85 atc cylinder questions...

[jcs003]

any info on set-up for an 85 atc cylinder?

-jetting changes.

-cylinder and head differences.

-powerband differences.

i previously had and 86 cylinder with long rod and spacer plate.

-cylinder is on its first bore and is unported.

thanks for any info i may recieve.

[SilverLake250R]

That is exactly what the previous cylinder I ran was. 85 ATC cylinder, unported, but mine was 3rd bore. It was pretty smooth, but had a decent hit for an unported cylinder I thought, and with just an FMF Rev pipe and a stock carb I could just edge out a stock 08 YFZ in a sand drag. However, I can't comment on the head because I have always ran a cool head w/ 20cc dome. Now I have a ported 88 cylinder and it is much better IMO, and when I ran it last year with the same carb/pipe, the jetting was still very close. This year I got a Sparks TT pipe and 38 A/S and the jetting was richer with the new setup.

[86 Quad R]

which bottom end(crank) do you plan to run with this cylinder? if a long rod, i suggest you get an 87-89 cylinder to run. otherwise i'd go with a short rod crank. reason being, you wanna eliminate having to use a spacer plate as they tend to decrease the crankcase pressure and getting away from the characteristics that make the R engine run as well as it does. this isnt nearly as critical/noticable when running a b/b setup but nontheless effected.

[jcs003]

it is an 86 bottom end with a 87+ long rod crank.

carb is an 38 lectron.

i will have to use the spacer plate as i did with my 86 cylinder.

[86 Quad R]

then why are you switching?

[jcs003]

Originally posted by 86 Quad R
then why are you switching?

the sleeve cracked and it was cheaper to get the whole package from BDT motorsports than get my cylinder resleeved with piston and such.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=270586252792&viewitem=&sspagename=STRK%3AMEWNX%3AIT

[86 Quad R]

ahhhh i gotcha.... then go for it. :cool:

[jcs003]

Originally posted by 86 Quad R
ahhhh i gotcha.... then go for it. :cool:

thanks. i just wanted to make sure all my bases are covered before i reassemble it. i have been told its a faster cylinder than the trx, but they arent as reliable.

[86 Quad R]

Originally posted by jcs003
thanks. i just wanted to make sure all my bases are covered before i reassemble it. i have been told its a faster cylinder than the trx, but they arent as reliable.

cant believe everything you hear..... i've got an '85(crate)engine that i've been running nearly 15 years now and i'm just on the second bore. :p

[jcs003]

Originally posted by 86 Quad R
cant believe everything you hear..... i've got an '85(crate)engine that i've been running nearly 15 years now and i'm just on the second bore. :p

good to hear sir:D

i assume i will have to richen my metering rod. there is no intake bridge so i believe i will have more intake volume. correct me if im wrong...

[SilverLake250R]

Didn't you say your old cylinder was an 86? They don't have intake bridges either...it should be very close to the same.

[jcs003]

Originally posted by SilverLake250R
Didn't you say your old cylinder was an 86? They don't have intake bridges either...it should be very close to the same.

ok good. i havent looked at it in a while.

[atvmxr]

Originally posted by 86 Quad R
, you wanna eliminate having to use a spacer plate as they tend to decrease the crankcase pressure and getting away from the characteristics that make the R engine run as well as it does. this isnt nearly as critical/noticable when running a b/b setup but nontheless effected.

hmmm, never heard that before. Back in the day the spacer plate was the setup to have for MX. the spacer setup increased crankcase volume (which I suppose would lower the pressure) to improve low end power. anyway felt like throwing my 1.5 cents.. :)

I got a 85-ported cylinder & rebuilt engine bottom end from bdt motorssports and it is the strongest running 250r I own, I have a pre jetted 39 pkw, fmf faty pipe, 13/38, and run pump gas, for a 66.5 bore, it rips most stock 450's, :-)

You should be set with the 85 cylinder by bdtm.

[atv fan 28]

Originally posted by atvmxr
hmmm, never heard that before. Back in the day the spacer plate was the setup to have for MX. the spacer setup increased crankcase volume (which I suppose would lower the pressure) to improve low end power. anyway felt like throwing my 1.5 cents.. :) I had a spacer plate on my 310 6mil when i got it, but after talking with Tim@ Titan Racing he convinced me to get rid of it. Like 86 Quad R said and also Tim, you lose crankcase pressure. Tim said my motor will run better without it.

[jcs003]

do you guys go back and retorque the cylinder and head bolts after or during the break-in period???

[deathman53]

I always re-toque them. Usually after the first tank of gas.

[86 Quad R]

i retorque after the initial breakin ride and also take this opertune to do a final compression check.