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ktm 350 xcf top end rebuild. Top end rebuild

Top end rebuild 2018 Ktm 350 xcf (same parts as sxf)

This is not a repair guide.. plenty of those online.. this is more of some specific situations around the rebuild that caught me.

So I decided i would do a top end rebuild my self.. IT was more expensive to do it myself but the benefits where huge.

Year: 2018

make KTM

Model: 350 xcf

this is my 2018 ktm 350 xcf

Great Bike!

So the rebuild was only like $250 bucks for the replacement piston ring set and gaskets.

So why was it so expensive?

While I was learning how to take the engine apart and put it back together… I had to ride so I bought another bike..

Basically the tear down was not very difficult and i youtubed a lot of videos and that helped alot.


So this was not a maintenance rebuild.. at 129 hours (i know over due) this is a trail bike and my take on the recommendations is they are based on race specs. Anyways; the bike failed on the trail. the scraper ring got stuck in the grove of the piston which was allowing oil to pass by the ring into the ignition chamber.

How to do a top end on a 4 stroke

  1. Watch Youtube videos – many of them
  2. check for manuals online. you will need to see specs for various steps in the process.
  3. make sure the bike is as clean as possible before opening engine
  4. Be organized. place all parts on clean table in order of removal
  5. Take photos through the process that you can refer to later if needed
  6. be sure you have all new parts required
  7. Ride!

the reason the ring was stuck is from debre getting past the air filter… basically i was using spray on oil which was not really covering the entire surface very well. I have now moved to the no toil system and saturate my air cleaners.

Basically take pictures at various stages and place the parts that you take off in the order that you removed them and things will go back together fairly easy.

It was time. used some gas and rags and very little wire brush to clean. All valves seats looked great.

couple things that happened to me that were strange.. the timing chain got folded over in the bottom of the engine. I was very careful to keep it up out of the engine but on an off the cams it got bound up some how. this was a treat to figure out as it would not budge. eventually I rolled the rear wheel while in gear and the chain came free.

Piston replaced.. short money but looked very good.

So now I have the bike together and running and realised that the stock chain tensioner was now failing. when we manually tried to compress it the teeth inside must have failed.

Still see the original cross threads from honing.

when the bike startes up and at idle when cold the oil pressure was enough that you could not notice but as soon as you take a load of the engine the tensioner would contract. wrapping sound from the engine.

The main issue if this continues is the chain will skip and the timing will be off. Must fix.

replaced with the dirt tricks tensioner and back in business.

One other trick is when installing the piston in the cylinder install from the bottom and compress the rings with your fingers and slide the piston right in. you will see a half moon slot where your can see that the rings are seating correctly.

About the author: Dirt Surfer

Current: 2021 TX300, 2017 TX300, 2018 SX150
Previous: 2015 YZ250, 2006 DRZ400, 2018 KTM350, 2016 TC250, KX 100