crankshafts? pistons? heads? possible mod ideas?

[Torpedo]

a while back i posted about my engines crankpin being sheered, in the end i did add a new one that i promptly sheered thickly by hitting it too hard when inserting it  however, tightened down and carefully aligned i didnt have a problem, somehow got it almost spot on and ran fine  bar that it became apparent shortly after running that the engine had some major other problems.

although its crank is fine AFAIK, the pistons and bores im quite sure arent... smokes like a bugger. is quite rattley too but i wonder if that could be a problem with the valves, naturally no way of knowing unless i get a garage to open it, some daft bugger rounded off the rocker bolts.

anyway, ive got a newer engine thanks to jay wolf on here  thanks man, legend  and now ive got a crusty crapped up motor sitting in the garden that needs some serious attention. while im at it, im wondering what i should do to the thing. Ive got a few pistons and barrels in the shed, plenty of spares, but id like to do something interesting with it!

i hear a lot about pistons and the 555 mod, might be nice to try if i can get the kit i suppose. Something i have heard is the head, cutting a gsxr 750 head up and making it fit the top of the gs500 engine. interestingly i wondered if there were any bikes with similar crank dimensions that could be cut up to fit possibly to give a bit more stroke, and get some pistons made to suit using the original bore. though i think that might be anything but possible lol.

any standard pistons from other bikes that might fit (with honing the bore to suit obviously) ? just - anything really. wouldnt mind trying something out with the spare 

[ohgood]

sorry, i'm still working on destroying my first

some of the guys here have done the rebore deal. do a search if you don't get hits.

[ben2go]

http://gstwins.com/gsboard/index.php?topic=14401.0

[dgyver]

The 79mm pistons for the 555 are no longer made. Very difficult to even find them. I built a 555 a couple of years ago and have 1 more 79, may find another eventually.

If interested in the 4-valve GSXR head swap, FJ1200 pistons will fit and may require some valve to piston fitting clearance. Stock FJ12 pistons are 77mm. Otherwise custom pistons are required.

The GR650 crank could be made to fit. It has been a while since I looked at it. The cases would need to be bored for the larger diameter crank. Also, the inside (I think) journels would need to be milled by 5mm due to crank being slightly narrower. Then you will need to deal with the extra stroke and the cylinder. Stock will not work. The GR cylinder will fit but the oil channel to the balancer is on the opposite side. 

You can also swap sleeves for pistons larger than 79mm. I am assembling a 569 motor using 80mm pistons. 

The 78mm pistons for a 541 is the best straight forward mod.

[Jay_wolf]

No problem for the engine dude, the heart of the 1996 

[Torpedo]

The GR650 crank sounds interesting, so the cylinders are spaced at the right distances to fit the crank then? do you know someone whos tried im curious? and do you think the sproket running the cam would be okay, or would the sprokets on the cams need to be changed to match the sprocket on the crank?

FJ1200 pistons being swappable is useful, as i was thinking with a different head maybe different pistons might be useable.

i dont know how its done, i imagine with heat or a press, ill have to talk to some people i know to find out, but the sleeves are replaceable on the gs barrels? was thinking if the crank is changed to increase the stroke, the barrels might need to be raised slightly? would it just work to press out the sleeves on two barrel sets, get one barrel machined down and skimmed level, then have both pressed with the same sleeve to make up the increased stroke?

when i get back from uni next week ill have a look at the old motor and see what i can work out on it, ill look up some cheap parts on ebay as well.

given that the gsxr head (was it the early 750 or 1100?) engines found there way into the gsx and bandits, would heads from bandit 600's gsx600's or gsx 750's work? (or bandit 750 but i have no idea if this was ever made lol... i know theres a lot of various sizes though!)

sorry to ask so much, but i know dgyver is the man to ask these things!

[dgyver]

I never compaired at the cylinder spacing. The GR has a 70mm stroke and the GS has a 56.6mm stroke. With 13.4mm more stroke you would have to use GR cylinders, unless you make a spacer to raise the GS cylinders. Raising the sleeves will not be enough. The sleeves are replacable, just heat them up in an oven. No one (that I know of) has done a crank swap.

The Kat heads will work, just smaller valves. 

[Jay_wolf]

I have a Whole Kat engine left over from my parts bike , what parts are we talking about , the Clyinder heads?

[Kurlon]

Time to revive this given my interest in stroking a GS...

Anyone got pics of a GR650 crank and a GS500 crank?  I've talked to Moldex, as they made a one off billet GS500 crank in the past, they don't have a pattern but can make one again with a crank in hand to work from.  If the GR650 crank just needs rework on the bearing areas, I'm betting they can make it happen.  I'll check with Falicon to see if they can do similar work as well.

It's sounding like a little crank rework, get it rebalanced to run sans counter balancers, either run shorter rods and the GS cylinder or stock rods and the GR setup and everything else will mesh?

[Kurlon]

Found a GR650 crank on ebay...
http://cgi.ebay.com/ebaymotors/1983-suzuki-tempter-gr650-gr-650-crank-shaft-and-rotor_W0QQcmdZViewItemQQ_trkparmsZ72Q3a1171Q7c66Q3a2Q7c65Q3a12Q7c39Q3a1Q7c240Q3a1318Q7c301Q3a1Q7c293Q3a3Q7c294Q3a50QQ_trksidZp3286Q2ec0Q2em14QQhashZitem270336900689QQitemZ270336900689QQptZMotorcyclesQ5fPartsQ5fAccessories

GS500 crank pics:
http://gstwins.com/gsboard/index.php?topic=45697.msg513644#msg513644

The obvious difference to me is on the flywheel side, it looks like the GR uses that end of the crank to drive the CB, the GS uses it for electric start.  It looks like that's all press on though... so still a possibility.

[dgyver]

I looked into installing a GR crank in a GS motor a couple of years ago (with a 4-valve GSXR head & 77mm pistons)... The GR inner bearings are spaced the same as the GS. The GR outer bearings are about 5mm inwards per side. The GR bearings are larger in diameter. The rod bearings are the same diameter. There are some shifting and clutch fit-up differences, I do not recall what they all are.

It has been a while since I had the GR motor out and looked at it. I have a complete GR motor and most of the bottom end of another. I also have a complete GSXR head and the 77mm pistons. Just lack of desire to build a money pit keeps it all in boxes, until it all goes to ebay this summer.

[Kurlon]

I've got the desire to build a money pit (see my minis...) but not the raw talent.  Unfortunately the GSXR head swap would close the 'almost anything goes' motor build loophole in CCS for older air cooled twins I believe.  Although, they don't say anything about converting from a 2v to a 4v, so maybe it would be legal...

My hope is the GR crank bearings can be machined down to match the GS cases.  The outers might require welding up before cutting to supply an appropriate thrust surface/locating shoulder once recut to match the GS positions?  I can't tell if there is a large gear on the clutch side right up against the porkchop like there is on the GS crank, and it's not a press/bolt on so that may be a show stopper?

[dgyver]

If I have time this weekend, I will pull the loose GR crank and match it up against a GS crank to take some pics for side by side comparison. 

[Kurlon]

I would be very appreciative if you could.

So far the bearing journal work looks to be 'easy' for reputable crank shops, including welding up new thrust stops to move the outer journals to match the GS bottom end.  At least on paper. : )  So the real kicker will depend on how much is required to make the crank end bits play nice.

[Kurlon]

Falicon says they can usually do up to a 6.5mm stroke job on a plain bearing crank, although it all depends on where the oil passage is in relation to the journal, etc.  So up to a touch over 62mm stroke, matching SV650s.  Cost with balancing is $800 to $900.  Not good enough for me, I want MOAR torque than an SV to justify this.  Falicon has no interest in fabbing a billet crank.  Not unless say, 30 of us all went in on one. : )  They also didn't have any interest in reworking the mains on the GR650 crank to match the GS cases.  (They suggested reworking the cases instead...)

So, not ready to give up yet... http://www.crankshaftsupply.com/crankmoto.htm  They don't see any real issue reworking the mains, but want to get the cranks in their hands first.  So it's not confirmation, but it's at least a start.  Still have to sort differences on the clutch side of the crank as well, going to plan on running total loss so the flywheel side isn't as big of a concern, as long as A flywheel fits up.

[dgyver]

I have not forgot about those pics. I was sick this weekend and could not get to them. I will try to do something tonight or it may be next week before I have time.

[Kurlon]

No worries, I'm just doing some preemptive research in the background. : )

[Kurlon]

Couple minor updates:

Spoke to a friend, turns out they know Cedric Smith, the guy that built the 650cc 'CSXR' crazy GS500 that got my gears going and proved the GSX-R 750 head can be made to work.  Bike is still together in his garage.  : )  My friend suggested I talk to APE about the crank work.

So, spoke to APE.  The owner of the company was involved in one GS500 stroker project in the past.  APE did the crank work, and the bike ran.  Problem is the stock crank is made from really poor materials and it spun itself apart in very short order.  Talking to a couple other people I've been able to scare out of hiding, there have been a couple other stroked GS500s in the past, with the stock crank the sweet spot is to only push it 2mm from stock, any further and the cranks just don't hold up.

The gentleman I spoke to at APE is going to do some digging around for me, and see if billet is an option, and if so what the cost would be (est was $3k to $4k...  ) as well as any other info he could dig up for me.  He was also up for helping with the top end work which was cool to hear.  Turns out he owns a GS500E as well. : )

The one other bit of advice I picked up today was to find a stud girdle for the cases to help them cope with the increased stroke.  APE made one for older GS inline 4s that should be adapatable given the common stud centers (Ala the GSX-R 750 head dropping on).

Interestingly APE also noted that they cannot balance my GS500 crank if they stroke it.  I didn't press for more info but I suspect their balancing setup is rigged specifically for inline 4 machines?

So... maybe the trick will be to use a GR650 bottom end, and finding a way to dump the double clutch mess...? Who knows, I'll have more info from APE re working the stock crank tomorrow hopefully.

[Kurlon]

APE never called back... I'll take that as a sign and focus on reworking a GR650 motor instead.