406 10.6 Build Worries

[08400ex'er]

I have finally gotten most of the parts together for my build and the wife's ok to spend the money to get it done however I have one last question on the engine build and its reliability. I was wondering if for long term reliability I should also get the rod replaced with a cp or will the stock rod hold up long term. I want something that will be as close to stock reliability as possible and in my reading online it seems as if the rod is the first thing that fails in higher HP builds.

This is a list of what I have:

450r shock conversion front and back re-valved and re-sprung

Everything else is stock but these parts are waiting to be installed:
JE 10.6 ceramic coated top/ skirt coated piston
Uni Filter
EHS Airbox lid
Hot Cam stage 2
CT full Exhaust
CFM +1.25 qrt Oil Tank

Also what gaskets are best and do I really need to change the rod or am I worrying over nothing. I really want to be as reliable as possible. (the reason I got the piston coated from JE.)

Please let me know what you think and thank you for the wealth of information on this site it has really helped me on my build!

How long have you been running your bored or higher compression 400 with no issues?

[CJM]

You dont need a new rod or anything like that, it will be fine.

I would get cometic gaskets, when it came to doing my 416 11:1 setup I got some EST ones they sell-they claim they are better since they are "extreme seal technology". All I know is so far no issues and I probably have 250+ hours with no issues.

Key is to make sure its jetted and in my case use 93 octane.

[SPE_Motorsports]

I would personally keep the stock rod in it right now if you are keeping the bottom end together, 10.6 and a 406 bore isnt much to be worried about as far as reliablility goes. Almost every 400 I have seen has had to replace the shift shaft sometime in its life. Once that happens and you open the bottom end up, then I would change the rod. Keep the bottom end together like it is until you have to get into there. I dont see a need to right now.

[slightlybent47]

You'll be fine.

[08400ex'er]

Do you think it will run cool enough with 93 or should I install a larger oil cooler instead of the larger oil tank or both?

[tri5ron]

Your waaay too worried over this build.

A 406 @ 10:1 is REALLY not much difference than stock.
The variance in the days tempuratures will probably have more effect than your build.

A larger oil tank/cooler is NEVER a bad thing. Even for a stock engine.

If it would make you feel better, or satisfy a burning A.A.D.S. Outbreak, then add a spal fan to your original oil cooler, and be done with it.

You won't NEED to run 93 octane with a 10:1 compression piston.
remember the compression listed on the piston won't be quite that high in a 400EX, due to a TDC deck height of about .040 below the top of the cylinder.
BUT, Here again,...
if it makes you FEEL better to run the 93, then by all means,.... Feel Good !

[08400ex'er]

Thanks tri5ron.

I have always heard that the JE pistons compression rating was really close to what you actually got. My thinking was that I've seen people post that at 11:1 some, only some, had to mix in a little race gas or they had issues with pinging. Since 10.6:1 is close to 11:1 and with JE advertising a more accurate compression ratio then if I wanted to be safe I might need to run a little extra cooling.

Really the only time I have cooling issues is when I'm at Silver Lake MI a few time a year that's with a stock motor and 93. Just seem to run at a much higher rpm and have a lot of resistance on the sand.

[CJM]

Its not actually the piston thats causing the compression measurement problems-its the cylinder to height deck itself. The XR400 uses a thinner gasket as well as I think the head might be a few thou of an inch less.

So in reality your losing a bit of compression due to cylinder/deck height. Many use the XR400 head gasket since its thinner to get it back closer to spec.

I also think many who have problems with pinging are running the bike to lean, proper jetting is key to any engine-too lean and it gets to hot and will ping. The engine isnt getting enough gas in this situation and thats a bad thing. Using a higher octane just masks the problem. Issue is, many feel they are jetted properly b/c the bike runs well-this isnt always the case.

But seriously: Your gonna be perfectly fine with your setup. If anything the only recommendation I can suggest is to buy cometic brand gaskets. They are made very well and much better than even stock. I have the EST (extreme seal technology) set and I have been SUPER happy.

[08400ex'er]

Thanks CJM,

I will defiantly get the EST gaskets then. That is about the last thing I need before a schedule a time to get it done. I appreciate your help ad will let everyone know how it goes.

Thanks again for the help everyone!

[CJM]

Your welcome.

[redrider440ex72]

Does cosmetic make a gasket for a 440?

[400exrider707]

At TDC the piston in a 400ex sits .040" down in the hole. The XR400 is not like this, but almost all of the pistons (if not all of them) on the market are actually made for an XR400 (since it was out a long time before the 400ex ever came out).

You can measure your cylinder volume and calculate your static compression if you so wanted to.

Some common things to do with a 400ex motor when doing this, remove the base gasket between the cylinder and the cases, and just run a SMALL bead of gasket maker (yamaha and honda both have some nice stuff) for your seal, this lowers the cylinder a little and pushes the piston farther up towards the head. You can also run a thinner head gasket like the stock XR400 gasket, or go even thinner to a "thin" cometic gasket. I ran 11:1 with the thin cometic and the stock base gasket for about 2 years, never had issues and ran like a champ.

[timp224]

I have a 416 11:1, jetted with 52 pilot and 180 dyno jet main. My quad started to ping when i went on my first long trail ride. I now mix my gas 50:50 with race fuel and it runs awsome. I dont think im too lean on my jetting, but i am running a xr 400 head gasket and to get the deck hieght perfect i ran honda high temp gasket maker for the base gasket. This is what they do at FourStrokeTech when you send your engine for a mild bore with a high compression piston.

[400exrider707]

Originally posted by timp224
I have a 416 11:1, jetted with 52 pilot and 180 dyno jet main. My quad started to ping when i went on my first long trail ride. I now mix my gas 50:50 with race fuel and it runs awsome. I dont think im too lean on my jetting, but i am running a xr 400 head gasket and to get the deck hieght perfect i ran honda high temp gasket maker for the base gasket. This is what they do at FourStrokeTech when you send your engine for a mild bore with a high compression piston.

That sounds ridiculously rich, but you'd know more than me since it's right in front of you. Whats the plug look like?

Don't forget (not just you, but an FYI for everyone) that dynojet numbers do not = kehein numbers. Dynojet 180 main is larger than a kehein 180 main...