Planet Minis

cyclerider57

This is a follow up of my other thread about stimulating the minds of the forum to think about the technical aspects of an engine (specifically how it relates to minis). This will be a long process (gives plenty of time for discussion) as I have a lot of things on my plate.

The project...

88cc with the bore / stroke of the standard kit (52mm bore / 41.4mm stroke).
Takegawa Superhead +R highly modified by yours truly.
Valves custom made 32mm intake (titanium) / 26mm exhaust (titanium).
Stock crankshaft lightened with aluminum rod.
Everything will be done in house unless otherwise specified. Very few things within the engine will remain untouched. More details will be posted in the future.

For now, here is something to ponder. It isn't completed in the picture but it is something to stare at. This is before final machining and before bearing race and piston pin bushing are installed.

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aj191

sweet, i look forward to the future of this thread

Grafixxs

Your a sick man.... very cool!

50rider340

the cut in the middle does that go all the way through??? Awesome you started and started posting up pictures. 32mm intake valve on a super head is SICKKKK.

vetmxer

What grade of aluminum is that?

ar design

Where can I buy a rod like that?

PHATDAN420

Im Pretty sure it's custom made

cyclerider57

The notch in the middle doesn't go all the way through. It's an H section rod rather than the more common, in production single cylinders but not necessarily in the racing environment, I section style rod. I made it from billet 6061-T6 Aluminum (not standard crf50 length). The tricky part is designing it so it will be strong while still giving enough flex to absorb high shock loads all while reducing weight. Something that is extremely rarely considered is that a very clever design will even allow rod compression at bdc and extention at tdc due to momentum of the piston and the combustion forces. When a rod does that it is literally increasing the length of the stroke and changes dynamic displacement. A lot of engine builders will take into account that dynamic compression will change considerably with rpm when graphed against static compression. Very few consider the fact that a rod can change length under high rpm and high loads. It takes a large bore to actually take advantage of that fact so it is pretty much irrelevant on these engines but it is something interesting everyone should think about.

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50WHIP

Just curious what kind of estimate is the life span of the rod?I know when I ran circle track they were only good for so many laps and the guys would change them out due to them stretching.I like that you have the knowledge for these builds and are willing to share your work for us to see but the motors have to be good for more than just #'s on paper they need to last.Like they say you have to be in it to win it.

cyclerider57

Aluminum doesn't have a spot on the S/N curve where it goes to zero slope so no matter how strong your design is, aluminum will always have a finite fatigue service life. This is unlike steel which as long as stress is kept within limits, it will have an infinite life. I'll have to do some final FEA (finite element analysis) to help determine the life then follow it up with regular tear downs to confirm but right now it is looking like it won't have problems going quite a few hours of high rpm run time without issues. Confirmation of this will only be completed through actual on dyno and track testing.

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The wise understand by themselves; fools follow the reports of others. Goodness speaks in a whisper, evil shouts. -Tibetan Proverb

way2fast4u7

cyclerider57. I don't ususlly dapple into the vast array of knowledge that hides in the crf50 section, because I find a lot of the threads here don't really pertain much to what i own (110). But this thread has now intreagued me. Very cool!!! Anyways, after linking back and reading the tread on what everyone thinks should go into this mini rocket that you speak of, I wanted to ask this question in that forum as I thought that it would be most relevent there but would only put some info here and some info there so I figured I would ask it here.

What is your thought on fuel injection on an off road 50cc. Honda has done a lot of the ground work in making a 50 cc fuel injected four stroke (mainly I think, to just throw it in every other companies face about what Honda is capable of). I have seen on Tak's side about an 88 kit with programmer and such. What kind of work would it take to build, and retro fit, for lack of a better term, a "fuel injecion" kit for the carb 50's.

Obviously at the very least, the rotor would need to be changed, just because I am guessing that is where crank position is obtained, which in turn would require a crank position (hall effect) sensor. From there, you would need a mass air flow (Tbap, Tmap or whatever you want to do with it) sensor. And most importantly, need throttle body, and injector.

Anyways, I tried looking for the info on the Japan website, but could not find anything and am now thinking coffee would be a good idea. What are your thoughts on fuel injection, and if it is even feasable, what would it take to put it on a carb'd fifty. Thanks for all your input!!

Grafixxs

I would like to see a Honda 50 engine left ALL stock other then taking every single piece and making it as light as it can.

The finish it off with all the goodies like porting and so on.

chrisc161076

To Cyclerider57,

How have you decided upon the size of the valves 32 & 26mm, that sounds massive? What carb are you thinking of running and how are you going to calculate that?

Motarded

can you post a picture of the rod next to a stock rod? is that rod going to clear the skirt and sleeve?

schofell84

i was wondering abou tthe clearance issue too.

as far as the aluminum rod stretching ... i know some manufacturers use titanium (nsx's) for weight and that it doesnt stretch so they can determine exact squish numbers ... does the titanium have an infinite lifespan like steel? i thought titanium valves were prone to stretching (early crf450's).

cyclerider57

If I was doing it I would stick with port pressure sensor and eliminate a mass flow sensor as they can create flow issues. For a dirt crf50 or even one taken up to 124cc I would still refrain from FI merely because the cost and time to actually go through and program it at each combination (they are no benefit at all if you don't take the time to do this properly) would kill all benefits when you consider what else you could be doing with development money and time. Taking that time to do more port testing would probably yield a higher gain (I have not done FI on a dirt mini so this is my personal opinion and experience). Now, I am currently working on a FI system for one of my projects that is 90cc per cylinder... but it isn't one cylinder and it isn't for the dirt. If I was going to try to do FI for a dirt mini I would cut all the crap and go straight for direct fuel injection to the combustion chamber.

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cyclerider57

It is massive, in fact, it would be quite difficult to get anything bigger into a 52mm bore. Valve sizes being so large will allow me to run a less aggressive cam so i can focus on low lift flow. The ports are not going to be as big as they could be with those valves. I will be able to keep some stability within the rpm range by eliminating the huge overlap and duration that most aggressive cams require. I will be able to reach my target area under the curve (flow area) without some of the normal side effects. The shorter rod will help eliminate some of the negative effects by pulling harder at the start of the down stroke to get the flow started. From that point, I can rely some on flow momentum to keep cylinder filling when the piston starts moving up again. I will more than likely be running an fcr 28 modified somewhat. We will get into that at a later time. I have created a "program" of many excel sheets based on a ton of books, past experience, etc to help me diagram various things within the engine. One is intake and exhaust flow and "nominal" port sizes depending on what aspects I am looking for. I am sorry but I will not be going into more details about my program as I have way to much time and money invested in it and a lot of my race engines rely on that information to have an advantage.

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The wise understand by themselves; fools follow the reports of others. Goodness speaks in a whisper, evil shouts. -Tibetan Proverb

micro75

Jordan looking at the connecting rod very nice work. When you install the lower end bearing race how much interference and do you think the stress from it will be a problem

cyclerider57

I will try to post more pictures at a later date.

The stock stroke, even with this rod being shorter, doesn't allow for a lot of rod angle so clearances are ok.

The number one reason I didn't use titanium (alloy Ti-6Al-4V) is cost. It shares similar properties to steel in that designed correctly it will have infinite cycle fatigue life. Titanium is actually the second most common rod material in the race environment. Aluminum is pretty rare these days except in drag race and dirt oval applications where there are extreme shock loads. Some estimates by rod manufactures assume a titanium rod with the same development time of a steel rod will still only yield about a 10% reduction in weight but merely copying a standard steel rod in titanium will produce a 44% mass reduction. Obviously there is some discontinuity in there and my guess is it because they just know the properties of steel so much better from experience that they give steel too much credit. Aluminum normally doesn't yield much of a weight reduction because you have to have so much extra material. I'm giving a little strength and longevity to let it be a little lighter though. It I were to take the time to make a steel rod I could probably make it lighter than this aluminum one... that is not as interesting though. And I just don't like steel.

Most of the time when you hear of valves stretching they are actually beating into the seating surface letting them seat with the stems higher in the head. This gives the illusion of them becoming longer.

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cyclerider57

A few thou. I made it knowing those stresses would be introduced so I allowed for them. They shouldn't create any unseen issues but that doesn't necessarily mean they won't. Analysis only takes you so far.

These are the reason I didn't go with trying to make a composite rod. When I was doing a lot of work doing my composite push rods for some of our engines those stresses introduced by the interference fit of the tips created a lot of issues.

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The wise understand by themselves; fools follow the reports of others. Goodness speaks in a whisper, evil shouts. -Tibetan Proverb