91 top end rebuild ?'s

dog walker · Post by **dog walker** » May 6th, 2009, 8:48 am

Hi guys, newbie here. You know that though! I've been lurking around here for awhile, really need some help now!

Last weekend at Sand Mnt., I was about 10 minutes in and hauling butt up a dune when my engine starting clanking (pinging) and before I could reach the top, the engine just stopped. I thought I seized it, but was able to kick it over. It had almost no compression. My thoughts were wasted rings, or cracked/broken piston.

After pulling it apart a couple days ago I found the piston to have verticle scrapes from about 3/4 to the top of the piston spaced about even with the the skirts. So there's like 4 marks on the piston. The rings are ground into the grooves as well (on these marks). The cylinder has the same marks, but not as severe. I can try and post pics tonight if that would help.

I'm trying to figure out what the cause was before I bore and replace the piston. I did not find any broken or foreign peices in the cylinder. Thanks,

Jeff

south central hoon · Post by **south central hoon** » May 6th, 2009, 3:04 pm

post photos. probably just hot and tired.

dog walker · Post by **dog walker** » May 6th, 2009, 6:29 pm

I could'nt figure out how to attach images this thread, so I uploaded 5 pics into this album.
http://www.bannedcr500riders.com/galler ... ?cat=10801

lewisclan · Post by **lewisclan** » May 6th, 2009, 8:23 pm

Seizure from holding it open or not having your jetting right
have a nice day

iggys-amsoil · Post by **iggys-amsoil** » May 6th, 2009, 11:19 pm

Stock porting? D needle.

hoofarted · Post by **hoofarted** » May 7th, 2009, 8:24 am

lewisclan wrote:Seizure from holding it open or not having your jetting right
have a nice day

X2! Check your jetting. What ratio u running? Oil?

dannygraves · Post by **dannygraves** » May 7th, 2009, 8:53 am

you were pinging from running lean pull your main jet and take a look at what number it is and report back. also, were you WOT when it started pinging? if not, it could also be the needle taper or clip setting.
in the sand you really want rich jetting because, first off the load the sand puts on the bike, then also because of the extended WOT that you won't see in MX style riding and also, most sand dunes are at low elevation which would also require more fuel.

a bone stock newer style 500 motor should run between a 172 and 178 in the dunes, maybe more. my gen-4 with a bone stock '90 motor and a pwk ran a 175 in the dunes.
good luck dude, and don't forget, if you get a wiseco, don't let your machinist do anything closer that .004" I usually specify .0045" on a wiseco, and find a machinist who will releive the bridge for you as well as chamfer the ports. if you can't get the machinist to releive the bridge, it is simple and we could help you do that yourself.

hoot270 · Post by **hoot270** » May 7th, 2009, 4:35 pm

A classic four corner seize. Was there any scoring on the wristpin? Make sure to check for air leaks after its back together. I torched my top end last Sept. with stock jetting, live and learn....

dog walker · Post by **dog walker** » May 8th, 2009, 8:31 am

Thank you guys for all you're input! I prety much figured it was jetting as well, but wanted to get some more input from CR500 experts. You guys really seem to know your shit about these bikes. I was worried about it maybe being a crank seal, and (hoot270) you kind of have me worried again! How would I check for an air leak?

MAIN JET: is a 170, I didn't check the needle clip postion yet. Any input on where it should be set and what size main to run would be appreciated. I realize every bike is different, but a general set up would atleast get me in a safe zone to run at.

By the way, Sand Mnt. is at 4000ft elevation. This is where I will do most of my riding and simular elevations at. This is my first CR500 and I've only had it for about six months. I've always ridden 2-stroke 250's in the past. So I've got some learning to do with this bike. Thanks again for all the help from everyone!

Jeff

Exnav · Post by **Exnav** » May 8th, 2009, 9:06 am

Here is the what the manual calls out as baseline settings with a stock 38PJ. Obviously these are for moto conditions and not dunacy.

dannygraves · Post by **dannygraves** » May 8th, 2009, 9:42 am

I alway run a super fat jet that blubbers, then keep stepping down until the blubbering stops. then I know it is safely on the rich side. if you simply go by feel, lean is mean, it will keep feeling faster until it squeeks. I'd drop a 178 in there and see if it blubbers, if it does, then try the 175. 175 seems to be a good all around jet for the 500s.

Daveedo · Post by **Daveedo** » May 13th, 2009, 1:34 pm

Do you know how long that piston and ring set have been in the motor?

britincali · Post by **britincali** » May 13th, 2009, 2:21 pm

Exnav wrote:Here is the what the manual calls out as baseline settings with a stock 38PJ. Obviously these are for moto conditions and not dunacy.

That chart would seize both my bikes solid in 20 mins flat.

Im at 2500 ft and ride in 90 deg f temps all the time and I run a 172 main which is as lean as it will go without pinging constantly. Try running a 165 main at dumont (200-1100ft) on a mild spring day (80) and see how long a bike lasts without melting.

dannygraves · Post by **dannygraves** » May 13th, 2009, 2:33 pm

britincali wrote:
Exnav wrote:Here is the what the manual calls out as baseline settings with a stock 38PJ. Obviously these are for moto conditions and not dunacy.

That chart would seize both my bikes solid in 20 mins flat.

Im at 2500 ft and ride in 90 deg f temps all the time and I run a 172 main which is as lean as it will go without pinging constantly. Try running a 165 main at dumont (200-1100ft) on a mild spring day (80) and see how long a bike lasts without melting.

165 = squeek, not even half way up comp

south central hoon · Post by **south central hoon** » May 13th, 2009, 4:38 pm

looking at the dome i would say that thing leaned out in a hurry....it wasn't running lean for long....just long enough...I think you sucked a seal dude....

dog walker · Post by **dog walker** » May 14th, 2009, 12:51 pm

The seal thing was my original thought. How could I check for this without destroying it in the process?

I think the piston and rings had been in there for maybe 2 years.

Jeff

dog walker · Post by **dog walker** » May 28th, 2009, 8:41 am

Nothing?

dannygraves · Post by **dannygraves** » May 28th, 2009, 8:51 am

to check the seals, you cap off the intake and exhaust. a rubber stopped with a wingnut from home depot works for the exhaust, and a freeze plug with a shrader valve attached works for the the intake. you pressurise (not very much), then check for a loss and where the hissing sound si coming from. to check the ign side seal, just remove the flywheel and look for evidence of a leak. if there isn't anything there and you are still losing pressure, inspect the base gasket and case gasket. if it still loses pressure, ti would either have to be the case gasket by the trans, ior the seal. so then you would remove the right engine cover and see if you can norrow down where the hissing comes from.

dannygraves · Post by **dannygraves** » May 28th, 2009, 8:52 am

of coarse, I never gop through all that effort, if I have reason to believe there is a leak, I tear the whole SOB apart, and reseal it.

Post by **AlisoBob** » May 28th, 2009, 9:02 am

Do I make my " ...another seized Wiseco" comments now..... or later?

Cast pistons simply dont do this.

The piston isnt drilled, which didnt help...

I think the jetting was prolly' pretty close, it just made some good horsepower, piston got hot and expanded..... too little piston / cylinder clearance.... 4 CORNER SQUEEK!

dannygraves · Post by **dannygraves** » May 28th, 2009, 9:20 am

I have seized 1 wiseco... it got stuck WOT on its side until it finally blew. wisecos need special treatment, more room and holes drilled, thats all.

torque monster · Post by **torque monster** » May 28th, 2009, 9:38 am

Get Glenn at GSS to do your machine work, fast-as cheap as you will find professional work-very quick turnaround time. Just my experience with him, I will send him ALL my motor work as long as I can.

Post by **AlisoBob** » May 28th, 2009, 10:01 am

Glenn is the man..... and has taken care of many, many Hoons cylinders........

Coolidge · Post by **Coolidge** » May 28th, 2009, 10:03 am

Where is GSS located?

Post by **AlisoBob** » May 28th, 2009, 10:06 am

Coolidge wrote:Where is GSS located?

http://www.bannedcr500riders.com/board/ ... .php?t=606

BannedCR500Riders.com

91 top end rebuild ?'s

91 top end rebuild ?'s