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Discussion Starter #1
I’ve owned my 2000 400EX about a month now. Got it bone stock with only issues (I thought) was leaking carb and toasted rear axle bearings. I’m still not familiar with good brands and ones to stay always from. I ordered a complete carb for 48$ and complete axle bearing carrier for 35$ off eBay.

I also ordered an uni filter, hmf performance full exhaust and a DynoJet kit+42 piliot jet.

With everything installed I was very happy with it except gearing so I dropped from 15/38 to 14/39 with a new gold oring chain, all from primary drive. I knew they are cheap but I wanted to test the gearing before I dropped cash on nice gears.

Problems:

Hmf’s head pipe is a different shape and my clutch cable was laying on it so I went and got some of those spark plug heat sleeve things for it but it’s still making the cable stick after a hard ride and cool down.

With the new carb, I put in the DynoJet needle to same length as stock. 170 main, 42 piliot, and about 2.5 turns out on the idle screw. It won’t start with out choke and even after warm has a weird idle. Sometimes it idles high, other times it barely idles and dies, usually high then starts to drop until it dies. It doesn’t pop through the exhaust on deceleration but I noticed about the first 1” of the head pipe starting to turn orange when riding at night. It doesn’t bog or blow black smoke so I think I’m pretty close on the jetting

And here’s the big one that I’m all butthurt about lol. I rode for about 2 hours Saturday, moderately hard on it and it did great, no issues. Sunday I took it to my dads, he went first and babied it 1st through 3rd. Came back, shut it off, we talked for a few minutes. I got on, started fine and I ripped on it 1st-3rd, when I let off he said it shot a flame out the exhaust and a few seconds later it died when idling. When I started it back up, it sounded like it had something rattling/slapping in the engine, not the trans for sure. It was low on power and every time it made that slapping sound, maybe timing chain?, it would miss, catch it’s self and repeat. Throttle made it worse. Full on oil, no metal on the dipstick, not hot. Drove the truck to it and pushed it up the ramps.... when I got home I checked the valves, they weren’t loose so I pulled the cover, no rocker arm damage, cam looks good but I’m not sure how the timing chain should look/feel. I was thinking about ordering a stage one hotcams since I’m already that deep and it includes a chain but I don’t want to rip the clutch cover off if I don’t have to.

Sorry for the long post, I’ve been procrastinating making an account here
 

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Sorry bud. I over looked this one. Im gunna have to read your whole post though and i cant do that at work. I will get back to you with an answer later.
 

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Answer to question number one. Stay away from cheap carbs. You want to only use the oem carbs on these quads. The aftermarket ones will generally have all kinds of issues. They are better used as a paper weight. You will be much much better off buying a moose or shindy carb rebuild kit and rebuild the oem one. Bearing carriers dont really matter the brand. They all wont hold up real well. I have a lonestar carrier and i run national bearings in it i get from the autoparts store. They are the same bearings as an a/c clutch bearing on a car or truck. I also buy special triple lip seals with spring garders from a local electric motor place. They are far better then even the factory seals that came in it.

Dyno jet kits are junk. Another paper weight scenario. You can jet with oem jets and do just as good or better and spend 1/3 the price.

Primary drive is actually not bad. I have been running there sprockets for quite a while. I just recently upgraded to a RK z-ring chain. But i had 2 full seasons of riding and racing on the original o-ring primary drive chain.

More than likely the reason your clutch cable is resting on the head pipe is because you are missing the cable holder that should be a metal loop that should be held on by the front motor mount bolt. Should look like this.

Look at this on eBay
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/173576551709

The rattling noise is very concerning. Expecially with the loss of power. The timing chain slapping will have no effect on power. Unless it skipped time. Which at that point more damage is almost un avoidable. Kinda sounds like a rod bearing let loose to me. That would cause lack of power and a noise. You also wont get metal shavings on the dip stick. Not unless you have all the oil full of metal which wouldnt really ever happen. To see that you would have to drain the oil. Hope this helps!
 

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Discussion Starter #5
It’s ok, I was thinking if there weren’t many guys into the same quads I like, I’d try like trx forum. I do appreciate the info.

I’m on oilburners.net and I know my way around those trucks very well and can point new comers in the right direction on stuff like you said on the carbs and jets. Now I’m the new comer here lol.

I didn’t know my hmf exhaust was going to come with jets. They are hex like the stock where the DynoJet kit is round with the adaptor. Would the hmf jets be better? My 42 pilot is Honda though. The cheap carb was just to keep gas off the quad and garage floor, I do have intentions of rebuilding the oe one.

My quad does have the little loop for the clutch cable but the hmf head pipe is bent different than stock. I’ll have to get a pic for you later

I think I found what was making all that noise last night when I pulled the clutch cover off last night. and it won’t let me post a picture.... I think it’s piece of a piston skirt and when I drained the oil it smell like gas. So with that said, 416, 426, or 440? Lol

I also wanted to post a picture of my cam. It has a “H” stamped in it and I was wondering if it was for Honda or hotcams. I don’t “think” I see the decompression valve

Thanks again for the help


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No worries. There arent alot of 400ex guys here. But plenty enough to stick around. I would stay away from the 440 unless you are planning on alot of extra cooling mods. I like my 416 and its plenty competitive with 450s on the track. Straight drags not so much. But the reliability is hard to beat. The dyno jet to the oem jets arent really gunna make a difference one to the other. But the sizes on them are in a completely different scale. There are certain upgrades you will want to do to keep the big bore reliable. Gt thunder hd studs, crf450 timing chain, and cometic mls head gasket. That will get things started in a reliable direction.
 

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Discussion Starter #7
Wouldn’t mind doing some cooling mods. Considered the cfm oil tank, fan on stock cooler and adding another cooler. Planned on everything you mentioned except getting head studs from arp.

I tore in a little deeper tonight. Piston is fine but I found a small piece that was bouncing around the cylinder and couldn’t get out. There is a mountain of chewed up cast aluminum under the oil pump pick up screen. There are blued heat marks on the crank next to the rod bearings, input shaft of the trans, and plates in the clutch.

REALLY didn’t want to even get as deep as the timing chain, found that piece I thought was piston skirt and REALLY didn’t want to do a complete top end, and now I’m ready to scrap it or spend 3k to build a monster 400EX...

I feel like everything I touch blows up. I don’t abuse things and I’d like to believe I’m not an idiot. Maybe it’s bad luck.... lol


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Oh its without a doubt bad luck. I beat the crap out of my quad everytime its started. Arp studs are expensive. And they dont really fix the problem. Just an fyi. The studs dont stretch. They pull the threads out of the jug. Gt thunders go deeper and use a bigger diameter stud. Arp just gives you a stud made of stronger metal. Hang in there bud. If you do the little extra work and money you will have a bullet proof quad.
 

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Also the heat coloring on the crank big end is normal. You will want to grab the rod and feel for any and i mean any up and down play. Grab hard and feel real real carefully. If there is any up and down play just change the crank now.
 

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Discussion Starter #10
I have a magnetic dial indicator. What’s the allowed run out for the rod bearing? So with those gt thunder studs, can that be done at home or is it a machine shop only deal?


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Discussion Starter #11
Can’t post pics from tapatalk but can on web browser apparently. There’s the big piece i though was piston skirt, the little piece that got stuck in the cylinder, crank with blueing, and a pile of metal under the oil pick up
 

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I have heard of people doing the gt thunder studs themselves at home. But i would advise against it. I actually live 45 minutes away from snure interlocking which is who has the rights to make gt thunder studs. Since they went out of business when the owners passed away. So i had the place that makes them install mine. But any machine shop can do it with his directions. They need to be put at a very specific depth.

I have a magnetic dial indicator and cant seem to get a reading when i try. The biggest issue is the rod rotates as your trying to get a reading. The only way i could see it working is if you had a fixture to hold the rod steady. I have always gone by feel and it hasnt given me any issues yet.
 

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Discussion Starter #13
Well mine does feel just ever so slightly loose. Maybe it’s the amount you’re talking about, maybe I’m just paranoid. Lol Did you see that pic with the heat marks near the rod?

I got the bottom end completely out, pulled the stator cover, then flywheel bolt and couldn’t get the magnet/flywheel off with a 3 jaw gear puller. I had it very tight, like way more than I was comfortable with, then started tapping on the center, then heated it a little, then tapped some more with no luck. Read reviews that tusk pullers strip easily.

Talked to previous owner and he said I should’ve left it stock, that’s why it broke and showed me a picture of his new 450. I told him this is just an opportunity to build it to beat his and he laughed. Now I’m going to go broke lol


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I saw the pic of the crank yes and i think in one of my posts i said the blue color is normal. Maybe i just thought it in my head and didnt post it lol. The tusk flywheel pullers do strip usually the first time you use it. I have a bolt that threads in its grade 10. I actually got it from a local john deere dealer. Its a crank bolt for one of there tractors. I have used it atleast 10 times and it has worked perfect. I have to usually hit it with my impact to get it off. They are on there good!
 

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Discussion Starter #16
I saw the pic of the crank yes and i think in one of my posts i said the blue color is normal. Maybe i just thought it in my head and didnt post it lol. The tusk flywheel pullers do strip usually the first time you use it. I have a bolt that threads in its grade 10. I actually got it from a local john deere dealer. Its a crank bolt for one of there tractors. I have used it atleast 10 times and it has worked perfect. I have to usually hit it with my impact to get it off. They are on there good!

You did say it was normal, but I didn’t know if mine might be excessive. There’s also heat marks on the rod. Just the nature of air/oil cooled engine?

Would you happen to have the part number of their flywheel bolt you use? Or maybe the thread dia+pitch?


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I can get you the pitch. Diameter always confuses me. Is it measured from the peaks or the valleys of the threads? And yeah mine looked identical and so has every single one i have pulled apart. And thats quite a few lol
 

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I can get you the pitch. Diameter always confuses me. Is it measured from the peaks or the valleys of the threads? And yeah mine looked identical and so has every single one i have pulled apart. And thats quite a few lol

I’m not sure honestly. I usually just slid them through the little plastic gauge or test nuts at the hardware store. Is it a grade 10 or 10.9? If it’s a 10.9 I can probably find it in town easily. The tusk puller says it’s 20x1.5.

Leaving the flywheel on, I still got the case split this morning. Gears came out on the clutch side and crank stayed on stator side. After searching every inch of the case for cracks and holding the large piece I found, I noticed machine marks. Now that everything is out of the way I can almost turn the piston 90 degrees which allowed me to perfectly match up the casting as an old piece of a piston skirt. Previous owner told me he rebuilt the engine last year, so I’m assuming it cracked the skirt, he put a new top end on it and sold it so he didn’t have to do what I’m going through now of digging all the metal out of the case from the skirt that fell down in there.

All of the gears and oil pump look great surprisingly. Only real casualty was the cylinder.

So now that I have it stripped down as far as I never wanted to mess with I’m thinking about using this to my advantage to build the motor I never wanted to mess with lol. Now I’m still considering a basic clutch, and 416 kit but then I see hotrods 460 kit and clutches from Hinson and gt thunder and think about this guy that laughed when I said I’m going to build my 400 to beat his 450.

You and some reading convinced me on the gt thunder studs. Probably have a machine shop check out my head and hardface my rocker arms. Hotcams stage 1 with a 416 kit or stage 2 with the 460 kit. I’m ok with adding oil cooling I just want it to be reliable and not need rebuilt once a year. Idk, I already miss having this thing running but I’m already this deep....

I noticed the oil smells like gas a little too. I thought I was pretty close on the jetting but that and soot in the exhaust makes me think I’m super rich but even with this jet (170) I still get rare exhaust popping on deceleration and I can see the first 1 or 2 inches of the headpipe (hmf stainless) turning orange when riding at night.

One of these days I’ll have this to where all I have to do is put gas in it.... lol


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Haha i do the samething. But this bolt is like 3 times the size of the biggest one they have. It is a 10.9 hardened bolt. I will get you the pitch and caliper the outside diameter. As for all the other stuff. I wouldnt do the 460 kit. Thats a 440 bore with a 4mil stroker crank. The 440s have alot of over heating issues. Im actually contacting wiseco about a custom piston. Im gunna have them make me a 87mm with the wrist pin placement higher for the stroker crank. It will be a 440 without the over heating issues. That will be my next winter project. My 416 is plenty competitive just human nature to want more lol
 

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Discussion Starter #20
I don’t understand why they’re not using a shorter rod instead of the custom piston. I’m building a stroker for my jeep and that’s what I did. Shorter rods and stock pistons. If I did the 460 build I was planning on an additional oil cooler, fan on the stock cooler, and a cfm oil tank. Might wrap my head pipe too. You think that still wouldn’t be enough to keep it cool? Do you know how much psi these oil pumps produce?


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