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Gs750 big bore kit

  • Thread starter Thread starter david fava
  • Start date Start date
D

david fava

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l am concerned about putting the big bore kit in my 1976 GS750.the liners are only 3.9mm thick and the big bore is 2 mm oversize which wil leave less than 2mm left on the liners.ls this sufficient enough or should l atleast out an oil cooler to put up with a hotter temperatures due to the big bore kit.the engine is stock standard.anybody out there that has done it , l would love to hear some feedback.

thankyou
 
IIRC, 1.5mm is the safe limit.
An oil cooler is not a bad idea on an air-cooled engine anyway. ;)

Daniel
 
are you saying 1.5mm oversize limit or 1.5mm left after boring meaning the wiseco big bore kit will be ok
 
2mm overbore should be no problem. Most people around here don't bother boring a 750 cylinder when you can get stock 850 parts for cheap.
 
1.5mm thickness remaining.
If you already bought the kit, you might still be able to find a stock bore
850 cylinder cheap that will clean up and save you the cost of boring your 750 cylinder and still have thicker liners. ;)

Daniel
 
7981GS said:
1.5mm thickness remaining.
If you already bought the kit, you might still be able to find a stock bore
850 cylinder cheap that will clean up and save you the cost of boring your 750 cylinder and still have thicker liners. ;)

Daniel
Click to expand...

If the stock liner is 3.9 mm, a 2 mm overbore will leave the liners at 2.9mm. Remember, 2mm increase is the bore diameter, so 1mm comes out of the liner all the way around.
 
the big bore kit for gs750 are from a stock 65mm to 69mm meaning its 2mm oversize not 1mm which means l will only have approx 1.9 mm left on the liners
 
also do the gs850 cylinder barrel go straight on with no modifications whatso ever or do you have relieve the crancases for example to clear the liners
 
david fava said:
also do the gs850 cylinder barrel go straight on with no modifications whatso ever or do you have relieve the crancases for example to clear the liners
Click to expand...

My 850 liners hit the crancase with about 10mm to go but it was a simple matter to grind/scrape a couple of ml of the aluminium inside to make them fit. However my 79 750 cylinders were only 3 ml thick so I don't know if suzuki also modified the crankcase between 76 to 79, as some people have reported the 850's fitting straight in?
 
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Edit: Sorry I made a mistake the first time I looked at this thread, I must have been thinking 67 to 69 mm and not 65 to 69

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the big bore kit for gs750 are from a stock 65mm to 69mm meaning its 2mm oversize not 1mm which means l will only have approx 1.9 mm left on the liners
Click to expand...
Umm... I'm sorry that's incorrect.


You will have 2.9mm as Nessism has stated.



What is happening is that you are taking one millimeter off of one side and 1 millimeter off the opposite side for a total of two.


Your actual wall thickness is twice what you measured.


So you measured 3.9mm liner thickness

but you really have 7.8 mm of metal to play with

Your taking 2 mm of that away leaving you with 5.8mm

Half of that is 2.9mm


The general consensus is to not go any lower than 3mm overall which means you will have 1.5mm of liner thickness.
 
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Mekanix said:
Umm... I'm sorry that's incorrect.


You will have 2.9mm as Nessism has stated.


What is happening is that you are taking one millimeter off of one side and 1 millimeter off the opposite side for a total of two.
Click to expand...


I'm afraid he is correct, it's actually 2ml off all the way round not 1ml. 65mm to 69mm pistons.
 
Oh crap,, Well looks like i've contributed nothing to this thread.

Sorry i must have had a brain fart.

Your right, it is 4mm overall my mistake.

I can only find one big bore kit that lists 69mm effectively making it 844cc

http://gszone.biz/pistons.html
 
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thanks for all the feedback guys.l spoke to a reboring guy today and he said it wil ok .he said you wouldnt want to go any more than that unless you wree resleeving or getting a gs850 barrel.

Can any body tell me what paint to use to give it the original look.the color is like a silver grey color.

p.s the problem with getting a gs850 barrel is you have to keep it the original bore size. it would be good if you could buy a big bor or oversize kit for a gs850 barrel that way you can have fresh rebored bores
 
david fava said:
thanks for all the feedback guys.l spoke to a reboring guy today and he said it wil ok .he said you wouldnt want to go any more than that unless you wree resleeving or getting a gs850 barrel.

Can any body tell me what paint to use to give it the original look.the color is like a silver grey color.

p.s the problem with getting a gs850 barrel is you have to keep it the original bore size. it would be good if you could buy a big bor or oversize kit for a gs850 barrel that way you can have fresh rebored bores
Click to expand...

Why not just us an 850 barrel and bore it over to use the stock 1000 pistons?

843cc's become 868cc's ;) Or, you could use somebody's :-\\\ 70.5 pistons and make it 880cc's. :D ($85.00 with shipping for the 70.5 pistons/rings/pins)

Daniel
 
david fava said:
the big bore kit for gs750 are from a stock 65mm to 69mm meaning its 2mm oversize not 1mm which means l will only have approx 1.9 mm left on the liners
Click to expand...

That's a 4mm over bore, not 2mm.
 
7981GS said:
Why not just us an 850 barrel and bore it over to use the stock 1000 pistons?

843cc's become 868cc's ;) Or, you could use somebody's :-\\\ 70.5 pistons and make it 880cc's. :D ($85.00 with shipping for the 70.5 pistons/rings/pins)

Daniel
Click to expand...
I like that idea, but don't the 1000 pistons use fatter wrist pins than the 750/850? :-# Too lazy to go out into the garage and look.
 
you are correct the wiseco big bore kit is 4mm oversize (65mm to 69mm) but you actually only bore 2mm (radius) meaning you have actually made the bore 4 mm oversize.

getting back to the gs 850 barrels.you could get genuine 1mm oversize pistons and this would bring up the ccs to approx 900cc.the problem is they are expensive and and hard to get. depending on which suzuki dealer you deal with some have the rings but not the pistons and vise versa.

does anybody know of a suzuki dealer in america that deals with old stock genuine parts.l live in australia and we have a couple of dealers like that but l have been un succesful
 
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