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Old 03-22-2007, 06:11 AM   #1
rideaholic OP
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Difference between LC4 620 and 640 motors?

Hi,
I have been reading this site a lot. Especially in the last week or so since I bought a 1997 KTM RXC 620. I see a lot of talk and info about the LC4 640 motor, but not as much on the 620. Is there a great difference other than the 20cc of displacement? Can all those how to articles at the beginning of this section by Creeper apply to my bike also? Are there any weak points that I should keep an eye on? I know about the crank bearing that may need replced. Does that apply to the 620 also?
This is a great site and I have gain a great deal of knowedge here already.
Thanks in advance for any help.
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Old 03-22-2007, 07:39 AM   #2
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I'm not a KTM expert, but they are both the LC4 motor (625cc).

Read through the creeper sticky, you'll find the answer.

I asked this question on another forum:

"Can anyone point me to an article comparing the LC4, 620 SXC, and the 640 Adventure?"

And recieved this answer:

"
sxc- least fuel cap. 9L (75-90 mile range about)no cooling fan, less oil capacity, longer wheel base better hispeed stability that lc4e, power band hits pretty hard, more of offroad bike
lc4 e 18l fuel cap.(200+mile range) cooling fan more oil not as stable at speed , but better in the tight stuff smooth power delivery, an excellent big bore enduro bike/dual sport

adventure more fuel 28L and lots of other stuff


I am quite partial to my 640E

they are all 625cc "


hope this helps, Jon
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Old 03-22-2007, 08:57 AM   #3
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Most of what applies to the newer 640s will apply to the 620 (609cc actually). The bearing problem applies, the cam bearing weakness applies. The 620's internal gearing is lower than the 640's so your sprocket combinations will be different. Brakes same. Electrical probably similar. Carbs will be different. Suspension different (forks) but the shock and linkage in the rear is the same. Airbox same. Tank and bodywork different but some folks have updated older bikes with the newer plastics, you have to do everything including the seat to make it fit.
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Old 03-22-2007, 09:51 AM   #4
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Thanks guys for the help. So it's a 609 cc and not a 625cc? I hadn't seen the cam bearing problem thread. I am going to have to look for that one. Is it something I should change out now or wait until a noise develops? I was thinking of putting on the orange plastic some day. I may try krylon first just to see since it can't hurt before dishing out all the money for upgraded plastics. Thanks again. If there is any more info and help I would and do greatly appreciate it.
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Old 03-22-2007, 02:03 PM   #5
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The 640 is 625cc, the 620 is 610cc (609?) Ive never heard 609 before but you might be right.
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Old 03-22-2007, 02:16 PM   #6
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The 620 motor is indeed a 609cc. The stroke and bore are different, as is the primary gearing.

The early non-electric start 620's had SEM ignitions and a very primitive electrical system. Counterbalancers came in '96. E-start in '97.
The other difference is the carburetors. D'ellortos, Edelbrocks or Mikunis, depending on the year.

The 620 is a good motor. Take care of it and they last and last. I have a '96 620RXC that just keeps pulling, and is faster than any 640 I've owned. I'm not sure why either.
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Old 03-22-2007, 05:05 PM   #7
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Thanks again for the help and responses. I tore the bike down somewhat to go over everything and make sure all is tight and in good working order. It has 4000 miles on it and I am hoping to put many more on it in the future. I think I may replace the seat with something a little softer so that I can ride it longer distances. I may also design some type of highway bars that are compact for longer distance rides. I again thank everyone for the help and welcome any more info that can be benificial. I am reading as much as I can...there is a lot of great info on this site.
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Old 08-11-2007, 12:22 PM   #8
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KTM aftermarket heavy duty kickstand?

Just got a brand new thumper a 95 620 RXC,love it! but no kickstand. I see heavy duty units for other models but not a 95! Hoping someone has found one ,made one or knows if the newer aftermarkets are interchangeable or can be modified?
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Old 08-11-2007, 03:20 PM   #9
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There's a lot of information on this site. Try using the advanced google search page to search http://advrider.com. If you can't find it, you'll have better luck starting your own thread in the thumper forum than posting off-topic in someone else's thread.

Quote:
Originally Posted by Deahkid
Just got a brand new thumper a 95 620 RXC,love it! but no kickstand. I see heavy duty units for other models but not a 95! Hoping someone has found one ,made one or knows if the newer aftermarkets are interchangeable or can be modified?
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Old 08-11-2007, 11:42 PM   #10
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I didn't read all the responces and am not an expert, however I would say about 20cc




















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Old 08-12-2007, 07:36 AM   #11
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Bearings and kickstands

I wouldn't let the bearing daemons keep you up at night. I changed my cam/water pump bearings over the winter (11K '95 RXC) and they appeared to be in good shape.

Change the oil & filters, ride it for 1K miles or so and send an oil sample off to blackstone labs. for an oil analysis so you have a baseline and repeat. I'd let the analysis tell you when to change out your bearings, science over hearsay.... I could be wrong but I doubt that your bearings will catastrophically fail, leaving you stranded. In my opinion the less you have your paws inside that finely crafted sewing machine the better off you are.

Kickstand: on the '95 there's a KTM stand that attaches to the swingarm. I _may_ have one. please PM me.
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Old 08-13-2007, 05:14 AM   #12
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Quote:
Originally Posted by beerjonny
"sxc- least fuel cap. 9L (75-90 mile range about)no cooling fan, less oil capacity, longer wheel base better hispeed stability that lc4e, power band hits pretty hard, more of offroad bike
lc4 e 18l fuel cap.(200+mile range) cooling fan more oil not as stable at speed , but better in the tight stuff smooth power delivery, an excellent big bore enduro bike/dual sport

adventure more fuel 28L and lots of other stuff"
Anyone know what the wheelbase difference is and also how much more oil does the LC4E have over the SXC?
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Old 08-13-2007, 07:22 AM   #13
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Quote:
Originally Posted by ekaphoto
I didn't read all the responces and am not an expert, however I would say about 20cc
620 = 609cc

640 = 625cc

more like 16cc.
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Old 03-18-2011, 12:12 PM   #14
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Talking

the bore is the same and the stroke is 2mm different (76 and 78 mm)
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Old 12-11-2011, 08:14 AM   #15
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I have a 97 620 egs. Not much info on the net about these. I hear some 620' don't have. Cooling fan. Mine doesn't but think it should. Can anyone shed by light on that?

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