KTM 380 - rebuild req'd? Help a 2T n00b.

[mugget]

Cheers, I'll have a crack next chance I get...

I do have a pair of circlip pliers (both internal and external, even!) but this clip is more just like a piece of thick wire bent into a circular shape, no holes at the ends. The old ones were the same. Maybe that means that it isn't actually a circlip, just a snap ring or retaining ring?

I like the idea of using the old wrist/gudgeon pin, but no way this clip is going into the hole, not even if it's crooked. It looks about 3mm oversize... gonna take some "convincing" I think...

[mugget]

Okay, new piston installed. Solution was to stop being a pussy with it, put some muscle into it and put some scratches on it! (Just some small marks in that recessed area from the spring clips.)

Just took off the stator cover so I can finish up and check the X dimension and it's a bit dirty!

KTM 380 - Dirty Stator by mugget, on Flickr

At first I was kinda shocked, was expecting it to be a bit oily in there, not so dry and dirty! But it seems like the appropriate response when working on a 2 stroke is to not worry about it, so I'm just gonna finish what I was doing and put the cover back on. haha.

But a question about the 4 nuts that hold the base of the cylinder - do they need to be torqued? I mean really need to be? I was reading somewhere that as long as you get it close, get it tight with a regular spanner and torque the head bolts it's okay? Is that right?

[Jeram]

yeah, ive never used a torque wrench in my life.

Tight, but not so sight that your going to break the base of the cylinder! you'd have to really be trying hard to do that though.

[mugget]

Haha, ok then!

Next question - "X" dimension, how important is this really? The manual says 0.00mm (+0.1mm). I'm using a Moose gasket kit which looks like it has a 0.3, 0.5 and 0.8mm base gaskets. I went straight for the middle option and using a ruler and set of feeler gauges I would say I need to add an extra 0.13mm gasket to get it any closer... (so the piston at TDC is sitting slightly over the cylinder).

Also I could only get the 0.127mm feeler under one side of the ruler/cylinder gap. But it was sitting flush, no gap between the ruler/piston. Something tells me this is one of those situations where 0.03mm is not worth worrying about?

It doesn't particular worry me because I figure there's room in the head (squish area?) so the piston won't be anywhere close to touching the head unless it stretches more than about 1.5mm when it's running? Just had to ask to be sure!

And thanks Jeram, saw your reply on SMA as well.

[Jeram]

was that with the cylinder torqued down? it will compress the base gasket a little too

[mugget]

No, not torqued down. I only used two of the cylinder base nuts as well (that was something else I read from another forum and that person also said not to install the piston rings, seemed to make sense to make it easier & quicker to change base gaskets).

What do you reckon? Is it preferable to have the piston slightly below the top of the cylinder or above? (Is "+0.1mm" referring to the piston above, or would that be -0.1?)

[Jeram]

measure it again with a little torque, you might find that the thicker gasket squashes down 0.1mm and gives you zero

If you cant compress it down by torquing the following may be helpful:
firstly, +/- .1mm will do sweet f-all to your port timing.
But more importantly it will alter your squish. what did you shave your head to be (squish mm's)?
if you have 1.2mm squish you can choose between having 1.1 or 1.3 with your gaskets. 1.3 is OK, 1.1 is too small!
if you have 1.3mm squish you can choose between 1.2 or 1.4. 1.2 is best!

[mugget]

Cheers Jeram, got it!

Haven't got back to checking the base gasket measurements again... but had a friend over just taking a quick look at the bikes & projects on the go. I showed them the KTM, new piston and they mentioned "is the top of the piston not sitting flush on both sides of cylinder?"

That kinda figures with what I was seeing using the feeler gauges between a metal rule and the cylinder, it was not exactly consistent all around. And now that it's been pointed out to me I can see that on one side you can catch a fingernail on the top of the piston, but not on the other. Don't know if that's a major problem tho? I'll probably just keep putting it back together and see how it runs?

[mugget]

Back into this project finally - making some good progress now!

I have a newfound love for dirt riding now, so that's given me a good bit of motivation to get this finished. And the chance to take it camping & do some beach riding next month.

I did check the squish finally and it seems bang on 1.3mm. Or damn close enough. I see lots of people on other forums saying "don't overthink it". Seems like good advice!

Finished cleaning up the power valve parts. Oven cleaner did good. People say not to leave it on aluminium for too long, so I put the cleaner on a piece of scrap I had laying around and haven't cleaned it off yet. Going on 24hrs now... I bet that warning is kinda blown out of proportion. Oven cleaner ain't what it used to be I'll bet.



This damn spring had me scratching my head for a bit...
Didn't help that the manual is wrong in the way it says to install a spacer there, made me doubt the spring orientation but got it in the end.



Now all refitted to the engine and the overload spring works as it should. Checked the port valve openings, not 100% open? But it's as close as I could get it?? There's a little bit of the control roller that is visible in the top of those side port areas. Same on both sides. Guess that's just how it goes? You can see it on the left, just past where the power valve flapper ends, the little silver bit sticking down from the top of the port:



Also wanted to ask people about steering head bearings... I realised I'll have to buy a 2nd set because I already got the bearings from the bearing shop, but they didn't have the seals.
What do people usually do? Just stick with the cheap All Balls type aftermarket bearing kits? Is there any way to source just the seals? I think I'm just gonna install the NSK bearings and keep the All Balls ones spare I guess...

[mugget]

Ok, Z-dimension is pretty much spot on. And I've ordered the last of the missing parts, the bike should come together pretty quickly now!

I just wanted to check on break in procedure for a new top end? I've been having a look on KTMtalk and see lots of advice ranging from "first time it was started was on the start line.... 200 hours later..." (and that was talking about a brand new bike). Other end of the spectrum are people letting it idle & blipping the throttle until it gets up to temp (radiators too hot to touch). Others just ride it so the engine is under a bit of load, going easy at first but not constant RPMs.

This seems like another area where it's best not to overthink...

What would you do for just a new top end? I would lean towards the Motoman "hard break in" method, did that on the only new bike I owned (a Kawasaki Z750). Just warmed it up with a bit of idling & easy 5-10min ride, then accelerated from low RPM gradually increasing to half-3/4 throttle, keeping away from redline though. Did that & changed the oil at 20km. Maybe 30-40mins of running. For 2T I'd think a similar thing is fine, just warm up the bike before riding then gradually increase speed over about 10-15min? Then stop to let it cool down & check for leaks, re-torque bolts etc? Then have at it?

Also I put a bit of oil on the cylinder wall/piston before I assembled - rubbed on premix with my finger so the whole surface was coated. Not sure if this was too much? Others say they just wipe it on with a rag so it's just enough to lube but not so much that it will burn and glaze the cylinder? Wondering if I should just put a clean rag in and wipe a bit out?

[hybrid]

I wouldn't want too much oil in there, particularly if it's good synthetic stuff.
The only thing you really need to worry about these days with the good tolerances is to make sure the rings bed in properly.

[mugget]

Ok, just wiped out the cylinder with a clean cloth then put some fresh premix on the cloth and wiped some back in. A bit of oil in there now, less than before. There will still be some in the cases & below the rings anyway.

Also remembered that I should do a leak down test before I put the engine in the bike - tomorrow...

So assuming the leak down is a-ok, what would you say is the best way to wear in the rings?

[hybrid]

Well that's the 64 thousand dollar question isn't it?

Most will agree not to labour the engine too much, but that's about all they agree on. Vary the RPM.. no need to baby it.
Personally, I would even consider running cheap mineral oil in it to start with to help bed the rings in, but I don't know if this is even a concern with Nikasil cylinders, as I've never owned one.

[mugget]

Haha ok I hear ha. I agree not to lug the engine & vary RPM. I do get the feeling that it's something you just don't overthink too much on a modern Nikasil cylinder.

1 other question before I torque up the head - the manual says to clean the mating surface of the cylinder. Is that only if it's dirty? Mine is clean, & there's no gaskets there anyway, just the 2 O-rings and then metal to metal from the head to cylinder.

[BRG1200]

You're probably overthinking it again ;-)