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

[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

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

[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.

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?