1982 GS650G oversize pistons

[Berti]

Hi everybody,

As many before (and probably after me) I'm dreaming of building my own Cafe Racer. I know - another hipster bla. Anyway, for me it's a nice project to learn new skills and just fun tinkering on machines.

Early last year (2018) I got a 1982 GS650G for verrryyyyyy cheap, but in questionable condition(not working at all). I got a carb rebuilt kit, cleaned everything and after some more TLC I got the engine running. Well, that was last summer. Turns out even more is broken and I needed to take the engine apart. I probably should not have jumped on the cheapest bike on craigslist, but no pain - no gain. Not much happened over the winter and this spring I found the exact same engine for $40 on craigslist.

The original engine from the bike had around 73k (km!) and you can tell by the inside. Unfortunately the cylinders are in pretty bad shape and honing is not enough.
The second engine is in way better condition (only ~25k), but it was sitting way too long and the cylinders are also pretty rusty. So again, needs boring

TL;DR - My cylinders need to be bored to oversize and before bringing it to the shop I would like to find the right oversize pistons. Which appearently is a big problem! I can't find oversize pistons for GS650G anywhere. Not even the STD ones.
The only thing I could find is this: https://www.cruzinimage.net/2018/12/...t-65mm-piston/
And this somehow feels not legit.

Can anybody help me here pointing in the right direction?

Much appreciated,
Berti

[Nessism]

Cruzin Image pistons actually have a pretty decent reputation. I'd roll the dice. Tons of CB750 guys running them happily and frankly I've never heard anything bad. Boring out to 740 with a 650 is getting out there but what the heck? No guts no glory. Plus, there doesn't seem to be any other options available.

[Steve]

Are you SURE you need oversize?

It might just need honing, which would not usually require oversize pistons.

If it does require boring, Cruizn Image is a good way to go.

.

[bwringer]

Hold up a minute...

You used carb kits and the bike actually ran OK?

First time I've heard that.

[Berti]

Cruzin Image pistons actually have a pretty decent reputation. I'd roll the dice. Tons of CB750 guys running them happily and frankly I've never heard anything bad. Boring out to 740 with a 650 is getting out there but what the heck? No guts no glory. Plus, there doesn't seem to be any other options available.

Thanks for the input. I was hoping, that somebody might have possible leads on where I could find (oversize) pistons for a GS650G. I measured the cylinder wall and its 3mm thick. Using these Cruzin Image pistons, I would have to take 1.5mm off. That's 50%! Doesn't sound right....

Are you SURE you need oversize?

It might just need honing, which would not usually require oversize pistons.

If it does require boring, Cruizn Image is a good way to go.

.

Sure, no... But I went to the local machine shop and showed them the cylinder. They pretty much directly said, that honing is not enough. I mean, they are the pros. I kind of have to trust them. They charge by the hour and they also said, that it won't be cheap... So I'm willing to find other solutions.

Hold up a minute...

You used carb kits and the bike actually ran OK?

First time I've heard that.

Weeeellllllll, that 'actually runs ok' depends on the point of view. I hooked up a huge car battery, after endless tweaking and cranking I got the engine to start, idle and rev up to 5k rpm. I couldn't testride, blue smoke was visible, after disconnecting the car battery, the bike died instantly and I also found a cpl more problems. So, yeah, the bike ran Ok isssshhhh

[GregT]

Thanks for the input. I was hoping, that somebody might have possible leads on where I could find (oversize) pistons for a GS650G. I measured the cylinder wall and its 3mm thick. Using these Cruzin Image pistons, I would have to take 1.5mm off. That's 50%! Doesn't sound right....

The visible parts of the liner are 3mm, yes. But the visible end is reduced in thickness, it's thicker inside the block.
3mm oversize is quite feasible on those liners. The lower ends of the liners carry very little load, I've seen liners around 1mm thick in that area with no problems.
The job will be somewhat costly - simply because of the number of cuts required boring that far.

[BigD_83]

Somewhere on here is a long, on-going thread of oversized conversions...might be something in here worth reading

https://www.thegsresources.com/_forum/showthread.php?237720-Potential-Group-Purchase-Wiseco-GS650-741cc-pistons

[Berti]

The visible parts of the liner are 3mm, yes. But the visible end is reduced in thickness, it's thicker inside the block.
3mm oversize is quite feasible on those liners. The lower ends of the liners carry very little load, I've seen liners around 1mm thick in that area with no problems.
The job will be somewhat costly - simply because of the number of cuts required boring that far.

Well, yes. Of course. Stupid me.

Somewhere on here is a long, on-going thread of oversized conversions...might be something in here worth reading

https://www.thegsresources.com/_foru...-741cc-pistons

Oh boy... That's a lot to read. Will take me some time to read. But thanks for pointing me into that direction!