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Billy: I missed a lot of the reading, I’m trying to rest today. As long as everything is centered & square with the cylinder center you’ll be just fine. The next most important thing is the deck height.
JT
 

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You mention that you would do the plugs for the original stud holes different next time. I wonder if a guy could get away with just filling those with epoxy too?
 

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Discussion Starter · #83 ·
You mention that you would do the plugs for the original stud holes different next time. I wonder if a guy could get away with just filling those with epoxy too?

I think so. I would drill the threads out before I did though so it was just a smooth hole.
 

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IMO NO EPOXY: I would drill & tap the originals large enough so that they could be plugged with a steel stud.
Most of the cases weld like S**T, You need some integrity in your work.
IMO, Many years of practice.
 

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If you need me to crunch some numbers on my port program
I can help you figure out what your state of tune is and if anything needs changed
I would need to know a few simple parameters though



 

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Discussion Starter · #88 ·
Quick update, a friend on 3ww offered up a set of stock reed cages that he is sending me for experimentation. The intake will need to be angled. I will either end up making a custom aluminum one (similar in construction to the rad valves) or perhaps something different entirely, depending on what I decide once I receive them and get to look at it a bit more and how much of an angle change I need from stock.
 

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Discussion Starter · #89 ·
If you need me to crunch some numbers on my port program
I can help you figure out what your state of tune is and if anything needs changed
I would need to know a few simple parameters though

Denny, I have a crank (OEM 250R, will end up with a +4 & the KTM Rod before this is all over with) installed in my cases and the piston I'm going to use finally. I have done a little playing around with the degree wheel...let me know what you need #'s wise and we'll see what we can work out on this thing. My goal is a very much all-around motor, I don't want something with a 200RPM power range. I think the RAVE valve will help with that a lot, but my preliminary checking so far is that the exhaust port is open about 200 degrees with the power valve wide open, which in normal circumstances I think would give much more of a peaky range than I'm wanting, but I don't know how much the rave valve is going to help with that. Have no experience riding anything with one of them on it...
 

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Discussion Starter · #91 ·
My next few steps before I go much further in ordering the crankshaft and KTM connecting rod will be to make sure I can get the deck heights right on this thing and (Probably more importantly) make sure its airtight once its all bolted together. I'm shipping off to Cometic Gaskets a template of what I need for them to make for me in an aluminum plate. That'll be the next step.



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Discussion Starter · #92 ·
Small update: I have the custom gaskets and spacer plate ordered from Cometic, which were just superb to deal with over the phone and incredibly reasonable for custom work, highly recommend them. Stuff should be here this week.

Over the weekend I built a custom exhaust flange since the cylinder didn't really have a typical flange setup like we are use to it, it had a whole section of pipe that basically bolted onto it.

I also ordered a couple of end mills to properly repair the area near the shifting shaft and exterior seal on these cases that had been damaged and I had re-welded up, but had never finished machining for the seal or the shaft itself. I found a very handy chart some of you might find use in printing off and using,

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Cool yeah I've always had great service and quality from cometic
It wasn't cheap but as the saying goes :
Cheap things are seldom good and
Good things are seldom cheap



 

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cool video. i seen one of the other video also. this is only my unprofessional opinion but i would be more concearned with where the piston is at BDC regarding the transfer floors rather than the exh floor. by keeping the piston above the transfer floor your just robbing yourself of available transfer area. not that the engine wouldnt still run fine but why let a bunch of extra transfer area go to waste.
 

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All the ports are important of coarse but The top of the transfers is the critical part because most all the pressure
Is released when they open . That's why every builder preaches to
Really get them shaped angled and pitched evenly on their tops
I forget the pressure loss percentage was but I want to say
It's over 50% as soon as its open. This is same concept for the
Exhaust , that's why triple exhaust designs have such an abrupt
Power band after midrange .. All three ex ports are exposed and there's
A sudden drop in cylinder pressure after only a few degrees . That's
Why when companies develop power valves they close off the sub ports
Not only to reduce total area but also To retain high cylinder pressure at lower rpm
And increase efficiency



 

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Discussion Starter · #97 ·
cool video. i seen one of the other video also. this is only my unprofessional opinion but i would be more concearned with where the piston is at BDC regarding the transfer floors rather than the exh floor. by keeping the piston above the transfer floor your just robbing yourself of available transfer area. not that the engine wouldnt still run fine but why let a bunch of extra transfer area go to waste.
I agree for sure. In the first video I was not anywhere near finished deck height (Still am not either), I was just getting rough guesstimates and ideas. Now that I have the spacer plate and the gasket assortments in different thicknesses, I should be able to get it dialed in almost perfectly. If I remember from reading one of my books, I think it was Graham Bell's, it is common and prefered for the exhaust to have a little bit of piston edge protruding above the very bottom edge, but for the transfer flows, yes, they should be an almost perfectly smooth transition
 

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How true you all, throw this in the mix.
Move the piston height, MAYBE; the proper port height should be determined before the cylinder is raised or lowered. Moving anything around without figuring where they should be can kill the power band. The very first, the cylinder should be positioned where the piston has the proper deck height at TDC. The builder should know the basics before anything is moved around, back to the bimotion.se programs.

:thumbsup:
 

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I agree for sure. In the first video I was not anywhere near finished deck height (Still am not either), I was just getting rough guesstimates and ideas. Now that I have the spacer plate and the gasket assortments in different thicknesses, I should be able to get it dialed in almost perfectly. If I remember from reading one of my books, I think it was Graham Bell's, it is common and prefered for the exhaust to have a little bit of piston edge protruding above the very bottom edge, but for the transfer flows, yes, they should be an almost perfectly smooth transition
can you give more details about the engine dimensions ? i assumed the rotax cylinder was nearly the same stroke as the 250r but aparently its not. looks to be 82x75.7 from the info i found. i got your 800 mixed up with the mxz 600 which is 73 stroke. are you gonna stay with a 72mm stroke original honda crank ?
 
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