Planning a engine rebuild before failure. Any advice welcome.


6 replies to this topic
  • f150jokerstyle

Posted April 30, 2013 - 08:10 PM

#1

Hi everyone I have a 03 yz450. As of now it has a ported cylinder head and it has an iron sleeve in it somewhere around 470cc. On the last rebuild it was pretty much just a sleeve piston,rings, and lapping of the valves and it ran like a spotted ape for quite a while but it is noticeably getting more tired on the bottom end and flatter on the top. Also the old yz knock it knocking a little louder now a days.

Typical use of the bike is 80+ mile desert races ranging from snow to over 100 degree temps depending on time of year.

So here is the plan as of now.

1. Remove head and have the seats and valves checked along with springs. I really want to replace them due to age but if they check out they check out. It's a large cost to just replace them if they check okay. Looking for opinions?

2. Replace cylinder with a nikasil 470cc version along with piston and rings. As to what brands of cylinder and piston i'm open to opinions and why.

3. Replace cam chain with oem unit unless anyone suggest an aftermarket.

4. Crank rebuilt with new main bearings and big end bearing and have rod checked. Again I know the rod is a weak point on this gen of motor and i'm leaning toward replacing it. Opinions welcome.

5. Replace current YZ 4 speed trans with Wr 5 speed trans I have, and check trans bearing for excessive wear.

6. Check water pump shaft for wear. Replace if needed also I was wondering if anyone has had any luck with the boysen water pump impeller for slower speed conditions as far as cooling?

7. What engine gasket kits are working the best for all of you.

8. All clutch components are aftermarket and in good shape so I should be fine there.

9. Plan on blocking off oil drain hole on oil filter cover with ball bearing that I read about some where on here.

Okay everyone what am I forgetting? I know someone will say buy a newer bike but I have this bike dialed in really well and don't feel like starting over. Also I have not ridden anything thus far that I can honestly say is any faster or better than this bike when it and my self are not tired. Not to mention I'm way to hard on bikes and I would take a nice looking bike and have it looking like mine in no more than 2 races and that would depress me :unsure:

  • grayracer513

Posted May 01, 2013 - 06:45 AM

#2

1) If nothing appears wrong with any of the valves, you could just replace the springs and seals, but it would naturally be a kind of guessing game as to how much longer before they wear through the coating and need to be replaced. OTOH, when they do show signs, it's only the head that needs to come off.

3) The OEM chain is $20 and made by Borg-Warner Japan. The Pro-X chain is $65 and made by Borg-Warner Japan. Follow?

4) I recommend using a complete new OEM crank for an '04-'05. All brand new upgraded stuff, with a new cam drive sprocket to boot.

5) Just replace the bearings, and don't forget the balancer shaft. Wear can be measured, but it's harder to predict if or when the races will start spalling ("flaking").

7) Cometic kits are good stuff, but don't generally include seals like the output or water pump seals. Personally, I haven't had a problem with them, but I prefer OEM head gaskets in particular, and OEM gaskets in general.

9) Here's where you read it (Common Threads): http://www.thumperta...ad.php?t=634724

  • f150jokerstyle

Posted May 01, 2013 - 02:15 PM

#3

1) If nothing appears wrong with any of the valves, you could just replace the springs and seals, but it would naturally be a kind of guessing game as to how much longer before they wear through the coating and need to be replaced. OTOH, when they do show signs, it's only the head that needs to come off.

3) The OEM chain is $20 and made by Borg-Warner Japan. The Pro-X chain is $65 and made by Borg-Warner Japan. Follow?

4) I recommend using a complete new OEM crank for an '04-'05. All brand new upgraded stuff, with a new cam drive sprocket to boot.

5) Just replace the bearings, and don't forget the balancer shaft. Wear can be measured, but it's harder to predict if or when the races will start spalling ("flaking").

7) Cometic kits are good stuff, but don't generally include seals like the output or water pump seals. Personally, I haven't had a problem with them, but I prefer OEM head gaskets in particular, and OEM gaskets in general.

9) Here's where you read it (Common Threads): http://www.thumperta...ad.php?t=634724


Thats good info on #4 I had no idea. Thank you

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  • grayracer513

Posted May 01, 2013 - 02:28 PM

#4

Thats good info on #4 I had no idea. Thank you


Here I thought all of it was good. :excuseme:

Fact is that you can't actually buy the original '03 crank. It's been superseded for some years now by the updated '05 crank.

  • f150jokerstyle

Posted May 01, 2013 - 02:59 PM

#5

Here I thought all of it was good. :excuseme:

Fact is that you can't actually buy the original '03 crank. It's been superseded for some years now by the updated '05 crank.


LOL I stand corrected because they ALL were good! Do you have any opinion of say like the cylinder works big bore kits by chance or big bores on these bikes in general? I guess what i'm getting at is do they wear out faster than OEM? I think I have a line on getting OEM stuff at a reasonable price. So if say the OEM stuff has better longevity I would rather keep it a 450 and go that route I think. I know a plated cylinder is a plated cylinder but I have had some problems before with cylinders from aftermarket venders where lets just say I question their quality control. As i'm typing this I'm leaning more towards new OEM 450 parts by the second :thinking:

  • grayracer513

Posted May 01, 2013 - 03:10 PM

#6

The absolute best in terms of reliability is the OEM stuff. But Luke's racing has a good reputation with big bore kits. In the interest of the longest possible ring life, ask them for a piston with two compression rings.

As an extra step, consider getting the crank rebalanced to offset the slightly heavier piston, as long as both would be out at the same time.

  • f150jokerstyle

Posted May 01, 2013 - 04:32 PM

#7

The absolute best in terms of reliability is the OEM stuff. But Luke's racing has a good reputation with big bore kits. In the interest of the longest possible ring life, ask them for a piston with two compression rings.

As an extra step, consider getting the crank rebalanced to offset the slightly heavier piston, as long as both would be out at the same time.


Thank you very much for your help and advice :cheers:





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