Does increasing your displacement decrease reliability?

[kbnorth99]

I have had my 400ex for a few months now and I am starting to think about my wish list. One of the reasons I bought an ex is that they Are pretty much bulletproof. I know there are a number of ways to increase displacement. Bore kits and stroking come to mind. I've heard some say that once you start to go down that road you lose that reliability that the ex is known for. Is that true? Are some approaches more likely to cause problems than others?

Thanks

[slightlybent47]

I’d say it depends on how far you go with it.
I have a 416 12/1 stage 2 cam 450carb and some other stuff, and I didn’t do the HD studs and it has at least 200 hours of racing on it and it still runs just fine and starts with just a bump of the starter.
And I am still running the same original clutch that came with the bike.

So the answer is yes you can do quiet a few mods and still keep it dependable.

But I will add that I’m very anal when it comes to keeping fresh oil and filters in it and keeping it clean after I ride it.

[togup]

The ex is so "bullit proof " due to its simplicity ,air cooled ,low compression ratio ,chain drive ,single piston and single cam. Any motor by any brand in any motor sport looses dependibility when you start modifying it, but how much fun is stock? Buy good parts build it correctly(emphasizing correctly) and youll be glad you did. Im currently riding my second 460 stroker and would not look back but engine failure does prey on my mind could be around the next curve so my advice is build what you can to replace!

[907Rider]

[i]so my advice is build what you can to replace! [/B]

Very wise words right there :cool:

[tri5ron]

Originally posted by 907Rider
Very wise words right there :cool: X2

[CJM]

More you bore out the more heat you generate, the hotter it gets the more chance it can fail. Ya run the risk of that, BUT:

If you build it right and dont skimp your good to go. I just did a 416 11:1, hotcam stage 2, CRF timing chain and cometic gaskets, spal fan, and the HD studs just cause and rejetted. IT rips vs my friends stock machine.

No issues at all, doesnt get hot at all worse than stock and has been reliable. But I take care of my stuff, oil changes alot, anything that seems off I check.

[JOHNDOE83]

my 440 does not run hot, I have it jetted correctly.

Ive had this same 440 kit for over 5 years, it runs super strong, beats highly modded 450s, does NOT run hot, has stock oil cooler, runs on regular car motor oil, regular pump gas.

heat comes from lean conditions, most people think that 440s run hot, it is not true, if your jetted incorrectly it will run hot no matter what your bore size.

if bore size made a motor unreliable, they wouldnt sell big bore kits.

[Pipeless416]

if you want to compare strictly to stock reliability, then yes, it will change it. any time you are putting out more horsepower than stock you are increasing stress levels and wear on certain components, thus reducing reliability. remember, that is an extreme view. will going to a 406 or so make any difference in the real world..? probably not.