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snowball

Removing exhaust bolts on Txt pro 250 and base gasket?

15 posts in this topic

I have just bought a 2007 TXT  and need to take off the barrel for a top end service, only problem is I don`t think the exhaust has ever been removed and the bolts into the cylinder block seem stuck in there. I`m worried about using too much force in case I break them off. Any Ideas how to loosen them  ie heat. Not a great design by gas gas using hex bolts 5mm me thinks. Also slight blowing through the left hand side base gasket  when engine revved so thinking of putting 2 x .05 mm base gaskets. Hopefully will sort problem.

Thanks for any replies

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 You need to tap the bolts a few times with a ball peen hammer or a punch. This will knock the threads loose. Better to use a socket type allan to remove.

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If lineaway's suggestion does not work get someone with a mig or tig welder to weld a nut onto the bolts or a length or rod you can grip with mole grips. The heat of the weld tends to be very effective at loosening seized threads.

Leaking gasket. Check the mouth of the crankcase and base of the barrel are flat within 0.05mm. Just use one gasket of the correct thickness. Before you fit the barrel paint a good coat of blue hylomar onto the joint face and let it go stiff / nearly dry before tightening the barrel down.

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Eventually I had no option but to cut off the bolt head and I'll weld a nut onto the stud. Piston a barrel look like this.

There was no gasket where it was leaking so that's a positive.

No looseness on big or little end bearings. Don't really want to spend much on a new piston as a clubman rider, any thoughts? 

Thanks

IMG_20170415_144523344.jpg

IMG_20170415_144504412.jpg

IMG_20170415_144320903.jpg

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Put the rings (one at a time) into the barrel. Use the piston o make sure they are "square" in the barrel and measure the end gap. It should b between 0.35mm and 0.6mm. Any larger gap and have the bore measured.

The dark deposits on the piston sides show that the engine has been run with insufficient and / or poor quality oil.

There has been insufficient oil to seal the ring to the bore. The mixture blows by the rings then chars onto the sides of the piston. The piston will run hotter than it should because there is insufficient oil to conduct heat from the piston to the bore and cooling water.

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Wow that end gap quote is huge for a GasGas. I have always known them to be .3mm to about .375 on the 280 and 300's. I would clean up the piston skirt, Pop a base gasket on and run it. As you can see its not a horrible job to get to and Pistons come with rings but it will be advised to do the whole cylinder piston and rings as a kit. I would run it first with a new base gasket after you clean up the piston. All you have to lose is a base gasket at this point.

--Biff

 

 

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Just now, biffsgasgas said:

Wow that end gap quote is huge for a GasGas. I have always known them to be .3mm to about .375 on the 280 and 300's. I would clean up the piston skirt, Pop a base gasket on and run it. As you can see its not a horrible job to get to and Pistons come with rings but it will be advised to do the whole cylinder piston and rings as a kit. I would run it first with a new base gasket after you clean up the piston. All you have to lose is a base gasket at this point.

--Biff

 

 

It may be the gap for a Sunbeam motorcycle from just post WW ll.

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Regarding piston ring end gap. Perhaps instead of saying gap "should" be 0.35 to 0.6 I would have been better writing "you can expect" the gap to be 0.35 to 0.6. These are slackish gaps, the 0.6 being the point at which the bore and rings should be properly measured with a view to replacement.

Others may have a different view with regard to controlling blowby but I prefer an adequate to large ring gap and plenty of oil as opposed to a tight ring gap and minimal (say 80:1 fuel oil ratio) amount of oil.

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On 4/18/2017 at 2:21 PM, oni nou said:

It may be the gap for a Sunbeam motorcycle from just post WW ll.

Well thats a bit harsh... i know that i have been critical of dadoftwo in the past but no need to get nasty. Lets keep focus here. Personal montra here for me is "offer someone an olive branch dont hit them with it."  Discrediting isnt a positive way of proving ones point. Dadoftwo is smart at pointing out a possibility but doesnt need to be scolded for being wrong. We should be in this together.

--Biff

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On 4/18/2017 at 7:56 PM, dadof2 said:

Regarding piston ring end gap. Perhaps instead of saying gap "should" be 0.35 to 0.6 I would have been better writing "you can expect" the gap to be 0.35 to 0.6. These are slackish gaps, the 0.6 being the point at which the bore and rings should be properly measured with a view to replacement.

Others may have a different view with regard to controlling blowby but I prefer an adequate to large ring gap and plenty of oil as opposed to a tight ring gap and minimal (say 80:1 fuel oil ratio) amount of oil.

The shorter the stroke the more one depends on compression... the smaller the piston the more you depend on stroke speed... put in you're back pocket. Not wrong but basic.

for this example speed and simplicity doesnt mean we have to dictate perfection. A trials bike is a tractor. Lets try a base gasket and clean up before we analyse molecular structure.

--Biff

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 If the piston looks that bad, how about the main bearings. Have you checked the mains by grabbing the flywheel and giving a good tug yet.  

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There's no free play when pushing pulling on the con rod. I assume that's the way to check main bearings. BTW I'm going to get a new B piston set.

Barrel is only lightly scored where that piston caught.

Thanks for all the info and replies

IMG_20170420_160328473.jpg

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On 21/04/2017 at 5:24 PM, snowball said:

There's no free play when pushing pulling on the con rod. I assume that's the way to check main bearings. BTW I'm going to get a new B piston set.

Barrel is only lightly scored where that piston caught.

Thanks for all the info and replies

IMG_20170420_160328473.jpg

Conrod lift would indicate big end play.  To check mains you need to try to lift the end of the crankshaft ie try to move the flywheel up and down.

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