Mind boggled on this R, need some R IQ's

[Brown2367]

Okay I'm building this 250R & had purchased a 295 engine, okay got the engine, ran like a damn raped ape for about 6 hours:eek2: then no more, lost compression :mad: (bought off ebay) enough said as that. Okay I get another top end from local honda placee :ermm: he hauls it out to .50 over. New wiseco piston, rings, gaskets, Okay I put the cool head on it & he replaces it with a dome that he says will work with the stock .50 top end....Ended up putting 2 base gaskets, and top is not thin or thick, was mid-thickness *shrugs* :confused: Well it runs WEAK on bottom end, once rpms get up top end runs good....compression test reveils dead on 160psi....isn't that low for a new .50 top end with a wiseco piston? Is it my gasket setup, lousy bore? I'll take any advice you have....I sure in the hell need it before weekend of 28th gotta get this thing goin...

[deathman53]

are you using a spacer plate? the extra gasket if you aren't using a spacer plate is the cause for the low compression. 160 isn't that low for a 250r, stock there were at about 180, the 89 year had less.

[zedicus00]

r u .50 over on the 295? y r u running 2 gaskets? yur entire setup sounds goofy. y did you get a new topend? and if the old one ran good for 6 hours you need to figure out y it crapped out b4 you start in on a new one. i dunno where to start answer my questions first.

[zedicus00]

while 160 isn low i would bet money the 295 you had on there at first was around 180 b4 it dieid

[beerock]

i dont even know how to help.

hauled to .50?

[Brown2367]

well i should have been more consise, i scratched the 295 i still have it, but went with a newer jug that needed bore, and bored it to .50. The guy that did the top end work suggested to take the 2 base gaskets. So practicaly its a stock topend bored .50 with 2 base gaskets & med thickness top. It has 160lbs...and hardly no low end....hope that helps a lil....

[Dave83]

Take out one of the base gaskets and check the squish with the dome you are using.What carb you running with it?

[etter696]

i am by no means an expert, but arent wiseco pistons, .20, .40, .60, .80 over, i didnt know they had a .50 over???also why are u running 2 gaskets on a stock dome

[Brown2367]

carb is an air stryker....pipe is a curtis sparks....also have a stock carb & fmf pipe.....

[Brown2367]

he told me that if i had used 2 gaskets on base & that it would bump up the compression a little...*shrugs* ya its a wiseco .50 over 66.5MM, part number 526MO6650, they also be ordered in increments of .25

[etter696]

ah i would think 2 gaskets would lessn the compression, being the cylinder is siting higher, meaning the rod and piston isnt reaching as high, and piston being farther away from the dome... sorry if i sound like an idiot just tryn to help

[Brown2367]

ya i know i understand what your saying, well at first we didn't know if the motor was stroked or not so was wonderin about cylinder hitting head, normally its the 2 base gaskets with a thin metal top gasket......which would make more sense, but he ended up giving me a mid-thickness top gasket...so i'm not sure what thats doin for the ratios there....probaly end up getting a single base & regular top....ya it has 160psi dead on right now...but low end is weak, i've done about everything possible to carb & nothing seems to help....do you think its the gaskets? is that compression of 160 low for a new top end? i'm not taking your opinions as smart ***:D :blah:

[zedicus00]

yes get rid of the 2 base gaskets and go to a thin head gasket. you want yur compression around 180-185. it will help yur bottom end power a ton. if you go much over that compression you will want to run mixed race gas

[zedicus00]

o and is that 295 jug a stock resleeve or an aftermarket jug? an do you wanna sell it?

[lil400exman]

my 265R has 240 PSI up top. It pulls harder than a 4-stroke off the line. Well anywhere for that matter!:cool:

[zedicus00]

dang i bet that is fun to kick. prolly doesnt over rev great either. but yeah that would prolly hang with my 300 off the line.

[Brown2367]

was stock jug that was resleeved.....naaa i don't wanna sell it yet...

[wilkin250r]

I'm trying to figure out exactly what's going on here, but it's difficult. Who is your mechanic, and does he really have any experience with 250Rs?

There is more going on inside your engine than just compression ratio, like port height, port area, port angles, squish band (both height and width), squish angle, squish velocity, and chamber design can all affect your power, and we haven't even touched on your pipe. You should educate yourself on these other aspects.

I would start off learning about the squish band and deck height (the two are related), as well as combustion chamber volume, and then see how they apply to your engine. Once you learn, test, and set these aspects properly on your engine, we can take the next step. However, most likely this will fix your problem.

[Brown2367]

Hes T&T Honda in bardstown, ky. His name is Jimmy Thompson....maybe you've heard of him? Hes seems pretty intelligent as far as I know of him. Maybe you can give me a little insight on what kind of things to look for so I can get this fixed? Thanks

[wilkin250r]

Well, intelligence and mechanical aptitude are one thing, and knowing the little tricks and secrets of a particular engine are another. Is it possible he's giving tips that work well on another engine, but don't work very well on the 250R?

As for advice and insight, again I recommend doing a bit of research and learning a bit about the motors yourself, so that you know what to look for, and what questions to ask.

For information about the squish band, I highly recommend the article The Art of Squishing Things Till They Give Power (http://www.aircooled-rd.com/default.asp?txtPage=dalea.htm). The article is written about RD350 streetbikes, but don't let that fool you, there is very good information in there that applies to ALL motors, even 4-strokes. (The RD350 motor is the basis for the Banshee motor).

A simple web search on deck height should clear up that issue. In a nutshell, it's the measurement of how far the piston come up in the cylinder. Does it come all the way to the top, or does it sit down in the hole below the top of the cylinder?

Combustion chamber is, in a nutshell, the space inside the cylinder head. Smaller volume means higher compression ratio. There are all sorts of parameters to play with, squish band, angle, and such. Many top builders and tuners will actually cut their own domes from a blank. You don't need to go THAT far, but the basic knowledge of what these aspects ARE is certainly useful when you're troubleshooting your engine and looking for maximum performance.

All these aspects are basically dealing with what the top of your engine looks like, and what it SHOULD look like. I'm willing to help you out and share my knowledge, but I'm not willing to spend 4 hours typing a book for you to read, especially when the knowledge is out there already just waiting to be found. I gave you some terminology, type them into google (or even on here) and learn a bit, and then come back to me with specific questions.

[87250rxrider]

yeah, listen to wilkin here. he def knows wat he's talkin about!:)