What Did I Do So Very WRONG??

[bsforever]

I will probably need some input from someone that has a very high knowledge of the GTR on this one. I have had my GTR running a few times and it is missing on the right cylinder, however, i was going to do a small test ride for a few feet ( which i never attempted before ). I pulled the clutch lever, stepped the shift into low and let the clutch go slowly, ummmm.... what happened next i was not expecting in the least...the bike was wanting to go in REVERSE!!!!!  i pulled the clutch lever and stepped out the shifter out of first.... and stopped the bike. I am totally freaked out by this....what did i do wrong? what would make it go in reverse?.... something i messed up on big time obviously, but i do not have a clue....i believe i put back the engine correctly after having it apart, and i did not remove the transmission gears...i am stumped and freaked out...... HELP!    thanks, bsforever

[srpackrat49]

 Beleave me   been there.... ???done that..... One day i was late for school back in 1967...  rolled the bike down the driveway backwords poped the clutch.... it was running clicked it into first,,, let it out and went back about 10 ft. stoped the bike.... firered it up again,,, now it goes foward ?   turns out a 2-smoker will run backwards too     try rolling forwourd and pop it...... just my 2 cents !!!!

[bsforever]

srpackrat - i will try that and check things out a little further this week when i have some time. I did start the bike up using the kickstart and perhaps the ignition timing is too far advanced?   it did have a tendency to 'kick back' at times, and as far as i know the only adjustment that can be done is to turn the generator to advance/retard the spark. I don't know that there is a 'wrong way' to assemble the kick-start system that would start the engine up in a reverse direction?  Still am looking for more input and advice, but glad to know that running in reverse can occur ...thanks srpackrat for that info!!

[coxy]

Your timing maybe too retarded I have heard of this never seen it

[farmerdl]

 There were some posts about this phenomenon on Do The Ton.  Does seem to be associated with retarded timing and was apparently  more common with trials bikes in the past.

[BS Mechanic]

This is more of a question than an answer!  My memory is a little vague, and I don't have a 350 engine apart at the moment to check, but is it possible to assemble a 350 with the rotary valves 180 deg. out of time? 

I think I remember it being hard to get a disk valve 2 stroke to run backward due to the asymmetric intake timing the rotary valve allows.

[OldSwartout]

I agree that there may be something wrong in the rotary valve area.  All the times that I've known of engines running backwards, it was always a piston port engine. Trials and woods bikes were most susceptible because of the mild port timing, but that usually happened when they stalled on a hill or against an obstacle and rolled back a little.

It is probably just the right side rotary valve.  That would explain why it was running the correct direction previously, but missing on the right cylinder.  This time, somehow, it kicked back just at the right time and ran backwards on the right cylinder and the left was probably not running correctly. My 350 bounces my foot by kicking back when I first try to kick it through cold. If it was inclined to run backwards, I could see that happening.

Rereading the original post, though, maybe it has always been running backwards, it sounds like this is the first time you actually put it in gear since the rebuild, so maybe both rotary valves are 180 out.

[BRT-GTR]

            You probably haven't done anything wrong, it is impossible to assemble the engine/kickstart to operate backwards  (subject to checking the discvalve positions as noted by BS Mechanic).  Might be possible to see through the carbs if disc port is closed when relevant piston is coming down on the crankcase compression stage of the stroke. . If so, OK.     With the discs timed correctly they obviously will run backwards, srpackrat49 proved that. I doubt a GTR engine would run at all with both discs mistimed but I stand to be corrected.  

      Model aircraft, piston ported, glow engines will quite happily run backwards, usually happens when they are reluctant to start and just catch late after flicking the propeller. You can actually see it happen, prop is just about to come to a stop, when it suddenly reverses and kicks back into life , running backwards.

    With a twin, this is what may happen after kicking, engine fails to start on first/second stroke, crank continues to turn and brings next piston up on compression but without enough inertia to take it past TDC, the plug fires and pushes the piston back down (kick back), reversing the engine but now with enough inertia to keep running. Conditions have to be exactly right for this to happens so doesn't occur very often.
      Confirm the ignition timing is OK using crank pin (can swing the points plate also to alter the timing) then see why it is missing on right cylinder. should be fine.
      Brian.

[bsforever]

I had the engine running for a short periods of time last year, and again this year recently again, there is one point to be made that makes things a little more clearer to me (1). The tachometer ( NOS and NOS cable) i have never seen once to work.....because it would be operating backwards. (2). The oil pump has never worked also ( which would also be operating backwards)...but i had been using a pre-mix to run the engine as a safety precaution before things get working/moving correctly. And yes, this was the first time i ever put the transmission in gear while the engine was running....my suspect is ...is that the engine has ALWAYS been running in reverse because of points one and two ( tach & oil pump not working ).I will check the timing and valve positions and get back with answers of my findings....thanks for the replies for the insight on this problem which totally had me floored 

[BS Mechanic]

This is a great mental exercise without hardware handy to fiddle with!

Srpacrat49, was the bike you're talking about a piston or rotary valve?
 
A piston port two stroke will run backwards, because by it's nature the piston porting is symmetric and opens exactly the same, on the upstroke, no matter which direction the crank is going. Usually the timing ends up close enough because what was originally the closing of the points is the opening when reversed, and occurs roughly in the right place to fire the mixture.

My mental contortions say that if you turn a rotary valve two stroke backward, the intake port will be open on what is now the downstroke of the piston, pumping air back through the carb.  There may be a little intake, but not much, so I doubt that the engine will run backward. If you can install the rotary valve rotated by 180 deg. then the engine will intake on the upstroke, and should run, assuming the timing is close enough.

This makes my head hurt, can someone with hardware handy verify any of this?

[slawsonb]

My head was hurting too. Thanks for the explanation of timing in the piston port case that allows this to happen.
I kept trying to figure out how the ignition timing could work, but the points opening = closing thing tied it out. I learn something on here all the time!
...bert

[bsforever]

It has been 4 years that i have been working on this bike, and the first thing i tackled outside of dismantling it was the engine. So it has been awhile, but i do remember i had ziggy send me a photo of the timing gears which i followed that to a 'T' . One thing i do recollect is working with the rotary valves, i had marked them for placement, but eventually when it was time to assemble them...the markings ( felt marker ) were gone. So i relied on placement which i found ( or i believed so at the time ) that the rotary valves could not be put on incorrectly because of the splines...they would only go on one way because the size of the splines were of different sizes and could not be turned to a different position.  I did some routine checking today and found that the openeings on the rotary valves are open ( can see through the carb ) on the up-stroke...but could it be that they are off and my belief that the valves can only fit on the splines one way??  I tried retarding the spark ( turn the generator ) and also advanced  ...same result...engine runs in reverse. Ignition off i kicked the starter lever and everyting is working in the correct direction ( i.e. points cam turns counter -clock wise ) but when running it goes opposire ( clock-wise ) . I bellieve BSMechanic is probably correct on the rotary valves....it can not be anything else....but if there is someone that can let me know for sure that the valves on the splines CAN fit in different positions,,,,then i know for sure some how that is what i messed up on....     thanks , bsforever

[hardy]

It is possible to install the disc valve in the incorrect orientation. I didn't mark it when I removed mine only to find it can go back on in two directions. I just worked out when it should be open compared to piston travel and installed it according.

Hope that helps.

Ryan

[BS Mechanic]

Here's a thread that discusses how to set the disks, hope it helps.

http://bridgestonemotorcycleparts.com/index.php?topic=3912.msg21908#msg21908

[bsforever]

Hardy, thanks for that info!!!!  looks like i will be taking apart the engine to get to the rotarys    and will make sure they are correctly  installed this time....even if i have to ask stupid questions later on when i get to that point of re-installing them again( making 100% certain they are correct. Will be atleast a couple of weeks for me to have this at that point i am sure, for re-assembly. Atleast i don't have to 'split the engine cases' to fix this ....( i just got to try and stay positive with my blunder.)  

[bsforever]

BSMechanic, thanks for the thread link, just reading that what Graham said on there pretty much verifies what i was afraid of... the opening on the valve is on the up-stroke, however, it is at the very bottom ( the piston ) when it is open ( the valve opening cutout ). And this according to what i was reading in the thread...my valve placements are incorrect. Thanks again BS Mechanic for the link. 

[BS Mechanic]

I was hoping that would be useful, and hope your bike is running soon! 

Memory says you can get to the valves with the engine in the frame, and if you're both careful, and lucky you can reuse the right side gasket too.  May be fairly quick to verify the valves and change if needed.  You can double check the mag timing also.

It would be really great if someone (yourself perhaps?!) who has a 350 engine apart could take a couple of pictures of the valves set up in their correct positions.  That would be really useful on the website since the repair manual isn't very clear about this.  I wish I had done that last time I had mine apart, but my hindsight tends to be a lot better than my foresight

[bsforever]

I can not take pics , but i can have someone that has a H.D. camera to take pics for me to post. And yes, that was what i was thinking also to check the gears for timing as long as i will have it apart anyways. Going to be a short riding season for me. 

[srpackrat49]

   Well i will confess    it was on a sears 50cc moped   yes piston port....... But it did go backwords fast.. first thing i did was thinking i broke someting..... i was just a youg pup back then   if anyone out there has an old sears bike.... try it yourself

[BRT-GTR]

      Another suggestion.............turn the engine and back wheel through 180 degs and it will then run the right way   , may require a few other minor mods though.  

  Just had a play with a crank, cases and discs on the bench, before reading latest posts. Here's a few observations that may help future restorers :-

     1) The disc timing pin and dot on the R/H crank end are both in line with the big end pin on that side. So when the piston is at TDC both marks point up the centre of the cylinder.  This is not true for the L/H crank end and is why it's important the R/H disc should be fitted first.
        Can never get my head round why the left end of the crank is not drilled at 180 degs to the right side and is drilled right through the crank. I know it's to do with the disc being flipped over, running in the opposite direction and allowed BS to use  identical discs on both sides, but still strange, clever and it works.
       Once you're happy the left disc is fitted 180degs to the right one put yourself a dot on the left crank end for future use.
 
     2) Graham covered this but worth repeating. To check the disc valve timing on a built up engine, with the piston at TDC,  its valve should be open when viewed through the carb and fully closed at BDC. It's either correct or not, can't be anything in between due to the spline arrangement on the drive collar.
    
     3)  This came up in a phone call with one of our members. When it comes to timing the drive side gears,  alternator/ ignition, most engines (I've ever worked on) are timed at TDC, not so the 350. Don't worry about it, just line all the dots up as shown in manual or Ziggy's excellent photo and it will be correct. . You will still need to finally set ignition timing using the timing pin or a dial guage on the pistons.

 First pic shows R/H side, both dots and pin lined up with right rod in TDC position Sorry, should have leaned over further, crank timing pin is between the two dots. Port would be open
Second pic shows L/H side with rods in same position, Crank drilling, drive collar and disc dot should all be lined up in lower right as shown. Port would be closed
Wider angle shot showing rod positions. Will put a dot on crank end if I ever use it. The discs don't seem diametrically opposed in the pics but they are (I had to go out a couple of times and check it ).
   Brian