Disturbing gearbox noise in a SEI
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Thread: Disturbing gearbox noise in a SEI

  1. #1
    Senior Member tucandugu's Avatar
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    Disturbing gearbox noise in a SEI

    Hi.
    From the very first road tests in my SEI I noticed a noise in the gearbox/clutch area. Is the "typicall" noise of a worn out chain/front sprocket, like if the sprocket teeth was sliding and jumping over the chain links. Seems to come from the front sprocket area but other times seems to come from the clutch area. Another important particularity is that this noise only appears when a considerable torque is needed, specially at low revs, uphill twisting the accelerator. I thought that after replacing the entire transmission kit (chain and sprockets), the problem would disappear; however it persists without any improvement.
    I can ride the bike without problems most of the time, enjoying of the engine sound, since only in the described conditions the noise is noticiable, but anyway worries me. I would prefer to be wrong, but it makes me to suspect about the triplex chain, which connects the crankshaft to the gearbox...
    Any suggestion what could be the cause?. Someone has experienced similar symptoms?.

    Thanks in advance.

    Carles
    Benelli TNT 1130 Sport EVO 2008 - Benelli 750 Sei 1977 - Moto Guzzi 65cc 1957 - Vespa Primavera 125 1977

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    Quote Originally Posted by tucandugu View Post
    Hi.
    From the very first road tests in my SEI I noticed a noise in the gearbox/clutch area. Is the "typicall" noise of a worn out chain/front sprocket, like if the sprocket teeth was sliding and jumping over the chain links. Seems to come from the front sprocket area but other times seems to come from the clutch area. Another important particularity is that this noise only appears when a considerable torque is needed, specially at low revs, uphill twisting the accelerator. I thought that after replacing the entire transmission kit (chain and sprockets), the problem would disappear; however it persists without any improvement.
    I can ride the bike without problems most of the time, enjoying of the engine sound, since only in the described conditions the noise is noticiable, but anyway worries me. I would prefer to be wrong, but it makes me to suspect about the triplex chain, which connects the crankshaft to the gearbox...
    Any suggestion what could be the cause?. Someone has experienced similar symptoms?.

    Thanks in advance.

    Carles
    Name:  benelli engine.jpg
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    Above,some of the Benelli 750 sei engine parts: I needed new timing chain,new primary chain, new gear selectors,two new gears,clutch assembly parts and most of all all bearings,seals and gaskets.

    Hi Carles,
    Suspecting anything relating to the noise coming from inside the engine is anyone's guess unless you pull the engine to pieces. If the engine of your bike is nearly due for revision may be it is a good idea to carry on with reapair and some preventive work.
    When my bike's engine had been pulled to pieces many parts needed to be replaced with only 26k showed on the speed clock.In case of noise coming from your bike.s engine it can be combination of few worn engine parts.
    Also as I mentioned to you before you can contact Enrique of Spanish Benelli Club who lives in Valencia.
    Cheers,
    Jerzy
    Last edited by GeorgeE111; 12-05-2013 at 03:19 AM.

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    Senior Member
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    I would fix the problem before the chance of a major fail.... Will be a lot cheaper stripping and fixing now



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  5. #4
    Senior Member tucandugu's Avatar
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    Thanks guys. In fact, the engine runs very smooth and powerfull and the bike is like new, now. Would be too hard dismantle the entire engine at this moment. I'll wait to see how it evolutes with the use, may be is not so critical, by the moment is not affecting the normal use. Lets see.
    Good work Jerzy, did by yourself?
    Last edited by tucandugu; 12-05-2013 at 05:05 PM.
    Benelli TNT 1130 Sport EVO 2008 - Benelli 750 Sei 1977 - Moto Guzzi 65cc 1957 - Vespa Primavera 125 1977

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    Quote Originally Posted by tucandugu View Post
    I'll wait to see how it evolutes with the use, may be is not so critical, by the moment is not affecting the normal use.
    One thing is for sure: the noise problem will not disappear by itself.
    As for the engine rebuilding i can not afford to mess up with is,..so I have left the job for professionals !
    Cheers
    Jerzy

  7. #6
    Senior Member tucandugu's Avatar
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    That´s right Jerzy. I am quite sure that is the primary chain, the wide chain that connects the crankshaft with the gearbox. The noise only appears on hard slopes at low revs, and is clearly identifiable as chain noise . When driving at normal conditions the engine is very smooth, even twisting the throttle, no noise is noticiable. It´s right to drive in current use without more problems. Nevertheless I will go on investigating how to fix this. I guess is necessary to take out the engine from the frame but I do not know if is possible to replace the chain without dismounting the upper engine part. If somebody have info. about the procedure, will be welcomed.
    Cheers
    Carles
    Benelli TNT 1130 Sport EVO 2008 - Benelli 750 Sei 1977 - Moto Guzzi 65cc 1957 - Vespa Primavera 125 1977

  8. #7
    Senior Member
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    Quote Originally Posted by tucandugu View Post
    That´s right Jerzy. I am quite sure that is the primary chain
    You might be right Carles !
    From the day one when I bought my Benelli 750 sei I started to look for all the information I could find about the bike in order to get it known better That is when I came across Spanish Benelli Club website.
    Enrique who runs the club in Valencia tells about all the issues with possible problems with 750' and how to fix them.One of the solution for the primary chain noise is to introduce primary chain tensioner and that fixes the noise problem.There are issues with engine overheating but that can also be resolved.And yes,to get to primary chain the engine need to be put apart,there is no magic about it
    Cheers
    Jerzy

  9. #8
    Senior Member tucandugu's Avatar
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    Quote Originally Posted by GeorgeE111 View Post
    You might be right Carles !
    From the day one when I bought my Benelli 750 sei I started to look for all the information I could find about the bike in order to get it known better That is when I came across Spanish Benelli Club website.
    Enrique who runs the club in Valencia tells about all the issues with possible problems with 750' and how to fix them.One of the solution for the primary chain noise is to introduce primary chain tensioner and that fixes the noise problem.There are issues with engine overheating but that can also be resolved.And yes,to get to primary chain the engine need to be put apart,there is no magic about it
    Cheers
    Jerzy
    Sorry Jerzy, I wanted to mean the primary transmision chain, the one which links crankshaft with gearbox.The cam chain appears to be healthy, without any noise, in fact as I told, the engine runs incredible smooth and powerfull. Agree with you, I did the same when I bought my SEI and during the two and a half years that I have been restoring it. Thanks to this, now I can guess that is that wide transmision chain the probable responsable of this prompt noise. What I do not know is if there is a way to reach that area without undoing upper engine area, such, for example, disassembling only the lower crankcase and lateral clutch cover.

    Thanks and regards.
    Carles
    Benelli TNT 1130 Sport EVO 2008 - Benelli 750 Sei 1977 - Moto Guzzi 65cc 1957 - Vespa Primavera 125 1977

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    Senior Member tucandugu's Avatar
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    HI again. Following your recommendation, Jerzy, I talked with Enrique about the above symptoms. He says that it's a typical gearbox sprocket wear, quite common in this model. He has also commented that it is not a serious problem as it does not affect other parts of the engine, but obviously someday will need to repair. I will wait some time -enough to save money...- and then will change all this, also the primary multiplex chain.

    Cheers!.

    Carles.
    Benelli TNT 1130 Sport EVO 2008 - Benelli 750 Sei 1977 - Moto Guzzi 65cc 1957 - Vespa Primavera 125 1977

  11. #10
    Senior Member
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    Quote Originally Posted by tucandugu View Post
    I talked with Enrique about the above symptoms

    Carles.
    I am very happy for you Carles that you talked with Enrique about the gearbox noise issue as he is the person with lots of experience.I have also got lots of advise from him about the modification tricks.I understand that when it comes to repair work of your bike you would consider applying tensioner for primary chain to stop the chain flapping.It is very needed improvement for any bike without tensioner. Once in contact with Enrique you will know best what you want to do with your engine and how far you would like to go with the mods.Good Luck Carles with your bike.
    I found interesting story about Benelli 900 sei .

    JENAL - Benelli 900Sei Special. A classic motorcycle for a classic barge - index page 1

    Cheers
    Jerzy

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