nasty looking piston 2003 rm 85

[rmrider45]

my son raced his rm85 in a harescramble last weekend and the bike ran fine . i rebuilt the top end a week before the race .just this saturday he was on the track and the bike just died .i got home and took off the cyclinder and never seen this type of damage. the top of the piston had lots of pits in it and whatever got in there went on the side near the ring and made the ring fail. the only thing i did after the rebuild was change the plug on race day. could a small stone fell in the plug hole when i changed the plug?i have rebuild this top end on this bike many times and have never seen this.strange thing is the cyclinder wall is perfect only damage was on the heaD (small pits) and the top of the piston

has anyone had this happen to them?

thx

here are some pics

 

[Rich Rohrich]

It looks like a bearing is coming apart. The big end connecting rod bearing failing is most common with this type of damage, but until you pull it apart it's tough to know for sure.

 

[rmrider45]

It looks like a bearing is coming apart. The big end connecting rod bearing failing is most common with this type of damage, but until you pull it apart it's tough to know for sure.

thx .someone also told me that. strange tho that the cyclinder wall was not damaged at all thats why i was thinking it wasnt the bearing.only damage was on the top of piston and the cyclinder head

 

[Rich Rohrich]

The bearing comes apart, drops into the crankcase, and then gets pushed up through the transfer ports and bang around on top. When the exhaust port opens they are usually forced out before they do much more damage.

 

[whenfoxforks-ruled]

The cylinder is harder than the aluminum piston and head. As are the bearing materials. Take a light and magnifier and look at your big end of the rod.

 

[rmrider45]

thx . i did alot of top end rebuilds but never went into the crankcase. do i need a case spliter to do the job.

 

[whenfoxforks-ruled]

The case splitter, like from motion pro, is expensive, and is worth it. A car harmonic balancer puller can do the trick also. And a puller for the ignition rotor. Drain the oil, and take all the impacted nuts loose first, the rotor nut, drive gear nut, and clutch inner hub nut. A shop manual comes in handy. Motosport or one of those usually has complete engine kits for around 300 dollars.

 

[rmrider45]

crazy ? what is the chance of the powervalve bearing coming apart and doing this damage thx

 

[Rich Rohrich]

I've never seen it.

 

[rmrider45]

I've never seen it.

just wondering cause i seen a bike on ebay that had that problem and they had to redo the hole thing over

http://cgi.ebay.com/ebaymotors/ws/e...0384350717&sspagename=STRK:MEWAX:IT&viewitem=

btw after i had took this piston out i replaced the top end again. bike starts up one kick. if it s the bottom crank bearing coming apart i will surely know when this new top end goes out faster than normal . :bang: :bang:

also this bike is bored out to a 105. who ever rechromed the cyclinder did a great job

 

[Rich Rohrich]

Continuing to ride the bike with the big end rod bearing coming apart is a really bad idea.

 

[whenfoxforks-ruled]

Bottom end russian roulette eh? Are you riding the bike?

 

[rmrider45]

i will try to tell my son not to ride it but it wont be easy .

 

[Rich Rohrich]

Maybe when the rod breaks and it hatchets the cases open down the middle he'll see the light. ;)

 

[rmrider45]

Maybe when the rod breaks and it hatchets the cases open down the middle he'll see the light. ;)

i know what you mean .just wondering if i should get the bottom end done or just part out the bike and get a newer one.i have never done a bottom end before and not sure what i am getting into.i am just worried about the transmission gears coming out or whatever.how many hour job is it to rebuild the bottom end? it dont seem to easy of a job .and to just replace the bearings in the bottom seems the easy way out if i get it apart i should replace the crank and rod also

 

[Ol'89r]

i will try to tell my son not to ride it but it wont be easy .

TRY? :whoa: Who's the dad? :coocoo:

You can buy a complete crankshaft from Hot Cranks for almost the same price as having your old crank rebuilt. You can remove the left engine case, leaving the whole gearbox intact in the right case. Remove and replace the crank and reinstall the left side case. It would be a good idea to purchase a service manual. Use heat to expand the cases, it will make it easier to remove and replace the crank. Do a search on this, there are many threads on the subject.

It is a good idea to remove the gearbox and inspect the gears and shift forks while the cases are split. This is the time to fix those things rather than after you take the time to put everything back together. Google Hot Cranks/Hot Rods for a new crankshaft.

 

[Patman]

TRY? :whoa: Who's the dad? :coocoo:

:laugh: That's the first thing that popped in to my head too! The second was get a factory service manual. Great minds I guess....

 

[rmrider45]

:laugh: That's the first thing that popped in to my head too! The second was get a factory service manual. Great minds I guess....

lol. btw i do have a factory shop service manual that the last owner gave to me 2 years ago. reason why i said it would be hard to keep son of the bike because he loves riding it.i talked to my wife she said maybe we will buy him another bike a new one or a decent used one .

one more ?what 4 stroke model out these days would put out the power like my sons 105 machine . i may buy a 4 stroke model

 

[Rich Rohrich]

http://powersports.honda.com/2009/crf150r.aspx

 

[whenfoxforks-ruled]

3~4 hour job, taking your time. I think it could go from roached to ripping in 2 hours personally. And about 300~350 in parts. Looking at a new 150f,$$$$.$$? They still sell new 85's? I know a guy who can make the motor better, http://www.eric-gorr.com/

 

[rmrider45]

3~4 hour job, taking your time. I think it could go from roached to ripping in 2 hours personally. And about 300~350 in parts. Looking at a new 150f,$$$$.$$? They still sell new 85's? I know a guy who can make the motor better, http://www.eric-gorr.com/

i should be able to do the job on the crank with no problem
i have worked on caRs for years .just splitting the case is not an easy task some say .just wanted to see what i am getting into

well $350 for crank parts $85 for a new piston and ring aint that bad if i do the work myself

?how long is the life span of a new crank ,rod and bearings ?




and yes they still sell new 85s . that is if they lifted the lead ban on the sales of small bikes

 

[whenfoxforks-ruled]

350 should include a top end. Go to motosport, or straight to wiseco, and see if they offer the complete engine kit. A fresh bottom end should last a long time, even thrashed but well maintained, should see 60 hours? Normal riding, years. A little dirt here and there, start it after washing, and it may last days?

 

[rmrider45]

350 should include a top end. Go to motosport, or straight to wiseco, and see if they offer the complete engine kit. A fresh bottom end should last a long time, even thrashed but well maintained, should see 60 hours? Normal riding, years. A little dirt here and there, start it after washing, and it may last days?

http://www.motosport.com/dirtbike/product/COMPLETE-BOTTOM-END-KIT/?prodId=287070&

$224.99 without piston sounds cheap :)

i do need to take the motor out of the frame to do the bottom end ? :ride: :ride:

 

[whenfoxforks-ruled]

Clean it, drain it, take it out. You will need a rotor puller. Any shop should have the puller, its a good cheap investment, it works on a lot of dirt bikes! Same with the other things, but that puller is specific, and improvising is dangerous on this one!

 

[rmrider45]

will a Harmonic Balancer and Steering Wheel Puller set work? i should have one laying around my shop somewhere or know someon who has one