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Piston replacement during valve job

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Hi all,

My '06X came to the point where I needed new valves. Actually, it came to that point 4 years ago, and I haven't ridden it since, due to my social circles changing their priorites, and I got left alone as the only one still owning a bike. I feel like a different person without riding, and I hate it. It's time to get back in the saddle. I'll ride alone if I have to. Anyway, I went with AS Racing and the TRX valves. The head is back, and looks brand new! Questions now though... I welcome as many informed answers as possible. Answer any or all of these as you like.

 

1. I assume it's time to replace the piston, but also don't believe in making assumptions in life. Should I go ahead and just do it, or measure specs first. I already have the new piston and rings waiting for me. I don't otherwise plan on needing to take the head off again, but it was not that difficult to me. If so, how do I measure. Can I use the same flat feeler gauges I check valve clearance with?

 

2. Since the pistons have cutouts for the valves, do I need a different Piston since my intake valves are now 36mm instead of 35mm, or do the piston notches fit either valve? Again, I assume any piston is fine, but that's a serious assumption. But I've not seen anyone ever mention it here.

 

3. I pre-bought a top end gasket kit from Athena. I since read that OEM is the only way to go (not a consensus, just one person really). But I already own this kit, and am poor. Anyone else want to chime in on Athena gasket kits? It's a top end kit, from the base gasket up, including valve cover gasket. I'm open to suggestions.

 

4. Carb - bike has been sitting for almost 4 years, gas is drained out now, but for the first year, it wasn't, because I didn't plan on it sitting at all. So I expect it to be bad. What should I look for to clean and/or replace in there?

 

5. To sum up, I've got new valves installed already, a new piston and rings ready to go, top end gasket set, and new camchain waiting. Any other parts I should replace or check while I'm in there? Do I need to replace the piston pin and circlips? I heard someone mention cam chain tensioner and guides, but I don't want to be overkill on this and just be throwing money at it.

 

Sorry for all the questions, I just like to be prepared. I know some of this stuff has been covered before in various posts. Any other non-solicited tips welcome.

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Depending on hours (over 100) I would replace piston now.

Yes you use flat feeler gauges to measure ring gap.

You need a micrometer to measure bore and piston. There are many how too vids floating around on how to do this.

As far as your gas issue. Plan on dropping it all and getting new jets and possibly cleaning out passages in the carb.

Depending on what piston/compression you are using it should fit with 1mm oversized valves. If you are really worried about that clay check them.

Glad to know you wanna get out and ride again now get to wrenching.

Edited by StonedInNy

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Hi all,

My '06X came to the point where I needed new valves. Actually, it came to that point 4 years ago, and I haven't ridden it since, due to my social circles changing their priorites, and I got left alone as the only one still owning a bike. I feel like a different person without riding, and I hate it. It's time to get back in the saddle. I'll ride alone if I have to. Anyway, I went with AS Racing and the TRX valves. The head is back, and looks brand new! Questions now though... I welcome as many informed answers as possible. Answer any or all of these as you like.

 

1. I assume it's time to replace the piston, but also don't believe in making assumptions in life. Should I go ahead and just do it, or measure specs first. I already have the new piston and rings waiting for me. I don't otherwise plan on needing to take the head off again, but it was not that difficult to me. If so, how do I measure. Can I use the same flat feeler gauges I check valve clearance with?

 

2. Since the pistons have cutouts for the valves, do I need a different Piston since my intake valves are now 36mm instead of 35mm, or do the piston notches fit either valve? Again, I assume any piston is fine, but that's a serious assumption. But I've not seen anyone ever mention it here.

 

3. I pre-bought a top end gasket kit from Athena. I since read that OEM is the only way to go (not a consensus, just one person really). But I already own this kit, and am poor. Anyone else want to chime in on Athena gasket kits? It's a top end kit, from the base gasket up, including valve cover gasket. I'm open to suggestions.

 

4. Carb - bike has been sitting for almost 4 years, gas is drained out now, but for the first year, it wasn't, because I didn't plan on it sitting at all. So I expect it to be bad. What should I look for to clean and/or replace in there?

 

5. To sum up, I've got new valves installed already, a new piston and rings ready to go, top end gasket set, and new camchain waiting. Any other parts I should replace or check while I'm in there? Do I need to replace the piston pin and circlips? I heard someone mention cam chain tensioner and guides, but I don't want to be overkill on this and just be throwing money at it.

 

Sorry for all the questions, I just like to be prepared. I know some of this stuff has been covered before in various posts. Any other non-solicited tips welcome.

1.  The best thing to do is measure the piston for wear.  If you are still in spec them maybe just throw on new rings right now and call that part of it good.  Use a micrometer to measure the diamater of the piston and compare it to a repair manual to see if you are in spec.

2.  I am with you on assuming that this will be fine, but dont know for sure.  If you do swap out the piston then make sure to put it in correclty...meaning the right direction.  Pistons are directional.

3.  I have no experiance with Athena gaskets so I cant comment.

4.  Like mentioned above, you are going to need to really go through the carb.  Try to stay away from harsh cleaners like brake cleaner and the such as they will really mess up your rubber gaskets and o-rings.  If you have a jet that is questionable after cleaning then just replace with new.

5.  When the valves go and the piston is done then it is a good rule of thumb to change at least the cam chain and guide on the tensioner side.  If you do change the cam chain you will need the gasket for the left side cover and a pulley tool just for the 450X.

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1) Replace piston, rings, pin and circlips. (if you want to measure the old one, do so 5mm up from the bottom of the skirt. Measurement should be 95.87mm at the extreme minimum. I would replace it if it's even close. On the bore/cylinder, if the crosshatching is still present and consistent, it's not a concern at all.)

2) The X piston is the same as the R piston. The R comes with 36mm intakes so the pockets are already designed for the bigger valves.

3) The Gasket kit A from Honda is cheaper than most all aftermarket top end gasket kits...your call on what you feel comfortable with.

 

4) Go completely through the carb...clean every passage and replace any jets that are sketchy. New floating plate seal as well.

 

5) Cam chain tensioner and guides are overkill if this is the first piston change (fairly low hour bike...)

 

Edited by CRF DOC
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Measure

Compare to service specs

Decide

 

Micrometers are cheap (harbor frieght)

 

If the motor needed valves, unless you are the exeception, you at 100 hours or more...so why tear it apart again in 6 mo, even if the piston is in spec, the rings are worn; just do it now.

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I would absolutely not bother with measuring anything. Just replace it and be done with it. All OEM is the way to go. As far as your head is concerned, it will likely be the last thing to ever wear out on your 450X and the next 450X you put it on.

Edited by cubera
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You guys are all awesome. I know what I'm doing in my spare time this week. I'm going to inspect and measure everything, so I at least know things have been working properly. With my hours, nothing should be out of spec yet, but obviously some wear shouldn't surprise me. But I do plan on replacing the piston, rings, pin, and circlips, regardless.

 

I trust the Athena gaskets, and since I already own the kit, I'm throwing them in. I got a smokin deal on the kit from the distributor.

 

The carb shouldn't be a huge problem. I'll pull all the jets and try cleaning and inspecting them. I got a Honda shop within a mile if I need to get new jets. They love to charge a lot for them, which sucks, but I'm so close to getting on this thing and firing it up, I'm ok with buying new jets. It was my fault anyway, for not storing the bike properly.

 

I'm also replacing the cam chain while the head is off, and throwing a new left crankcase cover gasket on there.

 

I'll report back if I have any questions, or with my success story.

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Just replace piston since you have it. Measure only if you're curious. Athena gaskets are fine. OEM is great too as a rule. I wouldn't worry about chain or tensioners. On carb, be really careful pulling bowl screws and consider changing to stainless allens. When in carb, just focus on Pilot (small jet near Main). Use the right screw driver for bowl screws and pilot and hold carb in vice (with towel).

 

RZ Rob

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