Crank/rods fatigue - Suzuki SV650 Forum: SV650, SV1000, Gladius Forums

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Old 08-18-2019, 08:25 AM   #1
fastegg
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Join Date: Mar 2019
Posts: 238
Crank/rods fatigue

If i had an '04 gen2 engine with 100,000 pretty hard road km on it and I wanted to put a 700cc Wiseco kit with head mods on, would the crank/rods be anymore likely to fail as apposed to using a band new gen3 engine ? Like, would the gen2 crank/rods have lost any of their 'toughness' as apposed to new ones ? *** Keeping in mind that my gen2 engine basically never gets revved past 9,500...

The reason I'm asking is as I look at my brand new gen3 engine I'm finding it hard to willingly pull it apart to put the big bore kit in...It looks beautiful as it is and common sense is telling me to leave it alone and mod the old engine. Trouble is the gen2 engine is 15 years & 100,000km old.. more importantly the gearbox, rods, crank have had a life and common sense is telling me to mod the new engine... That's my quandary.. I don't know which one to pull apart....

Last edited by fastegg; 08-18-2019 at 08:46 AM.
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Old 08-21-2019, 06:26 PM   #2
RecoilRob
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Re: Crank/rods fatigue

Seeing as nobody has chimed in on this one....I'll offer an opinion. The internals 'shouldn't' be stressed beyond their 'infinite cycle' load limits so them being more likely to fail not really a concern.

On racing engine where things ARE being pushed beyond the 'infinite' limits then for sure things have a definite lifespan and are replaced at regular intervals. Keeping the R's to stock redline or below would likely extend the life of reciprocating internals to a VERY long time. Pistons are the exception being they're sliding and will eventually show wear...but rods should be good to go so long as the little ends remain within tolerances.

The big end is protected by the bearing and unless it sees extreme over-rev or temps it should also enjoy a very long life. The bolts can only be torqued so many times as they're being stretched so on a new build some fresh ones would be a good move IMHO. Crankshaft is also protected by bearings....but can show wear or cracks but also can be inspected and if found good to go...it's good to go. The 700 kit is just a bore job...right? Stroker cranks can work but on the 650 I'd be really careful as there's not much room in there to move things farther than stock. The 1K can be stroked a bit before the pistons get too short and the pins get too close to the crown, but not by a lot.

Now....the real issue here is the transmission and bearings which WILL wear with normal use and even if you have babied the old engine the transmission will certainly show some wear, though with good lubrication if things check out within spec...you probably would be OK to use it. There is always the thought that a good used part has been thoroughly tested and would be immune to manufacturing flaws that might crop up with new parts, but with modern Japanese technology I'd be really surprised if many defective gears or shafts make it into a production bike or car.

So....long story short: if the old engine check out OK on all specs, it would likely be fine to reuse with the Big Bore kit while the new engine also would work without all the checking. One thing to keep in mind: the SV650 began life as a 400...and was punched out to the current 650 so it's already pushing the design envelope a bit, though certainly not beyond what the Suzuki engineers felt was production worthy longevity. The 700 kit IS pushing things beyond what they envisioned so it might not offer quite the reliability you enjoyed with the 650. Thinner cylinder walls aren't going to be as strong or offer the heatsink capability of the stock jugs while the larger pistons will create more thrust and bearing pressures. Wiseco makes a good piston just be sure to put them in with the proper clearances and watch the ring gaps. Good luck mate!
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Old 08-22-2019, 06:10 AM   #3
fastegg
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Re: Crank/rods fatigue

Quote:
Originally Posted by RecoilRob View Post
Seeing as nobody has chimed in on this one....I'll offer an opinion. The internals 'shouldn't' be stressed beyond their 'infinite cycle' load limits so them being more likely to fail not really a concern.

On racing engine where things ARE being pushed beyond the 'infinite' limits then for sure things have a definite lifespan and are replaced at regular intervals. Keeping the R's to stock redline or below would likely extend the life of reciprocating internals to a VERY long time. Pistons are the exception being they're sliding and will eventually show wear...but rods should be good to go so long as the little ends remain within tolerances.

The big end is protected by the bearing and unless it sees extreme over-rev or temps it should also enjoy a very long life. The bolts can only be torqued so many times as they're being stretched so on a new build some fresh ones would be a good move IMHO. Crankshaft is also protected by bearings....but can show wear or cracks but also can be inspected and if found good to go...it's good to go. The 700 kit is just a bore job...right? Stroker cranks can work but on the 650 I'd be really careful as there's not much room in there to move things farther than stock. The 1K can be stroked a bit before the pistons get too short and the pins get too close to the crown, but not by a lot.

Now....the real issue here is the transmission and bearings which WILL wear with normal use and even if you have babied the old engine the transmission will certainly show some wear, though with good lubrication if things check out within spec...you probably would be OK to use it. There is always the thought that a good used part has been thoroughly tested and would be immune to manufacturing flaws that might crop up with new parts, but with modern Japanese technology I'd be really surprised if many defective gears or shafts make it into a production bike or car.

So....long story short: if the old engine check out OK on all specs, it would likely be fine to reuse with the Big Bore kit while the new engine also would work without all the checking. One thing to keep in mind: the SV650 began life as a 400...and was punched out to the current 650 so it's already pushing the design envelope a bit, though certainly not beyond what the Suzuki engineers felt was production worthy longevity. The 700 kit IS pushing things beyond what they envisioned so it might not offer quite the reliability you enjoyed with the 650. Thinner cylinder walls aren't going to be as strong or offer the heatsink capability of the stock jugs while the larger pistons will create more thrust and bearing pressures. Wiseco makes a good piston just be sure to put them in with the proper clearances and watch the ring gaps. Good luck mate!
Thanks for all that.....

My best bike mate who is also a fab mechanic tells me to quit whining and just put the 700 kit in the new engine.. that's what i bought it for so quit stalling. And the fact that everything will be brand new will make me feel a $million so yeah... We've decided to mod the new engine and stop confusing myself.......Although now that i've just bought this K3 front end the engine will be on hold for a while...
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Old 08-27-2019, 03:01 AM   #4
Craig380
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Re: Crank/rods fatigue

Does the 700 kit come with cylinders too?
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