Jump to content
Sign in to follow this  

Cant keep a piston in my bike!

Recommended Posts

I have an 06 RM250 that I completely rebuild the motor on using all OEM parts and I had the cylinder re plated by powerseal usa. Well in the 35 hours (hour meter) since that rebuild I have fried 3 or 4 pistons (piston is chard black, rings are collapsed,tons of blow by). The first one was so catastrophic I had to have the cylinder re plated again. I thought the issue was the wiseco pistons I was using so I switched to OEM and it lasted longer but in the end I got the same result. After the complete rebuild I started using a different oil- klotz super techniplate. I thought maybe that was my issue so I switched back to a premix I had used forever and had good results with- golden spectro. I ran that and had good results but the stuff smells god awful so for the past 5 hours I have been using maxima's castor oil. And again, I just had another top end go. I pulled the pipe and took a look at the piston and there isnt a ton of blow by but it does look like the rings are collapsed. The only mods the bike has are boysen reeds and a procircuit exhaust system. I have stock jetting and am mixing sunoco gt100 at 30:1. I find it hard to believe the oil is the issue but it seems like every time i switch I have trouble.. anyone have any ideas? This two stroke is costing me more then my four stroke did and giving me wayyy more of a headache.

Share this post


Link to post
Share on other sites

do you do any checking of the plug or piston top ( bore light/scope )

your lean and killing pistons IMHO

 

but I only second guess that because I don't see how you don't know that ?

Edited by Zimman
  • Like 2

Share this post


Link to post
Share on other sites

Did you adjust jetting between pistons? What's your current elevation, temps and jetting specs? Everything is true and in spec? Crank is good?

Share this post


Link to post
Share on other sites

Before you rebuilt the motor the very first time, how many hours did you have on the top end? 

 

Also, when you rebuilt it the very first time, did you make any jetting changes or carburetor adjustments, or replace any engine seals?

 

Was the Boyesen and Pro Circuit already on there, or did you install them with the first rebuild?

Share this post


Link to post
Share on other sites

So you are running an aftermarket intake and exhaust with the stock jetting specs that were already lean as hell.

 

Sounds like after rebuilding your motor for the umpteenth time, you might want to spend 1/2 hour and jet your bike properly.

Share this post


Link to post
Share on other sites

Not a good idea to keep switching oils without a decent carb and top end clean. Also not a good idea to run castor and semi-syn or dino without a good carb and top end clean. Stay with 1 oil and ratio to eliminate that in your troubleshooting. Check your intake for a leak along with your air box seal. What kind of gas are you running? Most pump gas has too many additives or alcohol in it that could make it run lean and it doesn't keep very well.

I agree with the doing a leak down test. 

Share this post


Link to post
Share on other sites

RM250's are notorious for air leaks, I know several people that have had to rebuild bottom to top because of it. I know that's not what you wanted to hear but it's where I would start.

  • Like 1

Share this post


Link to post
Share on other sites

Talk to honda-power. He can make it last 100,000 miles apparently.

It's too late now.... he should of left it alone instead of molesting the perfectly healthy motor, so now he has to deal with it.

Share this post


Link to post
Share on other sites

Alright so I disassembled the top end and the rings arent collapsed everything actually looks very good and clean and there is a nice healthy coat of oil on everything. As for it running lean I have no symptoms of that and I have checked for that previously (used propane gas, also removed magnito cover and ran bike) I think my issue was my power valve stuck partially open. When I went to remove the bolt for the power valve actuator I felt the power valve snap closed. The power valves didnt look gummed up but I havent cleaned them since the last time I put a top end in it which was over two years ago (I hardly ride anymore). So its getting a fresh top end and im going to clean everything and see how it goes.

Share this post


Link to post
Share on other sites

So you are running an aftermarket intake and exhaust with the stock jetting specs that were already lean as hell.

 

Sounds like after rebuilding your motor for the umpteenth time, you might want to spend 1/2 hour and jet your bike properly.

I dont know where you live but stock jetting, at least for RM's is never "lean as hell". And trust me the bike is jetted correctly.. the pilot is fine- air screw is were it needs to be, runs fine in the mid range and I have done several plug chops and the main is fine as well. 

Share this post


Link to post
Share on other sites

. Well in the 35 hours (hour meter) since that rebuild I have fried 3 or 4 pistons (piston is chard black, rings are collapsed,tons

this is one reason  why your were  getting the "lean comments "the other is your mods vs " stock jetting  and what people have experienced jetting wise  but that can vary as we know  but a chard  black piston   is just that  

I would be curious to see a pic of  this piston top ??

Edited by Zimman

Share this post


Link to post
Share on other sites

Here are some pics of the pistons I burned up when I was running klotz super techniplate. Just to clarify the recent issue I though was another fried piston turned out to be a stuck power valve. So ever since I switched from super techniplate I have been fine... But here are some old pictures I have of the failed pistons

1307060763186.jpg

2011-06-02_20-25-23_722_Elbridge.jpg

2011-06-02_20-25-34_870_Elbridge.jpg

1307060875704.jpg

1307060830551.jpg

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×