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400ex top end rebuild..

13412 Views 56 Replies 9 Participants Last post by  SlammedRanger
Okay, so about a week ago at the dunes and noticed i had oil leaking from the head gasket. Finally got around tonight to tear down the inspect the engine and measure the bore. PO told me it had a stage 2 hotcam and a 440 kit but as i just found out, he was lying out his rear end. After measuring the bore, its an 85mm piston and looks to be a stock (very worn) camshaft. All in all, exactly what i was hoping for. Was also extremely surprised with how well the bike ran and how much power it had. When i removed the crank plug to rotate the piston, with the spark plug still in, i was able to move the piston with nearly just the weight of the ratchet.. I assume there should be considerably more compression on these..

Anyways, I want to do at the very least a top end rebuild. Thinking about doing a 416 kit and stage 1 cam. But from the looks of my head i need a new one.. center bearing has some pretty good grooves in it and i dont think there is much that can be done to save it (correct me if im wrong)

I want the best balance of power and reliability. So just off my head what i need is:

Wiseco 11:1 piston
Hotcams stage 1 cam
GT Thunder head studs
Cometic gasket set

Anything else I should worry about right now? What about valves and springs?

Anyways, few pictures of the parts..

First off the cam

The head

and the piston/cylinder
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Okay, so i currently have in my cart;

JE 87mm 10.8:1 Piston kit (Piston, rings, pin, clips)
Cometic 87mm top end gasket kit
Stage 2 Hotcam
Hot cam HD chain
New OE chain tensioner
GT Thunder HD studs
Cylinder head from a XR400R (Ive read its the same, also has same part # according to bike bandit)
Lexx slip on exhaust
Carb rebuild kit
K&N Airfilter with pre filter

Anything else i should order? Trying to order everything at one time.
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Phew!! I also have a Honda 400ex (The gray one in my profile pic) and I have the 16cc bore kit. I'm so glad that you considered this one and not the 40 kit. The 40 kit are known for overheating and ruining your bike. Hey let me know how much of a pain in the a** adjusting the timing is, cause it's a very large pain in the a** let me know if you have any tricks to help make it easier lol.

Good Luck,
I would be worried about the surface of the cam bearing area if it were mine.
Clean your head up with Emory cloth and polish. If you put the bearings on the cam and place it in the head you will see that the cam does not touch the head. Under heavy torque it may flex a little but if you clean that up you'll be ok. I've done it before with no issues.
Use a UNI filter too Much better for off road than a K&N
Also replace the timing chain with Part# 14401-MEB-671 this is a 02-08 CRF450R/X, Replace the guides too and tensioner.
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Clean your head up with Emory cloth and polish. If you put the bearings on the cam and place it in the head you will see that the cam does not touch the head. Under heavy torque it may flex a little but if you clean that up you'll be ok. I've done it before with no issues.
Use a UNI filter too Much better for off road than a K&N
Also replace the timing chain with Part# 14401-MEB-671 this is a 02-08 CRF450R/X, Replace the guides too and tensioner.
After sending out my head to get repaired, decked, and valve job done, found out the intake valves were toast. Would i be best off to get the kibblewhite intake valves by themselves? Or should i get the exhaust valves and their springs, especially if im going with a stage 2 camshaft, or will my stock springs and exhaust valves (which are in good shape according to the machinist) be fine with the new cam and bump in compression?

Also from friends that have done piston jobs and from reading online, Im told to do the JE kit over the Wiesco kit? Any input on this?

And lastly, Should i just go with a manual chain tensioner? Keep reading horror stories of tensioner failure. Planned on buying a new OE one, but if manual is a better option ill go that route.

Thanks for all the input
If you're going to replace the intake valves it's best to just go ahead and replace the exhaust valves as well I used all oem valves and Kibblewhit springs ..I have a stage 2 Magnum cam will the stock valve guides .. as far as the Piston goes wiseco is a good piston JE is a good piston but if I've said it once I've said it a thousand times your engine is only as good as the Builder I had a JE in my 250 x with the 80mm Big Bore Kit and I'm running up 11:1 88mm Wiseco in my 400. I also run a manual cam tensioner and a CRF450R chain make sure you replace the guides to the timing chain part number is a 14401-MEB-671

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Okay well i finally got around to ordering my parts last night and somehow slipped up when ordering my gasket kit... I ordered a C7826-EST kit which is supposed to be for a 89mm bore. I needed to order a C7924-EST which is for the 87mm im going with..

Can i just order the correct HG from cometic or are other gaskets different with the kit?
Yes you should be able to buy just the gasket. . . Make sure it's the MLS type (multi-Layered Steel) Wiseco sells them too
Well sent Cometic an email asking about the difference in the kits and was informed it is only the head gasket itself. If anyone is wondering, a 87mm (416) head gasket is part #H0401SP2027S

All in all its actually cheaper this way, the 89mm kit was only $50 and the head gasket is $28, where as the 87mm kits i was looking at were $90 and above, so actually worked out better for me! haha

Also, definitely going to have to rejet, any one have any recommendations for what jet sizes? Im completely tearing the carb down to reseal it, Will have an open air box with an uni filter, stock header and Lexx slip on.. And then the obvious 416 kit, 10.8:1 compression with a stage 2 hot cam..
My 87mm cometic gasket kit was 59.99 from alba racing. 90 bucks is highway robbery.
whats the deal with using the 450r cam chain?
It is 2 full plates thicker chain. It fits in the stock guides perfectly though. The stock chains stretch consistently. The crf450 chain dosnt.
Okay, so the time has finally came for me to finish the build i started nearly 2 years ago. Going to start the build on the this thread and try to keep it here.

Sending out my cylinder tonight to get bored and HD studs installed.

Going with the JE 10.8 piston and hot cams stage 2 cam. Already have the HD Chain and kibblewhite valves.

Right now i have the stock carb and exhaust. Trying to get this at least running but on a budget. Can I get away with the stock carb and header with a slip on right now or are those going to be a necessity?

And what is the proper way to rebuild this engine? Just follow the factory service manual for timing and then rejet as i go? Whats a good starting point with the jets?

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The stock carb should be fine. The jets have in my 416 are

48 pilot
170 main

Set the timing to factor settings

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Would I be better to just order a dynojet kit or single jets? Sorry carn tuning is all new to me.

And then about to make a parts order, going with the lexx slip on and factory header should be okay correct?
I have never ordered a jet kit before. I have a parts store very close to my house I get my jets from.

Also jetting all depends on elevation

A Lexx is fine on a stock header, I ran a lexx slip on for a while. I’m not impressed. You might as well just run a straight pipe

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Okay so I dropped the cylinder off to get bored on Thursday and am told itll be about a week turn around. Should be the correct size and have head studs installed just after Christmas! :yeahbaby01:

So I have a Honda powersport dealer right down the road from my work, i would assume i can just go through them for new jets? You said you're running a 170/48 in your 416? So would that be a good starting point for mine at sea level (Seattle, WA) or would you recommend any thing else? Im sorry, tuning a carb is foreign to me.

When i ordered my top end cometic kit, i accidentally ordered one for an 89mm bore. I keep seeing ads like this one that show they work for 87, 88 and 89mm bore sizes. Would the HG for the 89mm bore size work with my 87mm bore or am i just better off dropping the $45 for a new (correct) gasket? Would rather do it right the first time, but dont want to needlessly spend money if the other gasket will work.
Head gasket will work. But it will have slightly less sealing area. 2mm to be exact. I have used both and had zero issue from either way. Just be sure you torque to 40 ft lbs and you heat cycle 3 times and then remove valve cover and re-torque. Also when torquing the first time follow the 3 steps and the sequence and let it sit for 15-20 minutes then go back and check one more time at 40 before final assembly.
So got my freshly bored cylinder back this weekend! Looks like its about time to start putting her together. From kinda going over the web i realized i was throwing away money - or power - with leaving the factory exhaust, so i ordered a Yoshimura exhaust and figured i would start with a 42 pilot and 160 main. Curious however if i should move the needle or not, right now its clipped centered. Using only Keihin jets.. thanks guys!
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