Conquiztador
16th October 2012, 17:32
My boy is now 11 and will start riding 85cc in Junior MX soon. (Has been riding Mini's now for 4 1/2 years and 65cc for last two). We have had KTM's all the way and have been happy with them not having had any major issues (he has had not one DNF in all his riding...).
So based on that we wanted to get a KTM 85sx as his next bike. Not a new one as 1. I can not afford a 2013 model, and 2. He will need some time to get the hang of big wheels and senior tracks before becoming competetive and starting to use all the bike has.
I found a local 2009 one for the right price and made the deal. The bike had been giving the seller some grief and had seized two sets of big ends in two months. When I got the bike it had just been repaired. I did some research and found that this was not uncommon for these and it looked like the big end was their weak point. But I also managed to find info re how to correct this issue (Basically the big end bearing is poorly oiled and when this is corrected the issue is solved. The earlier ones also tended to heat up the shim/washer on the r/h side of the big end pin causing overheating with the same result.
We used the bike for approx 20 minutes on the beach for my son to get the hang of it, and I sorted an electric problem that occurred at high revs (did not deliver spark properly). I also adjusted the carbi in the middle range as the bike did not pick up properly. Once I finished she did run like a rocket!
He then rode for 2 1/2 laps in the practice before the big end seized again... (we also had his 65cc there so he reverted to that one and had a good day anyhow).
Once home I took the barrel off and found that the piston was perfect and no sign of overheating, but the big end was munched. I went to see the engineer who had done the two crank/conrod repairs and asked what his opinion was. He told me that it was a problem with the main jetting... so the second time he sorted the crank he had changed from a 118 main jet to a 125. He blaimed the past owner for the seizings as the past owner had not sorted the jetting...
I tend to disagree with him. (We run 40/1 mixture and I have never in my 45 years working on and riding bikes had a big end seize because of a small main jet...)I fitted a new spark plug after I tuned the carbi (the plug I took out was all black and oily). And when taking the barrel off at home after the bike died I found the plug to be nicely chocolate brown indicating that the bike had not been running hot. I personally think that the way he re-assembled the crank is the problem. But I wont argue with him as the past owner has agreed to pay for all what is needed to fix the bike. Cool!
So I am now on the look for a replacement crank and conrod (I won't trust the bits te engineer has worked on and I want to start from scratch).
Came across the Hot Rods unit: http://www.motocrossparts.co.nz/motocross-parts-accessories.php?id=2919&biketype=2&fitsbrand=8 that is priced very well. Does anyone here have any experience with them?
And if that is not the one to get, what would the recommendation be? (I am currently also pricing up a KTM one...)
I have also learnt that the conrods big end is at times being modified to allow more oil to get to the bearings. Any comments?
Looking forward to opinions/help from you guys who have more experience with this.
So based on that we wanted to get a KTM 85sx as his next bike. Not a new one as 1. I can not afford a 2013 model, and 2. He will need some time to get the hang of big wheels and senior tracks before becoming competetive and starting to use all the bike has.
I found a local 2009 one for the right price and made the deal. The bike had been giving the seller some grief and had seized two sets of big ends in two months. When I got the bike it had just been repaired. I did some research and found that this was not uncommon for these and it looked like the big end was their weak point. But I also managed to find info re how to correct this issue (Basically the big end bearing is poorly oiled and when this is corrected the issue is solved. The earlier ones also tended to heat up the shim/washer on the r/h side of the big end pin causing overheating with the same result.
We used the bike for approx 20 minutes on the beach for my son to get the hang of it, and I sorted an electric problem that occurred at high revs (did not deliver spark properly). I also adjusted the carbi in the middle range as the bike did not pick up properly. Once I finished she did run like a rocket!
He then rode for 2 1/2 laps in the practice before the big end seized again... (we also had his 65cc there so he reverted to that one and had a good day anyhow).
Once home I took the barrel off and found that the piston was perfect and no sign of overheating, but the big end was munched. I went to see the engineer who had done the two crank/conrod repairs and asked what his opinion was. He told me that it was a problem with the main jetting... so the second time he sorted the crank he had changed from a 118 main jet to a 125. He blaimed the past owner for the seizings as the past owner had not sorted the jetting...
I tend to disagree with him. (We run 40/1 mixture and I have never in my 45 years working on and riding bikes had a big end seize because of a small main jet...)I fitted a new spark plug after I tuned the carbi (the plug I took out was all black and oily). And when taking the barrel off at home after the bike died I found the plug to be nicely chocolate brown indicating that the bike had not been running hot. I personally think that the way he re-assembled the crank is the problem. But I wont argue with him as the past owner has agreed to pay for all what is needed to fix the bike. Cool!
So I am now on the look for a replacement crank and conrod (I won't trust the bits te engineer has worked on and I want to start from scratch).
Came across the Hot Rods unit: http://www.motocrossparts.co.nz/motocross-parts-accessories.php?id=2919&biketype=2&fitsbrand=8 that is priced very well. Does anyone here have any experience with them?
And if that is not the one to get, what would the recommendation be? (I am currently also pricing up a KTM one...)
I have also learnt that the conrods big end is at times being modified to allow more oil to get to the bearings. Any comments?
Looking forward to opinions/help from you guys who have more experience with this.