My grandson has a 2002 Honda trx400ex quad that is using an excessive amount of oil. We change oil approx every 10-15 hrs of riding - which is mostly on dirt track here at home and a couple of dune trips a year. He has had the quad about 4 years and rides it alot in the non-fire season. The quad is using about a half quart of oil every oil change. (we top up between changes). The quad has a foam filter with and extra filter bag over the foam head to help keep dirt out. Compression is still good. So I'm assuming that the valves seals may be needing to be replaced. ANY Other SUGGESTION to cause --- I'm an old time hot rodder, race car, dragster, 4x4 puller etc. so have many hours of working on vehicles but non on quads and a motorcyles. Are there any tips I should know before starting this project? Also I'm thinking I probably should go ahead and replace rings and rod bearings while doing this. My grandson keeps talking about big bore kits, etc to give bike more power. What are your suggestions and are these items really worth the money?

 

When is the quad smoking? On startup and decell only? Or is it smoking at a constant throttle? Not that it really matters anyway. Once it torn down, you might as well go through the head and rings at the same time. So that means guides, rings and seals all at the same time. At the very least check things out and mic some stuff.

10 hrs on oil is almost nothing for a modern oil in a 400. Have you ever sent your oil off for an oil analysis?

I would have a REALLY good look at the air filter system on the engine. Everybody tripps on the oil when a bad air filter can waste an engine in a hour of riding in dusty conditions.

 

Personally, I wouldn't go with a big bore kit. If the cylinder is worn, I'd go with the appropriate oversize to correct it. You would gain some power, but reliability with some of those kits isn't so good.

Anyway, I'd agree that you may as well take the top end apart and have the cylinder and piston measured, along with the valve stem and guide. It may just need a hone, rings, maybe valve lapping and seals to be good as new, or it may be time for a piston or maybe a rebore and OS piston and/or valve guides and a valve job.

 

Don't go with the big bore kits because you would have to rebuild alot more than the regular engine, get like exhaust, a rejet kit and all those things. Just like keffin td said you would probably need hone, rings and valve lapping.

 

Thanks for the replies and good information. Your advise was what I figured would be the way to go, relying on my automotive knowledge. But it's good to have the confirmation from people that know quads.

 

Have you done a leak down if not I would do that first.

If it dose need a rebuild I agree with the others just do whats needed piston,rings and valve job

Then on the other hand you can do a 440 kit piston,rings,cam,valve job,k&n,header,air box mod.

If done right they are very reliable.

I have had 4 of them and put over 4000miles on them befor i sold them and 1 502kit that has been running now for 6yr but I would not go this way as it takes a lot work to get right.