Engine Rebuild? - Kawasaki KFX450 Forum :: KFX450HQ.com
Engine/EFI/Drivetrain Discuss engine, fuel injection, air intake, and drivetrain modifications here.

 
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post #1 of 4 (permalink) Old 08-08-2019, 06:47 PM Thread Starter
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Engine Rebuild?

Hey everyone, I’ve been browsing the forums here for some time but finally decided I needed to join. So, to my problem, I bought a 2013 KFX450r in hopes to upgrade from my 2001 Mojave 250 as I was getting left behind on straight aways on trails. When I got it, I changed the fluids and oil filter. Then, I took the quad for its first ride, put about 2-3 hours on it, and it started backfiring/after-firing and making a rattling noise. I brought it to a shop to get checked out, was told the bottom end is toast and needs a full rebuild. What I don’t understand is the shop only checked the compression (which was low) and the oil filter. So, does anyone know how this shop knows the rod bearings and bottom end are toast just by seeing low compression. I was also told the engine was knocking but like I said earlier, the only noise was a rattle coming from the top end/radiator area and was definitely not a knock. I apologize for the long post but this machine was a big purchase for me and it doesn’t make sense, according to the symptoms and based on my knowledge, that I need to drop $2,500 on a rebuild. I appreciate any insight.
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post #2 of 4 (permalink) Old 08-08-2019, 10:04 PM
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Welcome to the Forum...!!

More info needed...?

(your quote) What I donít understand is the shop only checked the compression (which was low) and the oil filter...Low compression is usually not a sign of a bad main bearing....

What do you mean about the oil filter...low oil or what...??

Can you remove the valve cover and see if there's anything a miss...?

(Your quote)
and it started backfiring/after-firing and making a rattling noise.....after firing to mean dieseling or detonation...??

Is the motor stock or did the previous owner modded the motor with high compression piston....????

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post #3 of 4 (permalink) Old 08-10-2019, 12:10 AM Thread Starter
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Thanks for the reply. So, the shop only pulled the oil filter to look for metal flakes, which there were none in the oil. As for the backfiring, it was a loud pop on deceleration which I assume is from excess fuel that isn’t getting ignited which then ignited in the exhaust causing an “after fire”, or the loud pop. I’m sort of new to the whole 450 world and maybe I bite more than I can chew but if anything would be wrong with my motor, I feel the shop is wrong with the bottom end and it would be the top end that is having an issue. Also, the motor is stock as far as I have been told and can see. Thanks again...
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post #4 of 4 (permalink) Old 08-10-2019, 03:33 PM
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Quote:
Originally Posted by Evan View Post
Thanks for the reply. So, the shop only pulled the oil filter to look for metal flakes, which there were none in the oil. As for the backfiring, it was a loud pop on deceleration which I assume is from excess fuel that isn’t getting ignited which then ignited in the exhaust causing an “after fire”, or the loud pop. I’m sort of new to the whole 450 world and maybe I bite more than I can chew but if anything would be wrong with my motor, I feel the shop is wrong with the bottom end and it would be the top end that is having an issue. Also, the motor is stock as far as I have been told and can see. Thanks again...
Ok...If it backfires when decelerating it's due to air/fuel mixture being lean...excess fuel or extremely rich fuel mixture will cause dieseling or flame firing out the exhaust...

Lean fuel mixture or improper fuel octane can cause sever motor damage, burnt valves bad rings or warped head ect...(What was the compression test results) do you know, or can provide your own test by chance...?? Below 50 psi you'll need to rebuild your top-end...!!

Is your KFX motor stock or with mods (example) fuel controller, full exhaust, head porting high compression piston...ect...???..If yes...please list...

Metal shaving from failing main bearing would probably be found in the oil sump screens and "may not" be found in the oil filter...draining the oil into a screen or magnet fishing in the old oil is better to look for metal shaving...!!

Yes.. bad main bearing will cause it to knock.."like a hammer pounding? in the bottom end of the motor & it's best to listen with a motor stethoscope for a proper diagnosis...removing the cylinder a check for crankshaft play is best...!!

Did you pull the head/valve cover off to look for anything that would cause the rattling you heard...??

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