Has anyone ever Bored a GS?

[chevelle]

Hey everyone. I've got my engine apart fixin a few things and i was wondering what it would take to bore out the engine and port and polish the head? Has anyone ever done this? I know i'd need different Pistons and jetting and all that(anyone have an idea what size jets for a 750cc bore?) I might not go to 750, maybe just 650 or so. I haven't decided if i want to do this or not yet, i'm just gathering info at this point. I'm sure the bike would be a lot more fun to ride if this were done, but it would have to be streetable. I'm not going crazy with it.

Of course, i can always just keep it stock if i choose to, just thought this would be a distinct and fun mod.

Anyway, I just wanted to hear from someone who has done this. Any advice is welcome. The more info(from those that know), the better.

Thanx.

[scratch]

The racers have done this. Prefer the 555 kit vs. the 666 for reliability reasons, I imagine [added] heat would be an issue.

[dgyver]

The largest you can go with stock sleeves is 79mm pistons which makes it a 555cc motor. Stock bore is 74mm at 487cc. Getting the pistons is the hardest part. The are not readily available but can be custom made. I just ran my 555 Sunday.

Anything larger will require knocking the sleeves out and bore the cylinder to accept larger sleeves or nikasil the cyliner itself. Nikasil is pretty expensive in respect to the life you get out of it. Basically it is like plating the cylinder walls.

Suzuki sells 75mm pistons which would be 500cc. I ran a set for awhile before going to the 79's. Note that these pistons have higher domes and will increase compression. The 79's pretty much fill the head cavity. There is still a little room left to run a milled head.

[stefman722]

will adding 75mm pistons add any more power?

[dgyver]

It will increase the low and mid range torque, but I do not have any specs to back it up.

[stefman722]

How much would the 75mm pistons if bought from suzuki would cost? if you know a rough estimate.

[dgyver]

I think they are about $80 each. Not sure if that includes the rings.

[The Buddha]

Rings and pistons come as a set in all the suzuki overbore sizes. Suzuki considers it maintenence items ... so kits are available... just try to buy rings and you are screwed... of course they sell standard size rings ... no problem ...  
Cool.
Srinath.

[stefman722]

for the price, do you think it is worth swapping? My bike is currently at the zuki dealer right now, as they are performing quite a bit of changes
to my F. Wat do u guys think.

[dgyver]

Do not forget the cost involved to have a cylinder bored. 1mm over is probably not that much, $30-$40. But having a stock cylinder bored 5mm over cost me $130.

[stefman722]

so spending that kind of money to have the 75mm pistons, would it be worth it?

[dgyver]

It all depends on what you want out of the bike.

Also, while you have the head off...mill the head, neck the valves and clean up casting crap in the ports. Need to have an aftermarket exhaust and a better flowing air filter as well.

[dgyver]

Here are some links to pics of the pistons and heads:

75mm Pistons

79mm Pistons

Stock Head

Milled Head

I do not know how much was milled off of this head. But I talked to Ed (my engine machinist) Sunday at the track and he is going to mill another head to match that one. It has a bad valve seat and it will be cheaper to have another head milled than have the seat replaced. When this is done I will post the amount taken off.

[Lukewarm Wilson]

Once I had to ride the GS at 60kmh for 40 km poor thing was BORED shitless LOL :lol: