KTM 85 - Engine Compression

RickB72
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RickB72
Hello, I'm looking to purchase a used 2013 KTM 85 for my son. I was wondering if anyone could give me some advise on things to check and warning signs to look for? I have a compression tester however I'm not sure what an acceptable range of psi would be? (cold and hot)

Any advise you could provide would be greatly appreciated
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Paw Paw 271
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Paw Paw 271 1/16/2018 1:49pm
1/16/2018 1:49pm
110+psi

Paw Paw
chillrich
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chillrich 1/17/2018 9:25am
1/17/2018 9:25am
I'm not sure about that year engine but the earlier 85/105 were notorious for big end rod bearing failures. Hard to catch before failure without cylinder removal.
Tracktor
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Tracktor 1/17/2018 9:54am
1/17/2018 9:54am
Good bikes. I would just expect to put a top end in and get the deck height/timing & squish all set up from the beginning. Most mini dads don't do it. Buy a couple of each thickness base gasket & the Nihilo setting tool. The crank failures are from crank float which can be mitigated by replacing LH main bearing with a roller bearing and possibly shimming it. KTMtalk has a ton of info on it in the 85 section.
Pull filter and check for dirt in air boot. Check swingarm bearings as best you can.
These bikes are simple to work on a relatively cheap to fix. I can do a complete bottom end rebuild in a couple of hours. Top ends are cake as there is a ton of room. Vertex pistons work best, imo and are same as stock. Keep an eye on rear brake pads as they wear fast.........
kzizok
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kzizok 1/17/2018 6:36pm
1/17/2018 6:36pm
Hello,

I know Tamir had some Huskys at one point. Maybe KTM’s too. He would probably be your best bet.

The Shop

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RickB72
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RickB72 1/17/2018 7:25pm
1/17/2018 7:25pm
That’s great, thanks for the info Tracktor. Am I correct to assume that replacing the LH main crank bearing is something you would do during the first bottom rebuild? I think I can do the top end I have watched some youtube videos and it looks very straight forward. Is there any way to judge the health of the bottom end without taking it apart? I assume if it’s shifting correctly while riding and if you don’t see any large pieces of loose metal when you change the oil your good?
Hondas4Life3
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Hondas4Life3 1/18/2018 9:21am
1/18/2018 9:21am Edited Date/Time 1/18/2018 9:23am
RickB72 wrote:
That’s great, thanks for the info Tracktor. Am I correct to assume that replacing the LH main crank bearing is something you would do during the...
That’s great, thanks for the info Tracktor. Am I correct to assume that replacing the LH main crank bearing is something you would do during the first bottom rebuild? I think I can do the top end I have watched some youtube videos and it looks very straight forward. Is there any way to judge the health of the bottom end without taking it apart? I assume if it’s shifting correctly while riding and if you don’t see any large pieces of loose metal when you change the oil your good?
On a two stroke the crankshaft area and transmission area are separated. You can judge transmission and clutch by riding it and looking at the oil (or taking it apart). The crankshaft can be inspected by spinning it and listening to the bearings and feeling for any excessive friction or ruff movement. You also measure the I.D. where the piston pin goes (small ed of rod) and the vertical and lateral play in the rod. Any vertical movement is bad. All cranks have lateral movement so refer to service manual for measurement.

There is only so much you can tell from a bike before purchase. The only way to know its ready to go is to take it apart.
MotoX Luca 1/19/2018 2:50pm
1/19/2018 2:50pm
Clean Engine cases and Cylinder are a good sign that the bike was recently rebuilt and tooken care of.
lumpy790
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lumpy790 1/20/2018 7:15am
1/20/2018 7:15am
Paw Paw 271 wrote:
110+psi

Paw Paw
What does the 85’s manual say compression should be? I have 100 psi to be to low
RickB72
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RickB72 1/21/2018 4:25am
1/21/2018 4:25am
@lumpy790, the owners manual does not define what the engine compression should be
lumpy790
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lumpy790 1/24/2018 8:38am
1/24/2018 8:38am
RickB72 wrote:
@lumpy790, the owners manual does not define what the engine compression should be
Repair manual should

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