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Excessive Engine Noise


jondd21
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My 07 Rev 250 has developed an top end rattle. It does not effect performance and the bike starts and runs well.

The noise is from the top of the engine ( sounded by listen stick ) with no bottom end noise at all.

My thoughts are that it may be piston slap as it decreases a little when the engine warms.

I am tempted to renew the ring, small end etc as a first resort.

Is it false economy to not renew the piston at the same time and how much will I save if I dont ?

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I've found I usually get 3-4 seasons out of a Beta top end before I need rings and in that case it's more a matter of loss of bottom grunt and slightly harder starting. I've never had to replace a piston. Just out of curiosity did this noise start when the weather got colder? It might be a matter of bad fuel or a different fuel. In the US the fuel companies change their fuel mixtures for the winter. The other thing that happens is the colder winter air changes the jetting requirements and for many of us it's necessary to go up at least 1 pilot and main jet size to prevent detonation. With the water-cooled chrome bore engines the carb jetting is very lean compared to the old air-cooled engines. This makes them run very crisp but also makes them more susceptible to atmospheric changes. The fact that the noise gets better with a warm engine sort of points in that direction as a cold engine needs a richer mixture.

If you do think it is piston slap have it measured. No point in spending money when it won't make a difference.

Oh yeah one other thing to check is the top engine mount. Sometimes they loosen up and make a noise.

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I've found I usually get 3-4 seasons out of a Beta top end before I need rings and in that case it's more a matter of loss of bottom grunt and slightly harder starting. I've never had to replace a piston. Just out of curiosity did this noise start when the weather got colder? It might be a matter of bad fuel or a different fuel. In the US the fuel companies change their fuel mixtures for the winter. The other thing that happens is the colder winter air changes the jetting requirements and for many of us it's necessary to go up at least 1 pilot and main jet size to prevent detonation. With the water-cooled chrome bore engines the carb jetting is very lean compared to the old air-cooled engines. This makes them run very crisp but also makes them more susceptible to atmospheric changes. The fact that the noise gets better with a warm engine sort of points in that direction as a cold engine needs a richer mixture.

If you do think it is piston slap have it measured. No point in spending money when it won't make a difference.

Oh yeah one other thing to check is the top engine mount. Sometimes they loosen up and make a noise.

Hi Dan, merry Christmas to you.

I have only recently bought the bike. The seller told me of the noise prior to me buying it. Its a great condition bike, he was a really nice chap, honest and the bike seems genuine with the right mods to it. More importantly it was within my budget and I still have money to put it right if needed.

I will check all the bolts next before stripping, perhaps that wont be required.

I will let you know.

Thanks once again.

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My 07 Rev 250 has developed an top end rattle. It does not effect performance and the bike starts and runs well.

The noise is from the top of the engine ( sounded by listen stick ) with no bottom end noise at all.

My thoughts are that it may be piston slap as it decreases a little when the engine warms.

I am tempted to renew the ring, small end etc as a first resort.

Is it false economy to not renew the piston at the same time and how much will I save if I dont ?

It may be something as simple as a ring stuck (with gum) in it's groove.

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My opinion is that this is most probably piston slap. If the carb would make the bike run lean, then it doesn't make any extra noise. If it runs lean, then after 30 mins - 1 hour, the engine will be too hot, and detonation, preignition occurs, which really makes sound, but I don't think that this is the case.

It's a false economy changing the rings and top end bearing. It will make the compression a bit better, but the engine noise will remain.

Some engine noise is normal, but if your's is making really excessive noise, then you should drain the water, and open the engine. The best way is to put the piston Without the rings (!) in the barel, and see if it's loose. The piston has a very bit of play in the barrel (because the piston expands when hot), but the clearance should be less than 0.1 mm. If the clearance is big, say 0.15 mm or more, then your problem is piston slap. You need to buy a new piston. (Of course check the barrel, too, for scores and scratches (which can occur if you have a problem with the air filter), and be sure that the piston is worn, and not the barrel. But anyway it's uncommon that the barrel to be worn.)

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Merry xmas Jon, did you buy the Beta because Hovis has one. :rolleyes:

Same to you Jack. The reason for getting it was two fold ! Firstly it was cheap, ( rattling but cheap ),. Secondly and most importantly, I heard that HOVIS has a one piece lycra suit that he wants to sell, formerly owned by Dai Bedford, but Hovis has had his sponsors logo ( MAGNERS ) put on it.

I have heard that observers rub their eyes in disbelief when they see it on him that they forget to mark him so he gets cleans !

Merry Christmas.

Edited by jondd21
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the amout i have had, and intend to have tonight to drink, all i will see is a blur in tomorrows trial

but its my comeback tour after 5 years out of the game & i think it would be unfair to be sobar

normaly i like to go out clubbing & get wasted get in about5 am have 2 hours kip then go to a trial

Edited by hovis
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