Power Valves replacements

Discussion specific to the 1989 - 1994 (E Series) KDX200 model sold in the USA
ccdsg
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Power Valves replacements

Post by ccdsg » 04:23 pm Jun 29 2020

I got this 90’ a few weeks ago and it was really slow to start but if it ran it still would. After a few days it completely stopped starting and the compression was pretty bad so I figured it just needed to be rebored and given a new piston. After I cracked the top end open I found the LH power valve wasn’t functioning and then discovered it was completely sheared off the top and the teeth on the top gear were completely cut on one side. It seems to be a common issue that these aluminum valves break, is it recommended to get a steel set of replacements?

Edit: the LH valve was stuck open, would this have also been a reason for the poor compression?

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Re: Power Valves replacements

Post by SS109 » 06:12 pm Jun 29 2020

Powervalves do not affect compression as they are on the exhaust side. Most likely culprit for your poor compression is a very worn piston and rings.

As for the powervalves themselves, originals are pretty much impossible to find and even harder to find still in good shape. The steel replacement valves are your only real option.

You do not bore a cylinder with electrofusion/nikasil coating unless going to a big bore setup and even then it must be replated after the boring. Otherwise, you send it in to be replated and repaired back to a standard bore if needed.
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Re: Power Valves replacements

Post by ccdsg » 06:23 pm Jun 29 2020

SS109 wrote:
06:12 pm Jun 29 2020
Powervalves do not affect compression as they are on the exhaust side. Most likely culprit for your poor compression is a very worn piston and rings.

As for the powervalves themselves, originals are pretty much impossible to find and even harder to find still in good shape. The steel replacement valves are your only real option.

You do not bore a cylinder with electrofusion/nikasil coating unless going to a big bore setup and even then it must be replated after the boring. Otherwise, you send it in to be replated and repaired back to a standard bore if needed.
I don’t know what electro fusion or nikasil is, I was just going to buy a 66.50 Wiseco piston and a new needle bearing and the get the cylinder bored to fit 66.50 at a local mechanics shop

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Re: Power Valves replacements

Post by SS109 » 06:55 pm Jun 29 2020

ccdsg wrote:
06:23 pm Jun 29 2020
I don’t know what electro fusion or nikasil is, I was just going to buy a 66.50 Wiseco piston and a new needle bearing and the get the cylinder bored to fit 66.50 at a local mechanics shop
Do NOT do that! That would be very, very bad. Do a Google search on Nikasil cylinder plating and read up on it and why it is used. If you were to bore it, which would remove all the factory plating, all you would have is a pure aluminum bore and it would last no more than a couple of minutes of run time before it would seize up.

That said, your plating might be just fine. As long as there are no gouges or scratches you can feel with your fingernail, or chipping of the plating, you can probably just clean it up and install the appropriate A, B, C, or D sized piston in it and ride.
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Re: Power Valves replacements

Post by ccdsg » 07:26 pm Jun 29 2020

Image
SS109 wrote:
06:55 pm Jun 29 2020
ccdsg wrote:
06:23 pm Jun 29 2020
I don’t know what electro fusion or nikasil is, I was just going to buy a 66.50 Wiseco piston and a new needle bearing and the get the cylinder bored to fit 66.50 at a local mechanics shop
Do NOT do that! That would be very, very bad. Do a Google search on Nikasil cylinder plating and read up on it and why it is used. If you were to bore it, which would remove all the factory plating, all you would have is a pure aluminum bore and it would last no more than a couple of minutes of run time before it would seize up.

That said, your plating might be just fine. As long as there are no gouges or scratches you can feel with your fingernail, or chipping of the plating, you can probably just clean it up and install the appropriate A, B, C, or D sized piston in it and ride.
So what you’re saying is at most I’d need to rehone the cylinder, but I should get the same size piston?

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Re: Power Valves replacements

Post by KDXGarage » 07:41 pm Jun 29 2020

Welcome.

Can you post a few pictures of your cylinder? When new, it has a special coating that one can not simply bore and replace a larger piston.

BDK Engineering on eBay makes and sells the power valves.



If it is still coated / plated, one can not hone it or bore it.
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Re: Power Valves replacements

Post by ccdsg » 08:51 pm Jun 29 2020

https://ibb.co/KVChBkf
https://ibb.co/5RFq7W3
https://ibb.co/Swg0cxt
https://ibb.co/0nr4hF2
https://ibb.co/85SBsgc

Sorry about the links, can't make the image show up.
KDXGarage wrote:
07:41 pm Jun 29 2020
Welcome.

Can you post a few pictures of your cylinder? When new, it has a special coating that one can not simply bore and replace a larger piston.

BDK Engineering on eBay makes and sells the power valves.



If it is still coated / plated, one can not hone it or bore it.
I actually ordered the steel power valves from BDK's website

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Re: Power Valves replacements

Post by SS109 » 09:53 pm Jun 29 2020

Like KDXGarage mentioned, you don't hone a plated cylinder. You can clean it up using a Scotchbrite pad to scrub the bore or, at worst, if it has some aluminum stuck to the plating, a little muriatic acid to remove it. If it needs anything more than that then it will need a replate.

Looking at the last two pics I can see there is plating missing between the ports. It needs a replate.
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Re: Power Valves replacements

Post by ccdsg » 10:22 pm Jun 29 2020

SS109 wrote:
09:53 pm Jun 29 2020
Like KDXGarage mentioned, you don't hone a plated cylinder. You can clean it up using a Scotchbrite pad to scrub the bore or, at worst, if it has some aluminum stuck to the plating, a little muriatic acid to remove it. If it needs anything more than that then it will need a replate.

Looking at the last two pics I can see there is plating missing between the ports. It needs a replate.
How do I replate the cylinder?

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Re: Power Valves replacements

Post by SS109 » 10:59 pm Jun 29 2020

You need to send it out to a shop that specializes in it. It's not a DIY process nor one just any place can do. Two that are well known and highly respected is Millenium (https://www.millennium-tech.net/serviceInfo.php?id=1) and Powerseal USA (http://www.powersealusa.com/). I like Millenium and have done 5 different cylinders through them and have never been disappointed. Cost is about $200 and up depending on if they need to weld anything up before replating it. Whatever you do, don't let anyone talk you in to sleeving the cylinder instead of proper plating as it tends to create more problems than it solves.
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Re: Power Valves replacements

Post by KDXGarage » 12:08 am Jun 30 2020

I think a replate is needed. Look on the Millenium site or Youtube to see what plating a cylinder means. They can explain it with a video better than us typing. :-)

You will need a new piston, rings, circlips, pin, small end bearing, gasket kit, fresh coolant... AND you REALLY, REALLY would benefit from a service manual. Kawaski made one. Cyclepedia also makes one.
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Re: Power Valves replacements

Post by ccdsg » 12:47 am Jun 30 2020

SS109 wrote:
10:59 pm Jun 29 2020
You need to send it out to a shop that specializes in it. It's not a DIY process nor one just any place can do. Two that are well known and highly respected is Millenium (https://www.millennium-tech.net/serviceInfo.php?id=1) and Powerseal USA (http://www.powersealusa.com/). I like Millenium and have done 5 different cylinders through them and have never been disappointed. Cost is about $200 and up depending on if they need to weld anything up before replating it. Whatever you do, don't let anyone talk you in to sleeving the cylinder instead of proper plating as it tends to create more problems than it solves.
Well that’s a rough one.

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Re: Power Valves replacements

Post by KDXGarage » 01:03 am Jun 30 2020

What did you pay for the bike?
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Re: Power Valves replacements

Post by SS109 » 01:15 am Jun 30 2020

Yeah, it sucks but is the only way to fix that cylinder.
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Re: Power Valves replacements

Post by ccdsg » 03:04 am Jun 30 2020

KDXGarage wrote:
01:03 am Jun 30 2020
What did you pay for the bike?
1175 from eBay. Seemed like a really good deal compared to everything else that was local. It ran when I got it as well. Slowly the costs are going to add up though..

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Re: Power Valves replacements

Post by KDXGarage » 10:26 am Jun 30 2020

Sorry that it is not in better shape.
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Re: Power Valves replacements

Post by ccdsg » 11:52 am Jun 30 2020

KDXGarage wrote:
10:26 am Jun 30 2020
Sorry that it is not in better shape.
It’s no worry. I’m 18. It’s the first bike I’ve purchased myself, and it will lend a good bit of experience. I’ve never done engine work before and I’ve already learned a lot. It seemed really intimidating before but now it’s just a matter of time it seems.

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Re: Power Valves replacements

Post by SS109 » 04:05 pm Jun 30 2020

Eh, that's used bikes for ya. You'll still come out cheaper than if you you bought a more expensive bike and ended up more than likely doing the same repairs!
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Re: Power Valves replacements

Post by ccdsg » 04:51 pm Jun 30 2020

SS109 wrote:
04:05 pm Jun 30 2020
Eh, that's used bikes for ya. You'll still come out cheaper than if you you bought a more expensive bike and ended up more than likely doing the same repairs!
Oh well. I shipped the cylinder off to millenium for replating this afternoon. Eventually my power valve replacements will be in. Do you have a picture or guide for how to reassemble those the correct way for when I plan to start it up the first time after all this is done? You guys have given me a lot of good information and I trust you more than just googling.

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Re: Power Valves replacements

Post by KDXGarage » 06:27 pm Jun 30 2020

cyclepedia for a manual

people on eBay must have the special gold plated version

If you can spare a few dollars more, ask the plating company to just buy the piston kit from them. They will make sure it has the proper amount of spacing between the piston you buy from them and the cylinder they replate.

If you want, post up pictures of other parts of the bikes. We like spending other people's money on repairing dirt bikes. We don't spend a penny, and never get greasy. LOL
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