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Hello,
Just joined and picked up a 2008 kfx450 Friday with a known running issue. Turns out she had 30 lbs of compression and i pulled the head. The piston looked pretty good and i cleaned up the carbon with some scotch brite and brake cleaner. (See pictures)
A buddy of mine is an engine builder and we are going to open her up with a port and polish and he mentioned about cutting the seats as well a certain way to improve flow.

Question:
1. How does the cylinder walls look and would you replace the piston and rings?
2. Is this a stock piston / bore?
3. Do they make a cylinder head kit for these? I couldnt find a kit and i would like to replace everything minus the cams to get a benchmark.

Thank you and Dirt Devil, I appreciate the messagr back with a PDF manual. Greatly appreciate it!!
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28566


-respectfully
Charlie
20201026_140948.jpg
 

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Discussion Starter #3
The area you are concerned with is shadows from the picture where the piston is recessed for the valves. I will try and get some better shots to share for advice.
Attached is some pics of the head after a hot tank wash and the glassbead blast. Failed a leak down test out of the exhaust valve. Cams were also hand tight so that was definitely the culprit.
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Hand tight bolts holding the cams...

Are the cams holder bolt threads OK or needing helicoils repair...??
 

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***i did a leak down test when they were hand tight. This was to give insight that the cam was not in any way applying pressure to the buckets. Thats all.
 

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***i did a leak down test when they were hand tight. This was to give insight that the cam was not in any way applying pressure to the buckets. Thats all.
Red flags went up when I read "hand tight".. many advise against hot tanking an aluminum head due to the possibility of warping & chemical dip instead...

So you narrowed it down to worn valve seats or valve wobble...??

It is a stock piston ( die cast stamp circled ) see pic

Cylinders have a nikasil coating that's super hard & rings last longer that iron bore...unless grime & dirt get past the filter...The piston surface looks good, any movement or is it still tight...?

They make cylinder head kit... KFX450R

Ebay/amazon is another place to check for head kit or bigbore kits....
 

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Discussion Starter #7
Haha yes i knew that was alarming. I should of articulated that better.

Thanks for the piston information! Good to know! I was curious if it was stock or not but now I know.

Cylinder head should be done Thursday. Was acid washed, glass beeded, ported, new exhaust valves, cut the seats, and milled. Im hoping for 1.5 - 2hp out of this.

Question: I have been reading up and I wanted to check. This quad came with a DASA exhaust and uni air filter. Do i need to run a programmer or can I leave it as is? I know you get more power with one, but I do not want to risk running lean if I leave it alone for a few months.

Thanks again for the replies!
 

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Haha yes i knew that was alarming. I should of articulated that better.

Thanks for the piston information! Good to know! I was curious if it was stock or not but now I know.

Cylinder head should be done Thursday. Was acid washed, glass beeded, ported, new exhaust valves, cut the seats, and milled. Im hoping for 1.5 - 2hp out of this.

Question: I have been reading up and I wanted to check. This quad came with a DASA exhaust and uni air filter. Do i need to run a programmer or can I leave it as is? I know you get more power with one, but I do not want to risk running lean if I leave it alone for a few months.

Thanks again for the replies!
Is your intake tube stock or upgraded...?? see picture Stock is circled vs FCI Fuel custom intake...

If your intake tube is stock no you don't need a fuel programmer,Stock intake tube & an full exhaust a fuel programmer will provide better throttle response very little gains in HP ..But why port & polish without upgrading your intake...!!
 

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Just learning about these bikes and i saw the ltr intake mod. I had no clue they closed in like that. I will definitely be changing that! But that means i need a tuner... trying to keep my total investment under $3,000. Paid 1900 for this and so far i am in it $700.
 

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Just learning about these bikes and i saw the ltr intake mod. I had no clue they closed in like that. I will definitely be changing that! But that means i need a tuner... trying to keep my total investment under $3,000. Paid 1900 for this and so far i am in it $700.
Here's a thread on the LTR mod with stock airbox... LTR Intake Tube Mod with stock box.
Yes you'll need a fuel tuner...But will have around 40+ HP with a proper tune from a stock 32 HP
 
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