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Orange yokes are orange!


wazrs257
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The rear brake locking on has been traced to a missing lock nut on the height adjuster on the lever. Now replaced.

More shiny bits fitted, just waiting on a Venhill line so I can bleed it up

47873550701_5bbe37dc63_k.jpg

 

I'm no KTM technician, but I'm fairly sure that water-pump drive gear should have a couple more teeth than that! :(

47873553351_5062f3f17a_k.jpg

Edited by wazrs257
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Of the five people I know personally who have run KTM85`s for their kids every one has had a big end fail, often at low hours (<1 in one case). Last one a few weeks ago was on a 2017 (I think it`s a 2017, pretty new anyway).

I saw the inside of one after the big end seized at 9 hours, plenty of oil around mains and barrel/piston but big end overheated, after spending some time on the Kiwi Biker 2 stroke pages trying to educate myself  I`d guess the big end bearing cage had broken up and jammed the rod .

Suggesting there may be something wrong with the KTM 85`s crank and if on a budget sticking to a Japanese 85 on one of the KTM forums got me a bit of abuse ! "All the fault of poor maintenance or over-rev".

Granted, at least one of the riders thrashed the 85 mercilessly, but his previous KX 85, same rider and maintenance, kept going no problem, with same treatment.

I did wonder if the spate of local failures was due to a bad batch of big end bearings or substandard bearings being used, or being built to wrong clearance ? I am not anti KTM in any way, we have some 250 2t`s, and being around schoolboy mx only ever saw the 85`s have this kind of problem.

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5 hours ago, DougW said:

Of the five people I know personally who have run KTM85`s for their kids every one has had a big end fail, often at low hours (<1 in one case). Last one a few weeks ago was on a 2017 (I think it`s a 2017, pretty new anyway).

I saw the inside of one after the big end seized at 9 hours, plenty of oil around mains and barrel/piston but big end overheated, after spending some time on the Kiwi Biker 2 stroke pages trying to educate myself  I`d guess the big end bearing cage had broken up and jammed the rod .

Suggesting there may be something wrong with the KTM 85`s crank and if on a budget sticking to a Japanese 85 on one of the KTM forums got me a bit of abuse ! "All the fault of poor maintenance or over-rev".

Granted, at least one of the riders thrashed the 85 mercilessly, but his previous KX 85, same rider and maintenance, kept going no problem, with same treatment.

I did wonder if the spate of local failures was due to a bad batch of big end bearings or substandard bearings being used, or being built to wrong clearance ? I am not anti KTM in any way, we have some 250 2t`s, and being around schoolboy mx only ever saw the 85`s have this kind of problem.

Interesting, do you know if this just affect OE cranks, or aftermarket as well? I'm probably going to fit a Wiseco crank, waiting to hear back  from them on price and availability. I've not heard much from people running big power 105s about their cranks failing.

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As far as I am aware, they have all been OE cranks. 

The failures at very low hours had been rebuilt cranks, hence me wondering about how good the rebuilt or bearing was. Not sure how long the original cranks lasted, just nowhere near as long as the japanese 85`s , which tend to give plenty of warning of impending doom by vibration and noise.

KTM 85`s seem to go from sounding and running ok to seized big ends with no warning, but admittedly they are a much more "competition" engine than the Japanese 85 equivalents. 

If junior was serious about racing his 85 we would have gone KTM, but seeing as he wasn`t we had RM`s

( Still have RM`s, Mrs DougW has a pristine low hour 2001 RM85 big Wheel, and cannot I bring myself to let juniors old 2004 RM85 small wheel go. It gets used once a year in the TBEC moped and Pit bike Team charity race, blatant cheating but the bikes capabilities are offset by the lack of skills on the riders part . Great fun annoying the "Serious" competitors by wheelying past on the straights then getting in the way everywhere else :).

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Is Mitaka stuff any good? It turns out the Wiseco crank, mains, seals and gasket kit for my bike is best part of £400 and not in stock in the uk. I can get the same kit from Mitaka (using a 20mm big-end pin) in the uk for £230, but I don't want to end up buying rubbish.

Edited by wazrs257
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4 hours ago, wazrs257 said:

Is Mitaka stuff any good? It turns out the Wiseco crank, mains, seals and gasket kit for my bike is best part of £400 and not in stock in the uk. I can get the same kit from Mitaka (using a 20mm big-end pin) in the uk for £230, but I don't want to end up buying rubbish.

Used Mitaka pistons in Juniors old RM125 for 5 years with no problems, AFAIK Mitaka good.

Just found this on the KiwiBiker site regarding big ends :-

The bearings used these days in 2T - MX cranks are all flat construction , silver plated cages, so the quality isnt the issue.
Its the inertial loads of stress reversal at BDC and TDC, and the inability of the cage to accelerate fast enough to prevent skidding ( instead of rolling )
by the needles.
Pressure fed, shell bearings, as used in a 4T dont have these issues, and the bottom ends are pretty bullet proof.
As I said, by giving up service life, the 72mm cranks can be spun to 11,000, but be prepared to change the big end VERY regularly.
I have changed just the cage/needles on a KZ2 crank 4 times with no issues as the rod and pin dont wear at all.
Its the cage scuffing that causes failures, no matter how much, or how good the oil used.

Bit out of context, but it supports my theory that the rebuilt KTM 85 cranks may have been done with sub standard bearings, and would explain why no warning of seizure, bearing tolerances fine then cage breaking up ? 

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KTM cranks fuck up because of the crazy high oil ratios they recommend and nobody uses Castor synthetic oil. Had similar issues with every KX60 turned into a 65. With the KTM 85 on dirt track and a junior road race just add castor at 18:1 no more problems

 

Edited by 2T Institue
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3 hours ago, 2T Institue said:

KTM cranks fuck up because of the crazy high oil ratios they recommend and nobody uses Castor synthetic oil. Had similar issues with every KX60 turned into a 65. With the KTM 85 on dirt track and a junior road race just add castor at 18:1 no more problems

 

What oil ratio do they recommend Lozza? I was using fuel left over from my 50, so Shell vmax (or whatever the expensive one is) and Motul 800 @ 25:1.

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Just split the cases. The big end is heavily blued, even the webs are discoloured around the pin. It feels like the rod is catching on the plastic stuffers, which actually look burnt. I'll put a couple of pics up when flickr is back on line. Doesn't look like an OE crank.

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On 5/24/2019 at 12:29 AM, wazrs257 said:

What oil ratio do they recommend Lozza? I was using fuel left over from my 50, so Shell vmax (or whatever the expensive one is) and Motul 800 @ 25:1.

50:1 or something stupid like that. The crank looks like it doesn't have enough side clearance (between thrust and web on one side should be )0.8mm min. Run Castor/synthetic(Xeramic, Maxima 927, Agip Kart, A747)at 18:1

Edited by 2T Institue
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  • 6 months later...
  • 5 months later...

Today saw me and @El Gringo parked up on the M6 on the way to 3 sisters, eating Sainsburys taste the difference sausage rolls, whilst waiting for an accident to be cleared so we could continue on to the circuit. The ACU test session had been booked initially to test my new 50 race bike, but I thought I may as well throw the 85 in the van as well, in case we didn't have enough to do.

As it turned out, the 50 didn't want to play ball, so I spent most of the time out on the 85, while the 50 had jetting changes.

It behaved perfectly, even the gearing that I fitted for Whilton mill, turned out to suit 3 sister perfectly. I’ve now got gearing information for whilton mill.

I just need to find 10 seconds a lap to be competitive!

And the sun shone (mainly).  :beerchug:

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8 hours ago, wazrs257 said:

Today saw me and @El Gringo parked up on the M6 on the way to 3 sisters, eating Sainsburys taste the difference sausage rolls, whilst waiting for an accident to be cleared so we could continue on to the circuit. The ACU test session had been booked initially to test my new 50 race bike, but I thought I may as well throw the 85 in the van as well, in case we didn't have enough to do.

As it turned out, the 50 didn't want to play ball, so I spent most of the time out on the 85, while the 50 had jetting changes.

It behaved perfectly, even the gearing that I fitted for Whilton mill, turned out to suit 3 sister perfectly. I’ve now got gearing information for whilton mill.

I just need to find 10 seconds a lap to be competitive!

And the sun shone (mainly).  :beerchug:

And could you taste the difference?

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