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 Post subject: Short Barrel(s)
PostPosted: Tue Dec 04, 2018 4:47 pm 
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On the main road

Joined: Thu Nov 07, 2013 1:59 pm
Posts: 100
Country: United Kingdom
Bikes owned: A100 GT250 & 4t Yams!
Hi all

Some time back I bought a replacement (LHS) barrel for my GT250A due to damaged/crossed thread on the exhaust. I just got around to removing the damaged one and had them both on the bench to compare. Immediately I noticed the 'lip' on the top of the original was higher and I notice machining marks on the replacement. With my steel rule it looks like the replacement is at least 1mm shorter giving rise to raised compression no doubt, but worse than that it's a mismatch now against it's neighbour (the A has a one piece head remember).
Now 'luckily' the replacement barrel came as half a pair, both were a little rusty but have cleaned up Ok wit some 400 wet and dry and light oil and I cannot feel any pits.

So, I'm now thinking to replace the pair, but should I install an extra base gasket to try and reduce the heightened compression? This will have an effect on the tune as the exhaust port is now raised or course but what else can I do except look for another LH barrel.
The replacements are standard bore by the way while the 'original' are on +0.5 mm meaning I will also need t buy a pair of 54mm pistons.

Thoughts and suggestions welcome.


Last edited by daxman on Wed Dec 05, 2018 4:26 am, edited 1 time in total.

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 Post subject: Re: Short Barrel(s)
PostPosted: Tue Dec 04, 2018 4:56 pm 
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Joined: Thu Nov 07, 2013 1:59 pm
Posts: 100
Country: United Kingdom
Bikes owned: A100 GT250 & 4t Yams!
Hmm not good the verniers tell me the 'new' barrels are in fact 2mm shorter! I estimate this will raise compression up to 10:1 (or more). That is if it doesn't contact the head!


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 Post subject: Re: Short Barrel(s)
PostPosted: Wed Dec 05, 2018 7:25 pm 
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To the on ramp
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Joined: Sun Jul 13, 2014 7:55 pm
Posts: 246
Location: Greendale Vic, Australia
Country: Australia
Bikes owned: AS50, GS500, GT500, ex GSXR750 slabbie
Well, if you DO pack the cylinder don't just rely on extra gasket(s).
If you can get some good quality 2mm or 1.5mm brass sheet you can cut out a packer easily.


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 Post subject: Re: Short Barrel(s)
PostPosted: Thu Dec 06, 2018 3:22 am 
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World Superbike
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Joined: Thu Feb 16, 2012 11:50 am
Posts: 2172
Location: The Republic of South Yorkshire
Country: England
Bikes owned: GT550s GT750 GSX1400 and lots of spares
PM dollydog on here - he's in the UK, has 250 spares, and may be able to help - with spacers too!


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 Post subject: Re: Short Barrel(s)
PostPosted: Thu Dec 06, 2018 1:03 pm 
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Joined: Fri Aug 11, 2017 7:09 am
Posts: 307
Country: england
Bikes owned: several gt250 ramairs
obviously not that interested alan :cry: i've got a pair of 2mm thick bottom plates to suit, but will need the transfer ports slightly enlarging - mine were made for the ramair engine. but if he wants them he can pm me and i'll send them foc :D daxman, why don't you fit the 2 barrels with pistons, or just one side, take it up to tdc and see where the top of the piston sits? easy peasy. if it sits proud of the liner, fit the spacers, if it don't, then don't bother. simples :D if it sits level and you're still not au fait with it, get some 0.5mm thick copper plate and make a pair of head gaskets. and don't forget to anneal them before use :up:
cheers, dd.

_________________
GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.


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 Post subject: Re: Short Barrel(s)
PostPosted: Thu Dec 06, 2018 5:06 pm 
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Joined: Thu Nov 07, 2013 1:59 pm
Posts: 100
Country: United Kingdom
Bikes owned: A100 GT250 & 4t Yams!
Thanks for teh input guys. most helpful. I'm going to ponder this for a bit. Now that I've got the old cylinder of and had a really good look at the exhaust threads they may, just about, be rescue-able.. If not then I 'll start looking at the barrel fit and decking issues. Cheers again


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 Post subject: Re: Short Barrel(s)
PostPosted: Thu Dec 06, 2018 5:21 pm 
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World Superbike
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Joined: Thu Feb 16, 2012 11:50 am
Posts: 2172
Location: The Republic of South Yorkshire
Country: England
Bikes owned: GT550s GT750 GSX1400 and lots of spares
Keep smiling!!!! :wth: :up: :lol:


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 Post subject: Re: Short Barrel(s)
PostPosted: Fri Dec 07, 2018 2:15 am 
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Joined: Sat Jan 29, 2011 10:51 pm
Posts: 211
Location: New Zealand
I have a pair of GT250 barrells with great threads I may not require,Im doing a TT250 resto and have a few spare parts,will need a hone and over size pistons,also have matching heads.

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 Post subject: Re: Short Barrel(s)
PostPosted: Fri Dec 07, 2018 4:02 am 
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On the main road

Joined: Thu Nov 07, 2013 1:59 pm
Posts: 100
Country: United Kingdom
Bikes owned: A100 GT250 & 4t Yams!
alanr wrote:
I have a pair of GT250 barrells with great threads I may not require,Im doing a TT250 resto and have a few spare parts,will need a hone and over size pistons,also have matching heads.


An offer from teh Antipodes :shock: - thanks. Good to know there's options.

For deck adjusting could this stuff be reasonably used.. https://www.ebay.co.uk/itm/Aluminium-Sheet-1mm-1-2mm-1-5mm-2mm-3mm-4mm-1050H14-S1BH4-Various-Sizes/271210657802?
Fine blade on a jigsaw then hand finish maybe. 1.5mm thick would give modest exhaust port lift and only slight rise in compression.


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 Post subject: Re: Short Barrel(s)
PostPosted: Fri Dec 07, 2018 4:36 am 
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Joined: Fri Aug 11, 2017 7:09 am
Posts: 307
Country: england
Bikes owned: several gt250 ramairs
think of the postage from nz though :D
that ali sheet is what i used, but cutting 1.5mm thick with a jigsaw would be difficult as it would snag and keep bending or ripping. get a square of ali bigger than you actually need and screw the 4 corners to a decent slab of wood. using a hole saw [the adjustable sort] cut the middle hole out first. https://www.ebay.co.uk/itm/Priory-PRI20 ... :rk:2:pf:0 this sort, also known as a trepanner. then your 4 stud holes. then cut the basic shape out with a saw, a bit at a time, then trap between 2 pieces of wood while you file it to the correct shape. it's a lot of work, trust me :D to save yourself all that work, take a base gasket and your ali sheet to a laser cutter and let them do it :D doesn't give you the same job satisfaction though. i've done 3 sets now and it's a LOT of work.
cheers, dd.

_________________
GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.


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 Post subject: Re: Short Barrel(s)
PostPosted: Fri Dec 07, 2018 5:01 am 
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On the main road

Joined: Thu Nov 07, 2013 1:59 pm
Posts: 100
Country: United Kingdom
Bikes owned: A100 GT250 & 4t Yams!
Hi DD, Thanks.

Hmm I think my kid's school has a laser cutter :wink:


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 Post subject: Re: Short Barrel(s)
PostPosted: Sun Dec 09, 2018 1:29 am 
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To the on ramp
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Joined: Sun Jul 13, 2014 7:55 pm
Posts: 246
Location: Greendale Vic, Australia
Country: Australia
Bikes owned: AS50, GS500, GT500, ex GSXR750 slabbie
dollydog wrote:
think of the postage from nz though :D
that ali sheet is what i used, but cutting 1.5mm thick with a jigsaw would be difficult as it would snag and keep bending or ripping. get a square of ali bigger than you actually need and screw the 4 corners to a decent slab of wood. using a hole saw [the adjustable sort] cut the middle hole out first. https://www.ebay.co.uk/itm/Priory-PRI20 ... :rk:2:pf:0" onclick="window.open(this.href);return false; this sort, also known as a trepanner. then your 4 stud holes. then cut the basic shape out with a saw, a bit at a time, then trap between 2 pieces of wood while you file it to the correct shape. it's a lot of work, trust me :D to save yourself all that work, take a base gasket and your ali sheet to a laser cutter and let them do it :D doesn't give you the same job satisfaction though. i've done 3 sets now and it's a LOT of work.
cheers, dd.


Use brass sheet. Alloy sheet is too easily distorted. To cut out you need a Piercing saw, -with a very fine blade like jewellers/silversmiths use.
All that (above drama) is totally unnecessary if you use the right material (brass) and the right tool (Piercing saw).
I'd cut one in an hour or less. No biggie.


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 Post subject: Re: Short Barrel(s)
PostPosted: Sun Dec 09, 2018 6:54 am 
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Joined: Fri Aug 11, 2017 7:09 am
Posts: 307
Country: england
Bikes owned: several gt250 ramairs
but why would you use brass plate on aluminium barrels? surely it's common sense to use the same material? heat co-efficient and all that, brass holding heat a lot longer than ali? why brass? 3 times the price and a damned sight harder to work. anybody can make anything out of any material with the right tools. we're talking blokes in a shed with the basics. and PLEASE don't slag people off that are just trying to help somebody out. maybe it's no biggie to you, but to me it's job satisfaction and the 4mm aluminium lifter plates i cut out myself using the above method [not having access to fancy tools] and fitted to my gt350 work perfectly :D oh, and even though they were done by hand, they look good as well :D
Image

_________________
GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.


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 Post subject: Re: Short Barrel(s)
PostPosted: Sun Dec 09, 2018 7:06 am 
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World Superbike
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Joined: Thu Feb 16, 2012 11:50 am
Posts: 2172
Location: The Republic of South Yorkshire
Country: England
Bikes owned: GT550s GT750 GSX1400 and lots of spares
Well said DD.


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 Post subject: Re: Short Barrel(s)
PostPosted: Sun Dec 09, 2018 8:28 am 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3276
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
dollydog wrote:
...get a square of ali bigger than you actually need and screw the 4 corners to a decent slab of wood. using a hole saw [the adjustable sort] cut the middle hole out first.
...
then trap between 2 pieces of wood while you file it to the correct shape.
...

+1

Am no expert, but I cut thin aluminum for the GT250 & GT380 cafe builds by sandwiching the aluminum between two sheets of hobby wood that I got at Home Depot or Lowes. Used painters to hold the combo together.

Ideally at least two saw teeth are always in contact with the combo at all times. Three would even be better. Go slowly & don’t press too hard or the teeth will dig into the wood and bounce on the aluminum.

I was surprised by how well this worked.

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BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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