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Detonation

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hey all! new to the forum here and happy to be apart of it all!

now to the questions... I've had a 03 CR250 for 3 years and have clocked around 60 hours and before you say anything I know it is time for a top end. A full rebuild was done just before I bought the bike. 
The main reason I think it needs a top end is that it is detonating, and its at 60 hours.... However I am partly skeptical about it because it starts quicker than a brand new fuel injected 4 stroke, (Oh man was my buddy angry :p) it still screams through trails and dunes, and never fouls plugs. 

I mainly ride through technical wood trails and I am hardly in the mid powerband and rarely in the top. 

I am currently running 32:1 Maxima Super M with 91 Octane Ethanol free. After it started knocking I mixed in some octane booster to and it didn't help. It starts to knock about 10 minutes into riding at about 1/4 throttle with my water temp being about 110-130F. 

So other than that its probably time for a rebuild. Im going pull the head off tomorrow and inspect the best I can. 

Pic related; the beauty. 

biek.JPG

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Well, I pulled the head off and found the plating has started to chip off causing piston and head damage. Now for a big bore kit or replate?

cylinder.jpg

head.jpg

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12 minutes ago, mxsteve1968 said:

Tech woods and desert?   I would go 265 BB.   Man, that exhaust bridge is beat up.

I was thinking either a 265 or 280 from MaxRPM considering the 280 was only $50 more. I called him and he seemed to know his stuff. Who would you recommend? Eric Gorr isnt taking anything until May. 

 

UPDATE: Just called Millennium and they have a 265 kit for $575 which seems like a steal, plus their turnaround is only 2 weeks. 

Edited by murphkee

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Since you're ready to invest a lot in a new BB top end

confirm your bottom end is healthy and won't destroy your new parts (edit: as in rod bearings pounded by detonation as suggested below by ossagp)

Perform a crankcase leakdown test BEFORE running your freshly rebuilt engine, confirm there a no air leaks.

 

The damaged cylinder head and piston crown shows signs of detonation / running lean,

could have been a combination of bad fuel, wrong squish band height, air leaks etc.

 

Edited by mlatour
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I can't tell by looking if your pock marks came from some loose debri or some more severe detonation.  The area inside the dome makes me sway to detonation,  but of course I didn't see it before the build.  The big bore kit would make sense,  as most places would charge you to fix the bridge on that cylinder,  and boring may clean that up.  I don't think there is anyway that I would put a fresh top end of the rod and bearings though.  

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27 minutes ago, mlatour said:

Since you're ready to invest a lot in a new BB top end

confirm your bottom end is healthy and won't destroy your new parts (edit: as in rod bearings pounded by detonation as suggested below by ossagp)

Perform a crankcase leakdown test BEFORE running your freshly rebuilt engine, confirm there a no air leaks.

 

The damaged cylinder head and piston crown shows signs of detonation / running lean,

could have been a combination of bad fuel, wrong squish band height, air leaks etc.

 

After inspection I believe it was not detonating, but piston slap caused by the plating chipping off. If the plating hadn't chipped off and caused the pock marks I would hesitate to run this piston again. 

20 minutes ago, ossagp said:

I can't tell by looking if your pock marks came from some loose debri or some more severe detonation.  The area inside the dome makes me sway to detonation,  but of course I didn't see it before the build.  The big bore kit would make sense,  as most places would charge you to fix the bridge on that cylinder,  and boring may clean that up.  I don't think there is anyway that I would put a fresh top end of the rod and bearings though.  

I am 95% sure the pock marks are from loose debris. I unfortunately didn't see it before it was rebuilt either. As for the bottom end, the rod feels tight (up and down motion with the crank held)

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Having the rod feel snug is at least a start.  You can check the mains too.  But with some of the plating etc having access to the lower end,  I think i would do a few double takes.  I have put some back together that were worse looking blow ups.  The thing is that yours is going to be loaded a little more after this if you go bb along with the heavier piston.  

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1 minute ago, ossagp said:

Having the rod feel snug is at least a start.  You can check the mains too.  But with some of the plating etc having access to the lower end,  I think i would do a few double takes.  I have put some back together that were worse looking blow ups.  The thing is that yours is going to be loaded a little more after this if you go bb along with the heavier piston.  

Thats a good call. I've got the service manual for it and might as well go through all the checks since i'll be 2+ weeks out.

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Yeah, you have some time.   You can take a magnet and troll around the bottom of the crankcase and see if you get any steel fragments.   When I find those I don't run the existing bearings.  If I really want to run the existing bearings,  I skip the magnet:rolleyes:

9 minutes ago, murphkee said:

Thats a good call. I've got the service manual for it and might as well go through all the checks since i'll be 2+ weeks out.

 

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Update: I did a little bit of googling on the piston that's in it currently, as it turns out the engine is already running an over sized piston to bring the the displacement to 265. It is a Wiseco 801M06850. Since it's apparently already a big bore I guess i'll just have them replate the cylinder and maybe a little bit of port work done for low-mid rpm. 

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I figure this goes without saying..... (If detonation was not the issue) No way would I run those crank/rod bearings... Do it rite... you'll be glad you did. good luck

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On 3/22/2017 at 3:14 PM, murphkee said:

Update: I did a little bit of googling on the piston that's in it currently, as it turns out the engine is already running an over sized piston to bring the the displacement to 265. It is a Wiseco  801M06850. Since it's apparently already a big bore I guess i'll just have them replate the cylinder and maybe a little bit of port work done for low-mid rpm. 

I wonder if they did any headwork to get the bore to match the squish area when it was bored before.   Some gaskets accommodate  the overbore better than others.  Is that a 2mm oversize or more?

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1 hour ago, ossagp said:

I wonder if they did any headwork to get the bore to match the squish area when it was bored before.   Some gaskets accommodate  the overbore better than others.  Is that a 2mm oversize or more?

The cylinder is 2.1mm over bore according to the specs from Wiseco's website. So I'm assuming the piston is a +2mm....  I have no idea if the head was done to match the bore.

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No doubt the head damage is from foreign objects inside the combustion chamber.  Det doesn't leave sharp, angular indentations.  A piece of something went through there.

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9 hours ago, turbo dan said:

No doubt the head damage is from foreign objects inside the combustion chamber.  Det doesn't leave sharp, angular indentations.  A piece of something went through there.

Pretty much what I was thinking. I'm assuming it was the plating chipping off. 

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Not likely.  The plating comes off in super thin, small chips.  I would look at that bottom end with a fine tooth magnifying glass.  Bearings can shed debris like that before failing catastrophically.

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Detonation can sure speed up the demise of some tired needle bearings.  Murph, can you tell if it looks like the head gasket kind of folded into the bore a little bit on that one?  

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