Will 86-87 TRX 250R motor also fit 85-86 ATC250R ?

[whyzee]

just wondering ? guy needs 2 motors and there are some available but they are from TRX's. Will they fit right in our 250R's ?

[lndy650]

not positive but im pretty sure they are identical

[jeffatc250r]

85-89 all interchange. trx and atc

[Dirtcrasher]

^X2 - All the same beside colors, differences in cylinders and the longer rod in the 87 and up TRX motor........

[The Goat]

which one runs harder? long rod or short rod? stock for stock all other things equal

[lndy650]

short stroke revs faster

[The Goat]

but long rod has more torque?

[lndy650]

thats the general belief. the more square the boreXstroke the quicker reving the engine is. and a long rod engine has more torque

[whyzee]

thanks for all the sweet info guys!

[MagicJames]

85-86 does not have a bridged intake, therefore can create more power by less resistance.
As opposed to a 87-89 motor

[KASEY]

thats the general belief. the more square the boreXstroke the quicker reving the engine is. and a long rod engine has more torque

THE BORE AND STROKE IS EXACTLY THE SAME ON ALL OF THE MOTORS!!!!
SO YOU CAN THROW THAT THEORY OUT.....

[lndy650]

the bridged exhaust port allows the port to be much wider witout being a ring snagger therefor making much more power than the older style

the stroke is most certianly longer KASEY

[KASEY]

85-86 does not have a bridged intake, therefore can create more power by less resistance.
As opposed to a 87-89 motor

THE RINGS ARE THE ONLY PART THAT REALLY CAUSE RESISTANCE, THE PORT TIMING WOULD BE THE ONLY PART THAT WOULD CREATE MORE POWER,

[KASEY]

the bridged exhaust port allows the port to be much wider witout being a ring snagger therefor making much more power than the older style

the stroke is most certianly longer on the newr engine KASEY

DUDE ,,its not!!! all atc and trx motors have a 72 x 68 mm bore and stroke,,, and if you have had both cylinders side by side you would see that the top part of the intake port is the same ,, so the ring snagger theory is out the window too!!!

[lndy650]

you have no clue what your talking about do you? a wider exhaust port will always result in more power. and what are you talking about the intake port for?that is irrelevant to this subject

port timing changes what rpm you make power at. why dont you do yourself a favor and buy the 2 stroke tuners handbook and read a bit

[lndy650]

as for the stroke you should do some research before you embarass yourself next time

[KASEY]

ALL ATC ANT TRX CRANKSHAFTS ARE THE SAME,,, the rod length has nothing to do with stroke,,, sorry that you can't seem to phathom it... go to wiseco and look it up they are all the same... . thats why you can run any trx cylinder on any atc because they ARE the same,,,

go back to magicjames post he was talking about the INTAKE PORT!!! thats why my comment ,,,,

[KASEY]

we were not talking about ported cylinders either,,, i am well aware of what porting does,, all facets of porting,, i first started playing with a porting tool over 40 years ago,,, so i am well versed in all phases of porting

[lndy650]

then how can you say a wider exhaust port dosent make more power?

[KASEY]

as for the stroke you should do some research before you embarass yourself next time

:crazy: :crazy: yeah i guess if you looked before yaking you would see i am right,,, i was wrong about the bore ,, stock bore is 66mm ,,, 68 is ,080 over,,,

[KASEY]

then how can you say a wider exhaust port dosent make more power?

i was talking about the intake port and also you were too!!! because the rings are pinned on the intake side,, .. and if you did a little homework you would see that some of the hotrod aftermarket cylinders are going back to a single unbridged exhaust port too,,, so there must not be to much concern about the rings,,,,,,,,,,,,,

[lndy650]

i guess you got me on the stroke i was thinking 81-84 to the newer 85-86 87-89my bad. it dosent matter what side the ring gap is on the rings can still catch on an exhaust port that is too wide. what they have discovered is to make the port more rounded and to use auxillary exhaust ports. these designs are far supirior but the bridged design was better than the square port.

[KASEY]

just so we don't get a bunch of wrong info out of this thread,,,

85 ATC 250R 72 X 66 SHORT ROD 246CC
86 ARC 250R 72 X 66 SHORT ROD 246CC
86 TRX 250R 72 X 66 SHORT ROD 246CC
87 TRX 250R 72 X 66 LONG ROD 246CC ROD IS 5MM LONGER
88 TRX 250R 72 X 66 LONG ROD 246CC PIN LOCATION IN PISTON
89 TRX 250R 72 X 66 LONG ROD 246 CC 5MM HIGHER


ALL CYLINDERS ARE INTERCHANGABLE TO ALL MOTORS WITH THE RIGHT PISTON, WHETHER IT BE LONG OR SHORT ROD,, ALL MOTORS HAVE THE SAME BORE AND STROKE,,

[lndy650]

and just so we dont get any bad info from this thread... a wider exhaust port will always yield more power with no or very little loss on lowend where as changing the port timing and raising the exhaust port will take away lowend power and going too high make the engine very peaky. make sure to leave at least 5mm between the exhaust port and transfers

[Saul]

Quick tip for you 85-86 R guys or 86-89 TRX guys - use two stock base gaskets instead of one to change your port timing. Then use a CR250 head gasket to slightly raise compression.

Cheap and quick increase in power output.

[KASEY]

and just so we dont get any bad info from this thread... a wider exhaust port will always yield more power with no or very little loss on lowend where as changing the port timing and raising the exhaust port will take away lowend power and going too high make the engine very peaky. make sure to leave at least 5mm between the exhaust port and transfers

START YOUR OWN THREAD ON PORTING,,, this was a interchangability thread,, which you seem to be confused about :welcome:

[whyzee]

Quick tip for you 85-86 R guys or 86-89 TRX guys - use two stock base gaskets instead of one to change your port timing. Then use a CR250 head gasket to slightly raise compression.

Cheap and quick increase in power output.

is this true guys???? any dyno proof or just theory, seat of the pants ETC...very interesting, and fun. I love to play with these bikes. What about jetting changes, what did you find as a rule of thumb with that setup?

[jeffatc250r]

is this true guys???? any dyno proof or just theory, seat of the pants ETC...very interesting, and fun. I love to play with these bikes. What about jetting changes, what did you find as a rule of thumb with that setup?

I highly doubt the 10-20 thou is going to make a pisshole in the snow as far as power is concerned by using a double base gasket. A late 80's cr250 head gasket will make about 10 psi more on your compression, atleast that is what it did on one of mine, allowing you to benefit somewhat more with race fuel. If anything, go a hair wider with the ports with a dremel. I believe the general rule of thumb is never make your port wider than 70% of your piston dia. Maybe im wrong about changing the port timing, I just cant see how that would change anything. There are others on here that know how to squeeze the most outta these things.

[Saul]

I highly doubt the 10-20 thou is going to make a pisshole in the snow as far as power is concerned by using a double base gasket.

Believe what you want. OR - you could go talk to some rider, racers and engine builders who have done this for years and years and years. :rolleyes:

That's why I love getting in good with people who have DONE things and applied them to actual situations - when they pass off the knowledge to you one can feel confident in their practice and application.

Again - don't take my word for it. I wouldn't expect anyone to do that. rather, take what I said and go ask a very experienced engine builder who has built the watercooled Honda 250 platform - they'll tell you that two stacked 'stock' size base gaskets will indeed change your port timing.

[Saul]

is this true guys????

Do you think I just dreamed this up & posted hoping that someone would run off and do it and post back their results? :rolleyes:

[Saul]

But what, if any power do you obtain by doing this? No need to get bent, just dont see how that can make any more power. If it does, please explain,......


Maybe things don't come across so well on a forum - but I assure you I'm quite far from bent. :p

Regardless - I threw it out there - take what I said and spend 5-10 minutes in a search engine. Google is your friend. :beer

[KASEY]

hey saul.. that is the oldest trick in the book ,,,, when we raced gokarts we did all kinds of things to cheat in the stock class,,, on the short tracks we ran no base gasket,, on the long enduro tracks we did the double base gasket thing too,,, so i know for a fact it works,, its not a giant power boost,, but sometimes it was enough for a win,,,, i am not so sure it is much of a boost in power as much as it moves the powerband to a different rpm range,,

[whyzee]

Do you think I just dreamed this up & posted hoping that someone would run off and do it and post back their results? :rolleyes:
if that is you on the 250R in your signature, i am thinking you know what you are talking about
:beer

[Saul]

hey saul.. that is the oldest trick in the book ,,,, its not a giant power boost,, but sometimes it was enough for a win,,,, i am not so sure it is much of a boost in power as much as it moves the powerband to a different rpm range,,

Exactly Kasey! :beer I had hoped I'd throw it out there and one of the guys would wanna take their own time to go research it - obviously you didn't need to google squat as you've been around the block - once or twice. :D

[Saul]

if that is you on the 250R in your signature, i am thinking you know what you are talking about
:beer

NO!! Not me - I do talk to the man pretty regularly though. :beer

No friend, I'm just someone who spends a lot of time, maybe way too much, reading 2-stroke boards and old magazines. :p

Then my wife says I probably spend too much time out in the shed working on and applying what I read and learn to the toys.

[x.system]

hey saul.. that is the oldest trick in the book ,,,, when we raced gokarts we did all kinds of things to cheat in the stock class,,, on the short tracks we ran no base gasket,, on the long enduro tracks we did the double base gasket thing too,,, so i know for a fact it works,, its not a giant power boost,, but sometimes it was enough for a win,,,, i am not so sure it is much of a boost in power as much as it moves the powerband to a different rpm range,,

We used to try things like this for ice racing back in the 80's. Ever ran an R motor without a counterbalancer?

[Saul]

We used to try things like this for ice racing back in the 80's. Ever ran an R motor without a counterbalancer?

I bet uncomfortable feeling as your teeth rattled loose from your gums made up for any slight performance gains. :naughty:

[lndy650]

Saul is most certianly right. using one extra base gasket which is usually about 15 thousanths and cutting the head accordingly (or in this case the cr head) will change your port timing. it wont change a lot but you dont want a big difference for trail riding. i use metal spacers with 2 base gaskets. the spacer is usually .025 depending on the engine and the extra gasket adds .010 or .015 depending on the gasket. then i cut the head accordingly. say my cylinder is raised .040 i will cut the head .040 and recut the squish and if i want a tighter squish drop the head even more.
this is a very effective way to gain topend power and the last one i built instead of cutting the head i had the cylinder decked and then played with the squish band. it gets complicated for full mods but an extra base gasket and a cut head for trails is easy and cheap power.

[lndy650]

i ran my 83 without a crank balancer it wasnt that bad. more power but the balancer does help the crank last longer

[Tecate250]

So hehehe i was looking at my spare clutch case and noticed the case would fit my motor. The kicker shaft was too thick to fit through. So my question is the long rod motors would that change there cc value? if you take a atc 250r and put a long rod in it dosent that raise the ccs? What is this i hear about the 85 motor being faster then the 86? And what is the difference in 86 atc and trx motors? If any? As well as the difference in 86-88 trx motors?

[Billy Golightly]

So hehehe i was looking at my spare clutch case and noticed the case would fit my motor. The kicker shaft was too thick to fit through. So my question is the long rod motors would that change there cc value? if you take a atc 250r and put a long rod in it dosent that raise the ccs? What is this i hear about the 85 motor being faster then the 86? And what is the difference in 86 atc and trx motors? If any? As well as the difference in 86-88 trx motors?

No. The rod length has nothing to do with the displacement of the engine, any engine. Displacement is the throw of the crankshaft (stroke) and the diameter of the piston, thats it.

[Tecate250]

Really? So having a large bore and stroke would have the same hp rating as a large bore short stroke but with different torque specs? I was wondering about this when I had my Tecate and thinking of a long rod kit. At first i thought the newer 250rs had a long rod small bore and the older 250s had the short stroke big bore. Wow I have much to learn.

[Billy Golightly]

I didn't say that it wouldn't change the hp of the engine, just not the displacement.

Crankshaft stroke and connecting rod lengths aren't the same thing.

The main changes caused by the different lengths of the connecting rod is:

Dwell time (How long the piston stays at the top, and bottom of the stroke)
The side loads and forces of the piston inside the cylinder (shorter rod lengths cause a more aggressive angle at the wrist pin) which causes friction and accelerates the wear on the piston skirts.
And in 2 strokes, because the Dwell time changes, your port timing in the cylinder itself changes as well, and that can have large effects on the power created.


Stroke is actually how far, in a measurement of distance, the piston travels up and down in the cylinder. The connecting rod just dicatates to piston how far away from (or close to) the crankshaft that it travels that distance.