Low personal B.M.E.P.
Sorry, no, destroking the Honda crank is prohibitively expensive...when summit eng were doing submerged arc welding of cranks in Rotorua it was doable but dear...
Better option is to make it a 125 twin - primary is between 3 & 4 I think ? So cut off 1 and 4, blank off cases and barrel ends and with some care in assembly you've got an 18,000rpm 8 valve 125 twin....If you really want 150cc start looking for pistons of suitable bore size.
Hardcore Biker
Hmmmm. That's a pity.
What is the welding for? I don't really get what needs to be welded...
Could you explain that to me please.
The twin is a very good option as well. Quite a bit simpler.
Long Haired Yobbo
It think You would be better off cutting the left two cylinders off and making a twin.Originally Posted by Moooools
Time/Money wise better again would be buying an FXR....
Edit: Didn't read the second page... Yeah twin would be better but an established motor would have you competitive for a fraction of the time/effort/money.
Heinz Varieties
Re(tarder)
i think the aim is to take the road less traveled. Innovation only happens when you try something new.
For anything race related from arai helmets, to sprockets and chains, XT Lap timers, HRC parts you name it, Kev can get it www.racesupplies.co.nz
Come warm yourself by the fire
What others have said Moooools
The jappa IL4's don't like playing with much. So buy taking 1 out of the 4 out requires serious mods on the crank.
The only way I could see you getting away from doing this is by creating a 'dead' cylinder.......but that would be so inefficient I wouldn't see the point.
Modding to a supercharged twin would be sweet (2 + 2 charge pistons) - but alas you could not race that (but as a road bike would be pretty cool).
Making it a 2 cylinder by cutting the others off......after about 6 month sorting it you'll be wondering why you didn't build a twin from scratch.
If you hate FXR's so much and what to keep it honda, what about doing something wacky with an XR200 - the motor would be pretty bulletproof if you sleeve it down to a 125 and put a lightweight piston in it.
Reactor Online. Sensors Online. Weapons Online. All Systems Nominal.
Hardcore Biker
6 months of sorting out wouldn't realty bother me. It's all interesting experience and something to add to the cv.
I will have my current bike to race in the mean time.
A suzuki gsxr 400 is 53mm which would give 150cc from a twin. (and a piston already from a four valve engine.)
A single cylinder just doesn't really excite me.
There is a guy who races f3 with a gsxr 600 minus one cylinder. Might be worth me getting in contact with him and seeing how he did it.
Thanks for all of your input though. I have a habit of dismissing peoples input far to quickly, but once I get a bit deeper into shit I will evaluate it a bit more closely
Max
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you could maintain balance by putting a spacer on the unused crank pin (weight of bottom half of conrod). But short-stroking the crank would still be a lot of work, and would require welding or custom fabrication, so you may as well do a proper triple crank. Unfortunately the existing sizes don't seem to divide nicely into the numbers you need. Except possibly a 400 to super charged single conversion.... or somthing like an old CM200 parralel twin, also supercharged single.
"A shark on whiskey is mighty risky, but a shark on beer is a beer engineer" - Tad Ghostal
Low personal B.M.E.P.
The Honda is a one piece forged crank - to stroke/destroke the big end journals have to be welded and reground on new centers. As far as I know no one in NZ now does the required submerged arc welding process. I heard that Summit who did do it sold the gear to the main customer - a dairy factory ?
As far as making progress with adventurous design goes....I saw too much adventure and not enough progress with the Britten. Mike Sinclair's comment that next years winning bike is this years one with 5% improvement still holds true.
Hardcore Biker
Sweet. I'm glad someone told me that now.
I am kind of liking the twin bored out to a 150, idea at the moment.
If I remove conrods and pistons that are 180 degrees apart,would the crank not stay balanced? Or is that completely wrong...
Come warm yourself by the fire
Unfortunately last time I saw this attempted - they only did halve the work, but while the crank was balanced, the engine was not. It rocked like a washing machine.
However if you shortened the crank, cut up the block, remake a new head.......
actually the more I think about it, the easier twin built from scratch sounds.
Why not make a V twin out of 2 x 50cc kits with big bores out to 75cc?
That way all you would have to do is make a crazy crank case setup. There may even already be a kit out there (say from a compressor or something)
Reactor Online. Sensors Online. Weapons Online. All Systems Nominal.
111000101000100010011110
no that would unbalance the crank, as it is designed to counterbalance the lower half of the con-rod. And as avgas says, you still have engine balance to worry about. Which i guess is why parralel twins are so rare, I've seen one two stroke with it (KR-1, pistons 180 degrees apart) and one four stroke (CM200, pistons on a shared pin I think).
Also, you may not even need to bore out an extra 25cc if you can get a rejiggered twin to work, should have plenty of power, and that way you wouldn't put in extra effort before the concept is proven.
"A shark on whiskey is mighty risky, but a shark on beer is a beer engineer" - Tad Ghostal
Hardcore Biker
No I think what avgas was saying, is that although the crank is in rotational balance, the removal of the mass of the conrod would leave two reciprocating masses traveling in opposite directions, causing the engine to twist about the centre of mass of these two masses.
Would it be possible to put the entire crank in the lathe and spin it up, adding mass to the empty crank pins until it rotates without vibrating?
Actually that doesn't work at all because you would need the remaining two con rods to be in place. Otherwise when you attached them they would simply put the balance back out.
Perhaps I will need to work it out using some physics. All about rotational momentum really.
111000101000100010011110
the conrod is part rotational mass, and part reciprocating mass, while you can balance the rotational mass bit, you will still have reciprocating mass unbalanced in the pistons, if they are 180 degrees apart you would get a rocking from side to side vibration, if on the same pin, would be an up down vibration.
"A shark on whiskey is mighty risky, but a shark on beer is a beer engineer" - Tad Ghostal
Hardcore Biker
The reciprocating mass is usually delt with by a counterbalance shaft. It is near impossible to eliminate completely with any inline engine. (I think)
How about an analogy.
Say you had a 40gallon barrel spinning on a lathe. You then add four weights to the barrel. Two at each end and on opposite sides of the circumference of the barrel.
The barrel would rotate without vibration.
If you took one weight off of each end, however from opposite sides, the barrel would still be in rotational balance.
But when the barrel starts to spin it would vibrate, as the masses would always be traveling in the opposite direction to each other.
Does that make sense or am I talking rubbish?
Low personal B.M.E.P.
Oh fer crying out loud...who's a qualified engineer on here ???
the two center throws of a four are in the same plane - both "up" if you llike...
this makes it a 360 degree parallel twin...think triumph,Norton etc etc..
easily rebalanced - particularly as it's so small and short stroke. OE balance factor is probably around 35-40% so simply rebalance to around 65 -70% static.
all 360 deg twins without a balance shaft are a compromise in balance so it doesn't matter if it's not exact first time round - just change it until it's acceptably smooth in the rev range you use.
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