Is this crazy?

[bmxpsyco04]

Hey, I'm rebuilding the top end on my 185s. So far I bought a new cam and a 67mm Wiseco piston. Considering the stock bore is 63mm how crazy is it to have my cylinder bored 4mm over w/ a high comp piston. Wiseco has the piston listed on their site so I figure the cylinder can be bored that big although this raises more questions. On the 67mm piston kit wiseco says *cylinder boring required and that the displacement will now be 198cc on the other hand...for the single piston wiseco says *displacement will change to 192cc ? that doesn't make any sense to me. Lastly i'm not sure if the walls of the sleeve?(i guess, that stick out the bottom of the jug) are thick enough to be bored that big. Sorry for writing a daym paragraph of questions but let me know what you guys think bout all that stuff. Thanks!

[Texas 200x]

I just did my 200x with a 66mm bore standard is 65mm. They off er a 67mm 12:1 but that is a race part which i understand bores the head extremely thin needing a special sleeve. Which I think means it wont last long at all it would just be good for a couple of good runs most likely. Boring 4mm over I'd check your cylinder sleeve to see if it even has that much metal in it. I have heard of putting a 200x top end on a 185 for big power increases though. I would measure the jug and see how much metal is on the sleeve first. See how much sleeve is left if you bore it that big. Whats the compression on that piston?

[trizilla]

you need to find a cylinder from a 200s,200e,200m. these will bore to 67mm. i dont think your 185 cylinder will bore that far. as far as the high compression, 10.25/1 is a good piston and you can still run pump gas. the 12/1 that wiseco offers will require you to run race gas. i'm doing up a 185 myself and the route im going is 10.25/1 with the 67mm bore. im still thinking about a carb though. i think stock 200s has a larger carb than the 185. basically i will have turned my 185 into a 200 , 2mm over.

[Dirtcrasher]

4MM is massive.

2MM left nothing on the 250SX sleeve when it was bored and the bore charge was double.

2MM or about .080 does not change a 185 to a 200.

[bmxpsyco04]

hmmm....yea i don't have any accurate measuring device for mm that i could measure the walls with but i think it is to much. I will probably sell the piston right away, i would like more reliability. So i thought a 200 was just a bored out 185?

[bmxpsyco04]

wiseco 10.25:1 by the way

[84honda200s]

i had a 185 bored to 67mm with a wisco 10.25:1 piston. i wouldnt go higher than that seeing how a 12:1 may pull the sleeve out. it ran/runs great bored to 67mm with that 10.25:1 wisco in it. it was probably the most reliable motor i had. a fellow member just bought it from me and he said its still running great. it produced enough power to do what i wanted it to do.


it all depends on how you run it. if you rev the living *Edited**Edited**Edited**Edited* out of the thing it probably wont last too long. but like i said ...i had no problems with my bored cylinder. i even had a high cam, big carb, lighten flywheel, and small port job. it still wasnt too unreliable. it started 2nd pull everytime.

but it might be cheaper to just get a 200s, 200m, 200e, 200x cylinder and maybe a 10.25:1 or 12:1 std bore piston.

[bmxpsyco04]

Great to hear from someone who has done this before. Thanks for all the input i'll let ya know what I decide to do. There is a storefront on ebay that sells refurbished jugs for like $75 so i might buy on and ask them to bore it before they send it. This sounds stupid but if the piston is 67mm should I ask them to bore the cylinder to 67mm or do i need to leave some room for the rings?

[84honda200s]

i think it needs room for rings. mine had close to 1/8 of a mm for the rings. but you may wanna ask a pro that question.

[bmxpsyco04]

Will do, thanks. I do know that stock the 185s piston is 62.9 mm with a 63mm bore so i knew there was some room.

[Dirtcrasher]

Give them you piston, they do the math for you.

If it's a Wiseco (forged piston) it's about .002 or .003 clearance (I forget) and that takes care of everything. Nothing has to be figured in for the rings etc etc.

Lots of people think that boring cylinders increases displacement allot. A 2mm oversize might make a 185 a 186, thats all. Thats why big bores need "kits" with bored out jugs and huge sleeves. Or changing the stroke a few mm's changes displacement, but simply adding 1 or 2MM to the outside of the cylinder does very little except leave you with a cylinder that has few or no bores left in it.

As far as boring goes, the idea is to bore it to the smallest over bore size possible so that it cleans up the cylinder wall and keeps it true throughout the length.

Adding another mm or so does nothing as far as increased power.

[bmxpsyco04]

Thanks DC, it seems like kind of a hassle to send back the 67mm piston, considering I didn't get it yet. But i will have to think on it. I figure slapping a 200 jug on my 185 with a high comp piston will add some power over stock, i think thats the way to go for now

[1upfront]

actually 6mm's increases an airfooler from 248cc to 295cc, so you'll be gaining more than 1cc for sure with 2 mm overbore lol.

[trizilla]

1upfront, your right!!!! he will definetly be gaining more than 1 cc. in fact thats kinda retarded to think it will only gain 1 cc for each mm of bore. stock bore on a 185s is 63mm. stock bore on 200s is 65 mm. i'll say that a 185 is in the low 180 cc's. and no that is prolly not an exact measurement. then i'll say that a stock 200s is about 190 cc's. again not exact but rest assured very close. that means about 10 cc diference between the 185 and 200. again these are just estimates but surely not far off.. so i guess its safe to assume that boring your 200 cylinder will in fact put you very close to actually having a 200cc engine.

[TravEX]

The calculator I used show 180cc for 63X57.8 and 203.8cc for 67X57.8.

[Dirtcrasher]

A 200CC piston is about 65MM, so 1MM oversize is 1/65th larger. I still don't think 1mm increases displacement as much as you guys think. I could be wrong, but I'd really like to see the actual formula. Can anyone post it up??


Is the crank stroke on a 200 longer than the 185?

Take for instance the 85 vs 86 200X motor. They both end up about 200CC but they have different bores and strokes.

I know bore x stroke has a place in the equation but IDK how the heck to figure it out.....

Somebody must know?????????????

[trizilla]

i dont know the exact formula either. here's what i do know. mainly the only difference between the 185 and the 200 is bore size. not stroke. i believe the carbs are different also. obviously the 200 being slightly larger. as far as the 85 and 86 200x are concerned, i am almost sure that bore size on both are the same its the stroke that changed. 85 is 57.8mm stroke and 86 is 60mm stroke. stock 85 is about 192cc and i think stock 86 is 199cc. im not 100% sure but could the formula be bore x bore x stroke x # of cyl's?
thought i'd edit this, i think that formula may be for cu. in. displacment not cc's.

[84honda200s]

the carbs very from model to model. im pretty sure most of the 185 and 200 motors use the same carb size. with the exception of the 200x.



here is the formula... well one way to figure it out. Bore x bore x stroke x .0031416 divided by 4


dc bud... trizilla is dead on about the 85 and 86 2oox. the actual displacement of the 2 are totally different.




ooo yea and when you bore 3mm over it does help the performance aspect of the motor a little bit. not a ton but it does wake it up a bit. in my opinion there really isnt one great mod but if you do allot of small mods they all add up to get ya some nice power. ive bin there with both a 185 cylinder, and a 200 cylinder.

[TravEX]

Pi X Rsquared x hgt

185 displacement is: Pi x 992.25 x 57.8= 180.176 cc

67mm bore displacement is: Pi x 1122.25 x 57.8= 203.782 cc

200 displacement is : Pi x 1056.25 x 57.8 = 191.798

You have to move the decimal 3 digits to the left for cc using that formula.

[TravEX]

here is the formula... well one way to figure it out. Bore x bore x stroke x .0031416 divided by 4


It's radius squared, so 1/2 the bore times 1/2 the bore. Yes if you use Pi as .00314159 it will come out correctly instead of moving the decimal after the calculation.

[bmxpsyco04]

Thanks for the great tech. info. I had ordered a 67mm wiseco but i'm gonna sell that right away (payed about $110 shipped, cam w/ rings n pin) and I already bought a 65mm wiseco for about $95 shipped. I'll get my 185 bored to fit the 65mm. Then I can put my bike back together! prolly won't work lol, has had the wiring ripped off for over a year, so i'm sure there will be more questions.