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I have a crankshaft that I need to replace the con rod and the new con rod is stroker (longer) and has a 2mm (I think) bigger big end pin so it won't fit the crankshaft so do I drill out the hole or what?:
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I don't think you can bodge this. You need the correct con rod.
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znomit wrote:
I don't think you can bodge this. You need the correct con rod.
Can I get a different bearing with a different id to accept the smaller pin?
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Probably not. Do not bodge this or you will regret it. I'm an ex-engine design and development engineer and two stroke cranks must not be tampered with. You will upset the whole balance of the crank if you mess it about with non standard conrods and bearings. I've noted your other post about the sideways play in the wrist pin (gudgeon pin). You cannot simply shim a wrist pin it will affect the lubrication of the small end bearing and it will fail pretty quickly. What you are proposing will also affect the dynamic balance of the shaft. Why don't you simply get the right parts?
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Stromrider wrote:
Probably not. Do not bodge this or you will regret it. I'm an ex-engine design and development engineer and two stroke cranks must not be tampered with. You will upset the whole balance of the crank if you mess it about with non standard conrods and bearings. I've noted your other post about the sideways play in the wrist pin (gudgeon pin). You cannot simply shim a wrist pin it will affect the lubrication of the small end bearing and it will fail pretty quickly. What you are proposing will also affect the dynamic balance of the shaft. Why don't you simply get the right parts?
The thing is that this con rod is for this crank and piston. So I should return it and buy a different one correct?:
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Stromrider wrote:
Probably not. Do not bodge this or you will regret it. I'm an ex-engine design and development engineer and two stroke cranks must not be tampered with. You will upset the whole balance of the crank if you mess it about with non standard conrods and bearings. I've noted your other post about the sideways play in the wrist pin (gudgeon pin). You cannot simply shim a wrist pin it will affect the lubrication of the small end bearing and it will fail pretty quickly. What you are proposing will also affect the dynamic balance of the shaft. Why don't you simply get the right parts?
i dont want to buy a shitty bearing that is no name or not for cankshafts obviously. also is that too much play? im confused becuase that con rod is ment for the derbi bullet/piaggio zip and so is the cyl so it should work together but it dont.
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To make this simple
This is the WRONG conrod. If it is not materially the same as the one you are taking out (and evidently, it is not) it will not work. A longer conrod (without changes in the piston) will allow your piston to forcibly contact the cylinder head, not generally a good thing.

With the proper machine tools, experience, and a different piston, this could, perhaps, be made to work. But why go to the trouble when you can almost certainly get a correct con rod?
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Re: To make this simple
Jimding wrote:
This is the WRONG conrod. If it is not materially the same as the one you are taking out (and evidently, it is not) it will not work. A longer conrod (without changes in the piston) will allow your piston to forcibly contact the cylinder head, not generally a good thing.

With the proper machine tools, experience, and a different piston, this could, perhaps, be made to work. But why go to the trouble when you can almost certainly get a correct con rod?
Mmm thought it was right it says for piaggio/debri bullet/zip but apparently not. We're can I get the original? Also would the original hold up? Running 14:1 compression and alot of power so I dunno how that's gonna work
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Re: To make this simple
2smokersFTW wrote:
[

Mmm thought it was right it says for piaggio/debri bullet/zip but apparently not. We're can I get the original? Also would the original hold up? Running 14:1 compression and alot of power so I dunno how that's gonna work
Did you get JUST the connecting rod? I'm assuming that crankshaft is pressed together, so you need to find someone to press it apart, check that the journal is OK, press it back together with the new rod and bearing, and true it up. Might be just as easy (if you can stand the cost) to get an assembled crankshaft. Not sure many places still know how to properly rebuild a 2-stroke crankshaft.

I have zero experience with that model, but going back to the way old days of dirt bikes, generally only trashed a rod bearing when there was a lubrication failure (wrong oil, or wrong mix) , dirt got in via a bad air filter, or something else grenaded and the bits got into the bearing and trashed it. Had a cousin that drag-raced Kawi's, and he trashed one or two when the bikes went lean and detonated. Top of the pistons looked like aluminum woodpeckers had been at them.

Unless you have a turbo or nitrous on it, I doubt you are making enough power to trash the con-rod bearing. Make sure the crank seals are good, the air filter is good, use a good grade of oil (castor-based if you are worried) in the proper mix with good gas, and you should be fine. Oh, and if the timing is adjustable, make sure that is OK too. If your compression ratio is that high, probably use the highest-octane gas you can find.
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Re: To make this simple
Jimding wrote:
2smokersFTW wrote:
[

Mmm thought it was right it says for piaggio/debri bullet/zip but apparently not. We're can I get the original? Also would the original hold up? Running 14:1 compression and alot of power so I dunno how that's gonna work
Did you get JUST the connecting rod? I'm assuming that crankshaft is pressed together, so you need to find someone to press it apart, check that the journal is OK, press it back together with the new rod and bearing, and true it up. Might be just as easy (if you can stand the cost) to get an assembled crankshaft. Not sure many places still know how to properly rebuild a 2-stroke crankshaft.

I have zero experience with that model, but going back to the way old days of dirt bikes, generally only trashed a rod bearing when there was a lubrication failure (wrong oil, or wrong mix) , dirt got in via a bad air filter, or something else grenaded and the bits got into the bearing and trashed it. Had a cousin that drag-raced Kawi's, and he trashed one or two when the bikes went lean and detonated. Top of the pistons looked like aluminum woodpeckers had been at them.

Unless you have a turbo or nitrous on it, I doubt you are making enough power to trash the con-rod bearing. Make sure the crank seals are good, the air filter is good, use a good grade of oil (castor-based if you are worried) in the proper mix with good gas, and you should be fine. Oh, and if the timing is adjustable, make sure that is OK too. If your compression ratio is that high, probably use the highest-octane gas you can find.
.

But the problem is the pin for the new rod is 2mm bigger than the one I'm taking out? Also I'll be running 112 fuel and everything is new.
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