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Discussion Starter · #1 ·
Honda 2008 400 EX Engine Rebuild Time

Engine would smoke one out of 5 cold starts, ran great still, never smoked out the exhaust under power.

anyways, dummy me does not check the oil level and while we are out on trails it stops running, I get it restarted and I can Hear Clattering in the Valve, rocker area, stop it and tow it back.
Engine is not frozen, it rolls over, but I ran it low on oil.
How much Damage am I looking at?
I plan on sending it out to get someone more experienced than me to do this.
my plan is to have them tear it all down, and refresh it all.
Not doing anything wild, just back to stock for Reliability.

Question? what are some of the reasons that these start to smoke in the first place?

next I want to say that this is a great forum, and a great source of information, and I read more than post.
 

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Discussion Starter · #3 ·
Thanks for the Reply.
I expect to have to replace everything that moves in the Top End.
Maybe even Piston, rings, Sleeve, Hope not the crank, or rod, but we will find out shortly.
 

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The piston and rings if it lost lubrication, but the cam is the furthest from the oil pump and in the hottest part of the engine. It usually suffers first.The crank is usually fine even though the other parts are toast. The cylinder is a steel lined casting and the sleeve is not removable, but can be bored to an oversize if damaged.
 

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Discussion Starter · #5 ·
Thank You!
when I did drain what oil was in it, and checked the oil filter, there did not seem to be any Metal shavings in the Filter, so hopping it is all top end parts to replace.
 

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Discussion Starter · #6 ·
here is an update on what I found.
Cam has a bit of wear, but the engine guy says that will clean up.
Motor vehicle Wheel Automotive tire Tire Automotive design


piston is shot, has a crack in it.
Automotive tire Wood Gas Automotive wheel system Tread



cylinder was is messed up, guy says it will clean up with over bore.
Automotive lighting Automotive tire Motor vehicle Alloy wheel Vehicle brake


here is where I am confused.. this decompression lobe on the cam is no were close to where it would even touch the
pin


Automotive tire Auto part Gas Rim Automotive wheel system


Automotive tire Gas Bumper Auto part Metal


these was no pin, or spring in there, quad started as good as the other 400X that we have.
 

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I have my doubts about the cam - it looks like it has been blued from overheating - what do the rocker arm pads look like? The crack in the piston is not a problem - the fact that the piston was heated to the point of melting is more of a problem. I would need a better pic of the cam to assess the decompressor - it looks like the decompressor was removed in which case the actuator pin and spring would have been removed also. If a high lift cam was installed, they do not have a decompressor as the lobes are taller than the decompression lobe. As hot as the piston got, I suggest the small end of the rod be carefully inspected.

I'm going to guess that in addition to being run out of oil, the engine spent extraordinary lengths of time idling and was severely overheated.
 
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