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DT125R Forum -> Tuning -> Low compression...
Post Info TOPIC: Low compression...
dtrdave


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Low compression...
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I should have fitted the new piston rings after all biggrin

Just wondering, would it have a huge effect on performance only having 90psi ?
Took it out today and felt really flat! as if the powervalve wasn't working but i've checked and cleaned that and it works fine.

It didn't seem to be revving out either. The rev counter cable is snapped so i don't know what revs it was at but i'd guess about 7-8k rpm at most at which point it bogs down.

I was expecting it to be slow (compared to what i'm used to) but not this slow no

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dtrdave


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And another question...

My frame number starts with 4BL ?  I'm trying to find out what the measurements of my piston and rings should be but my manual only seems to cover 3RN model numbers?

Cylinder head has 3BN stamped in it and the cylinder has 3MB00 on the side.

I'm confuzzled  confuse help biggrin


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dtrdave


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No one know ? I thought you lot knew it all about the 125's ? lol



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craigbulmer


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The piston size should be 56mm standard mate, but will probably have a bigger piston in..

only 90 PSI, yes you will feel a power gain smile Id do the whole top end tbh. 90 PSI is low.

Sure the powervalve aint upside down?


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Yamaha DT125R - 2003
dtrdave


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craigbulmer wrote:

The piston size should be 56mm standard mate, but will probably have a bigger piston in..

only 90 PSI, yes you will feel a power gain smile Id do the whole top end tbh. 90 PSI is low.


Sure the powervalve aint upside down?

 


Cheers for the reply matey.

Found out that the cylinder is .5 overbore so it's all good.
Had the piston and rings measured up and it's all within tolerance  but- the top of the liner was slightly proud of the barrel and the head was slightly off too.
Hoping that's the only reason the compression was so low.

It's all in getting skimmed now anyway so will see what it's like when i get it back.

I'll tell ya, i knew the young'uns  didn't look after stuff but this is going a bit far. I don't think the bike has EVER seen grease or copper grease. It's had no mechanical sympathy at all !  pretty much everything i've removed has been seized. Even stupid little things like greasing/lubing cables and such like has been neglected no

My poor little blow torch has never seen this much use EVER  lol

 



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Spartan


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Dave mate, how do you test compression? Been wondering this for a while now.

biggrin



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DT125X 2007
dtrdave


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Spartan wrote:

Dave mate, how do you test compression? Been wondering this for a while now.

biggrin



Buy a compression tester. Remove spark plug and screw in tester then kcik the bike over a few times with the throttle wide open. It'll show you the compression on the testers dial...

 

Easybiggrin



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Spartan


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Yup that sounds very easy thanks Dave i'll pick one up.



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DT125X 2007
Spartan


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Never had one before but do you think this tester is alright:

http://cgi.ebay.co.uk/MOTRAX-HAFNER-MOTORCYCLE-BIKE-COMPRESSION-TESTER-G-LESS-/130411957535?cmd=ViewItem&pt=UK_Motorcycle_Parts&hash=item1e5d288d1f

Thanks alot

-- Edited by Spartan on Tuesday 10th of August 2010 07:43:28 PM

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DT125X 2007
dtrdave


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That's exactly the same as mine :) (although mine was only around £15 from my local car shop)

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Spartan


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Cool i'll have a look for one tomorrow.

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DT125X 2007
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