Planning an Epic Adventure - Will trade beer for use of couches

[motorbyclist]

RIGHT, so I'm broke and the riffer is almost out of gas, my computer died and i cant sleep; time to go to the shed!

*some hours later*

Guess who's honda has a toolkit that we never knew about

I've mostly stripped the bike and she looks good, but god knows how i'm going to get the crankcase clean without an air gun... the full circle crank occupies all the room in there.... maybe just hope for the best?

Oh, and i've got her bored out .25mm for the new piston, have some racing reed valves, and am looking at the head very closely as it hasn't been machined off quite right - time for moar compression maybe? maybe not considering it's aircooled and failed by detonation, but I hear there's a guy around these ways who bores 'em out 4mm and machines the intake port to fit a double set of reeds!


ALSO, what do we know of the "racing fuel" at BP Kumeu - they claim it's 105 octane leaded fuel

[motorbyclist]

FYI: by going out .25mm i've gained a whole cc of diplacement!

the guy who's going out 4mm is going from 100 to 116cc of RAW POWAH

[Danae]

Whoooo!

[motorbyclist]

right... well washing her out with kero wasn't too successful; i'm concerned that all i've done is washed aluminium into my main bearings.

a quick blat on a dirtbike later, the motor is now on my workbench.... bloody thing is a featherweight! (and the chassis weighs only marginally more)

SO, before i attempt to split the cases apart and begin what may be a nightmare rebuild, does anyone have any info pertaining to there being a seal between the crank case and the main ball bearings? I can't find a parts diagram so any surgery from here onwards will be exploratory.... not the kind of adventure i want to be going on in such fine weather

furthermore, i suspect my tools are all going to be too big...

[motorbyclist]

well it's been a few more hours and a few more litres of petrol but i reckon i'm nearly there just by flushing the thing out repeatedly

[Danae]

be good to see brown fury up and running again!!

[motorbyclist]

just spent 30 minutes closely exmining rings before giving up - it would appear they're identical and have absolutely no markings... some googleing later and i don't even have the end gap clearance....

what are the odds both rings are infact identical? they both are the wedged type so there is a taper on the top face as the ring sits in the groove (IIRC), but i can't detect any taper on the running surface to differentiate top from bottom ring

[jono035]

just spent 30 minutes closely exmining rings before giving up - it would appear they're identical and have absolutely no markings... some googleing later and i don't even have the end gap clearance....

what are the odds both rings are infact identical? they both are the wedged type so there is a taper on the top face as the ring sits in the groove (IIRC), but i can't detect any taper on the running surface to differentiate top from bottom ring

Thought that was relatively normal for compression rings?

[motorbyclist]

Thought that was relatively normal for compression rings?

now this may just be high performance four stroke experience talking, but isnt one ring meant to have a taper on it's outside surface to scrape oil or carbon something like that? my dirtbike has a different top from bottom ring plus the oil scraper...

Here's a pic of what it appears I have: (note the keystone rings and that arrows are force vectors, pink is the lower pressure gas that got past the top ring, grey the cylinder wall, and the rest you can figure out)

also see the bottom ring groove is deeper than the top one to accomodate a very thin, octagonal ring we can only assume it a spring to provide some more pressure (maybe at specific points, too)

If this is normal for 1980's commuter 2-stroke technology i'm happy to run with that

[jono035]

now this may just be high performance four stroke experience talking, but isnt one ring meant to have a taper on it's outside surface to scrape oil or carbon something like that? my dirtbike has a different top from bottom ring plus the oil scraper...

Here's a pic of what it appears I have: (note the keystone rings and that arrows are force vectors, pink is the lower pressure gas that got past the top ring, grey the cylinder wall, and the rest you can figure out)

also see the bottom ring groove is deeper than the top one to accomodate a very thin, octagonal ring we can only assume it a spring to provide some more pressure (maybe at specific points, too)

If this is normal for 1980's commuter 2-stroke technology i'm happy to run with that

Not a damn clue, only 2-stroke I've ever had to bits was about 15 years ago and I don't recall that we ever even took the rings off the piston (don't think we replaced anything). Will ask my old man tonight if you're still stuck, failing that throw a post up in the engine maintenance forum.

[motorbyclist]

just had a look at my YZ400f manual: top ring is rounded and bottom is tapered/chamfered

ie:
_
_) top
_
_\ bottom

of course that's a modern four stroke motorcross bike, not an 80's two stroke commuter...


oh and yeah - thread is up in mechanical forum

[motorbyclist]

oh FFS they gave me the wrong sized little end bearing

[Squiggles]

I'd be asking these questions in the bucket forum...

[motorbyclist]

Right, so after wemoto kindly sent out another bearing, uni kicked in and had me tied up for few weeks.....

I return to the shed to find someone's been in there and felt it neccesary to go fiddling with everything - and lost the piston circlip

some very angry rants later and an extensive hunt through the shed and the little bag with the clip is found under the dirtbikes in the opposite corner of the shed.

hopefully she'll be running again by midnight

[Danae]

some very angry rants later and an extensive hunt through the shed and the little bag with the clip is found under the dirtbikes in the opposite corner of the shed.

Ah we didn't check there...god knows what it was doing all the way over there. The wankers your brother's friends throw it or something?

Ah well, can't wait to see Brown Fury ring-a-ding-dinging once again!!