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Engine rattle Beta Techno '97, paranoia or real?

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Hello!

I read a lot about the problem and still confused if it is considered 'normal' or in very bad shape.

The rattle is every stroke, but when I listen to video of any trials bike I can hear that same sound. (I never had a trial near been close to one, it's very niche sort of bike over here)

The engine has 160 psi of compression and start first crank every time.

Engine sound I recorded, I think it sound just a bit worse in video than on real life.

Thanks!

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Sounds a bit like a top end rattle at higher revs, may need small end bearings, easy, quick, cheap fix

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3 hours ago, jonboy883 said:

Sounds a bit like a top end rattle at higher revs, may need small end bearings, easy, quick, cheap fix

Thanks ! I will look into that but still not sure if I can get Beta parts, made a few calls but not a lot of dealer.

If I open it, do I need new gaskets or I can reuse the same if they look fine ?

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you should try to get in contact with members of the local trials group  " ATAQ "

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18 minutes ago, reggie said:

you should try to get in contact with members of the local trials group  " ATAQ "

Didn't knew them, thanks a lot !! :D

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These guys have base gaskets and may have head gaskets.  IIRC, the head gasket is o rings that you may be able to source locally.  If gaskets are in good shape, it is possible to reuse but probably not recommended.     

https://trialssuperstore.com/products/beta-techno-base-gasket

 

More techno parts

https://trialstribulations.net/index.php?main_page=index&cPath=91&sort=20a&page=4&zenid=cfaa76cb7fc85861dcb71200c4442b65

 

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I open it up just to be sure and everything seems to be in specs. There is absolutly zero movement up and down on the crank and same for the piston. Thanks!

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Sounds like a bit of piston slap to me. The bore might be worn and the piston is rattling in it as it goes up and down.

If you search Youtube for 2 stroke piston slap or rattle, you should find a few videos of bikes with a similar rattle/knock.

If the barrel is off, try and get someone to measure the piston and the bore for you with a proper bore gauge. 

 

The bores are nikasil plated ( a hard silicon carbide ceramic coating), so you don't rebore them out and fit a bigger piston.

New coating is applied to the bore and honed down to match a new piston.

If I remember correctly, Beta manuals always stated that you measure the bore after x amount of hours and if needed, replace the pistion with one a micron or two bigger.

So a standard piston might be 72.5mm, but you could buy A, B & C piston kits, each one a micron or two bigger than the last.

Once you exhausted the piston kits it was time to replate, if I'm right about the slap, that's where you are.

 

Something I've done for years is apply a thin smear of grease to paper gaskets.

It stops it sticking to the surfaces. Sometimes you can get away with using the gasket again, but it mainly stops you having to scrape old gasket off the machined surfaces and perhaps damaging them.

Edited by Goudrons2
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Thanks for your response, appreciated a lot, yes it already has a B piston and from the video I listen to I think I was just not use to the 2 stroke sound + maybe a little slap.

 

11 hours ago, Goudrons2 said:

Something I've done for years is apply a thin smear of grease to paper gaskets.

It stops it sticking to the surfaces. Sometimes you can get away with using the gasket again, but it mainly stops you having to scrape old gasket off the machined surfaces and perhaps damaging them.

That's an awesome tips, I guess this will still seal even thos there is a little grease ?

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