Lessons from an Engine Re-Build

The most sustained war of attrition known to man.

OK, so I’ve struggled to get the motivation to write a post about my KTM engine rebuild for a month now. As luck would have it, today feels like the perfect time to start the story. The tale has come full circle, if you will – but I’ll start from the top.
I asked to keep all the gloved they used in my prostate exams. Look who’s laughing now!

While the KTM sheltered from the storms under a crisp blue tarp, it’s engine was having a much nicer time – wintering in the garage, getting all its bits tickled. The gently stretching October nights were limiting how long I could work outside, so splitting the engine would give me some work for the evenings. My dad threw a slab of mdf over my flimsy fibreboard workbench so the weighty lump I was frog marching over wouldn’t just drop through the bottom.

And for a short time, I actually felt happy – hunched over the bench under the blue white glow of garage halogen strips.

Just beyond those blissful perfect minutes lurked a whirlwind of problems. I have battled and battled through this whirlwind until, tired to the bone, I’m left wondering whether this empty, dead-inside feeling is the universal price for knowledge, or just a deep scar from my own personal struggle. Either way- now I can rebuild an engine…. sort of. 

“Maybe it’s meant to look like that?” 

If you’ve found yourself saying those words, I can say with some confidence, it is almost certainly not meant to look like that. Mechanical components tend to have this wonderful symmetry about them, or are otherwise shaped to reflect their function. Chunks missing, dents or plastic bits that look a bit ‘melty’ don’t really look all that engineered – which at some point they would’ve been. If something is smashed to within an inch of its life don’t just put it back in… throw it out and get a new whatever it is. Even if that does mean importing one (or even better, two!) balancer shafts from German eBay. Cost effective? Not. much.

Is it still OK? Balancer shaft from the KTM. They’re basically a counterweight to the piston, aimed at reducing vibrations. You can ask my numb testes whether it works or not…

Cookery Classes

During disassembly, I’d become a little too fervid with a hammer and smashed a bearing. No worries I thought. Then I found out it was £60. Worries. Either way, they all had to come out so I could get the cases blasted and repainted.

Honestly. Putting engine casings in your mom’s oven at gas mark whatever is one of the most fun/troublesome things you can get up-to. Especially if she dislikes engine oil going in the same place as her Great British Bake Off recipes. Hashtag Furious. Nevertheless it’s the best way to get bearings (and you’re teeth) to drop out – as the aluminium cases expand with the heat the steel bearing’s weight carries them out of their bores, one by one. Pitter pattering “all over my clean oven!!” 

School-boy Error

I feel that in the motorcycling community, stripping the threads in a sump – the port where the engine oil drains from during oil changes – is the yardstick for ‘absolute twat‘. It’s amateurism at its finest, getting your ‘lefty-loosey-righty-tighty’ all upside-down. We’ve all done it, but it’s usually inconvenient enough to never do it again. But here  I was, many successful oil changes to my name, stripping out the soft aluminium threads. Shit.

I knew the drill at least, and purchased a helicoil kit that matched the bolts dimensions. Fearing to even think about helicoiling my own sump (it can go SPECTACULARLY badly) I took the kit, sump bolt and the stripped case to a local garage. When I picked it up they told me they hadn’t needed to helicoil at all, instead just tapping the hole again. The bolt went in fine, but needed a little caution when tightening they said. It was only when I got home I realised I’d given them the wrong bolt… I don’t even…what?

In my defense they looked similar, the mistaken bolt was actually a fastening pin for the cam-chain guide. In the end I had to source a new sump plug that had matching dimensions to the newly tapped hole and hold my breath.


To save clogging oil channels with sand blasting grit, I had the cases soda blasted. Same principle, but the remaining soda dissolves in water or oil with no negative effects. It took a few repeat visits to hit all the hidden spots, but it was worth it – the matte aluminum finish was pretty neat. Shame I’d chosen to black over it, really.


Now – I’m fairly new to all this ‘cosmetic’ rubbish. My bikes tend to look as worn as they are. As such I’ve only been to two powder-coating shops in my life – both for this refurb job. Of those two, both have been utter dog-shit for one reason or another. I mentioned powder-coating the frame in my last post – but forgot to mention how the company left liters of aluminum blasting grit lodged within the frame tubes despite “being very careful”. I wasted a good few hours of my life washing it out and blowing through with compressed air – over and over, until there wasn’t a shard remaining that could sneak into my oil. Colour me pissed off.

For the engine, I’d made the executive decision to leave the blasting soda all over the parts. This prevented the aluminum from oxidizing before going to the powder shop – paint wont stick to oxidized aluminium. That’s why I was dead clear when I handed the parts over – saying something like, “it’s still covered in soda, you’ll have to scrub it off thoroughly first.” Did they? Did they dog-shit. A week or so later, when assembling the cases the first flakes tore away from metal, then it all went to pot. It bubbled under the heat of the engine and melted away under drops of petrol. And underneath the paint? A smooth veneer of blasting soda. Nice.

Apart from all the above shenanigans, engine rebuilds are actually quite simple if you’ve got hold of a shop manual. Interestingly, the KTM LC4 manual only really covers the engine, so reassembly was far easier than figuring out where everything bolts onto the frame.

I sank some fresh oil and coolant into the motor, threw in a new plug and began my less-than-eagerly anticipated lesson in kick starting big singles. I did get it to fire up before I stripped it down, but there was this whole ritual and chanting behind it. Seriously, it took me two days of near-constant kicking to get the bugger to bite. During the rebuild I replaced the carb for one that didn’t have a massive crack in it, so I didn’t even know if the jetting would be enough/too much to fire up. Tinker, tinker until… an idle accompanied by the pops and bangs you’d expect from Charlie’s chocolate factory. But she ran. She ran!

I bumped up the main and pilot jets, fixed some exhaust leaks and flushed with fresh fuel and she settled right down – no longer cutting out a few minutes after starting up. The longer running led to higher temperatures which presented a new, interesting problem. The penny had dropped.

Can you see it?

No – really. I’d not even noticed it until it had come back from the soda-blasters. A hole in between the exhaust ports, (god knew what it was for) had been plugged up with a shiny penny. The heat had clearly dislodged said penny which flew out and sat, red hot on the driveway. My lucky penny.

Situations like this that came thick and fast – always requiring a new part that was special order, putting the build back 5-7 days. Then, when fixed, another would present itself, and so on and so forth. The never-ending cycle.

Only it did end. I did (eventually) win. Apart from.. (herein lies the full circle)…

I don’t want to give away the next post, about the MOT and maiden voyage but I’ll share with you a picture. This is my work-bench last night. Guess who’s back again?





2 comments on “Lessons from an Engine Re-Build

  1. Strategic as ever boy!

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