LC4 Engine Rebuild Guide

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Where to start? I started writing this article six months ago; why I am only publishing it now? Well – here’s the full disclaimer. It went wrong, it went very badly wrong. I decided I would rebuild the engine myself after it overheated in Iceland, there was no way I could afford to have a dealer do it. I foolishly decided to do the whole thing, bottom end included, as it was full of pieces of exploded piston ring. Despite a complete lack of experience I did get it all back together and the engine did run; if only for 5km before a bearing exploded and blocked the engine. This was entirely my fault. I put a spacer which should have been on the gearbox on the balance shaft. I can even explain why – I checked the diagrams, I checked the service manual. I could not spot where this thing should go so the only possibility, as I saw it, was that it was a second spacer to get the right clearance. It wasn’t. The shaft was pressed hard against the bearing, the bearing came apart killing the cylinder, piston, crank and balance shaft. It cost a fortune to repair and broke my heart. There were tears once I stripped the engine down again and realised what had happened.

My first piece of advice to you, dear reader, is leave the bottom end to the professionals. If you are in Europe – that’s probably Pirate Racing in Germany. If you’re in the UK – that’s likely to be Lyndon Poskitt. If you’re in the US or elsewhere – no idea. But it was a mistake for me to do this part of the rebuild at home.

If you are neither a professional nor a self sufficiency freak send it away. I had a hellish time trying to get the bearings out of and back into my cases. I whacked them, I cooked it in the oven – which made the whole flat stink for days. It was horrible and I was lucky not to do more damage. Even on the cost front it makes no sense. Pirate Racing charg €350 for a bottom end rebuild including new aftermarket parts and all the work. Buying the parts from KTM, plus the case splitter special tool and a bearing extractor cost me nearly as much. They have the experience, they have the special tools and it’s dangerous in there. That one misplaced spacer cost me €3000 – it’s just not worth the risk. Where you’ll save your money is in removal and reinstall of the engine, assembly of the starter drive, rotor, clutch – that stuff takes up most of the time and is pretty hard to cock up. If you do make a mistake it probably won’t be too costly.

I felt it was critical that I was absolutely open about my mistakes before going further with this guide. The whole point of the guide is that you, dear reader, can learn from my experience; mistakes included. On with the guide.

General Observations

  • This guide is based on my experience; I am (obviously!) not a professional mechanic. Any advice I give on this post is to be taken in that spirit. I am not responsible for anything you break by following my advice.
  • Some degree of general mechanical competence is assumed; you wouldn’t – or at least shouldn’t – be trying this crazy shit if you don’t think you can do it.
  • You will need the official service manual to make use of this guide, in most cases I suggest you trust it – it’s very precise. My tips are mainly intended to avoid having to buy too many special tools and to clarify certain points. Obviously the service manual is a copyrighted document, which you’ll have to purchase if you want a legitimate copy. That said, if you drop me a message – my contact details are on the blog – I may be able to help you find a digital copy for significantly less than the RRP.
  • All of this information is based on my 2016 701 Enduro, most of it should apply to any LC4 but KTM can and do change things. Use the correct service manual and your common sense.
  • I strongly recommend reading everything before starting the job, both in this guide and the service manual. Next steps are often useful in making sense of current instructions. Do (most, there are exceptions – below) things in the order the service manual specifies, it’s in that order for a reason. Don’t skip things unless it’s absolutely clear you can skip it. Take your time.
  • Nothing about this process requires brute force. For example I was lucky not to do serious harm to my cases when I failed to remove the shaped washer from the water pump end of the balance shaft. I tried to force the cases apart before I noticed what I was doing wrong and ruined two seals and a bearing. I could have ruined the case itself.
  • Ask for help. I’m happy to offer advice to anyone who contacts me; the community on Facebook are hugely helpful and many even know what they are talking about. Don’t be afraid to talk to the professionals either, it was Lyndon who finally pushed me to send the bottom end away. I was all ready to do it again. Obviously there are limits, they do this for a job – but they’re human and there’s never harm in asking a question..

Of Special Tools and Shortcuts

The service manual makes it look like you need to buy a lot of special tools to do the job; many of which are – to put it lightly – pricey. I purchased four; only two of which were from KTM. One is only needed to split the bottom end, which I advise against.

  • 33mm Rotor Extractor – Replaces KTM Tool 58429009000
    • Used to remove the rotor; you could maybe use the claw puller if you were really brave and dedicated to saving money – but it would need to go in the holes and would be a long way from safe. A new rotor is very expensive. I got a replica of the proper tool from JMT, part number 722 49 18, marked as a M33 x P1.5 which I assume is size and thread angle. It did the job perfectly for a fraction of the KTM price.
  • Medium (150mm) Three Arm Claw Extractor – replaces both KTM tools below.
    • Timing Chain Sprocket Extractor – 59029033000
    • Primary Gear Remover – 75029021000
    • Used to remove the timing chain sprocket and the primary gear. The service manual recommends a claw extractor for the timing chain sprocket; it recommends a rotor extractor for the primary gear. I initially tried with a two arm extractor and wasn’t comfortable with it; I swapped mine for a three arm version and the primary gear came off nicely with no damage. The ‘protector cap’ 75029090000 seems pointless.
    • Mine was from a local tool shop, a quality tool for about 100 euros.
  • KTM Gear Segment – 75029081000
    • This is a great tool. It cost about €25 and I used it where it was intended to be used – to lock the primary gear and the clutch. I also use it in this guide to lock the engine for working on the rotor nut and as my TDC lock tool. Well worth the money.
  • KTM TDC Lock Screw – 77329010000
    • It’s a screw. I used the handle of the gear segment tool above, it’s a perfect fit. It does leave a little scope for things to wiggle; but as long as you look at the camshaft sprocket and ensure it’s lined up right you’ll be fine.
  • KTM Case Splitter – 75029048100
    • The KTM tool is markedly cheaper than the generic tools from MotionPro etc, it made sense to buy it and it did the job very well. You only need this if you are going to split the cases yourself.
  • KTM Feeler Gauge – 59029041100
    • I picked up a generic one from the hardware store; it worked for everything I needed it for.
  • KTM Cam Chain Release Tool – 77329051000
    • Totally pointless, you can push it with anything that fits in the hole to release it.
  • KTM Clutch Assembly Screws – 75029033000
    • They’re screws, people. Screws with little handles on the top. I used four M5x40mm machine screws with a big washer on the top.

Of Generic Tools and Stripped Threads

You’ll need a good selection of general tools. I have listed all tools required to work on the engine in a separate blog post and everything you need for the frame in another blog post, so I will not repeat myself here. What I will stress is that you absolutely, unequivocally, must have a torque wrench. Probably two; I have a small one which goes from 4 to 22Nm and a large one which goes from 20 to 200+Nm. Don’t attempt any of this without one; the cases are made of dry balsa wood. It’s extremely easy to strip a thread and repairing them is nerve wracking.

The Guide

The way I’ve written this is as a supplement to the service manual. Most of the information there is very clear, easy to follow and it’s all in the right order if you have the special tools. Where I ran into problems or found ways of avoiding expensive special tools I aim to offer some additional guidance.

Page 135 – 18.1
Page 138 – 182
Removing and Reinstalling the Engine

Read the next part of my guide before you do this step.

There is a trick to doing this without a lift stand that makes it fairly easy on your own and extremely easy with a friend. You can pivot the engine in and out of the frame on the “lower rear” engine mount, as in the picture below.

In order to do this the radiator needs to be completely removed – but that’s only two bolts and a couple of electrical connectors. You will also need to remove the three bolts that hold the ABS unit in place, photo below. It will stay where it’s supposed to be because the brake lines are rigid but you’ll gain enough wiggle room that you can push it out of the way as the cylinder head swings past it.

With the front engine bolt and the two engine hangers removed all you need to do now is remove the swingarm bolt and the engine will drop right out. My method was to remove the little “cap bolt” which holds the swingarm shaft in place and then drive the swingarm bolt out with a 1/2″ extension shaft. If you judge things right you can get it so that the swingarm and the frame are still held together by the bolt on one side and the swingarm is held in the right place relative to the frame when you pull the extension shaft out just far enough for engine to fall out. The same applies at reinstallation – you can have the bolt at one side, holding the frame and swingarm together there and the shaft doing the same at the other side. Photo below.

Dropping the engine out on your own is pretty intense, for me at least. If you happen to have the muscles of Stallone you’ll be fine. I would strongly recommend having a friend help; it’s a tricky manoeuvre to “catch” the engine on it’s way out and extremely challenging to simultaneously hold the engine in the right place and drive something into the swingarm bolt hole during reinstall.

For both removal and install a piece of wood of the right height under the engine helps, especially at reinstall – it helps you line the hole up more easily. Giggidy.

A final note here is that the swingarm bearing is a non-retained needle bearing. That means the needles can and do fall out pretty damn easily; they are only held in place by whatever grease is in there. Once the engine is in it’s extremely tricky to get the shaft back in place properly. My advice is – no matter what – do not let the shaft push the inner bearing sleeve out of place. It’s damn fiddly, it took me an age to get it in the right place, but bare with it – don’t be tempted to pull the sleeve out. Hold the sleeve in place, wiggle things about, tap the other side with a hammer. Like a lot of this it helps to have three arms.

Page 150 – 18.3.23 – Removing the Clutch Basket
Page 152 – 18.3.24 – Removing the Primary Gear
Page 148 – 18.3.17 – Removing the Rotor
Page 191 – 18.5.9 – Installing the Primary Gear
Page 191 – 18.5.10 – Installing the Clutch Basket
Page 194 – 18.5.16 – Installing the Rotor

I said above that the order in which you do things is generally correct in the service manual. One exception to this rule is when working with the very high torque nuts that hold the rotor, clutch basket and primary gear in place. One tool you’re very unlikley to have is the proper engine stand; generally this isn’t an issue – you can do almost everything perfectly safely on your workbench but unless you’ve got an assistant with a grip like a vice you will struggle to torque down – or undo – these nuts.

But you do have a very effective engine stand; the frame of your bike. Before you remove the engine from the frame take the clutch and rotor covers off. With the bike in neutral* take the KTM Gear Segment tool and use it to block the clutch and primary gear, as in this picture.

For this to work the clutch needs to be locked together, which KTM have a tool for, but you can use four M5x40mm machine screws; just snug them down to a firm hand-tight so the clutch is fully engaged.

Now you can use a large ratchet to remove the two nuts on this side (watch the reverse thread on the primary gear) but you can also use the same technique to remove the rotor nut – unless you have very long arms you’ll need an assistant to hold the gear segment. Sig the clutch still locked and the gear segment in place you can just undo the nut – the engine won’t turn. The same approach applies when reassembling the engine – I installed mine into the frame without the clutch and rotor cover. Once I had the engine hangers on and all engine retaining bolts tight I used the tool on the upper side of the two gears to block the engine and torque all three nuts properly.

*There are other approaches that I have read about. With the drivetrain in place you could probably just put the bike in gear and have an assistant stand on the brake. This would also block the engine and would probably be fine; the gearbox handles the engine’s ~70Nm of torque all day, every day and can probably handle 100Nm for a moment but for the sake of a cheap, multi purpose tool… it’s your call. You can also just blitz it with an impact gun, if you have one.

Page 150 – 18.3.23
Page 191 – 18.5.10
Clutching at Straws

The service manual suggests you lock the clutch pack and take it out as a single piece, personally I took my clutch plates out one by one and flipped them, in the same way you would if you were reading a multiple page document printed on loose single-sided paper, placing each disk “face down” and then the next one on top of it. At reinstall I put the plates back in using the reverse of that technique. The advantage is that you get to inspect the clutch pack as you work with it.

Update – in rebuild two I realised that I could use regular M5x40mm machine screws in place of the KTM “Assembly Tool”, so if you’re not interested in inspecting your clutch pack you could take it all out as one without the special tool. This has the advantage that you can’t put the plates in wrong or get confused by the “pretension disk” and the “protection disk”, which are not clear in any diagram.

To be clear – they are the two thin metal disks which sit inside the top friction plate (the smaller one that is installed offset by one tooth). The pretension disk is the thinner, angled one and goes on first (towards the inside of the motor). It is oriented like the roof of a house, or one of those Chinese hats with the slope going down from inside to outside. On top of it, towards the outside of the motor, sits the protection disk. It might be stuck to the inner clutch hub.

On the 2016 engine KTM have changed the bendy clutch lock nut to a thrust washer. I’ve no idea what a thrust washer is, does or how it works – sounds to me like something you might need after having sex at an inopportune time of the month. I upgraded to the new part anyway, it was dirt cheap and re-using a bent washer on so critical a part didn’t seem wise.

One final note about the clutch; don’t leave the push rod sitting out anywhere for too long. Mine got very rusty, very quickly when not bathed in oil.

Page 196 – 18.5.20 – Installing the Piston (and the Cylinder)

First up – in both rebuilds I had my cylinder refurbished by a professional workshop. This isn’t a task you can do in your home workshop; it’s a serious piece of professional machining. Don’t try. I don’t even know how you’d try.

KTM suggest the use of a special tool for two parts of this process; fitting the piston pin retaining clips and the installation of the cylinder onto the piston. Or piston into the cylinder. However you like it.

I did not use a KTM piston on either of my rebuilds; I used one from Wossner which was much cheaper so my process did not exactly match the service manual and neither did my parts. That said I am fairly sure that with care, you could install the retaining clip like I did on a KTM piston. I simply placed one end of the clip into the recess, held it in place by hand and pushed it into the groove with a punch. Be careful though – if it goes wrong that clip could ping off anywhere. At an absolute minimum stuff paper into the top of the engine to prevent the clip from going in there – you don’t want to have to try and get it out of the bottom end.

Fitting the piston rings was common sense. Put one end of the ring into the appropriate groove, slip it around the edge until the whole thing is in place. Lots of videos online on how to do this for various pistons.

The service manual fits the assembled piston into a special tool and then drops it from there into the cylinder. I realised that the shaped bottom part of the cylinder itself is a piston assembly tool. Once the piston has all of it’s rings in place and is correctly installed on the crank you can use the bottom part of the cylinder to complete the installation of the rings. It’s hard to describe and I have no photos, as the task requires both hands but it goes a little like this…

  • Lubricate piston rings.
  • Remove rag/paper from top of engine.
  • Check you have removed the rag from the top of the engine.
  • Apply sealant where the case halves join the cylinder hole.
  • Place cylinder base gasket in place.
  • Hold the cylinder in one hand and the piston in your other.
  • Slide the cylinder over the piston until the shaped bottom touches the top piston ring.
  • Without applying excessive downward pressure use the hand holding the piston to push the piston ring into it’s groove. With the ring in the right position (ends lined up with the cut out part of the cylinder) you should be able to push the cylinder down over the ring.
  • Now the cylinder will be resting on the second ring. Now repeat the process – making sure the “end” of the ring is at the opposite side, ideally 120 degrees from the other.
  • Now the cylinder will be resting on the oil scraper ring. Be damn careful here as these rings are very flexible and fairly fragile. Repeat the same process as with the other two rings on the oil scraper rings, but do not push down too hard or too fast.
  • Once all the rings are in place inside the cut out bottom part of the cylinder check they are correctly seated and push the cylinder down into place on the head gasket.

You have to do all of this fairly quickly because the sealant is drying and the head needs to be on and properly torqued down before the sealant is dry. Fun.

Page 153 – 18.3.29 – Removing the Oil Pumps
Page 188 – 18.5.4 – Installing the Oil Pumps

The biggest question I had with the oil pumps was “which way round”. The service manual says to have the bevel facing in, but both sides have a bevel. I never found a compelling answer on this one but the inner part of the oil pump, which can only go in one way, is marked with a dot that faces in. The outer part of the pump also has a dot, so I pointed that dot in towards the engine as well. It’s not caused me any issues yet so I assume this was correct.

The “THE A2-70” screws which hold the lower oil pump cover and the oil return line cover plate are crappy. Every one stuck to my bit when I took it out, I had to grip one in a vice to get the bit back out. I completely mangled one screwing it back in; before I even hit 6Nm on my torque wrench. I’ve replaced all of them with good quality M5 12mm torx head bolts. Mine were a couple of millimetres longer than KTM’s screws, but there is space in the holes. The critical thing if you replace yours is to ensure that the heads are not taller than the standard ones; as the drive sprocket for the oil pump sits directly above.

Page 193 – 18.5.14 – Installing the Timing Chain Sprocket

I’ve not got a lot to add to the service manual here except that it really does work. First time I used an electric heat gun and put a thick glove on my right hand. The second time I used a blow torch and used a normal riding glove. You do have to be quick, it cools incredibly quickly – but if you get it on there quick enough it slides on beautifully.

Page 199 – 18.5.23 – Releasing Cam Chain Tensioner

KTM suggest that you use their special tool 77329051000 to release the cam chain tensioner. Reading ahead and looking at the tensioner before install I was a little worried – I assumed there was something clever I needed to do for it to work. I assumed the little nipple on one side of it would need to be pushed somehow using this special tool. I was wrong. It goes in with the flat side facing out and you can push it with anything, a screwdriver, torx key… whatever you have to hand. Just don’t use anything so small that it damages the little ball bearing.

Page 72 – 10.2 – Installing the Manifold
Installing the LHS rear plastics.

You’d think this would be easy, right? Wrong. Took me a day. Here’s how you do it.

  • Install the manifold to the cylinder head loosely.
  • Install the heat shield on the manifold.
  • Install the plastic panel, locating on the two tabs from the heat shield correctly and screwing the panel on.
  • Install the middle support bracket to the manifold loosely.
  • Slip the middle support bracket on to the lower subframe bolt, loosely.
  • Tighten down the middle support bracket and the lower subframe bolt, switching between them until correctly torqued.
  • Tighten down the copper nuts at the cylinder head to torque, or the best you can do – I can’t get a damn torque wrench in there.
  • Remove the plastic panel.
  • Install the muffler.
  • Reinstall the plastic panel.

How the sweet zombie fuck do I get the starter motor back together?

If you decide you want to check or service your starter motor while you have it out of the engine my first suggestion would be to not bother. It’s incredibly hard to put back together if you happen to pull the back end, with the brushes, off of the spindle. If you do decide to take it apart – like I did – I found that the only way to put it back together was to press the copper brushes as far as I could into their housing with a screwdriver and then wedge the cut-off end of a cable tie in there. Do the same to each brush and you should be able to get the spindle in far enough that when you remove the cable tie bits everything is in the right place. It’s fiddly but it works.

Fuel Injector Cross Head Screw

The screw is crap. It’s a cross-head screw and it tends to strip; don’t remove the injector unless you have a very specific reason to do so.

Update 11/10/2020 Corrections for spelling, grammar and layout.

2 Replies to “LC4 Engine Rebuild Guide”

  1. Hey Tim,

    about those fuel injector screws… a lot of travelers/racers carry a spare fi (which is obviously up to your own discretion) but while you’re in there, it does make sense to change those crappy screws for something more field-repair worthy (hex, tx whatever floats yours…).

    I really like your writing, keep it up!

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