KX Guru Racing

Hey all.
Just having one of those days, I guess. So, last fall, when I put my bike up for the winter, it was running so so, but was loading up a bit, and smoking a lot. (Like the old video game Spy Hunter, a lot) I found a hairline crack in my carb body, so I blamed it on that, and bought a new Lectron for it. I figured, if nothing else, it was a good excuse to try one out. The engine only has about 20 hours on a full top and bottom rebuild, so what else could it be, right?
Well, today I had some fun, and put it on. It fired right up, and idled just great right out of the box. A bit smoky though. No worries. I’ll warm it up. It’ll clear out. (It did not) . Well, that didn’t work. I’ll go beat the hell out of it real quick. (That helped, but not as far as the smoke.)
It was on my return pass down the 1/8th mile, as I was navigating through the fog bank I’d just laid down, that I noticed the air quality around here sucks! In fact, it doesn’t have the pleasing smell of Klotz and Sunoco 110 that I’m used to. It smelled more like that stoner buddie’s car we all know. You know the guy. We all have one. Smells like weed and old french fries on the inside, but like an oil rig fire on the outside..... I know you know the smell; Burnt motor oil.
Now, the sludgy gears of my mind are really turning. Why would that be the smell, unless....
Oh crap! I figured it was either the crank seals, or the case sealant, or a crack. Unfortunately, I was right.
I got back to the shop, and let into the ole girl. After getting the top end off, I already knew I was screwed. It was pretty much spotless, with no signs of wear, (except carbon on the piston deck. Lots of it) I peered into the crank cavity, and it was about a half inch deep with gear oil.
For my next trick, I filled the crank cavity with parts washing solvent, and blew some compressed air up the gearbox vent tube. Even at just 5 PSI, the air was gushing into the cavity through the right crank seal.
Ok then. I have a 20 hour old motor with a bad seal in it. Why?
Here’s where I could use some help from out there in Guru Land.

First of all, I had Lindsay Machine in SLC do the crank when it was out, and They put a new Hot Rods connecting rod in with all new bearings and new crank seals. I installed all of it myself, like I’d been doing for years. New piston, .020 over too. They have always done good work. Ive never heard anyone complain about them. So, maybe I did something wrong?
Did I put the seals in backwards? They are currently oriented so the springs are toward the crank, flat sides out. The shop manuals (I have 3 different ones) don’t specify or show. The bearings feel just fine. Perfect side play on the crank. No vertical play at all. Anyway, they look just fine, if I haven’t split the case yet. That’s tomorrow. It didn’t feel out of balance when it ran. Just the usual 5hundo shake.
Anyone have any ideas, or similar experience? I’ve rebuilt this bottom 5 times since 2001. I’ve never had this problem. I’m pretty meticulous and a former jet mechanic. That doesn’t mean I didn’t screw up though...

Thanks.
Brent.

What does the area on the crank look like where the seals ride?
Also, measure the diameter right there and let me know what it is.
What brand of seals did you use?
You have them in correctly.

When I install mine I always use assembly grease on all my seals so they do not run dry.
Also, spin that main bearing on that side and see if it runs smooth or is it crunchy?

See if you can detect and leaking around the crank seal on the inside and out.
Especially look at this area:



They are known to leak occasionally.
We use to use JB Weld to fill them but now use 1211 Threebond or equivalent.

Update:
I managed to get the case split on Tuesday AM. Right away, I noticed something was not quite right. As soon I I got past the case sealant, the two halves slid right apart. That isn’t normal. They usually require quite a bit of persuasion, as the bearing outer races are fit fairly tight into the retainers in the cases. The side play that I felt earlier was actually due to the bearings walking back and forth in the bores. There was some evidence of the outer races spinning slightly in the bore too. This left some mild galling. I also noted that while the seals appeared to be un damaged, they felt a bit harder than usual. I sent everything through the parts washer, and put it back together dry, without the transmission gears. The bearings were a bit loose internally now, and could be deflected sideways just a bit. They are shot already. Damn. Well, off to the machine shop...
So I took the cases and crank over to Lindsay Machine Racing. They had pressed my crank pin and rod together, and did the .020 overbore. I assembled everything else. I didn’t suspect that they had done anything wrong, but I wanted to see what they thought. Immediately, it was noted that the seals were the improper ones. They were too deep (the flange) on the backside, and were blocking the oil drip holes somewhat. He also agreed that they were hardened. Probably by heat. Upon removal, they appeared to be just regular wheel bearing seals. On to the bearings. They showed signs of the outer races spinning or vibrating around a bit, and they measured out of round and of a slightly smaller outer diameter than they should be. He asked me where I had gotten them. I cannot remember for certain, but they were either the ones that came with the Hot Rods kit, or they were from All Balls. At any rate, they were low quality and out of tolerance. On to the case bores. Not great news there. They are slightly galled, but almost perfectly round. They are, however, now just a bit too big. About .1-.05 mm by our measurements. The crank did not appear to be damaged. He put it on the bench and checked it out. It was slightly off, the gap opposite of the rod pin being about 0.15” too close. He straightened it right out. We tried the new Moose Racing bearing set out that just came today. (Toyo bearings) They were tighter, but still loose.
What to do? There are only 3 choices now. 2 new cases, boreing and basically sleeveing the bearing retainers, or bearing retaining compound. I have decided to try the compound approach. Now, which one do I use? I have narrowed it down to Locktite 640 or 641. The 640 has a higher shear strength than the 641, but the 641 is supposed to be easier to disassemble when the time comes. How difficult is the 640? Is it permanent? I don’t know that either. The shop recommended 640, but said they never took one apart that had used it. Anyone have any experience there?
I will also take the advice and JB or Threebond those areas while it is apart.

Thanks,
Brent.

Update 2:
So, I went about pressing the new bearings from Moose Racing onto my crankshaft this afternoon. They went on just fine. Then I installed the new seals into the cases. I can’t put the bottom end together yet, because I had to order the bearing retention compound. Nobody in SLC had any on hand. As for that, and the questions I had in the first update, I solved that, sort of, with a call directly to Loctite Industrial Technical Setvices. The machine shop recommended the 640 formula. It sets up really hard, and will withstand 3000 Lbs of blunt shear. The other one I found is 641. Loctite says it will set up a bit less hard. It will handle 1000lbs of blunt shear before compressing and failing. So, naturally, I asked if the 640 would be better. In short, he said yes, but only if it was definitely the last time that the engine would ever be rebuilt. I asked why. He said it is because the 640 is permanent. The cases would likely break before the compound would release the bearing race from the retainer. The only release method for 640 is to heat the unit up to over 500F. He said that 641 is designed to be able to be separated for servicing. That’s why it’s significantly weaker. He assured me that it would handle the task if properly applied and cured before use.
So, I’m waiting for that magic stuff in the mail.
In the mean time, since they are so loose, I decided to drop one of the old bearings I had in a box from way back in about 05 into one of the holes I had just put a new Moose seal into, just to see what the clearance would be. Well, it’s not good. The inner race of the bearing, which is definitely the correct one (Koyo 6306C3) actually contacts the lip of the seal before the bearing makes it to the bottom of the retainer. This kit also has incompatible seals! Here’s a pic of the original seal and bearing from the factory, and the other is a picture of the old All Balls set along side the new Moose set.
Somehow, I had two of the original style seals, (34-1008) brand new in baggies, sitting with my old parts! I installed them, and everything clears just fine. Now I still have to wait for the Loctite 641, but things are looking up.

Thanks,
Brent.

There is so much to say on this one but I am wiped out tonight.
If I forget, send me a pm in a day or two and remind me,
Thanks.

Hey all.
So, it’s been a bit since I reassembled the bottom end, and eventually the whole bike. I did end up using Locktite 641 on the outer races of my new crank bearings. I ended up having a few more discussions with an engineer at Locktite about what I was planning on doing, including my many different paranoia issues about using a new product with such implications should it fail. Turns out, the guy is also a former dirt biker, and still tinkers on them from time to time. He has used 641 on several 125s and a 250 and a 450F (Honda) that all had similar issues to what my bearing retainers did. Just plain loose. The product is designed to hold up at around 300F, and cover up to .010” of slop, yet release if pressed or hammered lightly at “room temperature”. He assured me that it would be about as difficult as splitting the cases the first time, and perhaps the crank would slide out of the bearing instead of the bearing sliding out of the case. The product should hold up at 300F+ to a compression yield of over 1000Psi. There is also an anti compression yield (pulling) that is quite high, but he didn’t have conclusive specs on that. At any rate, given the radial nature of the bearing and it’s surface area, he did some fuzzy math. His lowest estimate was that the compound would begin to fail at around 6000-10000psi of load in this application. This could only be achieved by a serious crank imbalance, or a catastrophic over rev. So, that’s good news.
I also brought up that my local machinist’s recommendations were to use 640 compound in this case. He asked me if any had ever tried to split a bottom end after using it. That is a question that I do not yet have an answer to. I will go over there and ask as soon as it’s safe to breathe. His thoughts were that the answer was probably not. A machinist would want to use that for a component that could either be heated to over 500F for removal, or that was on its final use cycle.
So, looking back, how did this happen in the first place? Well, I did some memory searching in my WTF files about the brutal year the bike had preceding the seal and bearing failure. While there may be omissions due to my sitting in a hot tub drinking beer in a light snowfall as I compose this, I promise there are no exaggerations.
The first issue in the train of failures was just prior to the last bottom end rebuild. I was riding at Sand Hollow in southern UT in January. It was like 70f during the day there, and the snowboarding sucked here at the time. (January 18) We loaded up, no prep, and rolled out. The last time I had ridden it, I had it jetted for about 5k, and rode it in the woods at 7-11k, and then dropped a couple thousand feet, and rode it in the sand. I did check the plug a couple times, and it looked on the lean side of the ok range. After running through about 2.5 gal of gas, it was still running great. Time for one last shot at the big hill. That’s when it did it. For the first time since buying it brand new on October 12 of 01, it failed me. About 3/4 of the way up, it just spooled down. That was it. Not locked up, but no compression. The autopsy found a failed air filter element (rim separation from dome) and signs of heat and sand on the backside of the piston. The rings were frozen into the lands at this area, just between the two indexing pins. Although the bottom end seemed fine, I decided to rebuild it. I used an All Balls bottom end bearing and seal set. It all went back together ok,(So I thought) and I had a new HotRods rod and bearing pressed into my crank by my machine guys.
It ran great after that. The second issue I had was quite a bit later. I decided at the time that I wanted an auto clutch, mostly for fun, to use in my single track alpine adventures. Rekluse did not offer one at the time, so I went with a company called EFM. It was certainly an impressive bit of machining, but worked quite differently than a Rekluse. This unit removes the pressure plate and springs, and replaces them with a centrifugal compression unit that bolts directly to the clutch basket. Adjustment is made with shims under the clutch hub. This required my also cutting my stock clutch cover, and doing the 450F cover mod to gain 1/4”. Anyway, it worked great, with one exception; it would smoke the gear oil in one ride. I never quite got the right shim and sprocket combo dialed, and they had no customer service skills at all. One day, I got a bit stuck getting over a pile of downed trees, and it got really hot. Hot enough to boil Evans Waterless coolant. Thats friggin hot! (And smells horrid) When I pulled the clutch, the oil smelled burnt, and the centrifugal unit was permanently stained by hot oil. I flushed it out with diesel real quick, then cheap oil, then went back to the stock clutch, and put good oil in it. There were no further overheating issues. The third WTF happened about 5 rides later. After pounding out about 40 miles of single track as fast as I could, and finishing it off with about 10 fast miles down a dirt road to the truck to beat the sun, it started making some awful rattling noises just as I approached the finish line. I shut it down right away. When I got home, it turned out that I had cracked the weld on the new flange that held on the new clutch cover the prior time I had removed the case. Turns out that the top flanged bolt is tucked behind the other flange. If you take it out with a power driver, be careful! It will pinch the socket there, and crack the weld. (Not an issue in non modified case. Totally my bad!) At any rate, I lost almost an entire quart of gear oil on that ride. The clutch was just pounding it through that crack. I didn’t notice because it was muddy, and I no longer have a sight window. Repeat my previous cleansing steps to remove the nuked oil. Bought a new case and flange. Welded er up. (More prettier this time, with helicoils too, and off I went. Seemed fine, but starting to get harder to keep in tune, and required more beatings to keep the smoke down. (This was early in the crank seal failure stage, I guess). The next incident was the weirdest. It was idling in the driveway, warming up, and I went into the shop to get an air tank to fill a tire. Suddenly, it just started revving uncontrollably! I was about 60yards away, and went running for it. It wouldn’t stop! Braaaaaaaaaaaaaaapppppp!! Faster than I’d ever heard it run in my life. The kill switch had no effect at all. Afraid it was gonna granade, I threw a leg over it anyway, and put it in second gear, dumped the clutch, and stalled it. I found a somewhat mushy Paw Patrol sticker gooed around the fuel pickup tube in the tank. That was the fatal blow. Probably not the true lingering cause of death, but the last straw. Killed by an enthusiastic 4 year old boy. (Happy he likes dirt bikes though.) Anyway, somewhere in that horrible year, this bearing thing happened. If y’all read the previous posts, you know what happened before this prequel.
So, if you’re still awake, you’re probably wondering how it all turned out. Well, it’s all back together now. I didn’t rebuild the top end, because it wasn’t even broken in yet from last time. Just a quick re scuff and super thorough cleaning. I fired it up on the new Lectron (previously mentioned) and in about 5 kicks it was humming away again. It felt normal, if not smoother. This time, when sandwiching the cases, I left the bearings on the crank slightly short of bottoming out on the crank when I pressed them, so they would both hit the stops on the cases fully with the outer race, hopefully limiting their desire to walk back n forth like last time. I also put a shim that I machined out of a piece of bar stock between the crank halves, just snuggly, opposite of the rod pin, so I wouldn’t put any lateral loads on the crank pin as I brought it all together. I’m telling myself that also made a difference. In the end, after some light tapping, the crank was free, and perfectly centered. Only time will tell if it lasts, but it’s true I can say from my few ripps up and down the alley, it is running better than it ever has before. Like I said, only time will tell. I’ll keep y’all posted.

Good luck out there everybody!
Thanks for listening,
Brent.

It will be interesting to see how this pans out for you.
Please keep us informed.
Thanks!
Mike

I neglected to update everyone on the Locktite 641 main bearing outcome. I’ll keep this short.

So far, so good!

It has about 10 HARD hours on it so far, and running smoother than Charlie Sheen’s credit card at a cat house.

I’ll update when it has sone real long term abuse on it.

Like Sheen’s liver....

Till then,
Brent

Sweet.. Thanks

Hi, everyone.
Just thought I’d post a long term update on the magical bearing sauce. Well, it’s still going really strong. The engine is about half way through its second top end cycle, and the crank is still nice and tight and well balanced. I may have to split it soon though. Not because of the crank bearings or seals, but because I need to replace the counter shaft bearing. It’s going through a seal and collar set there every couple of rides, and I’ve had about enough of the automatic chain luber! Anyway, I’ll let y’all know how the Locktite 641 behaves when I try to split the cases, and how I manage to clean the old stuff up. It might be quite a while until I get to it though.

Till next time,
Brent.