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

[mugget]

Hey all,

I joined ageees ago when I picked up a '99 380 EXC (EGS?). Well everything is starting to come together finally so I have turned my attention to the engine now.

Here's what it was like when I gave it a quick ride around the block after getting it back home.



Not sure if you can tell much from looking at a vid, sound may be distorted, but I showed it around on a couple of forums and the consensus seemed to be that it's shagged.

I just took the cylinder off and here's what the piston looks like:

380 piston intake side by mugget, on Flickr

380 piston exhaust side by mugget, on Flickr

i'll have to wait until I can look at the cylinder in the daylight to get a real good look, but as you'd expect there's corresponding wear marks in the cylinder.

Now being a 2T n00b I don't know what I'm doing from here on. I have the engine manual, but I'm not sure if those marks on the piston warrant a light sanding or whether it's toast? How do you judge that?

Also didn't see anything in the manual about play on the bottom end of the conecting rod? Should there be any at all? How much is too much?

The rings look to be moving freely, not jamming, the groove is clear so no problems there.

I will measure the cylinder diameter as well.

But the big question is what do I need to do to get this running again?

And also wondering if I should just split the cases and replace all the bearings just to be sure and have a good fresh start with the engine? Or would that usually be considered overkill?

Really appreciate any help & advice.

Cheers!

[hybrid]

Hi, what you're seeing there is a minor siezure. The rings appear to be free, so it's not a huge problem, but as you've got the top off, it's a simple job to replace the piston anyway.
We'd need to get a good look at the cylinder to see how bad that is. There is some acid you can use to clean out any excess aluminium if the cylinder wall is OK otherwise.
I have not had a great deal to do with more modern engines, but that whole area looks very dry to me. Would you say there is an oily film in there?

I don't hear anything too alarming in that video for me to say that the engine is shagged. It sounds healthy enough.

[fred99999au]

I agree that the piston doesn't look happy.

In my experience with Yamahas, with the big end bearing there will be a small amount of side movement, but vertical movement of either conrod bearing is bad.

If the barrel has similar scores in it it may come out with a dunny brush hone or you might be looking at a new barrel or getting that one refinished.

Good luck.

[JonW]

Ive seen worse, I would whack in a new piston so long as the bore isnt scored and the crank Ok I would run it for a bit and see whats what.

If you get bored of the project let me know, Id love a 380 to rebuild

[hybrid]

BTW, what forums told you that the engine is shagged based on that video?

They're either geniuses who can pick something up that's not obvious, or I'd be careful of the advise taken from there

[mugget]

Thanks hybrid, that's a big help.

So, just trying to understand what might cause a minor seizure - would that be a case of the previous owner maybe getting the premix ratio wrong or trying to go too lean with the oil? I guess it must have come good with the right premix ratio or at least not be caused by any other problems in the engine because like you say the engine doesn't sound bad and it still runs...?

And I did wipe down the piston so I could get some clear photos. There was definitely oil on there, it was nowhere near dry when I removed the cylinder.

Okay, here's some pics of the cylinder:

380 Cylinder by mugget, on Flickr

380 Cylinder by mugget, on Flickr

380 Cylinder by mugget, on Flickr

380 Cylinder by mugget, on Flickr

380 Cylinder by mugget, on Flickr

I haven't ever touched an engine before so I don't know if this is usual to see? Judging by other comments on the 'net some side to side movement is normal?



There's no play vertically (radially?) So I would guess that's fine, no need to investigate further?

[mugget]

Thanks for the other replies. I am leaning towards just doing the easiest, minimal repairs/replacement first so I can ride the thing, and like JonW says, see what's what.

And I won't be getting bored of the project, I'm just getting to the good bits now!

Can't remember which forum exactly where someone said it was shagged, but it wasn't a 2 stroke forum. Haha. (Either Custom Fighters or one of the Supermoto forums I think.)

So I guess I will be looking at a new piston minimum, do you think the cylinder can be replated or honed?

Or if it seemed healthy enough when it was running before, is there really any need to replace parts yet? What is the risk if I keep using it as-is? The wear will just get worse and worse until eventually it seizes solid and parts of piston go everywhere?

I will probably only get to ride it 4, maybe 5 times before next year, so if you reckon it will last that long I would rather ride it, then look at it again next year and do whatever is required then. I would not be riding it super-hard either, although it would be on SM track days I would just be getting used to riding a 2 stroke (after that first ride around the block it makes my GSX-R1000 feel like an ideal learners bike).

Thanks all.

[JonW]

Most 4 stroke guys would say it was dead as they see blue smoke...

I have to say your cylinder does look worn.... Can you feel those gouges with a fingernail?

I would get a pro to measure it and decide what to do. These are plated AFAIK so you cant just hone or bore and move up a size, but i could be wrong, lets hope so... if you replate, then sit down when they quote you... also look at what other options you have.

cool at you keeping it, I would too.... and, well i had to ask

I doubt it will seize anytime soon with the extra clearance you probably have in there now, but it will not be optimal for power. A new crank and bore would be good for the road for sure where you would have it pinned a lot, on the small tracks i reckon youd last the year, but saying that it could grenade next week considering its had a life already... it is like that with 2Ts...

[hybrid]

There is a bit more side play in the rod than I would expect is normal there, but it's usable.

From my quick checks, it appears these cylinders are plated as Jon said, so it's not as easy as going to have it machined to the next size.

The seize could have been caused by any number of things.
Heres a quick read piston diagnosis:
http://www.smellofdeath.com/lloydy/pist ... _guide.htm

Longer read here:
http://www.dirtbikeworld.net/forum/show ... hp?t=21089

[JonW]

Yes I should have mentioned the crank play, get a feeler gauge and measure it - its not an ideal measure but you will find out how far its out, but it looks excessive to me. you can run it for a bit but its time for a crank rebuild if youre doing the top end before it goes bang with the added compression of a top end refresh etc. Speak to Link on here, he will know what to do.

[Jeram]

Just wash the alluminium off with pool acid and if there are still marks on the cylinder you can have it diamond honed for about 75 bucks (diamond hone is what you use for nikasil).

If you can afford it, go with a cast piston as they less frequently damage the bore during siezures and have tighter clearances when engine is cold.
Failing that, get a wonser.

The crank clearance is a little larger than usual but IMO its nothing to worry about, my 380's clearance is similar.
The thing to watch for isnt side-side movement, its up/down movement. Have you checked this? if any movement is there, the bearing is toast.
if there is no up/down movement, Id just do the top end and leave it at that.

Once you go the effort of splitting the cases, you really need to consider doing everything while your in there. on the 380 this includes:

-New rod ($350) and big end bearing plus crank rebuild ($100)
-New main bearings ($75)
.new gearbox bearings ($150)
-gasket kit $70
-aftermarket outet clutch basket (if its had a hard life this will be shagged) ($250)
-while your there if your bike is an SX or MXC model you can swap out 4th and 5th gear cogs to the taller EXC gearing to suit road riding. (ebay, used)

As you can see, once you delve into the bottom end, there is some decent amounts of money to be spent.

[Jeram]

by the way, while its apart get your head's squish shaved down to 1.3mm, for unknown reasons the KTM380 has a squish of 2.2mm which hurts the power and making jetting unpredictable.

No harm to reliability doing this, just free hp, improved throttle response and easier jetting
very common mod.

you put the head on a lathe and machine down the matting surface until the step-down between the surface and the squish band is 1.3mm
also you will need to take the same amount off the outer lip of the head so it doesn't foul on the cylinder when you bolt it down.

[JonW]

Great info Jeram!

[mugget]

Cheers for those links hybrid, just what I needed. Thus begins my crash course in 2T operation & servicing.

And to answer an earlier question - yeah I can definitely feel the score/gouge marks on the piston. Nevermind feeling it with a fingernail, I can feel it with my fingertip! But it doesn't feel anywhere near as bad on the bore, so here's hope that it's going to be all good...

Yeah I did check the up/down play on the crank, no movement there so I'm happy to just leave the bottom end and cases intact for now. I would want to do it "properly" if I split the cases, so I will definitely leave that little project for a future date...

Thanks Jeram for that info, was hoping that you'd stop by this thread!

About the diamond hone on the bore, you wouldn't do that without re-Nikasil'ing would you? Doesn't it need that to add back some material to get the proper size/clearance? Are you mentioning that just to say that it can be repaired before replating?

Ok so hydrochloric acid wash on the cylinder bore. Is there any trick or special method to keep the acid from dripping onto the jug? Assuming the jug is ally as well, I don't wanna go up in a flash of hydrogen?

Cast piston sounds good, at a quick look they only seem to be $40-50 more than a "regular" piston? What is the reason behind a cast piston being less likely to damage the bore? Is it stronger so it doesn't break into pieces as easily, or weaker so it doesn't gouge the bore as much?

And thanks for the tip on machining the head, will most likely get that done before it all goes back together. I would do that just to make tuning easier, not too worried about power at this stage... I may have to put a throttle restrictor on as it is just so I don't do something silly like kill myself or soil my leathers.

[Jeram]

Cheers for those links hybrid, just what I needed. Thus begins my crash course in 2T operation & servicing.

And to answer an earlier question - yeah I can definitely feel the score/gouge marks on the piston. Nevermind feeling it with a fingernail, I can feel it with my fingertip! But it doesn't feel anywhere near as bad on the bore, so here's hope that it's going to be all good...

Yeah I did check the up/down play on the crank, no movement there so I'm happy to just leave the bottom end and cases intact for now. I would want to do it "properly" if I split the cases, so I will definitely leave that little project for a future date...

Thanks Jeram for that info, was hoping that you'd stop by this thread!

About the diamond hone on the bore, you wouldn't do that without re-Nikasil'ing would you? Doesn't it need that to add back some material to get the proper size/clearance? Are you mentioning that just to say that it can be repaired before replating?

Ok so hydrochloric acid wash on the cylinder bore. Is there any trick or special method to keep the acid from dripping onto the jug? Assuming the jug is ally as well, I don't wanna go up in a flash of hydrogen?

Cast piston sounds good, at a quick look they only seem to be $40-50 more than a "regular" piston? What is the reason behind a cast piston being less likely to damage the bore? Is it stronger so it doesn't break into pieces as easily, or weaker so it doesn't gouge the bore as much?

And thanks for the tip on machining the head, will most likely get that done before it all goes back together. I would do that just to make tuning easier, not too worried about power at this stage... I may have to put a throttle restrictor on as it is just so I don't do something silly like kill myself or soil my leathers.

you can rehone a nicasil cylinder without replating, all your doing is lightly scratching the surface to give it a 'cross hatching', your not increasing the bore size by anything measurable.
I think when i had my 380 jug done it was a 1/4 thousandths of an inch larger afterwards

if the acid washes the cylinder nicely, and the bore still has a cross hatched pattern on it, you shouldt need to re-hone it.
to apply the acid you can just use cotton wool buds and ear cleaner cotton wool buds

with the OEM cast pistons firstly they dont expand as much as forged pistons which makes them less likely to seize, but when they do, they are a softer material so they dont bight in as hard causing the nikasil to crack/chip away. The downside to cast pistons is they are easier to melt if running very lean.

if you dont want to use all the power, maybe consider gearing the bike taller to take the edge off but also will make freeway trips are a piece of cake