Topic: oil burning mystery solved **graphic pictures**

[hymodyne]

After the bike stopped yesterday, I decided to tear down the head once and for all. Here's what I found:









what happened?

Bits of the oil ring were loose and what contributed to the scoring on the side of the cylinder and the indentations on top of the piston. I'm hopeful with a proper hone I can get rid of the scoring.

Now the big question is, where do I get a replacement piston for this one?

hym

[lrutt]

I'm thinking you will need to go an overbore on that cyl. Honing/glazbreaking will not take that out. You can go the cheap route and bore just the one cyl or do all and do it right.

[MPH2]

I don't know what I'm talking about but, was that running lean? or is that what a hole in the piston from running lean look like?

[JLeather]

Well, I can tell ya that was not caused by the kit having a 1-piece oil ring.  That piston freakin' melted on that side (crazy looking).  Running lean is a possibility, certainly, but generally lean pistons hole at the center.  Not entirely sure what caused that, but it wasn't debris in the cylinder.  That's a ridiculous looking piston.  Id I had to bet I'd say you developed a hot-spot in that area, primarily from running lean.  Those bits of oil ring you found most certainly came later in the death of that cylinder, after the hole was opened up.

I'd re-sleeve that cylinder and rebore it for whatever new piston you get.  Maybe a hone could get that scoring out, maybe not, but I'd not take that chance again.

[MPH2]

tghat about where the spark plug is depending on what bike it is

[scondon]

 Those pictures are beeeyoootiful. Thanks for sharing

You may want to check your valve/seats for damage as well, Hymodyne. All that stuff had to go somewhere, either down the cylinder or, more likely, out the exhaust valve.

[martino1972]

could pre-ignition have done that..?? like if the timing was set to early??
wrong heat range on plug???

[hymodyne]

Iridium plugs. deposits on all the other plugs were light brown.

I just emailed the supplier about breaking a set, but I doubt that will happen. Is there a 60mm piston with the same dimensions as these that I could replace all of them with?

hym

[bwaller]

For sure you'll need to replace that sleeve. Good luck finding just one piston.

[Cannibal]

Where's the ring gap? Did they somehow get lined up, because combustion pressure pushing through lined up ring gaps could cause such a failure. I've never seen it personally, but have heard of such things happening.

Steve

[Sam Green Racing]

Hym, I know you only finished the build recently but how long have you had the bike, did you ride it before the make over ?

Sam.

[hymodyne]

I've had the bike since 2005. I built it up from a rear wheel engine, frame and front forks I found in a junk heap behind a honda dealership. I've put about 6k miles on it since I got it running in 2006. I have about 800-1000 miles on the overbore kit.

hym

[Sam Green Racing]

Yes, I just looked at some of your other posts.
How long have you had the iridium plugs in it ?
Have you used any other plugs in it since the big bore, and prior to the iridiums ?

Sam.

[MoTo-BunnY]

YIKES! thanks for sharing. .  ..those pictures are quite graphic, indeed.

I would almost label them NSFW!  ('not suitable for work')


I'm sorry that happened to you and wish you the best of luck on the repair. . ..   

[hymodyne]

Yes, I just looked at some of your other posts.
How long have you had the iridium plugs in it ?
Have you used any other plugs in it since the big bore, and prior to the iridiums ?

Sam.

I ran ngk D7EA in the bike prior to the iridium

[scondon]

 Geez, didn't realize this was a new engine Hymodyne. Sorry if my first post sounded a bit insensitive, thought it was an old engine on it's last leg. No wonder the piston top looked so clean


    I honestly can't imagine a lean condition causing this type of failure in such a short period of time and would imagine the spark plug would have to be arcing to the piston somehow if it were the culprit. Boring/honing dust not cleaned from the cylinder and collecting at the piston rim? I'm at a loss

[Sam Green Racing]

Hym, did you have any issues with the d7ea  in that cylinder prior to putting the iridium plugs in ?
Did you have any mixture problems on that cylinder when you had the d7ea in ?
Have you ever burned a plug out in that cylinder since your last rebuild ?

Sam.

[MRieck]

 That looks like like a nitrous or turbo lean melt down. That is very, very odd. Either piston was total POS or.......I don't know what else it could be. Some pieces definitely took a walk through that cylinder judging by the indentations in the piston crown. I'd say the sleeve is junk too.

[Sam Green Racing]

That's what I was thinking Mike, To soft a plug or mixture very weak on that pot.
It looks like it was done a while ago and he's been running with a holed piston.
It dosen't look weak now but a lot of oil would have been coming up that hole, especialy as he over filled it a while back.

Sam.

[MoTo-BunnY]

I just wanted to say that this thread  is really interesting - it seems that in about any mechanics' shop I have seen, they always have a fascinating display of such "catastrophic failures" such as this piston, on a window ledge or being used as paper weights, etc.

Reading this thread, is like watching/listening in on Doctors diagnosing their patient - thanks again for sharing!  (and again, sorry for your 'illness'  )

[masonryman]

very sad when your back in it and you can still see the cross hatch hone marks.

could the source of the heat been at the oil ring and worked it's was up, maybe the oil ring gap was to tight or it rolled out of it groove when installed.

[Hush]

Can that please never happen to my bike!!!
Gotta be some junk that either got in or out of there, any photos of the plug from that cylinder or the underside of the head, now that's a picture I'd like to see.

[TwoTired]

Can we have a picture of the cylinder head, too?

I'd have to guess this was caused by installation damage when the piston was forced into the sleeve during assembly.  Possibly debris behind a ring, Insufficient ring end gap, cracked piston land, burred ring, etc.
Was the cylinder sleeve bored with "choke", or straight walled?

Did you have a difficult time putting the piston in this cylinder when you put it together last time?

The only time I saw something like that was on a piston with a three piece oil ring.  The top piece of the three piece ring jumped out of the groove and about 1/4 inch of the end folded up between piston and cylinder.  This put a serious groove in the cylinder wall and the engine had a serious oil burning problem.  Still, it didn't have evidence of hot gases melting the piston aluminum as the compression rings still did their job more or less.  But, the example engine had cast iron sleeves, not steel like the CBs have.  And, the engine never saw more than 4000 RPM, if that.

You sure have me worried about that 605 kit I have.

My condolences.

[Buber]

Maybe solution is as simple as metal failure, i.e. the piston had a structural fault on this spot? I mean, you can't really see what is the srtucture of the metal, can you?

So, maybe a defective piston? Something went wrong durign casting, and then the piece simply broke off. After all edges of the piston are somewhat "weaker", due to the grooves for the rings right under.

Just thinking aloud....

[Ichiban 4]

Can we have a picture of the cylinder head, too?

I'd have to guess this was caused by installation damage when the piston was forced into the sleeve during assembly.  Possibly debris behind a ring, Insufficient ring end gap, cracked piston land, burred ring, etc.
Was the cylinder sleeve bored with "choke", or straight walled?

Did you have a difficult time putting the piston in this cylinder when you put it together last time?

The only time I saw something like that was on a piston with a three piece oil ring.  The top piece of the three piece ring jumped out of the groove and about 1/4 inch of the end folded up between piston and cylinder.  This put a serious groove in the cylinder wall and the engine had a serious oil burning problem.  Still, it didn't have evidence of hot gases melting the piston aluminum as the compression rings still did their job more or less.  But, the example engine had cast iron sleeves, not steel like the CBs have.  And, the engine never saw more than 4000 RPM, if that.

You sure have me worried about that 605 kit I have.

My condolences.

I tend to agree with Lloyd here on this.  Have seen similar situations with improperly installed oil ring(s).  About everything he said seems accurate..except I think it was an oil ring installation issue mainly.

Hopefully you can re-hone that cylinder..install new piston w/rings..w/o having to re-sleeve or re-bore that cylinder. 

Who did the original build on the engine?  If you could get back to them..seems like it's a "parts and labor" issue that perhaps could be addressed (if others did the build/assembly).

A hassle for sure..but totally fixable.

Best of luck..

Ichi