THE TWTex XR400 Thread.

Re: Thrill-billy85's XR4 build thread.

If you decide to go to a heavier spring, I'll buy those .41s from you. No, they are not oem but are the same weight as oem from 98/99 forward. .39 was the oem rate from 96 till the change.

Re: Thrill-billy85's XR4 build thread.

Irishcoffee said:

If you decide to go to a heavier spring, I'll buy those .41s from you. No, they are not oem but are the same weight as oem from 98/99 forward. .39 was the oem rate from 96 till the change.

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You got a deal, man! I'll put some rides on them, and let you know.

They may not be enough spring for me

Re: Thrill-billy85's XR4 build thread.

thrill-billy85 said:

Ohh. And stock is like .38kg/mm, 5wt oil @120mm, and that's supposed to be for a 175 rider+gear. (The rider weight is scuttlebutt)

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That's about me then. Of course, confirming that would require taking a peek, inside.

Like yours, I got busy today. Got the new X-Ring chain installed, nice little learning experience & I found a great YouTube tutorial on easily installing the master link using a bolt & a c-clamp.

Got the power outlet installed & working, started her up (97,000 kicks, Monkey Wrench here I come) and headed out in the cold drizzle for an inspection. I guess because of the weather my local Quickie Mart decided not to open today. Anyhow, had a cold but fun 7 miles although very narrowly avoided a major wreck when Grandma pulled out directly in front of me!

You're going to love the gutsy pull of this thumper. I'm running a 14 x 42 & it's a smile a mile!

Re: Thrill-billy85's XR4 build thread.

XRs have a kicking pattern that they like. I would push mine through about three times with the gas on, then choke it if cold. Find TDC with the kicker then give it a good steady kick. You don't have to kick at warp speed, but it has to be solid and steady. The number one romper room rule is absolutely no throttle twist during the start procedure. Coming from two stroke MX bikes I had a hard time not twisting while I kicked. Watch your right hand as a twist is almost natural while kicking. If you find you are twisting throttle move your hand up to the fluid cover of the front brake while you kick.

No charge for the free advice!

Re: Thrill-billy85's XR4 build thread.

Yeah but... What if you got a pumpa cob???

Re: Thrill-billy85's XR4 build thread.

And then theres this:
I gave up kicking my XR4 several years ago!
And at my age it was not a day too soon.

Re: Thrill-billy85's XR4 build thread.

Endurordr, did you use an entire 400ex bottom end, or just add the left side stator cover and starter asst?

Re: Thrill-billy85's XR4 build thread.

I see you gave up on chain maintenance as well as kicking!

Re: Thrill-billy85's XR4 build thread.

Yeah but his zip-tie game is strong.

Re: Thrill-billy85's XR4 build thread.

thrill-billy85 said:

Endurordr, did you use an entire 400ex bottom end, or just add the left side stator cover and starter asst?

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Purchased a TRX bottom end off fleebay then split the cases and used the TRX Crankshaft and everything on left side. kept the XR trans, kicks shaft, clutch and top end.
To keep it simple I used all TRX electrics (CDI, rectifier/regulator - all wiring etc.) that way I have the DC circuitry I wanted for battery already worked out.

I tried the crank adapter a year earlier and DO NOT RECOMMEND that route. Ruined a bunch of parts when it crapped out. The Joe Racer design crank adapter used a 12mm bearing for the sprag gear, the stock honda TRX uses a 24mm bearing.

Trust me - after several times in that motor go with all Honda parts - if you plan to try it.
Get a TRX bottom end and just use the crankshaft and electrics - keep the kick for backup (although I never use mine - )

The trick is making a good battery mount!

Re: Thrill-billy85's XR4 build thread.

EnduroRdr said:

And then theres this:
I gave up kicking my XR4 several years ago!
And at my age it was not a day too soon.

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smart alec!!!

Re: Thrill-billy85's XR4 build thread.

So big day today. I got my cabinet put together yesterday. I honestly dont see how they're making any money off these things. I mean, it takes like $40 in hardware just to hold this thing together. Lol. This pic was while in progress, I'll get an updated one tomorrow.



Then I did one of the cases for the BrokeForce 750... Just to see what soda would do to it. Soda blasting is not very abrasive, and pretty much water soluable, it doesn't hurt gasket surfaces, or fragile components, or seals. Basically it just barely cleans muck off of whatever substrate its adhered itself to. I'm not powdercoating these, just paint, so this should be suitable.



Then it was time for my cylinder head. Blasted the combustion chamber with the valves in. Removed the valves, and blasted the ports.

This exposed some of the nastiest casting flaws I've seen. Mother of god. I didn't get a friggin picture of the casting flaws in the intake, for a bef/aft comparo, but I did get one of Tue exhaust, which wasn't nearly as bad as the intake.

I'm doing a light blueprint port job on this head. Basically removing flaws, and smoothing everything out. Not gonna remove very much material, and plan on staying away from the bowls for the most part. The exhaust will be mirror polished to prevent carbon buildup. The bowls will be marginal.

Another problem area is the transition past the bottom edge of the valve seats. Honda did a terrible job there too. So far, I've only done the intake port. More tomorrow.

Enjoy the cylinder head porn















I spent a lot of time on the port divider as it was very asymmetrical. This creates pressure differences and uneven fuel disbursement both in the intake plenums, which translates into the combustion chamber. Again, I friggin FAILED miserably taking before pics, but there was a rough flaw right in the smack middle of the divider, as well as a weird hump/bump on the floor of the left side. All pretty now. (I am by no means a professional at porting, and I'm sure that shows. I DO understand many of principles that apply to create good flow characteristics, and how to apply them.)

Re: Thrill-billy85's XR4 build thread.

Cool stuff going on there, I'm bringing mine over to you!

Re: Thrill-billy85's XR4 build thread.

Bring it! I'm an hour and some change from dallas

Re: Thrill-billy85's XR4 build thread.

Are you blasting with baking soda?
That all looks great!!!

Re: Thrill-billy85's XR4 build thread.

poser said:

Are you blasting with baking soda?
That all looks great!!!

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dr pepper!

Re: Thrill-billy85's XR4 build thread.

Xl soda grains

Re: Thrill-billy85's XR4 build thread.

thrill-billy85 said:

Xl soda grains

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ok, cool.
I've seen people blast carbs with baking soda to clean them up.
I kept thinking, "man, he's going thru a lot of Arm and Hammer!"

Re: Thrill-billy85's XR4 build thread.

Nice work!

Re: Thrill-billy85's XR4 build thread.

Poser- I recirculates the media, bit Tue soda wears out fast.

Irish- thanks man. Another head porting update in a little bit.

Re: Thrill-billy85's XR4 build thread.

Okay I'll just do all the before, then all of the after pics. There's a few where I'm pointing out the flaw that I'm most focused on.












Finished intake. I wasn't going for a mirror finish here. That can actually hurt things.


Intake bowls


Exhaust roughed-in


Exhaust smoothed


Other side


Polished. Now, the polishing is NOT because air flows faster over it. What I'm trying to accomplish is take as much surface area out of the ports, without increasing volume too much. Reason for this is two-fold. First it keeps heat absorbsion down. Second, it makes it harder for carbon to build. You want the exhaust gas temperature to be high (hotter gas flows faster) without transferring that to the head. Basically its to keep the thermal exchange to a minimum.




Again, I'm NOT a professional, nor do I think this job is at that level. I merely enjoy doing this stuff on my own. Keep the "why don't you just pay a professional?" to yo **** self!!!

Re: Thrill-billy85's XR4 build thread.

Ceramic coat the exhaust ports?

Re: Thrill-billy85's XR4 build thread.

That's another (and better) way to do it. I'm not sure if you're asking if that's what I did here, but no, they're just polished.

Re: Thrill-billy85's XR4 build thread.

I haven't looked into polishing at all, so this is not from my personal experience (I just don't think I care that much about how pretty the ports are), however, I was told this a while back by an experienced machinist and engine builder (again, that's not me):

"Polishing the ports smooth removes all the little dimples that are there to keep the mixtures suspended and off the port walls, and will slow the movement of the gases through the engine."

So I guess there will be arguments for both sides. I just like to share what I've heard, and if you know differently, you can share, too, I guess.

Maybe this is a topic that deserves its own thread...like an oil thread.

Re: Thrill-billy85's XR4 build thread.

Pretty! What are you using to grind/polish the ports?