C2 KDX engine rattle at higher revs

[xcracer]

Hello all,

New to this forum, and to dirt bikes. Have worked on cars & bicycles on the past, so I'm not entirely useless (or so I like to think).
Bought an 87 KDX 200 c2.
When I got it, it fired first kick, but also had a leaky float valve, so the carb bowl was always completely full and draining off. After re-adjusting float (I bent the arms level, don't I've the fuel level guage) it's not as easy to start. Still not bad, but I'm assuming the fuel level is messing with the tuning.

Regardless - main question. Was our riding for a few good hours on the trails the other day, and halfway through the day, I started noticing that the bike was sounding very very rattly once I got the revs high enough. (most of my riding was 1st & 2nd gear with low revs). It almost seemed to co-incide with the kips coming open, but hard to say. Ideas? Suggestions?

I also found that when I got the chance to open it up (WOT 3 & 4th gear)) it was backfiring (I think), when I let off the throttle. Too rich on the main jet or needle?
Also found that the bike will bog if I give it too much throttle when the revs are low while hill climbing. Could this be an indication of too rich too??

It's been a fun bike thus far. Hope it keeps on running for a while!

Thanks and cheers

[Julien D]

I would actually think lean. Check for air leaks. A rich condition will usually sputter, lean will bog down. As for the rattle, check the flywheel asap. They are prone to busting magnets. Also check crank bearings for play (can you jiggle the flywheel back and forth?), and piston to cylinder clearance. Welcome to KDXRIDER!

Sent from my DROID2 using Tapatalk 2

[KDXGarage]

Mine was rattly under high RPM. Check the engine mounts. If I am remembering correctly, Fredette once (August 1987 SUPER issue of Dirt Rider) recommended shims.

[xcracer]

So, got the chance to pull the magneto cover, and while I didn't pull the flywheel, I didn't need to. Just grabbing and spinning the flywheel back and forth, I could hear and feel that the small end bearing is FINISHED. Looks like I have to pull it and do the top end. I knew it was going to need to be for soon (compression was down at 125psi) but it's too bad this needs to be done as well now. Alas, the risk of buying used.
But, before I sink more money into it, how much is a bike like this worth? I eventually want to upgrade to a bigger, newer bike, so this might be a good time.
I've pretty much torn the whole thing apart, rebuilt fork, rebuilt shock, fixed and cleaned all the small stuff, etc. I'd say everything is in really good shape (aside from the top end).

Thanks for all the info this far.
Cheers

[Julien D]

The bike you have was an incredible machine, and is difficult to find in good running condition. Be aware of that if you decide to sell. If it cleans up well, and runs good, you have a real gem, and it should bring a decent price from the right buyer. As for what it's worth, that completely depends on what people are looking for in your area, and obviously the overall condition of the bike.

[royadams]

I would guess if you feel something its the big bearing not the small one.

[xcracer]

I would guess if you feel something its the big bearing not the small one.

What makes you think that?
I could guess its because the bottom end bearing sees full 360 deg rotation while the top end only sees oscillation in a small range of movement....? Therefore more overall load on the bottom end?

I have the Kawi owners / service manual for the bike, bit they don't get into the big end bearing. Is it automotive style with a bearing cap and journal bearings? Or is it a split crank with a conventional ball bearing?
How big of a job is it to change this bearing? Am I splitting the whole case and tearing the entire thing down?

Thanks

[KDXGarage]

It is a big deal. Basically, you will need to buy a connecting rod kit and take it / ship it somewhere. As far as technique/having the tooling/etc., I would say more than 99% of owners can not do it properly himself.

Look around for rebuilding a crankshaft.

[royadams]

I've never seen the small end bearing go out. If it did your rod would still be no good.

[xcracer]

So, I'm still not sure what's causing the rattling.

I pulled the jug off tonight, and didn't find any major up and down play in the rod. I did, however, find lots of side to side play on both the big end and especially the small end bearing.
Didn't have anything for measuring, but visual inspection shows the jug looking super clean, but the piston pretty beat up. Scoring & a tiny bit of galling on the piston just below the rings at 2 o'clock, 4 o'clock, and 10 o'clock (reeds at 12 o'clock).
My guess is piston slap; so I'll look at doing the top end. But at least I know nothing is going to grenade on me.
Thanks for the info & input.
Cheers

[froggy]

You should have zero up and down play on the rod. If you have any play at all, you need to rebuild the bottom end. Some movement side to side is normal.

[Goofaroo]

Even if you don't think you have any play in the rod bearings, the crank seals should be replaced. Your symptoms and the condition of the piston could very well be caused by an air leak.

I recently restored an 87 C2 and the top end was scored horribly. I ended up having to have the jug replated. The culprit turned out to be the crank seals. In my case, I found everything else in the bottom end to be in great shape.

Here's my build thread if you are interested- http://kdxrider.net/forums/viewtopic.php?f=77&t=12771

[xcracer]

I recently restored an 87 C2 and the top end was scored horribly. I ended up having to have the jug replated. The culprit turned out to be the crank seals. In my case, I found everything else in the bottom end to be in great shape.

I did find your rebuild thread already, and have read through it.

And yeah, I'm quite sure I'm in need of crank seals now too.

After pulling the jug (in my last update), I bolted it all back up, and rode it for an hour or so. Couldn't resist, even though I knew it wasn't running that well.
Well, ended up being a bomb of a day. Bike just didn't have any power anymore, and my kickstarter arm managed to fall off.... luckily I found it again, but the rest of the day was spent bump-starting & when that didn't work, I'd have to take my camelbak off, get out my kickstarter, start the bike, then put kickstarter back away, etc, etc.

And to top things off, the bike was leaking oil pretty good when I loaded it back in the trailer. The leak seemed to be coming from the coutnershaft (?? - the shaft the 13t sproket mounts to).

So, after that ride, I decided it's time to pull the motor. I pulled it out quite easily, and spent some time cleaning it up while it was on the workbench today. Had it tipped on it's side for a while to clean the bottom, and when I pulled the head & jug off, I found that the bottom end had transmission oil in it. So, crank seals are definitely required.

At this point, I think I'm in this bike for the long haul. I was hoping to keep the cost down, but at this point, I'm going to lose money to sell it as is right now, so I might as well finish it up properly, and hopefully I can enjoy it for a good bunch of years after all the work is done, and also that I don't get upgraditis too soon either.


Summary of build / restore so far.....

So far, I have done the following to it:
- New used rear wheel (rim was corroding from inside & spoke heads were ripping through)
- New used/rebuild rear shock (which doesn't hold air... so the rebuild was obviously not done proper - hopefully the old one still has a good bladder)
- New fork seals & bushings
- Rebuild / clean carb (float wasn't closing)
- Fuel petcock rebuild (was dripping gas)
- new air filter (old one quite ripped up and was just sitting in the airbox....??)
- replaced all nut & bolts with new stainless bolts (previous 20 owners had used quite a mix of metric, imperial, phillips head, hex head, allen head, etc, etc, etc)
- re-wired the entire bike and stripped off the lights (wiring was a rats nest, and I'll never ride it at night)
- new front brake pads

And now it looks like I need to do
- countershaft seals
- crank seals (maybe crank bearings while I'm at it)
- possibly the big end bearing
- piston kit

Thanks for all the info & insight thus far!

PS> Talked to a local repair shop - Twin Seasons Recreation - near my work in Georgetown, Ontario (just outside Toronto) and they said they send cylinders to a place in Quebec for boring & replating. Apparently they do amazing work, and it only costs $70 to get it done.

[KDXGarage]

Are you sure the oil in the crankshaft area was not 2-stroke oil? There is supposed to be a little pool of oil down there.

[KDXGarage]

$70 plating job might look like this:

[xcracer]

No, definitely not two stroke oil. Had the consistency of regular 10W40.
And I was pretty surprised as well at the price of the plating, but I'm assuming it's a good playing job, seeing as this shop goes so far as to post a disclaimer on their website, and at their service counter, saying "We will not install products from X, Y, or Z colonies because they are not of high enough quality".

If I do need it plated, I'll post up some pictures web I get it back.

Cheers

[Goofaroo]

It's good to hear that you see the potential and are putting some time and money into this bike. They are fantastic little bikes once you get them sorted out. I kept mine (my son's technically) all stock and it is a great set-up. I know I'm an old fart but there is something about the trail bikes from the mid to late 80s that seems right to me. A friend of mine had bought one new "back in the day" and I always loved riding it so when this one came up on CL I snapped it up. I've put an embarrasing amount of money into it but it has not disappointed.

As far as the oil in your case, it sounds to me like you need to take a close look at your case halves. Once they're spotlessly clean, hold them together and see if they mate up well. Also run a straight edge over them and see what you've got. The case halves could account for the air leak and the internal oil leak if they aren't mating properly or if the mated surfaces are damaged.

Plus, we need pics!

[xcracer]

I'll get pictures going soon.

But I did order a new Wiesco piston, small end bearing, and complete oil seal & gasket kit. The mechanic at this shop also said that he can hone the plated cylinder to take out the scratches too. I'm assuming he has special ultra fine honing stones to do plated cylinders, because I asked explicitly if it would damage it, and he said no.

So, top ends getting redone. And now that I have a full gasket kit coming, I won't shy away from pulling it further apart. Going to hold off on crank seals for a bit, but maybe I'll fill the crank case with oil to flush it and see if it leaks out either of the crank seals, or between the case hales, etc. It does look like whomever had it apart last used silicone for all the gaskets; so it could very likely be leaking there.

One note - I mentioned that they could plate my cylinder for $70. That was incorrect. $70 was the price for boring; plating is up near $300 apparently.

One question - was is the best chemical / method for cleaning / flushing the crank case? I tried to keep it as clean as possible, but some crap likely fell in.

Pictures will come once I have a chance. (Bike is being stored in my brothers barn, which is a half hour drive away, so my time spent there is precious work time, no time for pictures yet. )

[KDXGarage]

$70 bore and $300 replate sounds more like it.

In the USA, a replate is around $200, plus shipping both ways.

Is your cylinder plated or sleeved? From what I have read, a diamond hone is needed to cut into plating. Look on the Millenium Technologies page for more info.

[Goofaroo]

So, top ends getting redone. And now that I have a full gasket kit coming, I won't shy away from pulling it further apart. Going to hold off on crank seals for a bit, but maybe I'll fill the crank case with oil to flush it and see if it leaks out either of the crank seals, or between the case hales, etc. It does look like whomever had it apart last used silicone for all the gaskets; so it could very likely be leaking there.

Those crank seals are probably 25 years old. You sure seem to be putting in a lot of work on the rest of this bike so it would be a shame to have it shrapnel because it's sucking air. I know it seems like a lot of extra work but it will never be any easier than right now while it is sitting on your workbench. I'm guessing it's never been apart and the previous owner smeared silicone all over it to try to stop the leaks. It didn't work apparently.

It sounds like you have a complete gasket set on the way so all you need are the crank seals and some sealer for the case halves. You also didn't mention whether or not you have the seal and o-ring for the countershaft.