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333 big bore stroker?

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According to my calculations, a 290 athena cylinder (83mm bore) with a crank using a 4mm offset pin yields 333 cc's. Add a 4mm spacer plate under the cylinder and a possible custom cam chain if the stocker isnt long enough and you have a hell of a big little motor.

Any thoughts?

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Ill use my spare crank to do it for next summer. Maybe I will even get spare engine to do it on. I will have to use a carillo rod and balance the crank, but it should be pretty sick if done right.

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I could go nuts on the stroke to a 5mm offset and that yields almost 350 cc, not sure if the carb and head can support that. Id probably have to go to a bigger carb etc at that point. My base estimate at this point is over 3k for the entire deal with me doing all the labor...YIKES!!!! Ill have to start scavenging off of ebay.

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Any thoughts?

The main bearing attachment setup and the stock cases are barely adequate to handle the loads of the stock crank and piston loads. (lots of 2 year old RMZ/KXFs with worn out cases out there). So unless you have a 5 axis Haas in your garage to crank out some proper cases I think you'll find that the loads you are proposing will be more of an engineering excercise than you counted on. :banghead:

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We have a 5 axis haas available at school (actually a room full of them!) for research projects, as well as dyno cells etc.

Anyhow, can I sleeve the stock bearing bores? The cases are the least of my worries, I am more worried about the head being able to flow enough.

Rich, you willing to help me out on this one if I go through with it :banghead: .

I am actually gonna try to model my cases this weekend in Solidworks since I am doing a crank this weekend.

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This has got me thinking, yea its gonna have more force at the main bearing, but if the bearing is tight and the rotating assembly is balanced how much more force is it? I wish they had classes for this kinda stuff at the University of Michigan where I go to school.

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Anyhow, can I sleeve the stock bearing bores?

Even if you were to bore the main bearing saddle for a bigger bearing OD like the mains on the YZF 250 it still missing (and desperately needs) a pair of locking plates like every decent engine design uses.

I am more worried about the head being able to flow enough.

A logical concern and one you'll never get around without and a ton of re-engineering and $$$.

Rich, you willing to help me out on this one if I go through with it :banghead: .

No thanks. Exercises in futility don't interest me. 🤣

This has got me thinking, yea its gonna have more force at the main bearing, but if the bearing is tight and the rotating assembly is balanced how much more force is it? I wish they had classes for this kinda stuff at the University of Michigan where I go to school.

Time to be a REAL engineer and figure it out Aaron. You have the resources of one of the best engineering schools on the planet, make use of it. :banghead:

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Rich,

Thanks for the advice.

I probably wont end up even trying this because of $$$ and my last stroker attempt/demise on my 125

It is just interesting and this kind of stuff gets me thinking.

I would figure it out if I had a reference on a good book to read or SAE paper on internal combustion kinetics. Like I said, we have nothing for undergrads at school for this type of stuff.

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Like I said, we have nothing for undergrads at school for this type of stuff.

You have access to a GIANT library. The info is sitting there waiting for you if you really want it. :banghead:

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True true, but that requires work haha. Alright, point taken, to the library I go when I am back at school after this weekend and have some free time.

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