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Old 06-14-2019, 07:55 PM   #1
fastegg
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Are stock rods safe ?

I'm going to be using 3mm Wiseco's and shaving the heads to bring it up to 12.5:1 ... not racing but bike gets pushed hard. How safe are stock rods ?... Does anyone know what you can and can't do with them ?
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Old 06-17-2019, 10:05 AM   #2
RecoilRob
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Re: Are stock rods safe ?

Rod strength is only a concern when being pushed beyond stock rpm levels. In compression you are NEVER going to bend a rod!! It's only on the top of the exhaust stroke where the rod cap and bolts get yanked on as they pull the piston back down again and excessive rpm can stretch them and cause failure.

When a rod bends it's almost always due to the little end tightening up in both piston and rod. Severe detonation can cause this but most of the time it's actual contact with the head that does the damage. As the piston rocks over TDC this creates a bending force on the rod when the little end can't articulate and many revolutions works the rod until it breaks. This is one of the reasons we don't want the piston hitting the head. Close enough to work the squish properly, but far enough away to be safe is a good thing.

Years ago I ran RD400's with the squish so tight the piston over-bore numbers were in the carbon on the head. These were real hand grenade engines and never lived long...but ran a lot better when they were alive than most would believe. These were what I called 'reachers'.....they reached levels where they couldn't live very long. NOT a good thing for a street engine.
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Old 06-18-2019, 06:56 PM   #3
fastegg
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Re: Are stock rods safe ?

Quote:
Originally Posted by RecoilRob View Post
Rod strength is only a concern when being pushed beyond stock rpm levels. In compression you are NEVER going to bend a rod!! It's only on the top of the exhaust stroke where the rod cap and bolts get yanked on as they pull the piston back down again and excessive rpm can stretch them and cause failure.

When a rod bends it's almost always due to the little end tightening up in both piston and rod. Severe detonation can cause this but most of the time it's actual contact with the head that does the damage. As the piston rocks over TDC this creates a bending force on the rod when the little end can't articulate and many revolutions works the rod until it breaks. This is one of the reasons we don't want the piston hitting the head. Close enough to work the squish properly, but far enough away to be safe is a good thing.

Years ago I ran RD400's with the squish so tight the piston over-bore numbers were in the carbon on the head. These were real hand grenade engines and never lived long...but ran a lot better when they were alive than most would believe. These were what I called 'reachers'.....they reached levels where they couldn't live very long. NOT a good thing for a street engine.

That makes me feel alot better about using stock rods.. I never go near hi revs so they should be safe...
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Old 06-18-2019, 08:59 PM   #4
rcb78
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Re: Are stock rods safe ?

I always got a kick out of opening my old engines with tight decks. The chambers were almost always clean ;-)
I don't know about these specific engines, but rod bolts were something we generally paid more attention to that rods until boost came into play. ARP for stock rods and a good stretch gauge. But there are few things a sexy as a new set of H-beam Carrillos.
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