Tuesday, 29 November 2016

KTM 400 EXC 2002 - A New Piston?

The 400 has been burning a bit of oil lately, after my last two day trip, it had used about 250ml of oil, which when it only holds 900ml seems a lot to me, so I asked a mate, Geoff, who has built and repaired lots of engines to show me what to look for and how to check it over. I was keen to learn some stuff about doing this and Geoff is great at showing & doing this stuff...

Once the bike was at his place, we pulled it out, got changed into scruffy clothes, got the beer out of the fridge and set about getting the engine out of the frame.

Disconnecting all of the various ancillary bits, like the carb, the kick starter, the decompression lever, to name a few, was pretty straight forward. The twin exhaust pipes came off with some help from a big steel bar,they had part corroded, part heat welded themselves to the engine block, so took some effort to free up.

Also with this particular model the rear swingarm had to be dropped out as one of the engine mounting bolts doubles up as a swingarm bolt. There are three engine mounting bolts altogether for this particular bike, one at the front, one at the back and a hidden one at the bottom. All of these have captured nuts and so only come out one way.

The engine is a tight fit, it has to be taken out of the frame in a certain way which involves some tilting, some wiggling and a really bad position for your back! I can see why they have changed some of the design for the modern bikes as this would have been a pig to sort out for racing.

The frame and all the rest of the bike is filthy too from all that use, it needs a really good clean, which it can now have. If I do this again to this bike for whatever reason I'll have it completely to pieces and powder coat the frame again but for now, it's concentrate on the engine.

We mounted it onto a workmate bench and wound up the threads to hold the engine upright, then it was time to start stripping it down. oil pipe first, water cooler case, valve casings etc, etc... one of the bolts on the front of the valve casing has corroded in and it actually snapped off, so it'll need drilling out and a helicoil before being replaced.

We separated the cam chain with a mini chain tool, then after putting some wire in place to hold the chain, took the cam shaft off and laid it to one side. After a brief inspection of the valves, looking for seepage/damage, we moved onto the main engine bolts, two inside by the valves and two outside, these were really tight!

A little tap with a block of wood, saw the engine split and the piston visible, there is a lot of burnt oil on top, and the valve heads are a little caked up too, this is looking more like piston rings as we looked and discussed possibilities.

We removed the piston and checked for play in the big end bearing, looked over the bottom of the engine and then packed it with rags to stop anything dropping into it. That was it for this bit.

As for the cylinder and piston itself, it turns out the piston ring should have an 0.80mm gap, this one is 0.90mm so it's over tolerance. We didn't bother to measure the oil ring after this. After inspecting the cylinder, it has an edge to it on the front face, so it'll need replating and honing.

When Geoff was racing he used a place in Castleford called Lockside Engineering to sort all this type of stuff out for him, so we popped up there, they turned out to not be able to help, so we rang Eurotek KTM in Ripon, during the discussion and parts order, they suggested Langcourts in Weston Super Mare for the replating, so parts were ordered, due in two days time and then it was wrap up the cylinder and get it sent away.

One of the great things about the KTM's set up is the parts manual, there is no ambiguity at all, just quote the number and order the part, excellent, Eurotek also gave me a 15% discount as a TRF member, so even better! Total bill is £246.90 minus 15% = £209.87

02 January 2017...
OK so the bike is rebuilt and back on the road, running quite a bit quieter and with more punch to the power... Great I do love riding this bike!!

Geoff & I got together to rebuild the engine, but as with a lot of things, too many cooks spoil the broth. As we refitted the piston, we realised that Langcourts had pulled out the locating pins with a set of grips of some kind and chewed them up, (our fault as we hadn't removed them prior to posting), so we did the bits we could, put in the new cam chain, cleaned loads and whilst lining up the piston into the bottom of the middle section we caught the oil ring and it snapped. So back on the phone to all the local KTM dealers to get the bits, but as no one had them in stock, it was order time again and wait some more...

I got a text from Geoff, the engine was rebuilt and ready to be refitted... so another trip east and off we set to get it remounted into the frame. The job was fairly easy to do, except for lining up the engine mounting bolts which is really awkward as you have to be supporting the weight of the engine whilst straddled over the bike and someone else has to locate and slot in the bolts.

Once we'd got it all back together, it was time to press the button! Nothing, Nada... some kind of electrical fault, so we went through all the usual things, battery, connections, plugs, looked for poor earths and broken wires and drew a blank. Neither of us knew enough about electrics to sort it, so I loaded the bike up, said a hearty thanks to Geoff for all his efforts and took the bike home.

Once home I went back through everything over the next couple of days, looked again at the new stator/regulator install, looked and looked and finally gave up!

Call in a mate time. In 5 minutes he diagnosed it as the earth on the battery. Despite it being done up tight, the connection had corroded underneath and it wasn't earthing correctly, so we wire brushed and sanded off the connections and hey presto, bobble, bobble, bobble went the engine!!

I ran the bike in over 50 - 60 miles  to bed in the new piston, then changed the oil & filters again, the carb also seems to have the float sticking as some fuel is dripping out when it's standing so that's another job...

So now I'm going to replace the earth lead with a new one, this one is 16 years old I suppose and I've cleaned up the connections on all the earths. Now it's time to finish off the rest of the electrics install and get on some bigger multi day runs...

Total Costs - £436.11

Eurotek, Ripon
Piston - 89mm 595.30.007.000/11
Cam Chain - 590.36.013.000
Cylinder Head Gasket - 590.30.036.000
Cylinder Base Gasket - 590.30.035.050
Water Pump Gasket - 590.35.053.000
£257.64 less TRF discount @ 15% = £220.61

Broken oil ring - 595.30.031.000
2 x locating pins - 590.30.023.000

Clean. remove old Nicosil coating, recoat, hone to correct size + postage  - £142.20

Oil - 5 litres - Halfords - £29.00
2 x filters - Ebay - £21.80