400ex top end rebuild..

13450 Views 56 Replies 9 Participants Last post by SlammedRanger, Jan 14, 2019

Shadow91

Discussion Starter · Feb 27, 2017

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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21 - 40 of 57 Posts

SlammedRanger

· #21 · Jan 3, 2019

Move the clip one slot down. So closer to the pointed tip.

Reactions: 1

Shadow91

Discussion Starter · #22 · Jan 3, 2019

Well scratch the Yoshi pipe, got a great deal on a Duncan racing fatboy4.. should have it monday!!

Shadow91

Discussion Starter · #23 · Jan 3, 2019

Well go to install the head studs and find out that they were not drilled to the correct depth! Measured every hole and they all came out to be 1.82 inches! Spec is 2-2.22 inches for the GT Thunder studs!!

After some VERY CAREFUL drilled and tapping i was able to correct the depth and am awaiting some peratex sleeve retainer from the parts store.

So now time to rip the clutch cover off and replace the chain. Other then the case gasket, any other gaskets i should get for that or look at while its apart?

SlammedRanger

· #24 · Jan 4, 2019

No other gaskets needed. But i would suggest pulling the lower case filter screen and cleaning it with brake clean.

Shadow91

Discussion Starter · #25 · Jan 4, 2019

Well got to cleaning and rejetting the carb, having access to a ultrasonic cleaner is nice haha

Got the freshly bored cylinder back and head studs installed to exact depth.

And then finally got her to the shop to start this whole process! Man is this thing dirty haha

Should have the rest of my parts next weekend, hopefully burning gas by next sunday!

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SlammedRanger

· #26 · Jan 5, 2019

Is it just my eyes or does that front stud look crooked? It could just be an illusion. But it appears to be leaning forward a good bit?

Reactions: 1

_Wilson_

· #27 · Jan 5, 2019

I caught that to.....

Shadow91

Discussion Starter · #28 · Jan 8, 2019

Yikes! That front stud looks nasty in the pic!

The head slides right over and it appears to be square in person tho.

However, I put the front/rear studs in backwards so I gotta swap those around.

All the parts should be here this Friday, if I do this right it should be burning gas by the weekend!

Quick question, I see a ton of post about porting the head, and a bunch of people saying that I’m gonna lose a ton of power out of the cam and big bore due to a stock head. Is the gains really worth it? I’m no

SlammedRanger

· #29 · Jan 8, 2019

Honestly there are big gains to be made from head porting. But that being said my head isnt ported much. My engine machine shop guy did a few small casting mark touch ups but nothing crazy at all. He flow benched it and said it flows pretty well for not having any real porting done. The cam and 416 kit will wake it up alot reguardless. I even did +1 valves with basically stock porting and noticed a big gain. You will be limited mostly in your stock carb. The 400ex carb dosnt flow well at all. The fcr is 100% the way to go.

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fishfiles

· #30 · Jan 8, 2019

I don't know if this is true of not , but I was told when porting , take more off the top and round it out , so it looks like the opening to a dog house , hence the name dog house porting ????

misterclean59

· #31 · Jan 8, 2019

I do know one thing about intake porting........you can go too big. Air velocity is important for mixing and with a cam with a lot of overlap at high rpm's. Generally straighten the intake tract with minor increases to the diameter and a satin finish. The exhaust really can't be too big (generally). Straighten out the path and mirror finish.

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Shadow91

Discussion Starter · #32 · Jan 9, 2019

Okay. I might grab the dermal and just smooth the cast marks. Don’t think I’ll port it really. I don’t have the skills nor the cash flow, haha

Let’s talk about cooling mods real quick.
Different cooler, Different tank, Air scopes, etc.

Just don’t wanna overheat this after I’m done.

Rev boxes worth it with the cam and big bore?

Reactions: 1

misterclean59

· #33 · Jan 9, 2019

Shadow91 said:
Okay. I might grab the dermal and just smooth the cast marks. Don’t think I’ll port it really. I don’t have the skills nor the cash flow, haha

Let’s talk about cooling mods real quick.
Different cooler, Different tank, Air scopes, etc.

Just don’t wanna overheat this after I’m done.

Rev boxes worth it with the cam and big bore?

There are others that have much experience with your particular model on this site......I am not one of them. Again I have much general knowledge about your questions.......here is some of it in context to your questions. Anything you can do to help cooling an air cooled engine is a good mod. Increased horsepower equals "exponential" heat increase. Rev boxes work but they increase the heat and stress the valve train. Hopefully others here can consider the upgrades you have done and give you some specific advice. Good luck!

Reactions: 1

Shadow91

Discussion Starter · #34 · Jan 9, 2019

Thank you misterclean59. Ive been googling, searching and looking at FB groups and these are all over the place. And then i find post from 10-15 years ago and just want the most up to date answers as possible. Im currently bidding on an aluminum oil tank so hopefully ill get that and scoops to start with.

Guess ill see how she does with all the new parts before i start messing with a rev box and all that.

Anyways, bought some used nerf bars last night. and my uni filter, oil filter and spark plug came in today!

Friday needs to hurry up. Should have my parts from them and my exhaust friday afternoon. My end goal in to hear this sucker fire friday night haha

misterclean59

· #35 · Jan 9, 2019

Why don't you just run it without the rev box first? You can always add one later. Usually a rev box doesn't work well unless you have the motor built to rev. Building one to rev takes much money.

Shadow91

Discussion Starter · #36 · Jan 9, 2019

Got the cylinder and piston put back on! But go figure i left the bolts at home lol

Clutch case removed

Chain off

and my parts!

Can someone provide me the torque specs for the clutch basket, the big bolt on the crank and basket as well? my stupid manual i ordered online wont be here until mid next week and was the first thing i ordered!

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Shadow91

Discussion Starter · #37 · Jan 9, 2019

Yeah mister that’s the plan, just run it for now and if I fee I want/need a box I’ll get one later.

Gonna focus on cooling mods and suspension next. I’m sure this will be plenty for awhile.

Plus that the wife just asked for a quad.. so savings time again! ?

SlammedRanger

· #38 · Jan 9, 2019

Clutch Center Staked Nut 80 ft lbs and re stake it of course
The clutch spring bolts there isnt a specific torque. Just snug them done 100s like this with no problem

Primary Drive Gear Nut 65 ft lbs

Reactions: 1

SlammedRanger

· #39 · Jan 9, 2019

And just a reminder. As i have forgotten this two dang many times. Before you torque those head stud bolts please put the front timing chain guide in. It gets sandwhiched between the head and jug. I have personally ruined 3 head gaskets this way on various models over the years. Its a friggen bummer believe me lol

Reactions: 2

Shadow91

Discussion Starter · #40 · Jan 10, 2019

Well got the top end mostly buttoned up. New HD chain and cam installed.

Anyone willing to save me tho? I went to adjust the valves and two out of 4 caps broke off.. so i need new caps for the valve adjusters.. the 24mm ones..

if someone has 2-4 they are willing to part with and can overnight them to me in a small envolope i would be forever grateful. Just PM me your paypal info.

just awaiting the pilot jet and exhaust otherwise, both if which should be here friday! Shes getting there!

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