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high comp piston, yes or no?

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So my impatience has left me in turmoil, I tried to make improper rings fit cuz the guy I got em from said they'd fit, so I effed up my piston trying to make them fit

Now that I have the correct rings, the top ring fits snugly, but towards the outside of the ring there is about a 1mm gap between the piston and ring (half mm on each side)

Do I use this? Or since its messed up, keep screwing with it and try and make the improper rings fit

Or buy a wiseco high comp piston? I'm leaning towards that one but it'll run me 150 for the piston and another 50 for the bore, one, where do I get a head gasket for this(oh I would go with the 102.4mm) and two, how much would I expect to gain from this? Should I change the cams?

This is the best pic I could get

1373661067118.jpg

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You are talking about the gap between the ends of the top ring? That is supposed to be there, looks good to me. When you install cylinder over piston, that gap will reduce as the walls of the cylinder will compress the ring some. If you are going to get real tech with it, you measure the ring gap with the ring in the cylinder about 1/2 inch down from the top of the cylinder to see how large the gap is- there is a spec. for the ring end gap. In fact you need to get a tool [ I forget the name of it- it compresses the rings- looks like a sleeve that goes around piston /rings] to compress the rings as you slide the piston into the cylinder or the rings will get caught and not allow you to put cylinder on. Drip a little oil on all the rings before you install in cylinder to lube rings. Lightly coat inside of cylinder with oil also before piston install.

You say you messed up your piston. I do not see that in the pics. How do you mean?

Edited by bigbore2

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Did you file or alter the ring groove trying to make the wrong rings fit????????????? If you did you just ruined the piston,,period..

With a new bore and new high compression piston you will gain a little more power/torque but you`d see better results with a good cam and a new

High compression piston..

B

Edited by brianhare

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I don't totally understand what you did. Here is my take, if you have not bored the cylinder yet. A ball hone or visual

check will show if a ridge has formed, or check for out of round with a three point bore gauge. If the bore is still in spec and no ridge

put in a in new piston and rings for the bore size. Set the ring gap to spec. But PLEASE stay away from a High COMP piston. The closer you stay to stay to stock the better for you. If your bike just doesn't live up to your power needs get a bigger bike and live

with the extra weight.

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Stay away from HIGH but run fast toward 10.5:1 if you have to redo it. That seems to be the "Sweet Spot" of hotter, but still stable and reliable long term.

Just flat out wakes these bikes up in a nice way, but runs fine on premium pump gas.

I had a 650L with that (you don't end up with that number anyway, more like 10:1) and it was night and day versus a stocker.

Mine had a stage 1 hot cam but that wasn't really any better than the stocker. Go stage 2 if you change cam.

I had my 350 rebuilt a year before I got the L and now I could kick myself for not upping the compression.

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there is no stage 2 for the xr6 or xrl...there is for the brp aka xr650r but you need to have some valve work done so the intakes I beleive dont hit the piston..

my take

I went back to oem...while performance was better in certain areas on my xr with a big cam(I wasnt running high comp, and I needed that) the bike just felt more high strung, temps went up a bit, and I ran no oil cooler which I still need anyway...

for trailriding the stock cam and comp on the xr6 at least is just fine

on the xrl I would be more tempted I guess since you have a milder carb and slightly less comp stock...and a heavier flywheel so I bet youd feel more of a diference upping comp on the xrl versus the xr

anyways

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If you want to leave an engine stock then fine,,leave it stock...........

If you want these bikes to haul then you gotta put a high comp piston in it,,period......

Have you ever seen a high performance bike running 8.5-1 compression🤣 maybe,,with a turbo..

Go with something that gives you 10.0-1 or less final compression ratio and you can run pump gas..

But,,the only way to get decent power from these engines is:

(1) high compression ratio

(2) a good cam..(Megacycle is sweet)

(3) a pumper carb

(4) good exhaust system

You can pick any 4 of the above to get reasonable power...any 4......

B

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So yes, in short I destroyed my piston, with a small dremel.. I really regret it but, eh, so I don't wanna go to 11:1 if that means I can't run 91 octane cuz that's what I use, and have access to, I don't even know where I could 98 octane? 91 octane with a 3$ octane booster? where could I find that 10:1 piston? I like that idea, and can I get it in stock bore of 100mm as I don't wanna spend the money to, plus if sonmething happens In the future i like having the ability to bore it out,

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Oh my bad, ill fix that today, its an 84 xl600r

So talking to a buddy he's tryin to talk me into 2.41 oversize piston and is sayin that it'll really be a noticeable gain, a new wiseco 2.41 over for $139, seems like a good deal, but I'm also betting its the 11:1 compression, should I hold off?

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Only piston i see easily available is through Wiseco....JE doesn`t seem to make it for this old bike,and yes it`s 11-1........

I`m running 11.25-1 and have to use toluene in my fuel as i can only get 91 octane here........

Can you still get stock oversize pistons.......i`d take that route if i was you first....

B

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How expensive is it to run that in your fuel and where do you get it, just auto parts store? If its not to bad, ill be fine with running an 11:1 I have two of these engines I'm building, and I'm taking the other piston from the other engine to finish this one, got in there and there's some bad scoring on my other jug so it will need to be bored

Is eBay the best place to find this stuff or should I be lookin somewhere else?, ill see what my Honda shop can get me tomorrow

Edited by xs850triple

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So Honda is closed today, of course, I'm really being flip floppy about going with the wiseco or not, my biggest worry is if I oversize, where do I get a head gasket?

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How expensive is it to run that in your fuel and where do you get it, just auto parts store? If its not to bad, ill be fine with running an 11:1 I have two of these engines I'm building, and I'm taking the other piston from the other engine to finish this one, got in there and there's some bad scoring on my other jug so it will need to be bored

Is eBay the best place to find this stuff or should I be lookin somewhere else?, ill see what my Honda shop can get me tomorrow

Toluene is available at Sherwin Williams auto paint department here.........any decent auto paint supply shop can get it,,as well as your normal hardware store........

It is used in gasoline to up the octane rating...2 liters in 4 gallons is plenty for my needs...

Toluene bought in 20 liter drums here costs me about 2 dollars more pertank........i know you guys can get it down there cheaper than me too...so it`s an option when 93 or higher fuel isn`t available...........

But if you have to go longer than your fuel tank size,that could be an issue...i generally never run 4 gallons through before i`m home,,if i plan on going farther i can carry a couple liters with me..

Ebay..if you watch for awhile.can be decent pricing sometimes........but search arround you`ll find ebay can also be higher than storefront retail...

I try to buy most things from my local dealer,,consider doing that,,it keeps them in business when you need them,and my dealer prices some things as good as if not better than most internet stores..

B

Edited by brianhare

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So I was able to strike a sweet deal in my opinion with an eBay guy who was local to me, for 180 bucks I was able to get a used OEM piston in good condition to be used on my stock engine, and for my engine that needs to be bored I got a brand new 1mm over bore wiseco piston, now it says its an 11:1 compression but if I connect it to an OEM piston they sit as high as each other just the wiseco is flat, where OEM has a dome in it, is this really an 11:1 just curious if so I know what octane to use

1374013489952.jpg

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So I was able to strike a sweet deal in my opinion with an eBay guy who was local to me, for 180 bucks I was able to get a used OEM piston in good condition to be used on my stock engine, and for my engine that needs to be bored I got a brand new 1mm over bore wiseco piston, now it says its an 11:1 compression but if I connect it to an OEM piston they sit as high as each other just the wiseco is flat, where OEM has a dome in it, is this really an 11:1 just curious if so I know what octane to use

And you have the wrist-pin in both? Hmmm interesting..

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If memory serves me, Wiseco had their compression ratios overstated a few years back. You may have one of the pistons from that era.

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Hmmmmmmmmmmm...so what is the stock pistons compression ratio on that bike.....and is the old piston stock OE Honda or not..

Usually the stock Honda piston is cast and has a dish to it,,a cast piston is rough on the top as it`s sand cast..is it??????????

If so,,then it`s just a little higher than stock in compression ratio...

I am unsure what stock compression s on these bikes..

B

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