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Post by hunter on Mar 19, 2012 3:25:38 GMT -5
G'day Everyone, I been thinking a lot about that characteristic grinding @ approx 3,800 rpm too. My A model runs great except for that. I have some how minimized it but still there under hard acceleration at that rpm range. Experienced RE5 trained mechanics and others believe it is a feature or characteristic Harmonic at about 3,800 rpm. And that all rotary engines do it. I was not so sure. For a long time I wondered if it had to do with fuel/air mixtures just as the secondary throat opened, causing misfire or pinging. But my thinking over the last week or so has changed a little and I am confused and mistified totally. My Hercules and Norton both do not have this issue. "Harmonic" is posh way of saying vibration. Vibration caused by imbalance of eccentric shaft perhaps?? With counter balance not fully effective? Perhaps even separately the rotor not 100% balanced properly?? Production line parts don't get the same maching accuracy as design engineer produced prototypes. I have had car tyres shudder at between 95 and 100 km/hour and smooth either side of this speed. Wonder if this is what is happening with the RE5 engine. Something unique to the RE5 unit maybe compared to Hercules and Norton. It is much larger rotor size than both the Hercules and Norton. And of course, the Norton is twin rotor and would have different balance characteristics. To do something about this would take a lot of work and heaps of knowledge about the relationship between eccentric shaft, counter balance and rotor. It would mean taking down a proper unit etc. I thing this might be too much for most of us, me at least. I just wonder if this might answer some of our questions.
Kim. oz.
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Post by kettle738 on Mar 19, 2012 4:39:50 GMT -5
I have the same problem, no flat spot at all, but dreadful grinding, so I have also given it a lot of thought and read everything I can about it.
The most plausible cause (to my mind) that I have read was posted here by Wayne I think and it suggested a form of pre ignition (pinking) due to the nature of the inlet arrangement.
Given that it is a mystery, I have not heard or read anything that fits the bill better. That said it seems logical that some variation in the level of grinding could be achieved by varying the ignition timing if that were the cause, unless the inlet system precludes that.....and I haven't heard of anyone curing it yet by altering the timing, so perhaps it's still a mystery.
There have been postings in the past from owners who say their bikes don't have the problem, but there are quite a few regulars on here now who have ridden multiple bikes (four in my case) and they all seem to do it.
None of which means it can't be cured, but perhaps it's like the flat spot, what works for one bike doesn't for the next.
I also have a UK model DKW (probably up for sale shortly) and that doesn't grind at all.
Mick.............kettle738
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Post by pmcburney on Mar 19, 2012 7:45:05 GMT -5
I've been giving this some thought myself, and I reckon the root of it lies in the primary chain and tensioner arrangement.
Everyone knows how a drive chain, especially a longish one like on a dirtbike, will get up a 'whip' at a certain speed.
I postulate that the primary chain does the exact same thing.
A revised tensioner loading may almost eliminate it, if it is allowing 'whip' at 3800 rpm.
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Post by riversidogs on Mar 19, 2012 9:17:51 GMT -5
My bike has had a vibration at 3800 rpm since mile one. It does not grind but it is very noticeable. There was talk that Suzuki were the only people to have gotten a single rotor engine to run smooth at that time. Except for this one RPM point. I guess it is possible that this vibration plus wear could cause the primary to hit something in its path when it happens causing the noise. This is just my opinion but something to think about.
Tom
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Post by bdalameda on Mar 19, 2012 10:24:59 GMT -5
I posted about this a couple of months ago - Back in 1975 when I went to the Suzuki RE5 service school the grinding was a topic of discussion. The Suzuki tech told us the grinding came from a torsional harmonic that caused the primary chain to whip violently and would transmit this vibration down the drive chain. He said part of the problem was due to the fact that the heavy clutch and drive assembly is mounted on a fairly long unsupported transmission main shaft. If you ride next to an RE5 and watch what happens when this vibration point is reached you will see the drive chain whip up and down violently. Back in 1975 I experimented with adding additional tension to the primary chain tensioner by putting a valve spring behind the tensioner. This had quite a dramatic effect and reduced the grinding vibration quite a bit. I have always thought that having a hydraulically damped tensioner or a solid block type adjustable tensioner shoe that took the play out of the chain would eliminate most of the vibration.
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Post by Al Corelli on Mar 19, 2012 10:52:09 GMT -5
Maybe that's why they used a 630 chain instead of a narrower one? To dampen vibration?
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gerryggg
2nd Gear
I'm Lost In Thought, Please Send a Search Party.
Posts: 225
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Post by gerryggg on Mar 21, 2012 6:00:46 GMT -5
It certainly has the heft to do it. I'd forgotten how heavy 630 chains were until I pulled mine off.
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Post by wayne on Mar 24, 2012 1:38:59 GMT -5
If you missed my post elsewhere, I weighed my 630 RE5 chain and compared it to the replacement 530- 150 grams over 3 kg total. I was very surprised about how insignificant it was.
If my 530 chain has done anything, it MAY be fractionally smoother in that rpm band, but only fractionally and could be my imagination or could be just that I've got a new chain and sprockts, nothing else.
One simple thing that does reduce the grinding vibration: set your timing to 5 degrees BTDC.
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sam
1st Gear
Posts: 16
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Post by sam on Aug 26, 2012 12:01:29 GMT -5
The grinding issue also occurs on my gt750 though not as noticeable as the re5 probably because the gt is not as smooth. I believe the gearboxes are the same/similar to the two models which is the cause of the harshness. IMHO it's just a characteristic of the marque
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Post by wayne on Aug 27, 2012 1:42:45 GMT -5
I have never noticed any grinding in any of my GT's nor have I heard any other GT owner talking about it. You'd be the first Sam.
None of the GT tests of the day that I've read mention it, per se, either. But virtually every RE test does. I think the grinding that we're talking about is very unique to the RE5.
I believe it's fairly well established and accepted that the primary cause of the grinding vibration in the RE is the engine itself perhaps exacerbated by primary and other drive characteristics.
I'll pay attention next time I ride my GT.
EDIT: Sam I notice that you may not have an RE on the road (?) Have you ridden one ? If not, I can't think of a vibration on any other bike that is similar to this specific feature of the RE5 but you notice it when you ride one.
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Post by mike500 on Aug 27, 2012 7:00:00 GMT -5
the only noise i have ever had from a gt750 gearbox was in 3rd gear due to gear picking up slightly on a shaft which can sound similiar to the re noise but is not what the re5 noise is,im on about my 15th gt750 and only ever had 1 make a noise like harshness,all 3 of my re5's have some harshness / grinding 1 is worse than the other 2 though and i expect it has more lash in the primary chain as it rattles slightly on tick over with clutch lever out and when u pull clutch in the rattle goes regards mike
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Post by steve w on Aug 28, 2012 17:07:53 GMT -5
hi just to say, everything bdalameda says is true i went to suzuki GB on a full weeks service seminar on re5. and the technical chaps from japan were there ,and they talked about this vibration and the outcome was the same as bdalameda says.
steve
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Post by goandy on Aug 28, 2012 23:22:20 GMT -5
My bike grinds particularly well, to the point that the whip in the primary chain is so violent that the underneath of the tensioner both on the steel arm and alloy mounting block are scarred from the chain rubbing.
Interestingly the chain measures up absolutely fine and well within the limits at 276.5mm (almost like new apparently) so I shall have a look at my other tensioner and investigate a heavier spring or similar.
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Post by goandy on Aug 29, 2012 2:51:05 GMT -5
My other tensioner shows no sign of gouging and has a slightly weaker spring so obviously my (running) bike has some other issue that's contributing to the whip. Might just put it back together and see what happens. The tensioner is a bit ugly though:
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gerryggg
2nd Gear
I'm Lost In Thought, Please Send a Search Party.
Posts: 225
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Post by gerryggg on Aug 29, 2012 15:44:57 GMT -5
I remember that the US GT750 used to have a vibration, harhness around 55mph in top gear. This was evident in the J and K models. They made some changes in either the L or M and it seemed to go away until they changed the final reduction ratio on the A and B models. Then it came back. We used to cure it by going back to the M model sprockets. If someone needs it I can do a bit more research and see if I can get more details. As I recal on the GT it was closer to 3200-3500rpm rather than 3800, but I'm relying on 40 year old memories.
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