Author Topic: Rods and Pistons  (Read 1249 times)

Offline EdE

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Rods and Pistons
« on: May 08, 2011, 11:51:12 AM »
All right my fellow racers, I could really use some help. I just bought my first GS500, an 89, currently registered but ďseizedĒ. I opened her up, lost a rod.. destroyed the rod, crank, left piston and cylinder. Iím an old racer so I donít mind the work but Iím new to the GS500ís so Iíve got two questionsÖ

1) "I see a number of posts about broken rods, pistons, cranks.. what is this engines weak point? One of these or all of these? Iím not going to build an all out race bike but I havenít forgotten how to twist the throttle either.. so that means if Iím going to build a motor Iím going to address itís weak points.. what are this engines weak points?Ē

2) what are my parts options (within reason..).
I figure cost wise we're stuck with the stock crank.
But are there better rods? (I called Carillo, couldnít stop laughingÖ 378 a rod..) anything out of another Suzuki or other aftermarket?
Shot Peening the rods was good in the RDís I raced for almost another 1000 rpm without breakage so that may be an option if a better rod is not available.
Pistons, are the stock pistons any good or did my rod just freakishly kill my piston? It pulled the bottom right off..
I didn't see a listing on Wiseco's website.
and without going into the really bigbore (78mm) because it looks like thereís piston issues right now, how big can I go? (If your going to bore a cylinder anyway rightÖ)
Any help is greatly appreciated my fellow racers.  Ed
« Last Edit: May 08, 2011, 11:52:21 AM by EdE »

Offline burning1

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Re: Rods and Pistons
« Reply #1 on: May 10, 2011, 12:17:03 AM »
I looked into this a little bit a while ago. Short version, is that the first place I'd start looking is with APE racing, and with the guys who drag the big 4 cylinder GS bikes. They are going to have lots of experience with GS cranks and rods, and the 2 valve GS engines are very very similar to ours, with a lot of potential parts interchangeability.

I wouldn't personally go way oversize on the GS engine, but I've seen it done. Search for Wiseco pistons on this forum.

Most of the guys who race the GS500 these days race it as an economy bike, and don't put huge amounts of money into the engine. Most common mods is a balance job on the crankshaft to eliminate the counter-balancer, cams, pistons (valve relief) and shim-over-bucket.

I can't tell you a huge amount about engine mods from personal experience, unfortunately, as mine is stock. Most of my efforts have gone into the chassis.

Offline 5thAve

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Re: Rods and Pistons
« Reply #2 on: May 10, 2011, 12:28:54 PM »
yeah, I bought the Wiseco 78mm pistons and THEY DON'T FIT... they interfere with the head in a major way. I think valve clearances are OK (not 100% sure yet) but the height is too much because the Wiseco piston has a larger dome (seems to be the right height, but just too much volume --doesn't fit inside the combustion chamber relief in the head).

I'm thinking that those several posts that talked about dropping in 78mm pistons with no other modifications may have mistakenly referred to Wiseco when in fact they meant Vance and Hines???  I have not yet figured out where we went wrong.  I talked to Wiseco and referenced my part numbers with the "old" part numbers that previous modders used (I think the user here was named Dgyver) and Wiseco tells me that the dimensions of both old and new pistons are identical.

I am about to rebuild the engine to stock spec so at least I can ride. I will work on possibly carving out a larger combustion chamber from a spare head, but I HAVEN'T FOUND ANYONE WHO CAN GUIDE ME on this "black art" of shaping and sizing combustion chamber.

I'm a little nervous about moving ahead without some kind of advice on do's and don'ts.  I don't even have proper tools for the job.

References:
http://gstwins.com/gsboard/index.php?topic=14401.0
http://gstwins.com/gsboard/index.php?topic=28470.0
http://gstwins.com/gsboard/index.php?topic=48095.0
http://gstwins.com/gsboard/index.php?topic=47734.0
GS500EM currently undergoing major open-heart surgery.
Coming eventually: 541cc with 78mm Wiseco pistons; K&N Lunchbox; Vance & Hines; 40 pilot / 147.5 main jets; Progressive fork springs; 15W fork oil; Katana 750 shock

VFR750FM beautifully stock.
XV750 Virago 1981 - sold
XL185s 1984 - sold

Offline mass-hole

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Re: Rods and Pistons
« Reply #3 on: May 10, 2011, 02:21:52 PM »
I read that thread a while ago and was under the impression that the tops of the pistons were shaped slightly different on the current Wisecos but then used the same pin location and bore. I was under the impression that It could be done without other mods as well
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Offline The Buddha

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Re: Rods and Pistons
« Reply #4 on: June 01, 2011, 03:52:11 PM »
You should buy 2 valve pistons ... of course they can still be too domed to fit too.
Cool.
Buddha.
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