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Discussion Starter #1
Hello new to the site i have a question about my 1997 ktm 400 rxc. The motor that is on the bike is causing me some confusion it is a a lc4 and i have the head tore off to replace the the ring and piston and it is a elko 95 with a 1 under it and 2098 on the piston the engine number is 7-577*0065 it also has keihin 39 mm carb electric start. When I look up piston and rings for the year of the bike it shows 89mm piston which it is definitely not due to checking with calipers. Is this engine newer than a 1997 or bigger than 400cc? What piston would work for this engine. Any and all answers are welcome thanks
 

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Yep, should be a 89mm piston on a 400. The 620 had a 101mm piston. What size is your one?
 

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Discussion Starter #4
I tried looking up a reference for motor id stamped on the engine but im finding it a little difficult #7-577*0065
 

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When i cross reference the vin it looks to come as a 1997 400 rxc but not sure how to reference it to the engine number and having a 95 mm piston
 

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You are correct. The VIN# is for a 97 400 RXC. The motor number is for a 400 LC4-E. This engine should have a 89mm piston. The 95mm piston was used in a 520/530/540cc engine. It seems like the crank cases were the same in the 400 and 520/530/540 engines (But I am not 100% sure re that). The crank was different and also the cylinder.

I conclude that you have a 400 bike (based on VIN#) with a 400 motor (based on motor#) that has been retro fitted with a different/re-bored cylinder and bigger piston (used in 520/530/540 engines. Note that these engines did use different cranks) making your bike more than 400cc... As it looks like the crank cases were in some/all these bikes the same it is also a possibility that your motor has been fitted with a crank that was for a bigger cc motor...

My money would be on that the initial owner of the bike wanted some more power and realized that he only had to fit a bigger cylinder and piston (or re-bore) to achieve this.
 

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As the same 95mm piston was used in 520/530/540 engines the only way to change the cc's would have been to change the stroke. That would mean a different crank (with the pin a fraction further out on the crank). Only other way would be to have a crank pin where the part the conrod and bearing turns on is off-center, but I highly doubt this setup would have been used.
 
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