Need some piston advise please.

[thehotrodpig]

I am rebuilding my brothers xrl and need a new piston and rings.

He is not the most astute when it comes to mechanical things. He doesn't always hear or see the clues that something is wrong and doesn't always keep track of the gauges or maintenance. At least not to the standards that I think he should. For these reasons I want reliability over additional hp. A minor bump in compression is fine but not enough that heat is going to become an issue. My experience with forged pistons in my hotrod is they have to be run with more cylinder to wall clearance and can be noisy as well as not sealing up well until warmed up. Frankly I don't see the need for forged in his application. My thoughts were to find a 101mm cast or hypereutectic piston with stock or mildly raised compression.

Am I on track or off base? Recommendations for a piston? Any input is appreciated.

Thanks,

Dave

[brianhare]

Go OE Honda for the tightest clearance when staying at stock compression ratios..........

 

I have run a mulitude of JE forged slugs with no noise issues.......as long as the clearances are set

 

properly there is no issue.........

 

Honda makes 2 over size pistons for the XR650L..

 

B

[not_again]

Forged pistons are oval-shaped until warm. For that reason the rider should warm his engine before taking off. Of course, he SHOULD warm his engine anyway no matter what type of piston is in there- so it's kind of a moot point. But if your brother is the kind of jerk who fires up his bike and immediately wheelies away, he MUST run a cast piston.

[thehotrodpig]

Is there a 9 or 9.5 to 1 compression option out there? Something less than the typical 10.5 je?

[brianhare]

Is there a 9 or 9.5 to 1 compression option out there? Something less than the typical 10.5 je?

 

For the XR650L ........... YUP...

 

You can install a JE 10.5-1  XR600R piston in the XR650L at 100 -102MM

 

The difference is the pin is placed 1mm higher up in the piston on the XR600R JE......which lowers the piston in the XR650L bore 1mm and since it`s a flat top forged slug instead of releived in the center like an OE XR650L piston instead of 10.5-1 comp you get somewhere in the range of 9.2-9.3-1 compression if i remember correctly..

 

I ran that XR600R JE piston for 2 years,,worked great.ThumpNRED here is running one too..there are a number of people that have tried this and work great with no risk of detonation.......i think i was the first 3 or 4 years ago to try it if i remember correctly..

 

http://www.jepistons.com/Catalogs/Powersports/Offroad-Cycle/Honda/xr_600r.aspx

 

B

Edited February 13, 2014 by brianhare

[Go Big Red]

Is there a 9 or 9.5 to 1 compression option out there? Something less than the typical 10.5 je?

 

Is there a 9 or 9.5 to 1 compression option out there? Something less than the typical 10.5 je?

Pro-X makes an inexpensive, reliable and stock compression piston.  This would be a much better option for someone who is not looking for performance, but reliability.  Not to mention, stock compression will not add extra heat or extra stress on your crank making it a better option for someone who doesn't properly warm a bike, change oil regularly, watch gauges, etc.  Keep it simple and easy.

[valvesrule]

None of the older aftermarket 600/650L pistons were correct for theoretical CR. Not even close. They were really only good for a mild cr raise while the main advantage was a stronger forged construction. Noise is not much of an issue either since new alloys (hypereutectic?) are commonly used as well. JE has recently began issuing a new series of 650L pistons http://www.jepistons.com/Catalogs/Powersports/Offroad-Cycle/Honda/xr_650l.aspx that have recognized that the old series were highly overrated for CR. They now have a 9-1, 10.5-1 and 11.25-1 specifically for the Ls. They haven't done the same for 600Rs. After much discussion here on TT Wiseco similarly acknowledged (before JE) that their 10.5-1 was actually a 9-1 and released a new piston that has to be much more accurately rated at 10.5-1. The old pistons are probably very common in the market still. The important thing is to avoid going over 29mm comp height regardless of whether the piston is for an L or R to prevent other complications. Our piston chart needs serious revisions with these new offerings but I'm not inspired to buy them just for these dimensions as I did 5 years ago. I've still got a few of the old ones left.

Edited February 14, 2014 by valvesrule

[valvesrule]

Please excuse the unintentional "did" hyperlink. It's what you get when a computer makes decisions for you. Skynet anyone?

[brianhare]

None of the older aftermarket 600/650L pistons were correct for theoretical CR. Not even close. They were really only good for a mild cr raise while the main advantage was a stronger forged construction. Noise is not much of an issue either since new alloys (hypereutectic?) are commonly used as well. JE has recently began issuing a new series of 650L pistons http://www.jepistons.com/Catalogs/Powersports/Offroad-Cycle/Honda/xr_650l.aspx that have recognized that the old series were highly overrated for CR. They now have a 9-1, 10.5-1 and 11.25-1 specifically for the Ls. They haven't done the same for 600Rs. After much discussion here on TT Wiseco similarly acknowledged (before JE) that their 10.5-1 was actually a 9-1 and released a new piston that has to be much more accurately rated at 10.5-1. The old pistons are probably very common in the market still. The important thing is to avoid going over 29mm comp height regardless of whether the piston is for an L or R to prevent other complications. Our piston chart needs serious revisions with these new offerings but I'm not inspired to buy them just for these dimensions as I did 5 years ago. I've still got a few of the old ones left.

 

Valvesrule.....  change  "did"  to  "had" in your sentence  to get rid of that link,,i hate when that happens too.people think you inserted a link you never intended to..

 

 

 

Not sure that JE is correct even now boss..........part# 139550 is a 102mm XRL piston at 11.25-1......i have that installed in my bike and with the calculations we did it is closer to 10.5-1 if even that...i was getting 10.3 if if i remember correctly..unless they are still using the same part numbers,when i bought that piston the 9-1 .. 10.5-1  .. and the 11.25-1 was showing in their website at that time..

 

Cyclewizard had ordered it and told me the actual comp ration was 10.5-1...

 

I don`t think,,(correct me if i`m wrong,but i don`t think i am) that you can get 11.25-1 compression on the XRL without a seriously domed piston well above deck height..my piston sits 10 thou under deck at TDC..and it`s not 10.5-1 with that flat top..

 

 

B

Edited February 15, 2014 by brianhare

[valvesrule]

When we compounded the original chart JE only had 1 listing each for either the L or R and that was the last I looked at their online cat till today. The 9-1 is most likely very close to correct, maybe the 10.5 is close but the 11.25 is wishful thinking unless it has a raised dome. Perhaps they mean those figures are achievable with head milling, welding,..........fantasizing. At least 3/4 of a point is closer than what they advertised before. I don't mean to point the finger just at JE, ALL the manufacturers were let's say "optimistic" on their CRs. Wiseco eventually conceded that the math did not add up to support their claim and they produced the new piston to support said claim. I'm just glad they all seem to be paying a little more attention to the engineers not the "Madmen"

Edited February 15, 2014 by valvesrule

[valvesrule]

Note to hotrodpig: If you setup the modern forged pistons right noise will not be an issue. They can be sized to nearly the same clearances as a cast piston. The problem becomes watching your oil quantity and quality. They will not tolerate a low level condition. They will heat up swell and stick. Just as the old forged piston would. Old style forged slugs were typically set up loose in anticipation of those conditions. Hopefully when the engine got hot and lubrication got marginal the extra clearance would keep them from seizing but they were slappy when less than hot.

Edited February 15, 2014 by valvesrule

[thehotrodpig]

For the XR650L ........... YUP...

 

You can install a JE 10.5-1  XR600R piston in the XR650L at 100 -102MM

 

The difference is the pin is placed 1mm higher up in the piston on the XR600R JE......which lowers the piston in the XR650L bore 1mm and since it`s a flat top forged slug instead of releived in the center like an OE XR650L piston instead of 10.5-1 comp you get somewhere in the range of 9.2-9.3-1 compression if i remember correctly..

 

I ran that XR600R JE piston for 2 years,,worked great.ThumpNRED here is running one too..there are a number of people that have tried this and work great with no risk of detonation.......i think i was the first 3 or 4 years ago to try it if i remember correctly..

 

http://www.jepistons.com/Catalogs/Powersports/Offroad-Cycle/Honda/xr_600r.aspx

 

B

This sounds like a good option. What did you set the piston to wall clearance at?

[valvesrule]

Let me remind you Brian that the stock 650L piston is over .100" low at TDC. You installed your 139550 about a year after we created the chart I guess. The old JE #128995 600 slug rated at 10.5 was a much lower CR and comp height, nearly the same as a stock or Wiseco. It was at best 9.2 in a 650 and maybe 9.6 in a 600. We never bothered to engage JE about it as we did Wiseco. The comp height for the JE #139550 is almost almost 2 mm higher. Using the chart and doing the math is the only semi accurate way to figure a CR for these engines (rod Length + half stroke length + advertised compression height = <205mm deck height. General rule; any combination that gives stock 650l like numbers (.100" below deck @ TDC)is pretty close to 9-1 CR. If the numbers are close to matching 205mm CR is closer to 10.2 depending on combustion chamber volume.

Edited February 15, 2014 by valvesrule

[brianhare]

This sounds like a good option. What did you set the piston to wall clearance at?

 

JE includes an installation chart with the piston......do not go by Honda specs on a forged piston versus Honda cast piston..

 

Do not recall off hand what i set it to this time.  2.5 - 3 thou rings a bell though..

 

B

[brianhare]

When we compounded the original chart JE only had 1 listing each for either the L or R and that was the last I looked at their online cat till today. The 9-1 is most likely very close to correct, maybe the 10.5 is close but the 11.25 is wishful thinking unless it has a raised dome. Perhaps they mean those figures are achievable with head milling, welding,..........fantasizing. At least 3/4 of a point is closer than what they advertised before. I don't mean to point the finger just at JE, ALL the manufacturers were let's say "optimistic" on their CRs. Wiseco eventually conceded that the math did not add up to support their claim and they produced the new piston to support said claim. I'm just glad they all seem to be paying a little more attention to the engineers not the "Madmen"

 

The 11.25-1 sets 10 thou down from deck,,and is a flat top..no way is it as advertised? ....with all the calculations in at that time it wasn`t even 10.5-1.....it was though,,alot closer than they ever got before to 10.5-1...?

 

B

Edited February 16, 2014 by brianhare

[valvesrule]

The 11.25-1 sets 10 thou down from deck,,and is a float top..no way is it as advertised? ....with all the calculations in at that time it wasn`t even 10.5-1.....it was though,,alot closer than they ever got before to 10.5-1...?

 

B

My XL600 with the Wiseco 11-1 and small chamber head only comes out to 10.3-1. Fortunately CR isn't the only factor to building an engine.

[thehotrodpig]

Now I'm even more confused.

[Go Big Red]

Now I'm even more confused.

Don't be confused, Brother.  I think some folks took your request for info as an invite to overload on piston knowledge.  I will assume, and let me know if I am wrong, you just want something reliable for your brother's stock 650L.  That means standard bore and standard compression used on a stock cylinder and head.  Basically, you just want to get a top end done on his bike so he can get back to riding it.  If that is the case, Wiseco and Pro-X make a great stock bore, stock compression piston.  And, even if you have to bore it over, those are good choices.  The other stuff is great for someone seeking better performance.

[brianhare]

Now I'm even more confused.

 

 

?    clear as mud to me....what`s confusing to you bud..

 

If you want a 9.1 - 9.3 to 1  go with the XR600R JE 10.5-1 piston..........

 

If you want roughly 9.0-1 and a little under go with the XR650L JE  9-1 piston...

 

If you want 10.5-1 go with the XR650L JE 11.25-1 ......it`s not 10.5-1 but closer than most..

 

 

See..the issue is we`ve been into this for years,,,valvesrule and headtrama did alot of work on a piston chart here,,basically the manufacturers were way off on comp ratios........they still aren`t perfect..but closer to the advertised comp ratio than they were..

 

Longer life,tighter clearances,smaller ring gaps can be had too..just buy a OE oversize piston and you`ll have stock compression and stock reliability... ?

 

 

B

Edited February 17, 2014 by brianhare

[valvesrule]

My thoughts were to find a 101mm cast or hypereutectic piston with stock or mildly raised compression.

Am I on track or off base? Recommendations for a piston? Any input is appreciated.

Thanks,

Dave

Hard to go there without a little overload. Stock, Wiseco, JE and Wossner all have pistons that suit this request. My understanding is Honda doesn't offer a 101mm piston and the others are all forged. Someone has a decision to make and I think most if not all the options have been covered. Sometimes life isn't simple.