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So last year I purchased a 86 TRX. Now I’m in the process of rebuilding the motor. After some research I’ve realized I have a 86 ATC bottom end and a 85 top end with no port and a 87 or later crank. Also before I blew it up it had a 87-89 piston with no spacer plate. I never could get it dialed in. This time around I plan on running a 85/86 piston with a spacer plate and will have the cylinder ported and polished. Is this a safe setup for woods riding or would a short rod crank with no spacer plate be better? Help me out!!
 

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imo i wouldnt port a 85 cylinder.i would do a 87-88.and if your cylinder is under 68mm no reason to run a 85-86 piston and spacerplate.
 

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Discussion Starter #4
I have a 38mm air stryker and vforce3 reed cage on intake and PT trx89race. It’s what I have without spending a whole lot of money.
 

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imo i wouldnt port a 85 cylinder.i would do a 87-88.and if your cylinder is under 68mm no reason to run a 85-86 piston and spacerplate.
Could you provide some supporting information about your statement? The op's proposed engine set up is pretty much exactly what my son has powering his R and it flat out rips. He humbled a raptor 700 and a yfz in a 300 foot drag this summer.
 

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I would check out your ignition system before you fire up the newly rebuilt engine just to be sure. If you can't get it dialed in jetting wise it could be a contributing factor. Also a leak down test can save you a ton of money and frustration....
 
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Go ahead & run that long rod crank with an 85-86 style piston & spacer plate. I ran that combo in my 86trx for over 20 years & never had any issues. You can also have that 85atc cylinder ported & set up for woods riding & you will probably love it. OEM cylinders can be made to run very well & there reliable.
 

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Could you provide some supporting information about your statement? The op's proposed engine set up is pretty much exactly what my son has powering his R and it flat out rips. He humbled a raptor 700 and a yfz in a 300 foot drag this summer.
what do you need to know.the 85 cylinder has the worse factory port and without the intake support like the 86+ i wouldn't spend the money to port it.some like the sr piston as for cylinders the intake support on the 87-88 and port is also better.so not sure what your question is.ask and i can try to answer.
 

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If you have a top notch 250R engine builder like Pete at Hybrid Engineering set up your cylinder you will have nothing to worry about. Pete can take your cylinder and make it do everything you want it to. Like I said before my son's R has pretty much the same engine set up as you are going with. It is a very respectable engine.
 
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I’m actually fortunate enough to have a father who is willing to provide his expertise for free. He ports! I polish!

As far as air leaks...i had a faulty crank seal that proved to be the culprit for this rebuild.
 

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That's cool you and your Father work together like that.
 

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That's way cool your dad & you are building it together. My dad helped me work on my 86 quite a bit when I was learning.
 

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So last year I purchased a 86 TRX. Now I’m in the process of rebuilding the motor. After some research I’ve realized I have a 86 ATC bottom end and a 85 top end with no port and a 87 or later crank. Also before I blew it up it had a 87-89 piston with no spacer plate. I never could get it dialed in. This time around I plan on running a 85/86 piston with a spacer plate and will have the cylinder ported and polished. Is this a safe setup for woods riding or would a short rod crank with no spacer plate be better? Help me out!!
As long as you are below 68MM bore, you can use the 85 cylinder & Long Rod crankshaft with no spacer plate needed. If going with the 85-86 piston kit and Long Rod; use a 3/16" spacer late + two OEM base gaskets (spacer not needed with short rod crankshaft). Keep in mind neither setup is better than the other (other cylinder options like 87-88 will improve performance), except the 85-86 piston kits allow you to go to 69.50MM bore.

For WOODS; the emphasis should be on Low to Mid range power, therefore the Long Rod crankshaft is a better option than the Short Rod. Going to a stroker crankshaft like +4MM is your best choice as it increases low to mid range TrQ & Power....an OEM BDT276CC aka 68MM (67-69.50) bore x 76MM stroke (+4MM) is a great WOODS engine with a lot of TrQ & HP down low for WOODS...winner of many MX, XC & TT National events the last +7 years.

As American Opel-Martin stated; the 85 cylinder is fine, however; each progressive year Honda made small subtle changes to each cylinder. The 86 is slightly stronger than the 85, the 87 is a good improvement in reliability (less piston wear-longer life), the intake design & support as well as exhaust track angle & volume, the 88 cylinder (88 is 89 cylinder) is the best of all since it has all the subtle changes Honda incorporated over the years of development.

On builders; perform your due diligence, start with this forum, FB, and look at whose building winning race engines across MX, TT, XC, WOODS the past 7 years. Also who is available to answer questions, who stocks all the 250R parts, and who promotes 250R's, travels to National events, ect...the answer then becomes obvious.

Any questions PM or call me directly at BDT Motorsports, here to help as needed.

Great to read your Dad & you are involved as a Team; "he ports & you polish"....awesome. Best of luck,

Carlos
 

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Look another sales pitch......
 
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As long as you are below 68MM bore, you can use the 85 cylinder & Long Rod crankshaft with no spacer plate needed. If going with the 85-86 piston kit and Long Rod; use a 3/16" spacer late + two OEM base gaskets (spacer not needed with short rod crankshaft). Keep in mind neither setup is better than the other (other cylinder options like 87-88 will improve performance), except the 85-86 piston kits allow you to go to 69.50MM bore.

For WOODS; the emphasis should be on Low to Mid range power, therefore the Long Rod crankshaft is a better option than the Short Rod. Going to a stroker crankshaft like +4MM is your best choice as it increases low to mid range TrQ & Power....an OEM BDT276CC aka 68MM (67-69.50) bore x 76MM stroke (+4MM) is a great WOODS engine with a lot of TrQ & HP down low for WOODS...winner of many MX, XC & TT National events the last +7 years.

As American Opel-Martin stated; the 85 cylinder is fine, however; each progressive year Honda made small subtle changes to each cylinder. The 86 is slightly stronger than the 85, the 87 is a good improvement in reliability (less piston wear-longer life), the intake design & support as well as exhaust track angle & volume, the 88 cylinder (88 is 89 cylinder) is the best of all since it has all the subtle changes Honda incorporated over the years of development.

On builders; perform your due diligence, start with this forum, FB, and look at whose building winning race engines across MX, TT, XC, WOODS the past 7 years. Also who is available to answer questions, who stocks all the 250R parts, and who promotes 250R's, travels to National events, ect...the answer then becomes obvious.

Any questions PM or call me directly at BDT Motorsports, here to help as needed.

Great to read your Dad & you are involved as a Team; "he ports & you polish"....awesome. Best of luck,

Carlos
best post. from best builder. bdt carlos simply the best.


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Clearly the OP is on a budget & just wanting info to make his combination of parts work. He also stated that his dad was going to be porting the cylinder so obviously their mechanically inclined. He also never said anything about looking for an engine builder so there's no reason to do his due diligence & research builders...That 85 cylinder on an 86 bottom end with the long rod crank & 85-86 piston & spacer will work very well... American Opal said 85 cylinders are not worth messing with & there weak but that's only true if there ported for all out drag racing. The 85 cylinder on an engine set up for woods riding will last as long as any of the other oem cylinders would.
 

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Matuus, Let's just agree to disagree shall we? ESR is exactly the builder Carlos described. Has just about everything on hand that you need to build an engine. Has first hand knowledge of 250R's from day one. Rode and raced 250R'S from first production. Offered humongous prize money at 2stroke nationals. Developed and produced a new and innovative cylinder. Does his own work in house!!!!!!!!! And he showed up at a 250R event in our local dunes! He spent an entire day riding and sharing his wisdom with the 250R community.
Does Carlos personally do any of that? Or does Carlos sit at his desk farming everything out and play keyboard commando online? I think the latter is the accurate assumption..... I prefer taking my cylinders to someone that isn't jumping on every post on the forums. I prefer a builder that isn't online beating his own drum. I prefer a builder that actually does his own work. Pete at Hybrid Engineering, Arlen at LED, Eddie at ESR.
 
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Matuus, Let's just agree to disagree shall we? ESR is exactly the builder Carlos described. Has just about everything on hand that you need to build an engine. Has first hand knowledge of 250R's from day one. Rode and raced 250R'S from first production. Offered humongous prize money at 2stroke nationals. Developed and produced a new and innovative cylinder. Does his own work in house!!!!!!!!! And he showed up at a 250R event in our local dunes! He spent an entire day riding and sharing his wisdom with the 250R community.
Does Carlos personally do any of that? Or does Carlos sit at his desk farming everything out and play keyboard commando online? I think the latter is the accurate assumption..... I prefer taking my cylinders to someone that isn't jumping on every post on the forums. I prefer a builder that isn't online beating his own drum. I prefer a builder that actually does his own work. Pete at Hybrid Engineering, Arlen at LED, Eddie at ESR.
BDT does 100% our own work, all in house; anyone that has visited, knows BDT or me directly knows this is 100% true. On the other hand; everything you just stated is based on misinformation, spread by those that don't know, have never visited BDT, and are jealous & hateful...all based out of a dying website, made up of those kicked out of this very site for hateful attacks.

Why don't you 'farm' yourself back to the regions of hell, the bottomless pit of hatred aka the "other site"...the little that is left of it.

Carlos
 

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hate this. lol



i have the best. bdt built engines.
bdt261 oem
bdt363 prox
bdt431 puma
bdt561 saber
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