Top End

KenK · Post by **KenK** » July 18th, 2010, 10:46 am

getting ready to put in a new top end for the first time on my '93. Any advice as far as piston/ rings, processes from all you veterans out there? Any good advice welcome. Thanks.

Ken

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » July 18th, 2010, 12:29 pm

vertex piston

Post by **AlisoBob** » July 18th, 2010, 12:31 pm

Roostius_Maximus wrote:vertex piston

x2

http://www.bannedcr500riders.com/board/ ... .php?t=200

south central hoon · Post by **south central hoon** » July 19th, 2010, 10:23 am

For first overbore? OEM. Doesn't get better than stock honda parts.

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » July 19th, 2010, 10:51 am

oem is good, ya, vertex is possibly the best, coated, wide exh, comes with rings and pin for less than oem

south central hoon · Post by **south central hoon** » July 19th, 2010, 1:57 pm

roosty, can you explain for the folks what you mean by wide exhaust?
are you talking about the skirt shape?

Post by **AlisoBob** » July 19th, 2010, 2:00 pm

The skirt is wide enough to fully cover the exhaust port.

Some pistons ( like Wiseco's) are not and your primary compression goes right out the pipe.

100hp honda · Post by **100hp honda** » July 22nd, 2010, 3:22 pm

last 2 versions of wiseco have been fine regarding the width. wont be any issues unless they machine in front of the wrist pin, and even then it depends how deep they go with the cut, and how wide your exhaust port is. havent seen the very latest version so i cant comment yet.

south central hoon · Post by **south central hoon** » July 22nd, 2010, 3:28 pm

AlisoBob wrote:The skirt is wide enough to fully cover the exhaust port.

Some pistons ( like Wiseco's) are not and your primary compression goes right out the pipe.

even with stock porting? damn that's poor engineering. i remember roostius posted a photo showing an exhaust port not matching the skirt....i thought that was a result of some poor porting, not piston design.

100hp honda · Post by **100hp honda** » July 22nd, 2010, 4:12 pm

guess you didnt read the previous post. the last 2 versions have no issues. bob may be refering to the newest version that aint available yet.

south central hoon · Post by **south central hoon** » July 22nd, 2010, 5:20 pm

100hp honda wrote:guess you didnt read the previous post. the last 2 versions have no issues. bob may be refering to the newest version that aint available yet.

actually i was just trying to figure out what "wide exhaust" means in terms of piston design. couldn't figure what that meant considering the piston should be round.

I know now he was referring to the taper on the exhaust side of the piston skirt.

thanks bobber.

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » July 22nd, 2010, 8:45 pm

i tried the prox in stock 85,86,87,88,89,91and98 cyls, same deal, CRAP
the early jugs had more gap, stil, any pressure lost to the exh is unacceptable. Most guys will notice it by a hot pipe at low rpm and trouble jetting the pilot

100hp honda · Post by **100hp honda** » July 23rd, 2010, 9:52 am

tried calling wiseco. no one answers

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » July 23rd, 2010, 10:02 am

BS, I JUST called them at
1-440-951-6600
you want to talk to AL at extention 3105 about the new 500 piston

100hp honda · Post by **100hp honda** » July 23rd, 2010, 10:06 am

was on hold for 5min. no answer so i hung up. no BS

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » July 23rd, 2010, 10:21 am

south central hoon · Post by **south central hoon** » July 23rd, 2010, 1:49 pm

Roostius_Maximus wrote:i tried the prox in stock 85,86,87,88,89,91and98 cyls, same deal, CRAP
the early jugs had more gap, stil, any pressure lost to the exh is unacceptable. Most guys will notice it by a hot pipe at low rpm and trouble jetting the pilot

hmm. i just installed a pro-x. and my pilot circuit was really lean. i better pull that pipe and have a look. thanks for the tip.

qkenuf4u · Post by **qkenuf4u** » October 27th, 2010, 9:56 pm

Roostius_Maximus wrote:i tried the prox in stock 85,86,87,88,89,91and98 cyls, same deal, CRAP
the early jugs had more gap, stil, any pressure lost to the exh is unacceptable. Most guys will notice it by a hot pipe at low rpm and trouble jetting the pilot

hmm my pro-x has a very slight opening on one side (just looked last night) ..... wonder if thats my problem with my idle ? it seems really fat and its throwing alot of fuel out the pipe (not sealed yet so it spooged/flowed down head)
would not being sealed at manifold/pipe screw jetting ?
thanks
lance

kball1313 · Post by **kball1313** » October 27th, 2010, 10:54 pm

Qk, you'll piss around with the jetting gtill the end of time with that going on and get nowhere. Runs like hell, fuel charge burning in the exh, bla bla. A new piston will make you a happier rider.

qkenuf4u · Post by **qkenuf4u** » October 28th, 2010, 7:19 am

kball1313 wrote:Qk, you'll piss around with the jetting gtill the end of time with that going on and get nowhere. Runs like hell, fuel charge burning in the exh, bla bla. A new piston will make you a happier rider.

well thats a real bummer cause its a brand new top end with 3 mins run time on it. i didnt know about the piston skirt/exhaust port problem till i already had all my work done....
it acts way fat at idle ..... i was gonna drop the pilot down and see if i could get it to work that way but if this is gonna screw me over then i aint sure whats gonna happen....

98cr500rider · Post by **98cr500rider** » October 28th, 2010, 3:01 pm

Any chance someone can re post the picture of the ProX not filling the exaust port.

I just put a ProX in as well and would like to know exactly what to look for.

.

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » October 28th, 2010, 3:18 pm

http://cid-bd4aa2685d9bf2e9.office.live ... O-X%20Leak

98cr500rider · Post by **98cr500rider** » October 28th, 2010, 3:35 pm

Thanks for the link I can see what it is now.

With the piston rings above that section of piston and full compression not in force until the rings pass the scallops, does it matter?

Just asking, after all the effect of the expansion chamber is to cram more fuel back into the port just before the rings close it off.

Or should I go and stand in the corner now.

.

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » October 28th, 2010, 4:49 pm

the problem is that the crankcase needs to build a positive pressure to force the spent gas from the cylinder. if it does a bypass either like the prox, or under the skirt of the piston becasue someone ported too large, the clean pressured crankcase gasses get into the pipe and build heat, now the lazy intake charge needs more fuel to make it idle.

make sense?

98cr500rider · Post by **98cr500rider** » October 29th, 2010, 12:23 pm

Well I’m no two-stroke engine tuner so I’m assuming Honda designed it to have the port fully covered and that’s good enough for me.

The funny thing is I seem to remember hearing that ProX made the OEM pistons for Honda so you would think they were a safe choice for a replacement.

Oh well.

BannedCR500Riders.com

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