re-build

[bubba's400ex]

hey my 02 400ex started smoking recently so i am going to re-build it this winter. i want to put a higher compression piston in it but i don't know what to go with, i want to be able to run it on 93 pump so what do yall think, also what else should i replace while i am in there othere than gaskets?
thanks a lot

[stalefish_132]

go to a 416 11:1 comp. with a cam and air box mods and pipe if you don't allready have one and of course re jet and you'll end up with a smile on your faceand mud in your teeth :D and with 11:1 your safe with 93 pump;)

[bubba's400ex]

i don't have the money to bore.

[02440exkid]

just do std bore with 11:1 wiseco piston ect......... :D

[F-16Guy]

Originally posted by bubba's400ex
i don't have the money to bore.
You don't have $50? Save up until you do. It's pointless to do a rebuild if you're not going to do it right. Also, if your cylinder looks good (no big gouges or scratches - the machinist will be able to tell), just have it bored .040" over (406cc). Why remove extra material for no reason? Trust me, it would be very hard to tell the difference between a 406 and 416; the extra power will be from the compression ratio increase. Also, consider getting a cam. You might be able to get an XR400 cam off of eBay if you're really on a tight budget, otherwise, maybe a HotCam or other cheap drop-in. Start saving now and do it right, or you'll probably be doing it again.

[bubba's400ex]

so it is only $50 to have someone bore out the cylinder?
what else do i have to buy if i bore it to a 416?
thanks

[400eXr1d3rZ]

you will have to hone the cylinder too, but you can do that yourself, its a stone tool i think.

you might want to consider a Cam too, and you will NEEEEED Jets, and a gasket kit.

if your on a tight budget the cam can wait, its for increased performance.

get a JE piston.

[F-16Guy]

Again, I would go with the 406 (86mm piston) if you can; going straight to a 416 will give you negligible gains compared to a 406, and you're leaving that much less sleeve for future rebuilds. Most local shops will charge $40-60 to bore and hone, but you will need to take the new piston so they have it for reference. You will need a top end gasket set with a laminated steel head gasket, not fiber ($35); a piston kit ($100), and I strongly recommend a cam because you will see much better gains ($130 for stage 2 HotCams drop-in cam). Little things that you will also need are: 158, 160, 162 kehin main jets (about $3.50 each), a 42 kehin pilot jet (about $4), some gasket sealer for the base gasket, and some brake parts cleaner, a wire brush, and a straight edge razor blade to clean up gasket surfaces.

Some things to remember to do:

1. Start with a clean bike, and keep everything as clean and organized as possible as you go.

2. I like to use a Sharpie to number all of the bolts and their corresponding locations so there's no question about where things go (and it makes re-assembly much quicker and easier); just make sure you don't remove the markings with parts cleaner.

3. Set the ring gap. Follow the directions that come in the ring box carefully. All you need is a file and a feeler guage, just make sure you get all of the burrs off of the edge of the rings where you filed on it or it will score the cylinder. If you need help with this, PM me.

4. Jet the carb BEFORE you start it for the first time. Start with a 162 main and 42 pilot. You can go to a leaner main jet if needed after break-in. Refer to the "Articles" section at the top of this page for a how-to.

5. Adjust the valves according to the cam specs card before startup.

6. If you install a new cam, keep the RPMs above a high idle (2000 RPMs) for at least 15-20 minutes the first time you start it as long as there's no oil leaks or other problems. This is needed to break in the cam; VERY important! It's best to plan on taking it for an easy ride so you get some airflow and keep a light load on the engine.

7. Use a torque wrench for the cylinder and head bolts and/or nuts at the very least. If you are a good mechanic, you can tighten the smaller stuff carefully without one.

You should be able to do the rebuild for under $350 with a cam.

[TRXNIGHTRIDER]

sorry to steal this but thats what im doing to mine. 416 11:1 piston hot cam2, and i was wondering if i should get it ported and polished?

[02440exkid]

it would help a little but you will see the most impovment with a 440.

[bubba's400ex]

what series do i need for keihin?
and do i need the round or hex main?
also i can do an 11:1 piston with 93 octan pump gas?
thanks for all the help

[F-16Guy]

Take your old main and pilot in with you to match them up. The new pilot jet will probably be a little shorter, but it should look pretty much the same. The main jet should be exactly the same (long hex). If you go to a dealer, get the jets from their bulk jet assortment, not the individually packaged jets from Honda. Bulk jet: $3; Honda jet (same exact thing): $10
11:1 will run on 93 in most conditions. I mix 50/50 with 100LL AVGAS when I race, go to the dunes, or otherwise plan on beating the crap out of my engine.

TRXNIGHTRIDER:
From what I've heard and read, the 400ex head flows pretty good. You may just want to get a clean-up port to remove the casting flaws and match the intake boot and exhaust flanges. Getting a full on port and polish probably wouldn't help you much unless you had a very high compression 440cc or bigger engine. For the money it costs, there are other ways to get better power gains (carb, exaust, etc.)

[GPracer2500]

Mains are standard "hex head" mains (technically called Series 357 but no one calls them that). The pilot jet is a Series 26. The more common Series 21 is a little longer and will work just fine.

[F-16Guy]

Thanks for clearing that up. I remebered that the 42 pilot I put in was longer or shorter, I just couldn't remember which.:confused:

[bubba's400ex]

i want to go with a lower compression piston so that i don't have to worry about puting race gas in the mix but will there be a big diffrence betwen 10:1 and 11:1 performance wise?
thanks a lot for all the help once again

[GPracer2500]

JE makes a 10.5:1 85mm piston (stock bore, 397cc) and a 10.6:1 86mm piston (406cc). If you're smoking then your bore might not be in good enough shape to get away with not over-boring. You'd have to take it to a machine shop and have it measured/inspected to be sure. If a bore is necessary than the JE 86mm 10.6:1 might be just the ticket.

Do a 406 10.6:1 and a Hotcams stg 2 and you'll be happy.

To answer your question, yes there is a "significant" difference between 10:1 and 11:1--mostly on the bottom end, I think. Compression is more about producing torque than anything else. HP is a function of torque AND rpms, so high compression has less and less of an impact on HP as the rpms increase. In other words, if you had dyno charts of a 10:1 engine and a 11:1 engine (all else being equal), I'd expect the difference in power to be greatest at lower RPMs, with a gradually closing gap as the RPMs reach redline.

Actually, that's a comparison I'd love to see in real life. I can reason through stuff all I want but the dyno has the last word...

[bubba's400ex]

do yall know of any places online where i can get a JE piston?
i can't find one anywhere.
thanks

[F-16Guy]

C&D Racing (site sponser) should be able to get you everything you need, including jets. You can leave a thread in their forum with a list of what you need, and they will get back to you with a price. You can also call them directly, but they reply pretty fast to their forum.

[bubba's400ex]

o.k. well i was talking to my dad about this and he said iwould need a ring compressor for the piston.
do you guys know if a car ring compresor will work?
if not where can i get one for the bike?
thanks

[stocktires]

12:1 would be good, no more though because of the ole 400ex head gasket issue.

[F-16Guy]

Originally posted by bubba's400ex
o.k. well i was talking to my dad about this and he said iwould need a ring compressor for the piston.
do you guys know if a car ring compresor will work?
if not where can i get one for the bike?
thanks
You can get a ring compressor at Checker or Auto Zone for about $10. When I put a 400ex together, I put the ring compressor on the piston, line the piston up facing the right direction on the bottom of the cylinder, and then tap it in gently until the rings are in the sleeve completely. I leave the piston hanging out of the bottom of the sleeve enough so that you can carefully set the whole assembly down over the rod and slide the wrist pin in. Before installing the piston into the sleeve, you may want to install one of the circlips for the wrist pin; that will make it easier when installing the wrist pin and give you one less thing to drop. Make sure you install the base gasket BEFORE you get the cylinder and piston attached to the rod, and put some rags or something in the crankcase around the rod so you don't drop anything into the case.

P.S. - The 400ex has a bigger piston than a lot of import cars, so look for a compressor that will accomodate down to about a 3.5" bore.

[bubba's400ex]

when you did it did it seem like you would need the compresser to do it?
thanks

[F-16Guy]

Originally posted by bubba's400ex
when you did it did it seem like you would need the compresser to do it?
thanks
You might be able to get by without one, but it wouldn't be easy, and you could easily gouge your cylinder or damage one or more rings. Not worth the risk to save $10 and a trip to the auto parts store, in my opinion. Make sure you lube things up with new motor oil as you assemble it. It's ultimately your engine and decision, but when it turns out badly, you'll have yourself to blame. Remember, if you do it right, it should last many years. If you cut a bunch of corners, it may only last a few minutes.:(

[bubba's400ex]

does anybody know where i can get a valve spring compressor for less than $66
oh and i'm probably not going to be able to do the piston this time so what do you think about jetting if i have the fmf header,new stg 2 cam, twin air filter,and air box lid off?
thanks a lot