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XR400EX

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Alright guys, so I am new here so before I get started I just wanted to make a few opening remarks...

*If this post is in the wrong section I apologize and if it's possible to move please do so and I know this topic has been brought up before somewhere but I can not find it so here it is again...and hopefully gives more information on this build.  Also if anyone has questions about this ongoing project I should be able to answer them.  The reason I have decided to finally make this post is because I have finally got it all buttoned up (engine wise) and seems to be running well...aside from a few complications which maybe some of you can help out with.  Lastly, my apologies for the long post I felt that I should include most things I did because in my own research, this project is not talked about much at all it seems.

So here it is, I have been working on this project for around 5-6 months now and, mind you, it started as a basket case so it doesn't look great cosmetically by any means and most of the plastics are either gone or damaged but mechanically, all parts appear to be there and it working condition.  What I have done is exactly what the title says, placed a 400EX engine into an XR400 frame.  Now, most people that do this start with the XR400 and find a 400EX engine to put in, but I was given a frame and engine with a buck of extra bolts, nuts and clamps.  After two years of sitting in my basement I decided to test if the engine turned over, great news, it did.  SO, that motivated me to put it in the frame and it DOES fit, but the bottom frame mount is too far up to be used, but with three other mounts tightened down, it was fine.  BAD IDEA, turns out the engine had ZERO compression and needed a new top end because whoever had it last put the piston in backwards and bent the intake valves.  After a couple weeks I found the time to get the engine bored out 1mm over and changed the valves.

*REBUILD*

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Got the 400EX taken apart and slowly starting to find the issues associated to ZERO compression

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According to the piston, two intake valves were coming in contact with the piston itself, luckily this appeared to be a fresh rebuild...otherwise it may have detonated and caused many other issues..

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And just as expected...bent intake valves...which mean possible cracked or damaged valve stems...

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Clearly, these are the culprit for no compression...to the left is the PVC pipe valve spring compressor I used to get the valves out, but not in I will show that tool later on.

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Further investigation revealed build up of some sort on the piston wall, so after attempting to hone this away I quit and took it to get it bored out.

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Knowing that I had bent the valves, I decided it was best to check the timing chain and low and behold...it was slapping all over the place inside the case when it "started" for the first time I assume...

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Removed both inner and out clutch baskets, oil pump gear and drive gear to get to chain and found out that the oil pump does not need to be removed to get to the chain(rookie mistake) and also discovered that the springs behind the outer clutch basket move freely which is not what they are supposed to do I am guessing...so that will be replaced.

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New chain in and clutch baskets are torqued back down with a new piston on top...another rookie mistake...make sure to put the piston on BEFORE putting the jug back on...yeah felt like an idiot after I did that...

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Very hard to tell but from my measurements...the original chain(left) was stretched by half a link I believe

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Also found out that at some point the crank was replaced....just hope that whoever put the piston in backwards didn't do anything wrong here...

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Seated new valves(ended up going back through a few more times after I took this picture)IMG_3244.jpg

Valves and springs put back in the head and retaining clips in...I'd like to think I saved myself some money by making a compressor tool in the upper right corner

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Used a clamp and I duct taped a copper crush washer on the other end to help protect the head....the thinking was that the copper would dent before anything else would

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And finally all back together...but keep in mind this motor still hasn't been started in 4 years at the least....

**Starting**

1/15/17

Bike officially started today, but it is really cold here so it was running lean with a high idle and slight back fire when revving...will try again when weather warms up...

2/19/17

Had a nice 50 degree day and decided to take it out and try to start it again and she still comes to life...but the idle was still high in this video...I was able to get it adjusted to a nice even idle....the only problem was that it had to be at full choke...vacuum leak?  I figured since I am running an XR400 carb right now it probably won't run the best anyway...but full choke shouldn't be necessary regardless...if anyone has any tips or suggests feel free to let me know...willing to try out other carbs without the insane price tags..

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Of the four available engine mounting locations on the XR400 frame(I think) I only used three but have plans to move the bottom one down to put that to use..

Closing remarks

This is my first post and I did learn a significant amount in the process but keep in mind this is by no means complete so I will still be figuring more things out as I go...and as I said I have not many posts...(one really) about this project being done and the details of fitment.  The most I saw were people guessing that it would not be possible to fit this machine, but I believe that I can say it is "fitted" now but a few more kinks just need to be straightened out...other than that I am looking forward to finishing it up and going for a ride...one day!

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Edited by XR400EX
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Hi i converted my XR400 to electric start last year, keeping the standard engine but changing the crankshaft / cdi & many other parts, does yours start on the electric start ? did you use the trx400 cdi & harness 

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So should I check the valve lash again to be sure? I had a feeling they needed to be rechecked because they're a little too noisy while running

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It's all good just looking for other possibilities and it doesn't hurt to go over it all when it's all put back together

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Make sure you fit the XR4 cam shaft to the EX engine. They are a different profile & lift. The XR4 one is better all round where the EX one is more for low down torque & nothing else.

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On 2/21/2017 at 2:29 PM, bobmartin said:

Hi i converted my XR400 to electric start last year, keeping the standard engine but changing the crankshaft / cdi & many other parts, does yours start on the electric start ? did you use the trx400 cdi & harness 

Any pointers y'all can give in regards to the trx crank swap route? How bad is the electrical?

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6 hours ago, Still-learning said:

What electrical system are you using?? TRX or setting up your own? What country?

Im here in California,US, after reading these forums till my eyes bleed, i will probably go with the trx400ex stator, harness, aftermarket CDI, and somehow try to incorporate the baja designs dual sport wiring ..

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2 hours ago, littleredridingwood said:

Im here in California,US, after reading these forums till my eyes bleed, i will probably go with the trx400ex stator, harness, aftermarket CDI, and somehow try to incorporate the baja designs dual sport wiring ..

Hi I tried to keep the Xr400 as standard as possible, you need quite a few trx parts i fitted the trx crankshaft & generator cover etc, but i wanted to keep the xr generator/flywheel/pulse coil etc therefore i mounted the trx one way clutch on the xr400 flywheel which involves drilling the flywheel, you need a different cdi box as the standard one does not work at low enough rpm for the electric start i bought a cdi from www.hpi.be ( horse power engineering ) for a battery i fitted an "Allstart 550" lithium boost pack in a rear fender mounted tool bag, the xr400 already has a 12v supply used for lights/hooter etc so i fed this to the 12v charge input on the boost pack as it has its own regulated charge internally, therefore all the standard xr400 harness etc I'm very pleased with the final job 

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What electrical system are you using?? TRX or setting up your own? What country?

I used the TRX harness as it worked best with the TRX Stator and other electrical components which came with the motor. I also found that if you go this route getting a nice lightweight and small battery would help. I went with one of those antigravity LiPO4 batteries. It’s supposed to be pretty good and so far(6 months or so) it has held up quite well. Not sure if anyone is interested but this is how I mounted it.IMG_1511296057.840231.jpg
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8 minutes ago, bobmartin said:

Hi I tried to keep the Xr400 as standard as possible, you need quite a few trx parts i fitted the trx crankshaft & generator cover etc, but i wanted to keep the xr generator/flywheel/pulse coil etc therefore i mounted the trx one way clutch on the xr400 flywheel which involves drilling the flywheel, you need a different cdi box as the standard one does not work at low enough rpm for the electric start i bought a cdi from www.hpi.be ( horse power engineering ) for a battery i fitted an "Allstart 550" lithium boost pack in a rear fender mounted tool bag, the xr400 already has a 12v supply used for lights/hooter etc so i fed this to the 12v charge input on the boost pack as it has its own regulated charge internally, therefore all the standard xr400 harness etc I'm very pleased with the final job 

Nice! I literally just got off the phone with "Microstart" and they strongly advise not to do this. Lol! They say that if the jumper leads are always connected to power, the cells can drain beyond repair, and can also back charge and explode the cells... interesting thought keeping the stator/DC systems.  

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The booster has a separate input for charging it from a cigarette lighter in a car & this is what i have used, the lights on the boost pack show it charging while the xr is running then after about 15 minutes approx the lights stop as it is fully charged, the main leads which go to the starter solenoid & earth have no other feed 

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You have two factory Honda CDI’s that can be used with your setup. TRX400ex or XR250r 1996 & on. The XR part give a little more timing advance & a higher rev limit.
Non genuine units are also available.
If using the standard XR4 stator & pulse generator an XR650 CDI must be used.

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44 minutes ago, Still-learning said:

You have two factory Honda CDI’s that can be used with your setup. TRX400ex or XR250r 1996 & on. The XR part give a little more timing advance & a higher rev limit.
Non genuine units are also available.
If using the standard XR4 stator & pulse generator an XR650 CDI must be used.

I also have a trx400 & the plug is not the same as the xr400 cdi therefore i fitted the HPI one

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