KX85 for the Jesster

[gwcrim]

Worked a great deal yesterday on an '03 KX85 for my boy. It was part of a fleet at an MX clinic and due to running straight gas by mistake, it has a completely rebuilt engine. Tires, brakes, chain and sprockets have lots of life left. Landed it for $1500. And man, what a step up from his PW80 this will be. It's 220 miles away right now, but the Jesster needs to bring home a good report card first anyway......

Jesse is soon to be 8, 4'4", and 85-90 lbs. Other than his short stubby legs, he's a big boy. So the first thing I'll have to do is to lower the bike. I'll see what sag, dropping the triple clamps, and cutting the seat will do. If that doesn't work, I'll buy some Kouba lowering links. No big deal.

On the power front, I'm thinking of disabling the KIPS valve at first to tame the hit. Would this work OK?

Might go down to a 12t front sprocket too. We're trail only riders right now so speed isn't important.

 

[gwcrim]

Thougt I'd bump this back up....

A few of us were bench racing and wondered what kind of HP these 85 MXers put out. Anyone know?

 

[Vic]

Around 18 rear wheel HP.

 

[gwcrim]

A friend of mine has the bike now as I've yet to go get it. He rode it and said he thought it had as much HP as the old air cooled 125s. That ain't far off!

The Jesster is going to have his hands full of this bike. Last night I was watching him on the PW and it's apparent that the bike is now more affraid of him than he is of it. I believe that's a good time to move up.

 

[mdsutton]

Hello, I am not sure if you should disable the kips valve. I understand it is what helps smooth out the hit. Without it, the bike would act more like the Yamaha or Honda.

Remember this is a 85, I don't think you can do much to smooth anything out.... My son has a 04 KX85 we got in May, and it took him about a month to figure out the hit. Since then, he loves to drag race it. Laughing all the way.

Mike S.

 

[Martin Cole]

Don't disable the KIPS valve is is what makes the KX much smoother than the Honda or Yamaha. You can jam it wide open when he wants more top end and and can compensate for lack of grunt by better timed shifts and slipping the clutch out of corners.
By this time it may be better to replace it with a YZ or a CR.
You can get different length lower links to drop the suspension and make it lower.
Replace the piston, rings and small end bearing regularly - the pistons are prone to stress fractures. Also - when it is stripped keep a wary eye on the condition of the cylinder plating. The Kawasaki stock electroplating is very thin and it is much safer to have it bored out early and replated with something better. We had ours replated with Aptec and they did a superb job. At the same time - check there are no cracks around the bridge in the exhaust port. They can be welded up when the barrel is replated. When stripped, remove the KIPS valve assembly, pull it apart and thoroughly clean all the gunge and any carbon deposit from it. It will work much smoother and more effectively once re-installed.
Hope this is of some use.
MC

 

[gwcrim]

Well we got the bike today. First the good news. The Jesster took to it like a duck to water. 4-5 times to figure out the clutch and he was putting around my parent backyard really enjoying himself. It's a bit too tall, but with more sag and maybe cutting the seat foam, he'll do just fine.

Now the bad news. After no more than 10 minutes of first gear riding, the engine seized. He wasn't wringing it's neck; just ticking the bottom of the powerband now and again. And all of a sudden, the rear wheel skidded and the engine died. (He had the where with all to pull in the clutch and save it!) I pushed it back to the house and the engine will turn over but theres a rough sound and feel to it.

I took the plug out and it's fine. I pulled the flywheel cover. There's no huge amount of end play. But it still feels rough when I turn it over. I'm thinking the big end rod bearing.

Odd thing is, this bike allegedly had a crank kit put in it and all new bottom end bearings recently. I'll call the seller tomorrow to discuss, but I suppose I'm stuck pulling it apart and shelling out the ca$h to make it right.

What could be causing the bottom ends to fail? Is there anything like case mismatch that I need to be looking for?

 

[Martin Cole]

Bad news about the seizure. In my view, if it has just been renewed you have to suspect it was a poorly done job. But - you can never tell when a big end is going to seize. Our KX85 ran three seasons with no problem and I only had it rebuilt then because a water pump bearing seized. Someone who thought they knew about the strange noise the engine was making said "It's the crank" - so I had ordered the bits and got a reputable engineer booked to do the job. So we had it done anyway. It's perhaps just as well, but chances are it could easily have finished this season as well.
Conversely, friends of ours also have a KX85 and it is only about a year old. It isn't raced as often as ours and although it is a quick bike the rider doesn't wring its neck. It seized solid the other week and the big-end had locked up.
Another competitor started last season with a new KX85 and three months later, and after three rebuilds, they changed it for a Honda and had no more problems. However - other competitors also seem to run Kawasaki's relatively trouble free.
You just don't know, but it seems if you get a bad one there is no way you can get it right without going through a lot of wasted time and expense.
Ours (2001) has been pretty faultless. It was raced hard for two seasons by the first owner and it has been thrashed hard for two more seasons by my eldest son. He's just won the Peterborough Club championship in the big wheel 85 class and all its cost this year is a couple of piston kits, a chain, tyres, rear brake pads, a couple of front brake levers and a set of clutch plates. Last year we had to replace a clutch cable and have the rad repaired as well as the rebuild. All in all - fairly reliable.
Another useful tip for reliable operation is to slightly increase the amount of oil in the engine. Recommendation is for 0.65 litres. If there is a little more in there it is supposed to splash plenty up around the power valve mechanism and prevent any possible seizure.
Hope you get it sorted. The KX is not the fastest bike out there but it does ride well and has predictable handling. This will inspire confidence quickly.
Regards,
MC

 

[Mike's 2003 YZ250]

I am curious out of all the 85s, which is infact the fastest, if you compare all the same model years, say all 2004s. The CR85, RM85, KX85, or YZ85? Im guessing the YZ85, and no I am not saying that because I own a Yamaha YZ model myself. :) Mike :cool:

 

[Vic]

I am curious out of all the 85s, which is infact the fastest

The one with me riding it. :)

 

[Martin Cole]

Going on average results Honda CR85s seem to be the best of the bunch. Our meetings are largely populated by novice riders but occasionally we get visits from national riders who are filling in a gap in their schedule. This year the fastest thing I've seen is KTM SX85 but they have been so unreliable unless you have a good sponsor who is prepared to rebuild the engine after every 45 minutes racing - forget it! The KTM chassis is fantastic. If they get the engine as reliable as it is fast then only the best and highly tuned of the rest will be any competition.
My previous post said we'd won the championship this year. We've done it without a single race win. It was a combination of consistent good finishes, basic reliability and a kid who is prepared to ride the wheels off it. The quick kids on Hondas regularly take one or two seconds a lap out of us. We run a tight budget so apart from a Pro-circuit pipe, the KX is stock - promised appearance of V-Force reeds and a Boyesen Rad Valve have yet to materialise for a KX. Boyesen told me they were developing a unit last December but they haven't put one on the market yet so the results must have been worse than stock.
We are also told race gas would give us around two seconds a lap and more chance of a holeshot - but it costs £10 a gallon - so we make do with pump gas. I don't know if the competition are using it but they do seem to have an edge from somewhere.
Some of the RM85s can be quick too. Again, it is aways difficult to tell whether it's down to the rider or the bike. Some of them we can't catch and others we always beat.
YZ 85s don't seem to have shone just lately. They are a great bike though - so reliable. We bought a 2001 YZ 80 (small wheels) fitted with an 85 barrel from new. I sold it the other week and have virtually never laid a spanner on it. Apart from replacing crash-damaged clutch and brake levers, plugs and tyres it has only cost me one set of clutch friction plates. We fitted V-Force reeds and an HGS pipe because it wasn't as fast as the Hondas but this didn't seem to make a lot of difference - except it sounded great!
From what I understand, it is easier to tune the CR and the YZ but all this does is shift the power one way or the other. It is then down to how the rider can cope with it. UK rules stipulate no oversized barrels but it's common knowledge some of the Hondas out there have been bored to 105cc. I think the YZ barrel can go out to this as well - but the owners of doctored bikes are not about to make it common knowledge this is how they are getting an edge. At our level no official checks are made so they can get away with.
I'm sticking with the KX again this coming season for the youngest son. He isn't anything like as competent as his brother and the smoother power of the KX will suit him better than something snappy. The champ is getting his leg over a 2001 YZ 125 for next season and we get our first competitive try-out in two weeks. If its as good as the YZ 80 we just sold he'll enjoy a couple of seasons on it before he knows whether he wants something faster - if there is anything. Seems like here we go again!
Regards,
MC

 

[Mike's 2003 YZ250]

Nice write up Martin. :) Mike :cool: