cooling! the flywheel is going to be replaced as well. boy that thing's heavy..

and there goes the stinking 2-stroke bit. we just need the transmission after all, dont we

pre-fit the two, this looks like a potential fit.

we needed to shut the transmission box, milled some aluminium

welded it shut. Now thats starting to look like a powerpack, dont it.



We're going to finish the frame next. The engine doesnt fit in the standard 638 frame.
Then we can start to attach a dynamo and mill some more aluminium for covering the powerpack up.

keep you posted.

[Sphere]

Excellent, a nice thread with pics and all. Welcome to the forums

[coachgeo]

Nice machine work. Going to look sweet and should function good as well by the time your done.

[Dan J]

Really interesting build - and welcome to the forum.

Will be very keen to hear what you do with the flywheel...

[vincentyeager]

I'd love to have a DVV flywheel, but we're probably going to machine a normal one.
It will be much more lighter, indeed.
It has to include a v-groove for the dynamo belt as well.

first we are still busy with the aluminium work between engine/gearbox.
Then we can mount the powerpack and start with the frame etc.

Thanks for all the nice reactions.

[vincentyeager]

update;

some more welding done.

getting solid now. and it will also form the base to mount the cover on.
after all this side is ''wetted''

[Dougy]

Great Idea chopping the gearbox out of a bike mate, cant wait to see what the outer case looks like, its looking really neat so far .

[vincentyeager]

Right on!

[vincentyeager]

Since we're trying to keep the frame as small/stiff as possible,
and the engine must stay accessible (or de-mountable);

lugs

machine pipe in between

Jeroen doing the welding

[coachgeo]

in this pic.... my limited engineering mind tells me the lower joint might work best w/ screws upward? Probably a mute point now though.



Thanks for the updates!!

(ps- changed pic to better clarify what joint I was referring too)

[Dougy]

Its Brilliant and very cool ! But I crave more pics......

[vincentyeager]

in this pic.... my limited engineering mind tells me the lower joint might work best w/ screws upward? Probably a mute point now though.

Why exactly do you think so?

[pietenpol2002]

As long as this is a discussion by the uneducated, I'm qualified to join. In building wing spars, best practice is to position bolts in shear and perpendicular to load path. In this application, primary loads would presumably be vertical and thus the design is appropriate. In a similar vein, one never compromises the integrity of the spar caps with bolt holes. Any holes needed are drilled though the web. In fact, lightening holes are sometimes intentionally placed in the web near the wing tip to reduce weight. Admittedly, there is a difference between a spar and a tube. But, ultralights I have built using tubing had joints very similar to vincentyeager's design with bolts placed in shear.
With this application, the greatest load would be borne by the lower portion of the tube where a hole would heighten the potential for propagating a stress crack due to the presence of a stress riser. And since I haven't taken a math class since my first year of undergraduate studies, I would value being corrected by someone better educated.

[coachgeo]

Learn something new everday pietenpol2002. Would have thought shear to be weakest route to mount it. Agree forces are verticle. My assumption was with it rotated bolts up; more of the verticle forces are applied to the hard larger surface area of the thingamabobber joint's sliced rods end's; stacked ontop of each other, perpindicular to the verticle forces. As it is now the verticle forces run same direction of the sliced rod's ends. Saw this as the verticle forces now majorly being applied as shear on the bolts, which are smaller and I assume weaker than the larger sized joint's ends. That assumption may be where Im wrong?

Granted; though I didnt state it, I assume these fellows know shiat loads more than I do, judging by their fab skills, thus probably got it sitting in the right orientation.


What is that kind of joint called? Are they typicallly ordered or custom made most often?


UPDATE: looking closer at it.... maybe there is less on the bolts than I was first thinking. A good bit of the verticle force might be getting transfered by shear forces into the blunt ends of each side of the joint. Those blunt ends are much stronger. My lack of technical terms to use may well be making this discussion a complete confusion. BIRDS EYE VIEW Drawing below

[boutje]

..

[coachgeo]

This type of frame tube mounting is very common for motorcycles.

For example look at the suzuki bandit 1200.

Interesting. Looks like a great way to make the engine more easily removable for work. Are such joints available on the market.... what are they called?

[boutje]

I have never seen them on the market.
But they are easy to make with a lathe and a mill.

[Stuart]

I know you're using two bolts but maybe a forked join would be stronger? You have two shear points now (on the bolts) but with a forked joint you'd have four. But maybe less material would make it weaker? Just a thought

[Dougy]

I dont see any problem at all using this method of clamping on the frame, I had a 33bhp Honda 350 with the same type of fittings holding the engine in place and up there in the thread is the Bandit using them, I suspect they could cope with many times the horsepower this engine is pushing out though that fantastic gearbox.
What I dont understand is why alot more builders havent simply chopped off a bike gearbox ?

[Sphere]

Because people with lathes mills and equipment to weld aluminium are not a dime a dozen.

[vincentyeager]

look what i found on my mobile

[Dougy]

haha love it mate, your like me and get exited when you make progress , milling and lathe work really interest me, I'm going to enroll in a nightshcool course covering the basics, but it dont start till September , I hate paying out for small spacers ect and the few bits and pieces I've made on my new new lathe have saved me weeks and halfway paid for itself allready , I suspect we'll have picture and info avalanche here very soon....

[Sibbo]

My Chinese lathe and mill drill have been a brilliant investment. I don't use the mill part much but it is a seriously good drill press. Now i just need to learn to weld aluminium .

On the subject of the connection ,I would have thought a taper inside taper would be the strongest, with some kind of draw bolt arrangement to tighten .

[Sibbo]

Learn something new everday pietenpol2002. Would have thought shear to be weakest route to mount it. Agree forces are verticle. My assumption was with it rotated bolts up; more of the verticle forces are applied to the hard larger surface area of the thingamabobber joint's sliced rods end's; stacked ontop of each other, perpindicular to the verticle forces. As it is now the verticle forces run same direction of the sliced rod's ends. Saw this as the verticle forces now majorly being applied as shear on the bolts, which are smaller and I assume weaker than the larger sized joint's ends. That assumption may be where Im wrong?

Granted; though I didnt state it, I assume these fellows know shiat loads more than I do, judging by their fab skills, thus probably got it sitting in the right orientation.


What is that kind of joint called? Are they typicallly ordered or custom made most often?


UPDATE: looking closer at it.... maybe there is less on the bolts than I was first thinking. A good bit of the verticle force might be getting transfered by shear forces into the blunt ends of each side of the joint. Those blunt ends are much stronger. My lack of technical terms to use may well be making this discussion a complete confusion. BIRDS EYE VIEW Drawing below

On second thoughts this is way easier and with the blunt ends , much easier to mill .

[vincentyeager]

time for an update!

right side of the frame taking shape

[coachgeo]

have you done any gear calulations for sprocket sizes etc?

Im a complete novice so my question may be stupid... just wondering if gear ratios from a formerly 5grand+ rmp engine will work out at all for a low rpm lump diesel. Will sprocket changes be enough to compensate?

[vincentyeager]

a formerly 5grand+ rmp engine will work out at all for a low rpm lump diesel. Will sprocket changes be enough to compensate?

yes, because 5grand is a little over exacturated.

[Sphere]

Actually the original engine delivers max HP at 5500 rpm or something, but even then, nothing you can't fix by adjusting the primary reduction. If you gear it for 80-90 kph it should be fine.

[coachgeo]

... If you gear it for 80-90 kph it should be fine.

sounds good... but guess matters where you live.

for me 90kph (55mph) will get you killed cause the other cars would run you over. Two lane roads, straight with basically no stops for 48.3k (30miles) in my area have 120.7 Kph (75mph) speed limit. My home is 48.3k (30+miles )from my work down that road. Commute Im guessing is about to become 80.5k+ (50 miles+) since Im having to look for a new job.

[balboa_71]

This is quite a build...more than most would take on. We don't have any Jawa's here in the states, and no other 2 strokes to carve up, so most of us would never go this route Anyways your bike should be a good runner and light weight to boot.

Cris