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Detonation Diagnosis--please help

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Hey guys, I pulled my top end apart last night to replace the piston/rings/etc...

Unfortunately I got a nasty suprise, Detonation damage. Can you guys help me figure out what caused this? The bike has been rich from day one(or so I thought), powervalve is nasty with sludge, exapansion chamber is nasty. I blame it on the belray i ran for 6-7 months before switching to klotz.

Bike specs:

2008 YZ250, 175 main, 45pilot, stock needle #1 clip position, 40:1 Klotz Supertechniplate with 93 oct pump gas, br8eg plug. Oem replacement piston, stock pipe, FMF Q silencer.

FYI the cylinder looks great, no scoring, no gouges, not even much build up. Well within specs on taper & bore diameter. Wrist pin was dead on spec, piston still in spec, no head warpage. Reeds are in spec. The plugs i have used to tune jetting are all intact and read a tad rich.

pics

piston-tons of build up-i sanded a section to show the carbon depth.

383644436.jpg

Definite detonation discoloration

383644437.jpg

Skirt in decent shape

383644583.jpg

383644588.jpg

Head

383644442.jpg

383644444.jpg

What caused this? When did it go lean or what made it go lean? I did run a harescramble in the mid 30's but i had no pinging & the bike ran fine. Actually the bike ran fine saturday when I broke in my Rekluse. I just pulled it for a top end since it has roughly 60hrs(high estimate) on it. It appeared that the damage happened a while back since the carbon build up was heavy on the damaged areas. No air leaks that I could find when I was chasing an erractic idle.

Is the head salvageable? Should I just buy a new one?

Thanks for any info

jeremy

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you can use the head again, but you are prob going to loose a little power. up to you. maybe a good time to upgrade. how high up are you from sea level?

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Elevation is anywhere from 500-1200 feet. Timing is retarded 2 degrees as well. I can deal with a little power loss, i am not a power hungry kind of guy. I just ride trails & race harescrambles, im slow & old.

1st race is next weekend so i need to do something fast. Can I get by on this head cleaned up for a race, order a new one, do squish measurements & send the new head to RB?

can RB Designs machine out the damage if i send it off for squish mods?

Do you think the stock squish is so out of whack it caused this?

I do have a full machine shop at my disposal including a cnc lathe.

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I am going back to my normal sub 45 degree jetting, 50 pilot and clip on 2nd groove.

Foreign object huh? Like what? I lost no plug electrodes/ceramics or had the head off at anytime. I used a lexan piston stop when i installed/removed my FWW. I used a machined adapter and dial indicator to set my timing. Thats the only other time anythign has been in the head. I always clean the bike, & pull the tank before I pull the plug. I am extra careful about debris/dirt.

I am thoroughly confused.

Doesnt the discoloration under the crown on the piston mean a lean condition and detonation?

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that looks like foreign object...

I agree. Looks like some debris got smashed in there. Check your old piston, rings, wrist pin bearing, and crank. Make shure you flush it out really well.

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I agree. Looks like some debris got smashed in there. Check your old piston, rings, wrist pin bearing, and crank. Make shure you flush it out really well.

I will check the rod & crank when i get home, but the piston/rings/wrist pin/bearing are all intact. the only damage i could see was the piston crown/head.

That being said, I havent had this top end apart, I got thebike about a year ago(little less). The previous owner installed the piston that I just pulled. Debris could have been present when he did the install and the damage may have already been there when i purchased the bike. He may have been unaware of it.

I thought the debris was actually from the pieces missing from the crown of the piston, blown off by detonation. The areas with arrows are voids, i thought these pieces broke away and caused all the damage to the crown and the head.

383647037.jpg

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that doesn't look like detonation damage to me, Looks like debris.

I would send the head off to RB, I had him do the squish/cc mod on mine and the bike runs fantastic! From the carbon on the crown I would say you are running on the rich side, and you said you set timming, so unless you advanced it a bunch i doubt its detonation.

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I definitely retarded the timing. It was +1 advanced from factory so I set it at retarded 2*.

I always thought the bike ran rich, even with the 45 pilot at cooler temps.

debris, huh...Now I need to figure out where it came from. I will go back & check my plugs to make sure they are all completely intact.

I might have my wife pick up some solder tonight to do squish measurements & send the head to RB. Any idea what his turn around times usually are?

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thanks for the info...

a much closer inspection of all parts tonight. I am putting the cylinder, head & piston in the parts washer this afternoon. Maybe that will reveal something.

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usually if the main bearing cage come apart it does way more damage than this.

however, do NOT overlook the lower end!!! a small piece of a crank ball bearing may be the culprit.

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If I am not looking at it backwards it looks like whatever went thru your engine came from the right side, if it was a detonation problem from being lean more than likely it would be centered around the exhaust port. I guess it could be possible than a right side crankcase leak or water leak could pop off a piece of piston and cause that problem but I doubt it. it looks like something like a needle bearing went thru it on the head and the resulting damage cause a hot spot eroding the piston after the fact.

I would double and triple check your bottom end bearings,piston bearing,circlips and such. double check the intake and your exhaust(the reversion wave maybe strong enough to push something back in) for missing and/or chipped. Machine the head and a new piston and see what happens from there

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Power Seal just repaired my cylinder and head with detonation damage. I was very pleased with their work and turnaround time (about 10-14 days). I think it was $40-50 to weld and remill the head. The bike is running great but I am now mixing 110 octane with 93 50/50. Give them a try if RB can't get it done quick enough for you.

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I will double and triple check everything especially the bearings.

If the exhaust port is at 12 oclock, the damage is from 12 to 3 on the piston and the head. basically from the coolant port on the head to the right side crank seal.

Note the arrow on the piston.

The damage was very very shallow and the carbon made it look nasty. A few minutes in the lathe with red scotch brite resulted in this.

No actual machining just polishing with fine scotch brite pads.

383657637.jpg

383657638.jpg

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Wow! What a difference. I can't believe you were able to get those nicks out. I think I still see a little pitting on the edge, but thats a huge improvement. Are you going to try and run it like that?

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there is still a little pitting right at the edge. I am going to order a new head tomorrow, do my squish measurements when it arrives and try to send it to RB.

I might put the damaged/repaired head on and try to run it this weekend. The head is soft and there was obviously material removed, how much was removed is the question. I know the squish will be affected and most likely adversely so. I know I should be patient and wait for a new head but curiosity is getting the better of me. It ran decent with the damage, will it run worse now?

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If any happens to stuble across this thread later heres some pics of detonation for referance :thumbsup:

img3430ax.jpg

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Yes, look for a large end rod bearing that is going bad . Check it all the way around the rotation as this will clue you in to missing rollers...not that I learned that the hard way! LOL

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RB had my head turned around within a week. It is $90 total for the job including return shipping, and I promise you will never want to run a stock head again.

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