Grinding/harshness @ 3,800 rpm

[sam]

From Wayne

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.

Err - here's my baby which along with a RD400 are constantly on the road


Ive owned many water bubbles over the years (still have one now) including the J, L ,M & an A, I'm sure they all to some extent had this grinding issue, some more than others but as I said it is not so noticeable but definitely there. My present M model has it that's why I mentioned it in the earlier post...

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.

Have a look at this report from the 70's, my interpretation may be wrong but the harshness was mentioned here on an 'A' model test (mentioned on the second page of the GT article column 3) taken from the test report Bike magazine circa February 1975

www.abacuscaralarms.co.uk/bikes/Test_Reports/Suzuki_GT750-CB750.html

'This two-stroke megaphonitis built up between three and four thousand revs and created a low frequency vibration transmitted through the kick start and onto the riders right leg'

[wayne]

I only asked because, to me, the RE grinding is so unique that I felt that you couldn't confuse it with a GT unless you hadn't ridden one. While that one test describes a vibration (and the GT's have plenty unique to their triple cylinder layout), the description doesn't at all sound like the grinding one experiences on an RE in the 3000 band (exactly where often depends on load etc).

I think that it's well established that the harmonic in the RE is a torsional harmonic related to the rotary engine. I've heard similar from Mazda guys. It could also be related specifically to the peripheral ports.

[goandy]

...and another addition to the list of possible contributors to the rattle/grinding etc is the gearbox input bearing. My bike was making all sorts of noises at idle as well and I suspect it may be due to the clutch basket outer band (see photo below) and also the input bearing as I've just taken mine out and it is shot with alot of play in all directions.







Err photos not working right now... fiikw!

[ap951]

When I purchased my RE5 it had about 5,000 original miles on it however it had been sitting for 25+ years with a full tank of gas & was never turned over. I was very careful in my procedure before I ever attempted to start it. When I did finally get it on the road there was a horrible noise that came directly from the transmission. I kept changing the transmission oil and each time it would have a metallic sheen (lots of very fine metal bits mixed into the oil) I finally determined that something was very wrong and about a year ago I pulled the motor and completely went through the transmission. The main transmission input bearing located directly behind the clutch was self-destructing. I found a new Nichi bearing that was a direct replacement (I had to remove one of the shields) I replaced all the trasmission bearings while I had it apart.

As I think about it I wonder if the grinding/harshness at speed is what made the bearing self-destruct. A bad bearing would make the problem much worse. Maybe this is why the bike was parked 25 years ago. Many questions come to mind

Andy - I noticed in one of the pictures from your fabricated instrument screen what appears to be a new (NSK) transmission main input shaft bearing. Is that for the bike transmission with 20,429 km on it or for the one with 77,623 km on it?

[goandy]

The 77K one. "Ol' Rattler" as I like to call her. Hopefully not so rattly when I get it all back together.

[ap951]

I really don't know

all the other bearings in my transmission were fine. Just the one directly behind the clutch was bad. It could have been a factory defect. I showed it to the manger of a local bearing supply house and he asked me about the motorcycle. I told him that it had been stored for 25 years inside a metal shed located in the back yard of the previous owner. Temperatures would have varied from -20f to +115f. It was his opinion that this environment could have caused some condensation that would have compromised the bearing

[glankford]

After reading this thread with much interest, I have an idea. If it is truly the chain hitting some sort of resonance and whipping back and forth, how about a guide channel (delrin or some other chain-friendly surface) to keep the chain under control? Every car engine I've worked on uses guides for a timing chain. In fact, I've never seen a chain span that far of a distance without something to keep it in check.

There are plenty of bolts all around that area that could be used as attachment points.

Any thoughts?

[goandy]

Sounds like a good idea. I've put a bit of a guide on the tensioner arm and am thinking about making a guide up for the tension side as well....

I did this as there are gouge marks on the tensioner arm and also up on the ali mounting bracket. I don't really think they were caused by harmonics- probably a broken primary chain or similar. Still, can't hurt.



I posted this in another thread but here's the damage to my clutch basket band: