Project Old School KTM 380: Motor Clean-Up and Modifications

For the top end an OEM 2 ring piston was selected for durability and the available size options. KTM offers both #1 and #2 sized pistons with the #2 being a little larger than the #1 to account for cylinder wear over time. In our case the #2 piston was the right choice to ensure proper piston to cylinder clearance.

The OEM KTM piston comes in a kit with the piston, rings and the wrist pin. It doesn’t come with the wrist pin bearing so we made sure to order that as well so we could replace the original. The power valve parts, including the front cover, were bead blasted to remove the oil and carbon buildup. Whenever using the bead blaster make sure to thoroughly wash the parts in warm soapy water afterwards and either put some two stroke oil on them or spray them with some lubricating oil to prevent rusting.

With the cylinder itself it great condition we opted for a mild porting cleanup job. Porting is best left to the professionals who have done it many times before and have the proper tools for the job. We dropped off the cases, cylinder and head with DASA in Riverside, California for the performance mods.

DASA specializes in motors, 2 or 4 stroke and has years of experience in the field and even does motor work for some of the Supercross teams. They have a full machine shop with CNC machines that crank out custom billet big bore cylinders for jet skis and other things.

Even though they have all the latest and greatest they also still have the old school porting tools for whipping our 380 cylinder into shape.

Thoughts crossed our minds to start reshaping the ports in the cylinder but DASA recommended that since the cylinder was in such good shape and we were already happy with the power spread of the motor we should just do some clean up porting to remove factory imperfections. Their point being if the port shapes in the cylinder are altered then it is best to also get it replated.

By replating the cylinder after serious porting work the new plating flows into the ports and the risk of catching a ring on a rough spot is all but removed. For us we didn’t want to have to replate a perfectly good cylinder so altering ports and risk catching a ring kept us with just a cleanup. Of course many folks do in fact port the cylinder and don’t get a replate and never have a problem but we wanted stick with what would give us the best odds for a long life motor.

While the cylinder just got the clean up treatment the head actually did get some modifications. KTM 380s are notorious for being hard to jet and for surging in the midrange. Most of this is caused by an ineffective squish in the head. Dasa had measured the stock squish at .093 in which means inefficient combustion and lots of room for improvement. Since head modifications require having some specific measurements with the motor together DASA mounted the cylinder and figured in the proper base gasket before machining out some of the head to decrease squish to a safe .060. When you remove material from the head you are in most cases also removing volume in the head. Any time you remove volume it is critical that a compression check be done to ensure the compression isn’t dangerously high, or just high enough to require pump gas. Since our motor isn’t assembled we have to wait on the compression test until we get the motor together. At that point if the readings are within spec we can stick with the current modifications made by Dasa. If, on the other hand, the compression reads to high then the head will go back to Dasa for some reshaping work to bring it back down.

While the DASA folks are experts at engine performance mods they don’t claim to be experts in KTM bottom ends. They did manage to swap out one of the main bearings with ease for us but the other one they were reluctant to change out for fear of possibly breaking the case. The difficult side is a roller bearing with no way to get it out with a punch or press from the outside of the case.

One method of getting the bearing out is to remove the rollers, leaving only the race and then use a puller to remove the race.

We didn’t have the proper tools, and even if we did wouldn’t have attempted it without prior experience, so once we received the motor back from DASA we took the cases up to TrailTricks in Frazier Park for help on the other main bearing.

The owner Javier is well known for his suspension work but also knows his way around a KTM motor. Having been a mechanic for race teams in South America for years and a stable of KTMs of his own he knows his stuff and we trusted him for the bottom end work on the 380. He had the correct puller and the experience to change out the bearing and was able to do it with no issues.

The only negative in using him is that he is a small shop with a big workload. For us, and others we have talked with in the past, this has resulted in a few annoying weeks of him saying it would be done only to find out it wasn’t.

Difficult to plan around a shifting schedule like that but something we had to live with if we wanted the work done there.

We did have one hitch with the bottom end however. On my parts order I had thought I ordered a lower rod bearing and provided it for DASA to send out with the crank to be rebuilt. It was my understanding that the crank was sent out and rebuilt but about 15 minutes after dropping off the cases and crank with Javier he called and asked what was wrong with the crank.

When I told him I thought it had been rebuilt and I ordered the bearing myself he told me KTM doesn’t sell just the bearing, only the rod kit that comes with the rod, pin, washers and bearing. Who knew, obviously not me! I have no idea what the crank rebuilder used but the parts fiche clearly shows only the rod kit is available.

Needless to say we had a rod kit delivered to TrailTricks and Javier rebuilt the crank for us. Kudos to TrailTricks for catching that and rebuilding the crank for us!

Another goal for our Project 380 is to eventually be able to run HID lights and grip warmers. The stock ignition on our 2000 model is the beefy 2K3 version which has two leads coming off. One is meant to power the lights with AC direct from the stator while the other lead is only used on the European model to route to a regulator/rectifier to be converted to DC and charge the battery.

With one lead being wasted on the US version we had TrailTricks modify the stator to combine both leads into one so that it can be converted to DC. In a future article we will cover the wiring of the stator to a regulator/rectifier for the conversion and then onto a battery or capacitor from which we can run HIDs and other electrical accessories.

Everything else inside the motor looked to be in great shape. The next step is to go over the manual for the steps on reassembly and then get started. We have a Moose gasket kit on the shelf which contains all gaskets and seals for a complete rebuild. In addition we have decided to install a Rekluse auto clutch to make the bike even more versatile on nasty single track trails. While they don’t offer a Rekluse Pro model for the 380, the bike has enough power that the full clutch override probably isn’t as necessary as it might be on a small bore. In fact we might also go for a left hand rear brake setup to gain even more control in the nasties and on downhills. Between inspecting the motor, ordering parts and having two different shops perform work on the motor it certainly has taken a while to get to this point…but we are finally here.

Stay tuned for the next article covering the reassembly.

Contact information:

DASA
6251 Orco Parkway Suite A
Riverside CA 92509
951-681-1131

TrailTricks
620 Canada Trail
Frazier Park CA 93225
661-245-2358