Trx400ex = xr400? |
Honda TRX Discussions for the Honda TRX, 90, 250, 300, 400, 450, 700

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post #1 of 9 (permalink) Old 06-10-2012, 12:11 AM Thread Starter
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Trx400ex = xr400?

Are the engines the same?

Some accessories may be the same, what is interchange?

I am needing to replace my starter and clutch plates and springs.

My quad is a 2005.

2005 Honda TRX 400EX, FMF Slip on, K&N Air Filter, Pro Armour XC Nerf Bars, Big Gun CDI. Insert other ad placement here.

42 Pilot, 170 Main, 2 1/4 Turns out
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post #2 of 9 (permalink) Old 06-10-2012, 04:00 AM
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It has been done before I'm sure, but there are differences between the two engines. I would do some searching online to see what all would be involved in trying to do a swap, or borrow some parts.
The XR400r is a kickstart engine, and I'm sure the gears and clutch are beefier for the atv application. They also use a different carb, cam, and I believe the rear engine mount is different also. Without having an e-start on the XR the cases are probably different also.
It would probably be easier to just get the clutch and the starter used on ebay or oem or aftermarket for the 400ex than try to adapt parts from the XR400r. But like I said, do some searching and see what you find out, as practically all sport quad engines were derived from dirt bikes.

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post #3 of 9 (permalink) Old 06-10-2012, 10:08 AM
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doing an xr650 motor swap would be cooler

2004 400ex

yoshimura slip on
uni filter
426 kit
moose bars
dg bumper
msr clutch
itp c-series rims
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post #4 of 9 (permalink) Old 06-11-2012, 12:11 AM Thread Starter
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Just heard that info, so I thought that I it was somewhat true, then we could have an option when searching for certain parts.

Thanks for he info, I don't have any intention on buying parts to see if they fit, I don have a spare XR here to pull parts from.

Ya. A 650 would kick A$$, not too sure if the frame would handle all that power though....

2005 Honda TRX 400EX, FMF Slip on, K&N Air Filter, Pro Armour XC Nerf Bars, Big Gun CDI. Insert other ad placement here.

42 Pilot, 170 Main, 2 1/4 Turns out
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post #5 of 9 (permalink) Old 06-11-2012, 12:19 AM
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Moose could probably tell you the differences between those engines.

Most 4-wheeler problems are caused by a loose nut connecting the handlebars and the seat!!

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post #6 of 9 (permalink) Old 06-11-2012, 01:07 AM
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Yea the 400ex frame could handle it. My mechanic had one at it was sick. Outran anything around

04 kicker
Little bit of this little bit of that but a whole lot of fast
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post #7 of 9 (permalink) Old 06-11-2012, 03:41 AM

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x2 on the 650ex being super if you could only make it have reverse

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post #8 of 9 (permalink) Old 06-11-2012, 07:56 PM
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There's very few differences beween the XR400 motor and the 400EX motor. A lack of kick starter hardware in the quad motor is one, and a different cam profile is another, but for the most part everything else will interchange. Clutch mechanism is the same and I believe all of the transmission components are too, with exception of the quads with reverse. Just look at an online parts diagram and compare part numbers. The motors will interchange between the vehicles with no modifications at all, the cases are identical.

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Last edited by rich250rracer; 06-11-2012 at 08:02 PM.
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post #9 of 9 (permalink) Old 11-15-2013, 07:29 PM

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Originally Posted by rich250rracer View Post
The motors will interchange between the vehicles with no modifications at all, the cases are identical.
The cases of the two engines are not identical. They will not simply interchange between vehicles.

I just got done putting a 2000 TRX400EX engine in my street-legal 2002 XR400R. The swingarm bolt hole in the rear of the engine cases seem to differ by a few millimeters. Since that's the engine mount that can't be changed, the other mounts (except for the bolt-on front mount) must be modified.

With the TRX engine in the XR frame and the swingarm bolt in place, the front (bolt-in aluminum) mount will mate up to the engine like it's supposed to, but the lower (welded-in steel mount) is a couple millimeters low and to the rear.

Also, the upper (bolt-in aluminum) mount at the cam cover is about a half-inch to the rear. No problem really, just mock up new ones out of cardboard, lay out the design on 1/4-inch aluminum, then drill the holes and cut the mounts out with a bandsaw.

The welded-in steel mounts at the bottom of the frame must be removed (cut the welds with a cut-off wheel in a die grinder) and re-welded in their new place with the mounts bolted to the engine.

The end result is the engine being tilted forward about a half-inch, due to the slight difference between the TRX case and the XR case. One must therefore also re-locate the welded steel front muffler mount on the XR's subframe, and modify the airbox boot to come forward that half-inch to hook up with the carb's new location.

Engine internals are mostly identical, with the exception of the crank (TRX is longer to make room for the starter clutch & gear under the flywheel), cam profile (more low-end torque for the ATV), clutch (heavier duty for the ATV).

First gear is almost the same, but then the TRX has progressively lower gears compared to the XR...

2.830, 2.620, 1.840, 1.400, 1.120, 0.930

2.826, 2.916, 1.937, 1.473, 1.181, 1.000

The countershaft is a bit different, in that the non-sprocket end that you see under the clutch basket is a bit bigger than the XR's. That keeps one from installing the kickstarter idler gear from an XR4. I think I can get around that by machining a different bushing. Then simply install my XR right case cover and kick-starter.

A 2005+ engine with reverse would be nice, but those engines are about 500 dollars more than a 1999-2004, and I've spent a ton of money on this project already.

I used a TRX400EX wiring harness, CDI, Regulator / Rectifier, and ignition to eliminate mating troubles between the engine and bike. That wasn't a drop-in affair either... scads of cutting and splicing (solder, then heat-shrink tubing) to avoid thick wads of extra wire in some spots and too short of length in others.

Battery and box is from a DRZ400, with welded-in mounts on the left side of the subframe (opposite side of the muffler). It starts and runs great, with 14.5 Volts DC at idle.

At times like these, Honda's lack of modularity between seemingly similar engines can be quite maddening. It has been a lot of work over the past few weeks, but I love to tinker, and I now have one damned nice XR400.

Last edited by Stretch67; 01-14-2015 at 09:32 PM.
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