What are the advantages of a long rod crank?

[96_banshee_96]

I Just bought a stock cylinder with a 295cc sleeve pressed in. I wanna know what are the advantages of running a long rod crank. Are the 87-89 cranks +4mm over the 86 crank? Would it be better to run the longer crank?

I want this thing to rip. I want to tear on the banshees and 450's at the dunes. So if someone can tell me whats the best way to set this motor up I would appreciate it.

The cylinder I have now already has a very nice port job. I am not sure what type of port work it is but its not someones hack job. So the cylinder is already ported

I plan on buying a Coolhead with changeable domes I want to run whatever type of fuel to make the most power.

Also Vforce reads
Boyseen rad valve for a 38mm carb

what else should I get to set this motor up. I have the motor completly apart right now and I wanna do things right the first time.

[wilkin250r]

I won't get TOO complex, with details like dwell time and port durations, I'll give you some general guidelines.

First off, you get a little smoother powerband with the long-rod. The peak horsepower is about the same, but a long-rod engine tends to transition easier, while a short-rod engine revs pretty quick and "hits" a little harder.

Due to the changes in rod angles, the long-rod engines are usually much more reliable, because you don't get quite as much side-loading on the piston.

[1promodfan]

[QUOTE]Originally posted by wilkin250r
I won't get TOO complex, with details like dwell time and port durations, I'll give you some general guidelines.

First off, you get a little smoother powerband with the long-rod. The peak horsepower is about the same, but a long-rod engine tends to transition easier, while a short-rod engine revs pretty quick and "hits" a little harder.

Due to the changes in rod angles, the long-rod engines are usually much more reliable, because you don't get quite as much side-loading on the piston. [/QUOTE

X2 what he said^......also the one thing that I have noticed is a much better mid-range. My cousin has a lt250 suzuki (with a few goodies), and when he rode my bike he said when he pulled 3rd gear it really started "singing". He said his felt slow compared to mine.

[All250R]

Originally posted by 96_banshee_96
Are the 87-89 cranks +4mm over the 86 crank?

The rod length has 100% nothing to do with stroke. The displacement is the same regardless of rod length.


Originally posted by 96_banshee_96
Would it be better to run the longer crank?

This question is one of a sea of small questions that individually don't matter a tremendous amount. You're probably not going to win or lose a race or have or not have fun duning based on the rod length. You're going to get more for your energy picking the pipe that goes best with your porting. Because you don't know the porting of the cylinder, this isn't going to be easy for you to answer on paper. Your best bet might be to buy a couple pipes and see how they work. Remember CR250's run the short rod and as far as I know always have. The long rod isn't an "upgrade". It's just one part of an overall design meant to work in synergy. Anyone who tells you a long or short rod is faster all by itself doesn't understand clearly what goes into the overall design of a 2stroke engine.

Without the willingness to reverse engineer the cylinder and match or build the correct pipe for it, I'd say whether you want an OEM crank or not would be your deciding factor since you can't get the TRX short rod from Honda anymore.


Originally posted by 96_banshee_96

I plan on buying a Coolhead with changeable domes I want to run whatever type of fuel to make the most power.

You will have or not have a solid impact on how the motor runs by designing the head for your setup. Don't buy the head and then just bolt it on. You won't get the most for your money.


Originally posted by 96_banshee_96

what else should I get to set this motor up. I have the motor completly apart right now and I wanna do things right the first time.

Bolting on parts is fun. I like it too. But it doesn't yield best results. Bolting on parts to a 2stroke is easy but designing it so the parts actually do what they're supposed to can be enormously complex. Somewhere in between no design and years of R&D is the goal to get at least intelligent decisions made about your overall riding goals. To get solidly in the ballpark a comprehensive design should be done for how you want the motor to run for how you yourself want to ride it. You've got to figure out how much work you want to put into the engine. If the answer is not much and you still want a top notch motor asap you're going to need professional help.

If you do it yourself willing to hope for the best hopefully that cylinder fits the bill. It's really being blind to buy a cylinder and how know how its ported. The porting and the pipe will account for the majority of the engine's personality. I'd probably put an OEM long rod in simply because they're easy to buy, pick a pipe and see how it runs (don't forget all the maintenance parts). A 38mm carb with port matched boot hopefully and v-force reeds will probably give your engine acceptable flow. You can try bolting on a shrink wrapped head, but you're shooting in the dark. If things go well it will run well enough.

[All250R]

Originally posted by 1promodfan
X2 what he said^......also the one thing that I have noticed is a much better mid-range. My cousin has a lt250 suzuki (with a few goodies), and when he rode my bike he said when he pulled 3rd gear it really started "singing". He said his felt slow compared to mine. [/B]
Not to pick on you, but you can't compare two completely different quads of all things, notice a difference and attribute it to one having a short or long rod.

[1promodfan]

Originally posted by All250R
Not to pick on you, but you can't compare two completely different quads of all things, notice a difference and attribute it to one having a short or long rod.

I was just comparing my bike to my cousins lt 250. He just had his ported and polished and set-up, and he still says he likes mine better.

Its true you can't attribute it to being a long or short rod, but most will say they like a long rod better. As with my bike, I have noticed more of a mid-range. Again, like you said you can't compare 2 different bikes of any kind because of the variance of how its set-up. Just my 2 cents worth....which isn't much!!LOL!!

[96_banshee_96]

Originally posted by All250R
The rod length has 100% nothing to do with stroke. The displacement is the same regardless of rod length.


This question is one of a sea of small questions that individually don't matter a tremendous amount. You're probably not going to win or lose a race or have or not have fun duning based on the rod length. You're going to get more for your energy picking the pipe that goes best with your porting. Because you don't know the porting of the cylinder, this isn't going to be easy for you to answer on paper. Your best bet might be to buy a couple pipes and see how they work. Remember CR250's run the short rod and as far as I know always have. The long rod isn't an "upgrade". It's just one part of an overall design meant to work in synergy. Anyone who tells you a long or short rod is faster all by itself doesn't understand clearly what goes into the overall design of a 2stroke engine.

Without the willingness to reverse engineer the cylinder and match or build the correct pipe for it, I'd say whether you want an OEM crank or not would be your deciding factor since you can't get the TRX short rod from Honda anymore.


You will have or not have a solid impact on how the motor runs by designing the head for your setup. Don't buy the head and then just bolt it on. You won't get the most for your money.



Bolting on parts is fun. I like it too. But it doesn't yield best results. Bolting on parts to a 2stroke is easy but designing it so the parts actually do what they're supposed to can be enormously complex. Somewhere in between no design and years of R&D is the goal to get at least intelligent decisions made about your overall riding goals. To get solidly in the ballpark a comprehensive design should be done for how you want the motor to run for how you yourself want to ride it. You've got to figure out how much work you want to put into the engine. If the answer is not much and you still want a top notch motor asap you're going to need professional help.

If you do it yourself willing to hope for the best hopefully that cylinder fits the bill. It's really being blind to buy a cylinder and how know how its ported. The porting and the pipe will account for the majority of the engine's personality. I'd probably put an OEM long rod in simply because they're easy to buy, pick a pipe and see how it runs (don't forget all the maintenance parts). A 38mm carb with port matched boot hopefully and v-force reeds will probably give your engine acceptable flow. You can try bolting on a shrink wrapped head, but you're shooting in the dark. If things go well it will run well enough.

Well thats good to hear that the short rod isnt much different because I have one. I guess I will just run this crank. So are vforce reeds and the 38mm carb something that is needed with a 295 cylinder or do I need a bigger carb? Where can I get a boot for the carb? What do you mean by shrink wraped head?

[All250R]

Originally posted by 1promodfan
I was just comparing my bike to my cousins lt 250. He just had his ported and polished and set-up, and he still says he likes mine better.

Its true you can't attribute it to being a long or short rod, but most will say they like a long rod better. As with my bike, I have noticed more of a mid-range. Again, like you said you can't compare 2 different bikes of any kind because of the variance of how its set-up. Just my 2 cents worth....which isn't much!!LOL!!
All we can do is speculate sometimes so I understand that. When you say that most will say they like the long rod better, why do you think that? Also, if it were true, would they be making an appropriate evaluation of what the long rod is or isn't doing before deciding they liked it?

[All250R]

Originally posted by 96_banshee_96
Well thats good to hear that the short rod isnt much different because I have one. I guess I will just run this crank. So are vforce reeds and the 38mm carb something that is needed with a 295 cylinder or do I need a bigger carb? Where can I get a boot for the carb? What do you mean by shrink wraped head?

I think if you already have a 38 you should run it for now. 38mm is a good all around carb. Don't spend money on parts unless you have a specific reason to change what you have is how I look at it. A 39 is good for bigger bores (possibly like yours). Realize that the bigger the tube the engine sucks through, the more suction force is required to get the fuel you need. So, bigger is only better if you need bigger for what you're trying to accomplish.

The 89 CR boot doesn't have any stuffer tabs you'd have to cut off but depending on the version of the cage you buy some years will line up better than others and require less matching work. You can buy the boot new from Honda. Don't forget to buy the clamp that goes with it btw. If you picked a cage and a boot you could probably make both work reasonably well.

Shrink wrapped head... I meant pull it off the wall and unwrap if from the packaging.

The main point of my long post was that if you want optimum performance to blow people away you want to nail down a lot of fine tune variables all at once, otherwise your best hope is to try out the main performance makers (which is not really the rod length) and hope for the best.

[96_banshee_96]

I only have a stock carb right now. I thought if I went with a bigger carb a 38mm was the one to get. I bought this bike a year or so ago and never got around to fixing it. It never ran at all when I bought it. I bought a big bore 295 cylinder and piston for a good price and decided to build this bike over the winter for Silver lake dunes. I have a couple stock heads that can be used instead of buying a head with changeable domes.

If it were you, how would you go about building this motor. It is completly apart right now.
What carb?
What Reeds?
What Pipe?
Etc... Etc...
If you would like I could E-mail you some pics of my port work so you can get an Idea of how its ported and how to set it up just shoot me your E mail addy
Thanks.


Originally posted by All250R
I think if you already have a 38 you should run it for now. 38mm is a good all around carb. Don't spend money on parts unless you have a specific reason to change what you have is how I look at it. A 39 is good for bigger bores (possibly like yours). Realize that the bigger the tube the engine sucks through, the more suction force is required to get the fuel you need. So, bigger is only better if you need bigger for what you're trying to accomplish.

The 89 CR boot doesn't have any stuffer tabs you'd have to cut off but depending on the version of the cage you buy some years will line up better than others and require less matching work. You can buy the boot new from Honda. Don't forget to buy the clamp that goes with it btw. If you picked a cage and a boot you could probably make both work reasonably well.

Shrink wrapped head... I meant pull it off the wall and unwrap if from the packaging.

The main point of my long post was that if you want optimum performance to blow people away you want to nail down a lot of fine tune variables all at once, otherwise your best hope is to try out the main performance makers (which is not really the rod length) and hope for the best.

[1promodfan]

Originally posted by All250R
All we can do is speculate sometimes so I understand that. When you say that most will say they like the long rod better, why do you think that? Also, if it were true, would they be making an appropriate evaluation of what the long rod is or isn't doing before deciding they liked it?

When I said most say they like the long-rod......I don't think that....I KNOW that. And it is true, unless say the guys at Duncan Racing are "idiots"......which we know is NOT true. Thats just one example....if you want more I can give them to you. A lot of people that run a 250R, run a long-rod. I know of another guy, Neil Pritchard...(C-Leigh Racing).....if anyone knows 250R's its him. Ask him his opinion and see what he says. But, again....maybe I'm thinking......

[morse250r]

pm sent 96

[All250R]

Originally posted by 1promodfan
When I said most say they like the long-rod......I don't think that....I KNOW that. And it is true, unless say the guys at Duncan Racing are "idiots"......which we know is NOT true. Thats just one example....if you want more I can give them to you. A lot of people that run a 250R, run a long-rod. I know of another guy, Neil Pritchard...(C-Leigh Racing).....if anyone knows 250R's its him. Ask him his opinion and see what he says. But, again....maybe I'm thinking......
Take it easy. I think you don't recognize that I wasn't insulting you.

[8686]

Lol.

[All250R]

Originally posted by 96_banshee_96
I only have a stock carb right now. I thought if I went with a bigger carb a 38mm was the one to get. I bought this bike a year or so ago and never got around to fixing it. It never ran at all when I bought it. I bought a big bore 295 cylinder and piston for a good price and decided to build this bike over the winter for Silver lake dunes. I have a couple stock heads that can be used instead of buying a head with changeable domes.

If it were you, how would you go about building this motor. It is completly apart right now.
What carb?
What Reeds?
What Pipe?
Etc... Etc...
If you would like I could E-mail you some pics of my port work so you can get an Idea of how its ported and how to set it up just shoot me your E mail addy
Thanks.
To answer you question, again, my main concern would be the porting and pipe match. Everything else should compliment the build which revolves mostly around porting and pipe. No one can adequately spec a cylinder with pictures. If I told you I could I'd be doing you a disservice. I'm trying to provide with enough information to keep you from getting your hopes up falsely and save you some money. Your porting and pipe, porting and pipe... Except for maintenance, that's where I'd look first.

I think you should talk to some professional engine builders of your choice and see
which one makes you feel comfortable. If you want to do the work yourself which is fun too, there are a lot of threads on this site that should give you some pretty repeated opinions on the basic things you want to know about. Don't take one person's word for it and above all, have fun.

[1promodfan]

Originally posted by All250R
Take it easy. I think you don't recognize that I wasn't insulting you.

Allright bro. no problem!! No harm no foul.:D

[All250R]

Originally posted by 1promodfan
Allright bro. no problem!! No harm no foul.:D Cool.

[trx310R#24]

well if it matters to anyone.. i run a long rod an after 2-3years i still have 200 comp. an it runs great lol an i ride my bike hard so... it works for me i guess

[hammerdog]

im runnin a long rod as well with a spacerplate
my .$02

[8686]

I have a short rod engine in my garage I just stopped using last year that still has the original piston and rings in it. The top end has never been off. Still ran good when I pulled it.