Transmission Problem?? vibration and noise, please help!

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Peter T
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Transmission Problem?? vibration and noise, please help!

#1 Unread post by Peter T »

Hello there everybody!

I'm actually from England, and currently living in Spain, and I'm really hoping there may be somebody on here who can help out.
Appreciation in advance if so!! ,-)

Ok, I have a 4 stroke, single cylinder bike, that for some time now has been vibrating (coming from the engine area) between 6 and 8K rpm, in all 5 gears!!

This is accompanied by a rough feeling and engine noise and of course other area bike rattles!

OK, so, I have changed the chain and sprockets, the generator coil and magnet/flywheel (which showed signs of damage), crank position sensor, checked the engine mounts (which did actually break at one time but are now all welded-up again). I have replaced the valves (one had broken/worn on the top head) and replaced crankshaft bearings. I have had the crankshaft checked for balance too. All OK. The mechanic I was recently working with assured me that he had found nothing obviously wrong with the engine at the time of replacing the crankshaft bearings and checking its balance/alignment.

But, still I have this dam vibration! accompanied by a rough (not right at all!) slightly-metallic sound coming somewhere from the vicinity of the engine, but that vibrates through the whole bike - almost totally/only between the 6-8krpm range.

I guess the only area I have not examined now is the transmission/clutch. I have not suspected this simply because the vibration appears always around the same 6-8,000 rpm area, and in all gears!

Possible Clues:- I have also noticed the tachometer (at the troublesome rpm) moves erratically, and is not nice and smooth as in other rpm's. There are no warning lights coming from the Engine Management System at all. I have also noticed that as I depress the clutch ready to change gear in/or above the 6-8krpm range (and there is that moment of no-gear before the next gear is engaged) then the vibration/noise becomes VERY noticeable, as the engine rpm momentarily drops back down through that rpm range.

Any ideas??

I'd really, really appreciate anybody's advise or suggestions. I cannot really afford to pay any more garage bills, especially for something that may not cure the problem. (sure there are many here who cash relate to that!)

Your replies are most appreciated ,-)

Peter T.

NB. over the course of the last 12 months (approx. 14,000km) other things have broken (mainly brackets etc) on the bike because of this dam vibration. Would love to nail this once and for all.
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BRUMBEAR
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Re: Transmission Problem?? vibration and noise, please help!

#2 Unread post by BRUMBEAR »

Silly question is your rear mount solid or rubber? If it's rubber make sure they or it is not compromised as this can lead to all sorts of issues.
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Peter T
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Re: Transmission Problem?? vibration and noise, please help!

#3 Unread post by Peter T »

The rear mounts are fixed metal brackets, no rubber,
Thanks

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Re: Transmission Problem?? vibration and noise, please help!

#4 Unread post by BRUMBEAR »

Alright then if the vibration is occurring in an RPM range and occurs while sitting or moving neutral or in gear we can discard the trans for now and focus on engine harmonics. Does this unit have a separate trans or is motor and trans 1 piece? If one piece check clutch basket and then check timing chain tension/tensioner then check exhaust make sure it's not touching where it should not be.
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Peter T
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Re: Transmission Problem?? vibration and noise, please help!

#5 Unread post by Peter T »

Yo BRUM BEAR,

Cheers for responding.

Righty, so the engine and the transmission are 1 composite unit on this bike. Ok, so I will look into clutch basket (not sure what it is right now but will investigate), the timing chain, I will check. The exhaust, yeh, I know this can cause noise, but I've been pretty dam thorough with this this already. I'll double double check this once more just to be sure, but really it doesn't feel like its this.

Also, the noise seems to come more fro the left of the engine and i can feel the vibration through the gear shift lever quite severely.

Its even worse (VERY noticeable) as I pass between gears. Example. I pass through the rough area in revs, so now in about 8K, engage the clutch (in order to change gear) and the revs. momentarily drop before re-engaging next gear. At this point, (as the engine falls back down through the revs from approx. 8K down, ) the vibration is monumental!!!! Feels like the bike is gonna shake apart!

Your ideas still REALLY appreciated.

Thank you
,-)

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Re: Transmission Problem?? vibration and noise, please help!

#6 Unread post by BRUMBEAR »

AAAHHH check your rotor for the stator the nut may be loose that holds it on.
http://www.manualslib.com/manual/405368 ... ml?page=87
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Peter T
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Re: Transmission Problem?? vibration and noise, please help!

#7 Unread post by Peter T »

Nope, I had to actually replace the stator and rotor because of damage (on both pieces) due to the constant vibration. They are now new, and still the same problem. In fact many things on the bike have broken because of this vibration including the petrol tank mount, exhaust brackets, brackets that hold the horn and 2 of the 4 rear engine mounts… totally sheared..

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Re: Transmission Problem?? vibration and noise, please help!

#8 Unread post by BRUMBEAR »

Wow thats some serious vibration. Well I am a little stumped I would say Crank unbalanced to do that much damage it has to be a rotating mass it has to be.
Does this occur in or out of gear or it doesn't matter sorry if you already posted this answer I am just trying to get mt head into your problem.
Ok I reread your posts. There may be an issue in the trans or more to the point output shaft especially if there isn't a real vibration in nuetral. But man I would just replace the engine.
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Re: Transmission Problem?? vibration and noise, please help!

#9 Unread post by TimO »

Just had to respond to this thread - I have a 1973 two stroke single that is doing the exact same thing. I've canvassed loads of ideas on this, including from the Hodaka forum in the US, and no one seems to be able to put their finger on the problem. I've taken the engine apart twice, had a re-bore with new piston, new conrod with big and little ends, I've replaced main bearings and had the crank trued and I've even swapped flywheels. All to no avail. However, I am now sure the problem is not coming from the crankshaft.

There is one thing I would check first on your bike. You said the engine mounts had been welded up? Were they welded back in exactly the same place as they came from? Could it be that you're tightening the engine mounting bolts but that there is still a gap between the engine mount and the engine. This could cause vibration I'm sure, but I guess it's unlikely.

What I now think about my Hodaka is that the problem is coming from the gearbox. I have three shafts in the gearbox and the two main driving shafts (the other is the kickstart) have bearings one end, which are good, and bronze bushes the other. I haven't changed the bronze bushes in previous re-builds and I'm thinking that if there is play in these bushes then the oscillation of the single cylinder engine could resonate with the shafts, causing one or both to 'buzz' up and down at certain revs, especially when changing gear or shutting the power off.

This is only theory at the moment as I'm waiting for new bushes to arrive from the USA, but if my fix works I'll post to let you know. If you find out anything in the mean time please let me know. Like you I'd really like to fix this problem as I love the bike.

Good luck.

Tim O

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