Piston questions.

[JimmyHoffa]

I have a stock 400ex block, with a FMF Hi-flow header and Titanium 4 can. I have recently realized that my ATV is slow. However, I need to know what sacrifices I'm gonna be making here. I was planning on either JE's 11.5:1 - 415cc piston or Wiseco's 11:1 - 416cc piston, in combination with a longer duration cam, like Hotcam's Stage 2 deal. (I'm getting a XR400 head gasket too.)

I was talking to a guy at the track with a 450r (That I got to ride!) and he claimed that the Honda Service Manual recommended getting a new piston every 20 engine hours. That's a joke. Do 400 dudes have to do this too if the get a decent piston? I don't have the money for that. I do all my own work, and spend outrageous amounts of time doing crap like getting tires off of rims by myself all in the name of cash. If I get a solid/mild block together as specified above, and ride mainly only on the weekends and bomb around at the local track, can I expect to get several years out of my baby-before a teardown?

Just Curious. -Jim

[JOEX]

I've heard about the 20 hour piston on the 450r's, I don't know why but I think it's Honda padding their warranty:ermm:

On the 400ex you should get many years of use out of the motor if it's built and maintained properly, even with what you're intending on building. Don't take any shortcuts.

[F-16Guy]

The two engines are completely different; you don't need to rebuild a properly built 400ex very often. Either piston (JE or Wiseco) is fine. They are both what most would call a 416, but JE rounds down and Wiseco rounds up. 11:1 will give good, reliable gains, and would probably be fine on good pump gas unless you put a heavy load on it (dunes, etc.). Above that, and you're gambling. Personally, if you wanted a good, solid, fast, and relatively cheap recreational build, I would go with an 11:1 87mm (416) piston, stage 2 HotCams cam, Cometic Flexsteel 88mm gaskets (I don't think they offer 87mm) in the thinnest thickness they offer, and appropriate jets. Another thing that I would STRONGLY suggest is a set of heavy duty head studs from GT Thunder. The stock studs are threaded directly into the aluminum cylinder and have a tendancy to pull out, causing a blown head gasket. For less than $100, GT Thunder will eliminate that problem, and you could also have them bore it for the new piston while it's there. If you do all of these things, it will be a HUGE performance increase, and it will give you years of reliable service.

[JimmyHoffa]

Yes. Exactly what I was looking for. Any brand loyalties as far as pistons go? (Try to defend them with facts or credentials.)

[F-16Guy]

If you do a little research, you'll find that JE and Wiseco, along with several other companies, are owned by the same parent company. They may differ slightly, but their quality control is most probably identical. I have been building two and four stroke engines with Wiseco pistons for many years, and I have had no problems. People will jump on here and say that Wiseco's compression ratios are not accurate, but that is not true. My 416 was almost dead on using XR400R thickness gaskets. It comes down to personal prefence, but with today's manufacturing technology, you won't find many quality problems. The top names right now are JE, Wiseco, and Ross. I say pick a piston, the cam that fits your style best, a quality gasket set (I like Cometic "Flexsteel"), and get the studs done, and you'll have a strong engine that will be almost bullet-proof. One more thing; try not to go too high on the CR (above about 11:1) with the stock connecting rod. If you really get the compression up there (12:1, 13:1), they have been known to break. Keep it below 12:1 and you should be fine.

[JimmyHoffa]

Okay. I've done some more looking around, and I've decided on this for a future engine build.

Wiseco 11:1 Sandard bore/next size, depending on wear

Hotcams stage 2

GT Thunder studs

XR400R head gasket (yes, with that gasket, which Wiseco TELLS YOU TO USE, they tell the truth about comp. ratio.)

Next questions:

I've heard the CRF450 R or F timing chain fits the 400, and is stronger. Is this necessary with this setup, and should I get a new one anyway? Assume about 80 hours on my engine, with obsessive maintenance.

Also, rocker refacing. Hotcams says to get new rockers. Is this necessary or can I just resurface them - or do nothing at all?

[F-16Guy]

Originally posted by JimmyHoffa
Okay. I've done some more looking around, and I've decided on this for a future engine build.

Wiseco 11:1 Sandard bore/next size, depending on wear

Hotcams stage 2

GT Thunder studs

XR400R head gasket (yes, with that gasket, which Wiseco TELLS YOU TO USE, they tell the truth about comp. ratio.)

Next questions:

I've heard the CRF450 R or F timing chain fits the 400, and is stronger. Is this necessary with this setup, and should I get a new one anyway? Assume about 80 hours on my engine, with obsessive maintenance.

Also, rocker refacing. Hotcams says to get new rockers. Is this necessary or can I just resurface them - or do nothing at all?
Smart move. For some reason, everyone wants to immediately go to a 416 or 426. The difference is very small, and you'll have much more cylinder left to work with should you have a problem down the road. Most of the added power comes from the increased compression ratio and cam.
You can use a 2002 CRF450R chain. It is basically the same as stock, except that each link contains an extra plate, giving it that much more strength. When I bought one for a 406 I built for my buddy, it was about $27 from Service Honda. If you do the cam chain, you will also need a clutch cover gasket and access to air tools to get stuff apart.
As far as the cam goes, you shouldn't need new rockers unless you see obvious problems with the old ones (chrome plating flaking off, abnormal wear, etc.). You do not want to hard-face your rockers unless you are running a hard-faced cam such as a Web Cam. The idea is to keep the surfaces roughly the same hardness. The HotCams cam is close enough to the stocker that you can just drop it right in.
Also, good choice doing the studs. That $100 that people hate to spend usually comes back to bite them in the arse in the form of a much larger bill.:devil:

[JimmyHoffa]

Nice. I read lots of stuff about minor overbores in this engine, and apperently it's only felt at the 440-ish level.

I've decided to try to pull off the stud tapping in my relatively precise drill press. If I can, I'll get my shop teacher to let me use the Bridgeport, which I am well versed in the usage of.

Is the cam chain necessary, or just nice? I put a high lift cam/tighter valve springs in my buddy's RM-Z 250, and I was immediately scared of the stock chain after I turned the engine over. (You can't get a stronger one, so I didn't have a choice, but I just noticed it.)

If I have rockers that look decent, is it a good idea to get the contact faces re-ground or just to leave well enough alone? I wasn't really talking about hardfacing. Oops. Shoulda made myself clearer.

You're pretty valuable to me now, so I'm pretty much taking your advice and building my engine according to it. Thanks.

[1965 honda]

Originally posted by JimmyHoffa
Okay. I've done some more looking around, and I've decided on this for a future engine build.

Wiseco 11:1 Sandard bore/next size, depending on wear

Hotcams stage 2

GT Thunder studs

XR400R head gasket (yes, with that gasket, which Wiseco TELLS YOU TO USE, they tell the truth about comp. ratio.)

Next questions:

I've heard the CRF450 R or F timing chain fits the 400, and is stronger. Is this necessary with this setup, and should I get a new one anyway? Assume about 80 hours on my engine, with obsessive maintenance.

Also, rocker refacing. Hotcams says to get new rockers. Is this necessary or can I just resurface them - or do nothing at all?



the next size up is a 402 im pretty sure. thats what i have. i was told that it gos 5mm at a time.

[400exrider707]

Originally posted by JimmyHoffa
Okay. I've done some more looking around, and I've decided on this for a future engine build.

Wiseco 11:1 Sandard bore/next size, depending on wear

Hotcams stage 2

GT Thunder studs

XR400R head gasket (yes, with that gasket, which Wiseco TELLS YOU TO USE, they tell the truth about comp. ratio.)

Next questions:

I've heard the CRF450 R or F timing chain fits the 400, and is stronger. Is this necessary with this setup, and should I get a new one anyway? Assume about 80 hours on my engine, with obsessive maintenance.

Also, rocker refacing. Hotcams says to get new rockers. Is this necessary or can I just resurface them - or do nothing at all?


Wiseco 11:1 on std bore is still nice upgrade with noticeable power improvements... good choice

GT Thunder studs, not necessary on that compression, but still a very good investment for reliability sake.

XR head gasket - no its still not close to advertised compression ratios. Dont ask me why but Honda decided for some reason it would be a good idea to have the top of the piston sitting .040 down in the head at TDC. I would go with a Cometic thin head gasket, probably cheaper, better quality, thinner for more power, and readily available.

CRF450 cam chain is a great upgrade and I would definitely do it now while you have the motor apart. Honda recommends chain replacement every 50hours. You can go longer but the 400ex are notorious for stretching/snapping them. The CRF is much MUCH cheaper as far as price and a great reliability upgrade. Its is about $35 where a stock 400ex one is about $90. Its a no brainer.

Rocker refacing? On a hotcam? Not necessary, they are a billet cam as are the rocker surfaces. They do recommend it because they would like to see a new surface (your new cam) seating against another new surface (the rockers), but you will be fine.

[JimmyHoffa]

AAAAhhhh... So comforting. I feel like I'm doing this right. Thanks for all the input guys. Keep it coming if you're bored!

[400exrider707]

Originally posted by JimmyHoffa
AAAAhhhh... So comforting. I feel like I'm doing this right. Thanks for all the input guys. Keep it coming if you're bored!


It seems to me you are trying to build a bullet proof motor judging by the parts you are thinking of using. I would also consider a heavy duty rod for the ultimate in reliability, though not really necessary on 11:1 its there if you choose to up compression later on down the road. Also I would look at a good 3 angle valve job with new valve seals while its apart. Just a suggestion.

[JimmyHoffa]

I certianly appreciate it. Your suggestion was already taken, though. I would never consider re-assembling a motor without a good valve job, or at least an inspection and a lapping. I know what I'm doing for the most part, I'm just throwing out my plan and adding onto it with your suggestions. Thanks!

Another question. I just put my new front tires on, and I sat down next to my quad to admire it. During this sitting session, I noticed that the only thing that appeared to be holding the cylinder to the cases was like 3 or 4 little 8mm head screws. I'm confused. My brain tells me that the explosion in the combustion chamber should produce nearly the same tension stress at the base gasket that it does at the head. Why, then, is there all this emphasis on HD head studs when the base joint is subject to the same loads? I originally thought that the "head studs" went all the way through the cylinder to the cases. Am I wrong?

[400exrider707]

Originally posted by JimmyHoffa
I certianly appreciate it. Your suggestion was already taken, though. I would never consider re-assembling a motor without a good valve job, or at least an inspection and a lapping. I know what I'm doing for the most part, I'm just throwing out my plan and adding onto it with your suggestions. Thanks!

Another question. I just put my new front tires on, and I sat down next to my quad to admire it. During this sitting session, I noticed that the only thing that appeared to be holding the cylinder to the cases was like 3 or 4 little 8mm head screws. I'm confused. My brain tells me that the explosion in the combustion chamber should produce nearly the same tension stress at the base gasket that it does at the head. Why, then, is there all this emphasis on HD head studs when the base joint is subject to the same loads? I originally thought that the "head studs" went all the way through the cylinder to the cases. Am I wrong?

The cylinder to the cases doesn't see the compression that the head gasket area does. The crank isn't under any real pressure, well not to the extent that the head sees anyways

[JimmyHoffa]

Mmmmmkay. I'm just going to ingore some physics laws and go with the assumption that everybody else's engine stays together, so why shouldn't mine. :-)

[F-16Guy]

There are four long bolts that hold the cylinder to the crankcase. When you take the head off and remove the head gasket, you'll see them. The 8mm bolts on the side of the cylinder are just to add additional clamping force where the cutout for the timing chain is.
And just to clarify about compression ratios of Wiseco pistons, I cc'd my combustion chamber and came out with 10.9??:1 CR. That's pretty dang close, in my opinion. The deck height of the piston had nothing to do with what the compression ratio came out to be in this case. The 89mm flat top wiseco, however, did need some machining to achieve the advertised ratio. Some people tried to get around it (with some success) by using yamabond for a base gasket and running a thin head gasket or disassembling one of the Cometic Flexsteel gaskets and using one layer with high temp BBQ paint as a sealant (no kidding -- supposed to work great). The best option, of course, was to take the proper measurements and deck the cylinder accordingly, which some did. If you want to read a great engine building thread, search the powertrain forum for a thread called "Have you decked the cylinder?"; there is some excellent information in there.

[400exrider707]

Originally posted by F-16Guy
There are four long bolts that hold the cylinder to the crankcase. When you take the head off and remove the head gasket, you'll see them. The 8mm bolts on the side of the cylinder are just to add additional clamping force where the cutout for the timing chain is.
And just to clarify about compression ratios of Wiseco pistons, I cc'd my combustion chamber and came out with 10.9??:1 CR. That's pretty dang close, in my opinion. The deck height of the piston had nothing to do with what the compression ratio came out to be in this case. The 89mm flat top wiseco, however, did need some machining to achieve the advertised ratio. Some people tried to get around it (with some success) by using yamabond for a base gasket and running a thin head gasket or disassembling one of the Cometic Flexsteel gaskets and using one layer with high temp BBQ paint as a sealant (no kidding -- supposed to work great). The best option, of course, was to take the proper measurements and deck the cylinder accordingly, which some did. If you want to read a great engine building thread, search the powertrain forum for a thread called "Have you decked the cylinder?"; there is some excellent information in there.

Decking the cylinder down .040 which it would need to be would require an adjustable cam sprocket to make up for the loss in timing due to the shorter height now. I tried taking a gasket apart and using the bbq paint and it didnt hold up, though it was a tusk gasket, maybe if I tried it with a cometic....

What method did you use to find the compression ratio? I've heard reports of people with 11:1 pistons measuring a true 9.8~9.9:1 or a little less!!!!! Stock is only 9.1:1. Also what other components did you use to achieve the 10.9:1? Thin head gasket? No base gasket?

[JimmyHoffa]

Is there a good way for me to just buy a piston that achieves the 11:1 CR? I have milling machine access, and would not hesitate to do all of the work myself, but if there's a way to get higher compression without plugging in the Bridgeport, that would be desired. GT thunder also makes an adjustable cam sprocket for 40 bucks, but I was kinda trying to avoid degreeing/more adjustment and machining on my juggernaut engine.

What do people know about Namura, JE, and Ross as far as pistons and associated annoyances go? I looked up some stuff on Ross, and I'm confused. All I can seem to get is 'stock' pistons from Ross, unless I want to get a minumum of 4 custom ones made.

[F-16Guy]

Originally posted by 400exrider707
Decking the cylinder down .040 which it would need to be would require an adjustable cam sprocket to make up for the loss in timing due to the shorter height now. I tried taking a gasket apart and using the bbq paint and it didnt hold up, though it was a tusk gasket, maybe if I tried it with a cometic....

What method did you use to find the compression ratio? I've heard reports of people with 11:1 pistons measuring a true 9.8~9.9:1 or a little less!!!!! Stock is only 9.1:1. Also what other components did you use to achieve the 10.9:1? Thin head gasket? No base gasket?
I used this formula:
http://www.greatplainsas.com/icompratio.html
Decking the cylinder and using thinner gaskets will both retard the cam timing a little, but I don't think the average Joe would notice the small amount of difference. I guess if you wanted to get really precise you could degree the cam, but the 400ex isn't exactly a top fuel dragster.
My 416ex has an off-the-shelf 87mm Wiseco piston with a Cometic XR400R Flexsteel gasket set, and I used the base gasket.
My CR was determined by finding the real volume of the combustion chamber at TDC using some light weight oil and a seringe. I don't remember exactly how many CCs it was, but it worked out to just a hair under 11:1.

[JimmyHoffa]

Okay. I think I'm almost done. If I run mainly fast trails and semi-open sand flats with occasional MX, I want a stage 2 hotcams, right?

[400exrider707]

Originally posted by JimmyHoffa
Okay. I think I'm almost done. If I run mainly fast trails and semi-open sand flats with occasional MX, I want a stage 2 hotcams, right?

It depends on what kind of rider are you? Are you a redline kind of guy or a lugger? I lug my motors, so with my EX I took the 11:1 wiseco std bore and a hotcam stage 1, I loved it, and it had awesome power.

[JimmyHoffa]

I'll probably go with the Stage 1. I'd be a lugger if I had real power, but I have to ride my 400ex like a cr125 right now to get the power I want. The whole story behind this starts was when I was at the MX track and I got really frustrated because there was a turn that led into a tabletop that I know my bike doesn't have the power to clear in a normal way. I tried everything and I kept casing it, and I got really really mad when this guy with an LTZ just tossed himself over it in 3rd. I finally got it, but I had to start from off the track and launch my quad over a birm and onto the exit of the corner to get enough speed without bogging. Pinned in 4th and a little of a horse hop off the lip was just enough to get me over. I decided I want actual horsepower.

[400exrider707]

Originally posted by JimmyHoffa
I'll probably go with the Stage 1. I'd be a lugger if I had real power, but I have to ride my 400ex like a cr125 right now to get the power I want. The whole story behind this starts was when I was at the MX track and I got really frustrated because there was a turn that led into a tabletop that I know my bike doesn't have the power to clear in a normal way. I tried everything and I kept casing it, and I got really really mad when this guy with an LTZ just tossed himself over it in 3rd. I finally got it, but I had to start from off the track and launch my quad over a birm and onto the exit of the corner to get enough speed without bogging. Pinned in 4th and a little of a horse hop off the lip was just enough to get me over. I decided I want actual horsepower.

Go with the piston and the stage 1 cam... you'll love it.

[2muchquad]

but I had to start from off the track and launch my quad over a birm and onto the exit of the corner

I know this is old but i thought it was funny:D

[JimmyHoffa]

nice catch. How'd ya come across that? I have a 450r now, and a happy forum member now has my 400ex. I can only assume it's doing well. Needless to say, all is well with my horsepower deficit. It's gone. I'm tearing the R down in 3 days to put the updated crank in.

[2muchquad]

Yeah thr 450r are fut but dont think just because its a Honda you can run'em 4ever without working on them a bunch,save your money for valves,shim them twice and get new valves after that,otherwise you'll destroy your head;)

I would do this:

1) Curtis Sparks or HMF full system. What you have isnt bad.
2) 10.5:1 JE or 10:1 Wiseco Piston
3) Stage 1 or 2 Hotcam
4) K&N air filter with outerwears and remove the airbox lid
5) Jet it properly. You get so much more power out of a properly jetted machine
6) Razr rear tires to get that power to the ground. You will feel something be faster when its actually getting traction. My brother and I have almost the exact same performance mods but his feels like it pull more only because his Razr rears hook up and my stock tires are spinning. Not a lot but enough where your not feeling the pull like the Razrs give you.

From what you have now those mods will probally make your jaw drop in comparison to. It will be plenty fast with those mods and perfectly safe. All those together make the 400ex so much faster. My brother had an HMF slip on, K&N w/ outwerwears and lid removed, stage 1 hotcam, wiseco 10:1 piston, Razr rears, and jetting not on spot and it still ran good man. Compared to stock those mods made it a beast and if it was jetted properly and had a full exhaust whooo! lol

[TRXRacer1]

I think you're 6 months too late on this one FHR..........:p