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Post by wayne on Jul 25, 2011 20:28:02 GMT -5
I was at an engineering shop today sourcing O rings for the digital gear indicator. At the end of the transaction, fellow asked what the gear indicator was and I told him it was from a rotary motorcycle.
The usual conversation followed but he started asking some very specific questions (width of the rotor as an example). I also told him it was peripheral ported.
Turned out he was a trained rotary mechanic but only in his late thirties and more interesting for what followed, he'd never heard of an RE5 or a rotary motorcycle.
He then casually asked "so does it have a vibration ?"
I started with the "it's pretty smooth compared to bike's of the day but, as a matter of fact, it does have a grinding vibration in a particular rpm band."
"Yeah, that's the p p" The P P ??
He claims that the grinding vibration is a direct function of the porting design. The fact that he knew enough to ask if it vibrated after I told him about the peripheral porting and that he is unfamiliar with the bike lends his comments some real credibility.
I told him that I had understood this to be a characteristic of the engine and not some fault which he confirmed. And as I had been told in the past, cars have it too, but it is damped by the twin rotors and isolation mounts.
However, this is the first that I'd heard about it being a direct result of peripheral porting. I specifically asked him if a sideported motor would then be free of this particular feature which he confirmed is the case.
For what it's worth.............
Wayne
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Post by bdalameda on Sept 27, 2011 1:23:39 GMT -5
I am a newby on the forum here. I went to the factory Suzuki Service training school back in 1975 and I asked several of the Suzuki rotary experts there about the vibration. I was told it was a torsional vibration that when it reached a certain harmonic the primary chain would begin loading and unloading and whipping up and down and this further transmitted the vibration through the final drive chain. You can definitely see the final drive chain whip violently when you reach this point. As an experiment I made a modification on my own bike by adding a coil spring behind the primary chain tensioner. This reduced the to the point where it is almost completely gone. Now that I have another RE5 that I just recently acquired (my 3rd) I am thinking about designing a hydraulic dampened tensioned for the primary chain. I have always believed that the primary chain tensioner makes the problem much worse. I think a dampened tensioner or an adjustable fixed tensioner would work better.
Dan
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Post by wayne on Sept 27, 2011 1:59:42 GMT -5
Very interesting Dan. Many early tests blamed the vibration on the primary chain but simply assumed that it was loose. Given that the fitting of a coil spring made a marked difference, it sounds like you've hit upon a cure.
The rotary mechanic was pretty black and white about the vibration being a feature of the primary port design and this may still be true. As you note, it is the passing of the harmonic to the primary chain and its subsequent whipping which we are probably feeling.
Can you tell me what sort of coil spring you used and an approximate strength ? I have the clutch cover off my rider at the moment so why not try a new idea.
Wayne
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Post by bdalameda on Sept 28, 2011 2:25:52 GMT -5
It was many years ago when I made the spring mod - I used a valve spring and fitted it over the rubber bumper on the back side of the tensioner when compressed against the case and fitting over the rubber bump stop it can't fall out and it added pressure to the tensioner. I worried somewhat if the roller would stand up to the extra load but I never had any problems with it. I wish I could tell you what type of spring it was but it was 35 years ago!
Dan
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Post by hunter on Oct 30, 2011 7:12:06 GMT -5
This possibility now explains something with my A model I found when I first purchased it. I found a crude attempt to insert a bolt and lock nut fixed where the bump rubber would be on the primary chain tensioner. This would use the engine casing as a back stop to make it like a fixed tensioner. Some owners have also had some improvement with this issue by changing primary jet sizes. Perhaps a combination of improved primary chain tensioner and jetting could get some good results.
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Post by kettle738 on Oct 30, 2011 12:08:08 GMT -5
I took my clutch cover off today to deal with the rattling clutch (many thanks Wayne for the picture of the screws that can be left in situ, it makes the job way easier) and it's true that the primary chain can flail about a lot; mine seems remarkably loose and is going to get replaced.
That said, the most convincing explanation I heard (on this board) for the vibration problem was pre ignition, it seems to fit all the circumstances very well.
If that were true it should be possible to reduce or at least vary the vibes by retarding the ignition timing; I have been unable to do that as the previous owner seemingly put the clutch cover back with the ignition one tooth astray (easily done) and 8 degrees BTDC has been the limit of adjustment available.
Once it's back up and running if I've managed to get the timing gear right I'll have a crack at retarding it a bit at a time and see what happens.
Mick..............kettle738
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ap951
2nd Gear
Posts: 280
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Post by ap951 on Oct 30, 2011 18:37:37 GMT -5
Hello, I'm new to the Board however after two years of lurking I am compelled to post. I'm 50 years old and have owned/repaired many motorcycles since I was 12. One year ago I purchased an M model with 5000 original miles however it had not been started in over 25 years. I have been dutifully following some of the very sound advice that has been offered on this site. I did get my M on the road however I have been trying to fix the flat spot at about 4000 RPM as well as the vibration. Last week I removed the clutch cover and upon inspection my very first instinct was that the spring on the primary tensioner felt very weak indeed. Your comments are confirming my thoughts & I shall try to find a slightly heavier spring but not too heavy. I will post the results but I'm planning on doing a thorough inspection & it might be a while before I'm on the road again. Thank you all for sharing your thoughts!
Bill in Colorado
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Post by HGH 770N on Oct 31, 2011 17:00:24 GMT -5
With Ref Grinding/Vibration.
On Trying to ballance out the hessitation problem at 3500-4000 rpm I had cleaned and adjusted carb & cables and it ran very lumpy and would not tick over . I then went to the points and found that by static setting the timing at 12 BTDC the tick over came back and on test ride found the hessitation had amost completely gone and also the Grinding/ vibration had gone too. I have digested the workshop manual again and put it back to 10 BTDC and on a further test its was awfull again,
Any segestions ?
Rog
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Post by ziggystardust on Nov 1, 2011 7:28:44 GMT -5
Try a larger main jet, there are posts on here regarding up jetting. Works for some.
Z
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