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Good items to replace while top end is off?

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Any advice on what should be replaced while I have the top end off for a valve replacement. Will do headgasket and springs of course, anything other parts you would recommend while I'm going at it?

 

Thanks!

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The list of things you can replace is long and expensive.  Just do the work that needs to be done otherwise you will be in for a complete top end replacement and a ton of money.

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On 9/7/2018 at 1:52 PM, crfjunky1320 said:

Any advice on what should be replaced while I have the top end off for a valve replacement. Will do headgasket and springs of course, anything other parts you would recommend while I'm going at it?

 

Thanks!

What bike and year. That makes a huge difference with some Hondas at least.

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3 hours ago, cjjeepercreeper said:

What bike and year. That makes a huge difference with some Hondas at least.

2003 crf450r

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As I’m doing my first valve replacement on my own on a 2003 Honda CRF450R that I’m bringing back to life I noticed that the piston has a rough surface around the outer perimeter. Im not sure if this is just how the stock piston looks (I wouldn’t imagine that it would be) or if it’s a result of detonation, extreme wear, etc. Does this need to be replaced or would it be okay on a simple trail bike? 

 

Any help would be appreciated!

16B94F3A-7ECB-44BB-B50C-1D1A8773B366.jpeg

1661D43B-9B96-416E-8A26-670FE3C7BF04.jpeg

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I think it looks like the roughness is from the manufacturing process.  Casting or forging process. The shiny spot in the center is from the machining process.  Just my opinion.

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25 minutes ago, 250xhonda said:

I think it looks like the roughness is from the manufacturing process.  Casting or forging process. The shiny spot in the center is from the machining process.  Just my opinion.

The roughness seams pretty excessive for a manufacturing process. Could it be from sucking dirt through the carb? I’ve never seen a piston with this much pitting in it so I’m just curious. 

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I wouldn't worry about it. If it was all pitted up from ingesting something or something else that shinny spot in the middle would be to I would think.  

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1 hour ago, crfjunky1320 said:

2003 crf450r

Take a very close look at the valves.  Early Rs had valve issues up to 07 I think.

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Yeah man!!! With all the details you posted, I have a ton of recommendations !!

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13 hours ago, 69fastback said:

Yeah man!!! With all the details you posted, I have a ton of recommendations !!

Typical Thumpertalk technical question:  "I have a bike, what parts should I replace?"  🤔

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Have the cylinder professionally measured.  It may need replaced or fixed. Cylinder Works are nice if you need to replace it. Consider putting a new head on it from Big Bore Thumpers if fixing the one you got gets more expensive than the BBT head.  http://www.bigborethumpers.com/newheads.html  New and comes with stainless steel valves and heavy duty springs.

Best of luck brother.

Edited by HRC27

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It'd be derelict  to not pull the cylinder and at least measure the piston and cylinder. 99% of the time, unless there has been a catastrophic failure, the cylinder is reusable. The pistons on the other hand, they are so short that even a little wear makes them hazardous to run again. Knowing how and where to measure is key. And the fact that you're asking about what to replace makes me bet you dont have the proper tools to do that task.

The rule of thumb is 100 hours on a piston and 200 on a crank. It's an 03. Unless it was quite pristine when you obtained it, Im betting your beyond at least one of those, probably both.

Cam chain tensioner should be replaced about every 50 hours IMHO. The OEM part is a piece of shit. Just a little age on the thing is more than it'll usually deal with. They'll let go, reset themselves and the timing ends up 1-2 teeth to the retard. Most guys wont notice a performance change other than the kicker being way stiffer because the auto decompressor mechanism is coming on way late in the stroke. My advise is to buy a TT manual tensioner. It wont let go. Reliability to rival the sunrise. Contrary to what some people will say, once it's set, you wont have to mess with it until you get back into the top end, or change the timing chain, which, for 30 bucks, I'd also suggest.

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19 hours ago, CDNSXV said:

Typical Thumpertalk technical question:  "I have a bike, what parts should I replace?"  🤔

Simple question. If you don't have any advice keep scrolling.

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like stated above...your one bolt  away from pulling the cylinder I would pull it and look at the skirt wear. Its a casted piston, that's where your rough pitting look is coming from.  An OEM piston is cheap. In my experience Ive always been sketched out about throwing an aftermarket piston on a crank that could be 15 years old. Id put a new Honda piston and rings in it....possibly a stainless valve swap and ride it

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On 9/11/2018 at 3:52 AM, MX450R said:

like stated above...your one bolt  away from pulling the cylinder I would pull it and look at the skirt wear. Its a casted piston, that's where your rough pitting look is coming from.  An OEM piston is cheap. In my experience Ive always been sketched out about throwing an aftermarket piston on a crank that could be 15 years old. Id put a new Honda piston and rings in it....possibly a stainless valve swap and ride it

Actually, it's not a cast piston. The CRF450R, the 250's and just about all the racing four strokes run a forged "slipper" style piston. A cast piston in that configuration would fail within hours because the skirt is so short.

Your advice is solid though. That pitting looks like someone has had it part once before and sand blasted the carbon off, but that center machined section hasn't been touched, so I'm not certain what's going on there.

If it were me, and I was short on dollars, Id put the 04 piston in it with a new OEM or even a HotRods crank and ride it. There's nothing wrong with the HotRods cranks. If you wanted to get one of those "kits", the 04-08 parts are what you want. From 03 to 04, Honda raised the compression ratio from 11.25:1 to 12.5:1. It's only a slight difference, but you'll feel it for sure. No, you wont have to re-jet the carb or anything else. But do yourself a favor and clean the carb, the inside, not the outside...

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