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

[bryanj]

I seen that before caused by one of two things:-

(1) piece of ring broken and "flutters" in groove till it wears piston away--used to be common on 175 and 250/350 K series if pushed hard from cold

(2) Excessively rich causing "petrol wash" on the liner which removes oil then the piston "Nips" and the damage just gets bigger---Hapen to me on a Ford V6 when the acellerator pump diaphram went, should have guessed earlier as oil level went up and was doing about 6 to the gallon

[hymodyne]

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? I can find out, but I don't know at the present

Did you have a difficult time putting the piston in this cylinder when you put it together last time? No but this is the piston that I broke the top ring from the kit on when installing about a year ago, so I replaced the top ring with a 750K top ring.

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.

[JLeather]

Hmmm.  Did you check the end gap of that CB750 ring before installing it on the piston?  Also, in the pic you posted both of the compression ring gaps appear to be lined up.  Did you just do that for the picture, or was it installed that way?

[goon 1492]

I may just be silly but that looks like piston pre-detonation, thats what i was taught in school and actually have a 93' ford 150 at home with a brand new 302 in it because if this. click link below and read away, also look at the detailed pictures and tell me that doesn't look just like your pistons. Hope this helps in your rebuild

http://www.4wheelatv.com/ME2/dirmod.asp?sid=&nm=Tips+and+Tricks&type=news&mod=News&mid=9A02E3B96F2A415ABC72CB5F516B4C10&tier=3&nid=347BC67E43CB4E158163A7B484CCF84F

[PJ]

I would guess that the exhaust valve was not sealing properly maybe even off it's seat?? The damage is right where the exhaust valve would be and you need air for a fire that hot

[hymodyne]

this engine just had a Serdi valve job and stage 2 porting done on it.

I have a set of stock 550 sleeves and pistons. should I insert those sleeves, get new rings for the pistons and have the sleeves honed before I put them back in?

I'm looking at how to get on the road without lots more $$ leaving my pocket right now. a new overbore kit would be $300, another 250 for bore and rehone...

or the cost of a new head gasket , a top end rebuild gasket kit and the cost of a honing tool...

hym

[goon 1492]

I would guess that the exhaust valve was not sealing properly maybe even off it's seat?? The damage is right where the exhaust valve would be and you need air for a fire that hot

Not completely, read up about predetonation and its strikingly close to what you see in his pics, have you ever had a torch, propane or whatever and put it on something, well the first thing that happens is any bumps, scuffs, nicks or whatever on the surface that is getting troched will get hot first (white hot in fact), that is where it starts with pre-det. It could have been just a carbon deposit that started it, becoming a hot spot until getting hot enough to melt through and volia what we have in the above pics

[hymodyne]

pictures of the head



and plug

hym

[mlinder]

daaaaaaaaamnnnnnn......


And whats with that big assed crack there too?

[martino1972]

look closely at that exhaust valve,it seems to miss a tiny chip on the edge..

[hymodyne]

My napa store will bore a new sleeve and re-hone all four as well as check the head for damage on that cylinder for about $125.00. Now I just have to get a new kit...

hym

[mlinder]

That big crack in the head would make me loathe to reuse it...
But maybe it's not a crack. Sure looks like one in the pictures, though.

[MRieck]

That big crack in the head would make me loathe to reuse it...
But maybe it's not a crack. Sure looks like one in the pictures, though.

It's tough to tell from the pic and the actual damage was on the other side of the cylinder. We'll see. That head was in mint condition too. There is plenty of other stuff embedded in the squish area and intake seat.

[gregimotis]

daaaaaaaaamnnnnnn......

Pretty well sums up the last three pages.   

[mlinder]

That big crack in the head would make me loathe to reuse it...
But maybe it's not a crack. Sure looks like one in the pictures, though.

It's tough to tell from the pic and the actual damage was on the other side of the cylinder. We'll see. That head was in mint condition too. There is plenty of other stuff embedded in the squish area and intake seat.

Yeah, like I said, it's hard to tell with pictures.
Should have recognised your combustion chamber work, though, MRieck.
Be a shame if the head wasn't usable, after your hard (and pretty) work on it.

[Jerry Rxman Griffin aka MuthaF'er]

Did that plug get hot and burn up or do Iridiums look like that?

Did something get between the piston and the edge of the chamber where it wasn't opened up to match the bore? Or did the piston destruct and mark the head?

[TwoTired]

Did you have a difficult time putting the piston in this cylinder when you put it together last time? No but this is the piston that I broke the top ring from the kit on when installing about a year ago, so I replaced the top ring with a 750K top ring.

I did some math on posted part sizes.

605 piston ring groove width 1.59mm
605 top ring width 1.45mm
expected clearance 0.14mm

750 piston ring groove width 1.52mm
750 top ring width 1.5mm
expected clearance  0.02mm

605 piston ring groove width 1.59mm
750 top ring width 1.5mm
installed clearance 0.09mm  <<<smaller than 605 design expectations

605 piston groove depth 3.02mm
605 ring depth 2.60mm
expected clearance 0.42mm

750 piston groove depth 3.3mm
750 ring depth 2.8mm
expected clearance 0.5mm

605 piston groove depth 3.02mm
750 ring depth 2.8mm
installed clearance 0.22mm  <<< smaller than either design expectations

It would seem that the 605 pistons expected a larger clearance when new.  If we assume the piston maker new what he was doing, maybe the 605 piston alloy expands more than the Honda 750 piston and your ring seized in the groove when hot?
I don't know.  Maybe the engine experts can enlighten us?

Did you check the end gap of the ring at the top of the bore before installation onto the piston?

Cheers,

[martino1972]

here is a well explained site,that shows all different piston damage and how to read the piston>>>

http://www.theultralightplace.com/pistons.htm

[martino1972]

some thyings you might wanne check when you have it back together
-small intake airleak on that cylinder,rubber boot etc.
-carb float setting,might be set too low,fuel starvation at higer rpm on that cylinder
-go back to the correct sparkplug,heat range might have been wrong
-proper break in period,the better you break it in,the better engine you get.
-set timing right..

a melt down like that occures only when the combustion temp gets way too high..
most likely due to a lean condition(float set too low,heat range plug wrong,timing too advanged),that will heat up carbon deposit so high it will detonate the fuel mixer with glowing carbon deposit in stead of with the spark plug,resulting in a too early detonation,and also causes the fuel mixer to explode on the wrong spot,mostly on the edge of the piston,due to less room between piston/head..causing the piston to melt there...
take a good look at the other pistons,and please post  pictures of the remaining pistons,top view and side view...that will help in spotting the problem(if it was one cylinder problem or multyple cylinder problem)
it might be that due to the problem they where all doomed,but the one gave way the earliest..
so,yeah,please make pictures of the other cylinders and post them here,thanks,martino

[JLeather]

TwoTired, you're on the same track I was a couple posts back when he said it was coincidentally the same piston he installed the CB750 ring on.  The CB750 pistons are cast, and I believe these 605 pistons are forged.  The forged pistons expand much more than the cast pistons do at operating temp.  It is extremely likely that's the cause for the larger expected clearances in the 605 ring vs the 750.  It seems possible, therefore, that this damage may have been caused by that compression ring from a CB750.  With tighter tolerances when the piston hit operating temp it would have been able to expand enough, causing the beginning of the deformation that eventually led to the pictured destruction.  The clearances for the 605 ring almost seem excessive, but it's a pretty high quality kit and I'd bet the manufacturer knew what they were doing.  Just because the 750K ring "fit" doesn't mean it worked properly.

[bwaller]

I'm not sure where the truth lies with Hyms problem, but here's my experience. These are rather goofy little flat bottom, no skirt, 61mm (not 60mm) pistons which I believe are cast. I ended up with a "like new" set from a used mill I acquired and decided to use them in my 550 engine. On the underside of the skirt they are marked Haindst (which stands for Henry Abe Industries) on one side and 600cc on the other, but only displace 592cc, truth be known!

Who knows if these are the same as TT's or Hym's "605 kit" pistons. I would have imagined they would be, but from TT's measurements maybe not. Compared to a standard 61mm CB750 piston the compression ring lands on mine were practically identical. I had the oil ring groove widened on the HA pistons and then used standard CB750 rings. I can say with certainty that all ring side, and end gap clearances fell within Honda specs. The end gap was 0.014-0.015", not exactly tight, but none of the ring ends needed filing.

Since the pistons didn't cost me anything and in talking with MRieck I decided to have the pistons coated, both skirt and crowns. Not because they are priceless, but because of something that Mike said...old #$%* is still old #$%*!!!    Fiqured I give them all the help I could.

In my case there are about 3500 miles on this engine now, it uses no oil, and the oil is relatively clean when I've changed it. It makes excellent power as well and is not babied.

I'm sorry for your dilema Hym, maybe you'll get to the bottom of the piston problem, maybe not. For certain jetting and timing issues need be addressed right away before many miles are ridden. If it's a lean condition or detonation, it should show in more than one cylinder.  If anyone knows much about Henry Abe stuff they aren't saying, were they any good long term... might well have been like others have said, just a bad casting.

[turboguzzi]

Hey Hymo

Bearing with you here.

Something must have gone very wrong with the top ring/piston , Like two tired said, it's too much of a coincidence if that happened in the piston you had the ring mounting problem with.

The little 550-550 are pretty though bastards. Seen some failures during my two seasons of racing (not my bike, touch wood...) but nothing looked like that. Did my whole first season of racing with too lean a mixture and it didnt give such trouble. looking at your piston, it doesnt show any signs of seizures (I think), so hard to believe that detonation caused that. If it was too early ignition, then the other pistons should show seizures too, if it's carburation only on the hole, then the piston should have heavily seized before breaking like that. 

Also took appart once a guzzi V50 that been running quite nice only to find a broken ring and yet, it didnt do any damage like in your case.

My guess is that at some point the edge of the piston broke, ring was exposed to heat, melted and from there it was down hill. Maybe when you snagged that ring it created a little crack in the top groove. Or last, a manufacturing defect.

my 0.02 cents

TG

[hymodyne]

thanks for all the replies and theories. I'm sure the truth is somewhere in the middle of all of the speculation and diagnoses. when I get a new sleeve and piston I'll start over again.

hym

[martino1972]

do us all a favor(and urself) and take some pics of the other 3 pistons for us...
the discussion just got started,
but really,then we can diagnose more correctly...

[scondon]

do us all a favor(and urself) and take some pics of the other 3 pistons for us...
the discussion just got started,
but really,then we can diagnose more correctly...

 plus we really like pictures of stuff and theorizing endlessly. Yours is the most interesting bit to come along in a long while