Piston crown photo, what's it showing?

Piston crown photo, what's it showing?



Iceteaandlemon took this before his recent gasket resealing. Its interestingly confusing to me, what's it all mean to you?

Ya can see where the gas blasts escaped. This could work harden the low spots so retorque might not smash it down tight again. I am now pensive of reusing a blown by gasket as work hammered a bit thinner in spots annealing don't fill in. There are degree's of gasket trauma so may not happen to you. Btw if those gas paths had really opened up - the factory fuel lines are in the line of Fire.

Mr. Singh says it a good sign where combustion surfaces are clean as implies good turbulence combusting all carbon in that area. I wondered where a groove or two might work for our heads, yours implies one or two oblique ones between the exh valve and plug aimed from rim to plug each about 1/2" long. When piston about smacks the squish band it'd jet into the dark stagnant area then as piston jerks down it'd suck back some flame into the rim area, by theory. Not for extra power, just cleaner engine and less detonation potential. Ok maybe a bit more grunt on low octane if ya pressed luck advancing spark with hi throttle low rpm in upper gears. What would make one crown thin carbon all over and the other more crusty but with good clear areas? - turbulence or pressure differences side to side form the gasket leak affect or just carb differences or intake guide leakage? I doubt anyone can really answer that w/o many more experiments so prolly all of em ugh.

With a leaking head gasket you might not be able to diagnose a reliable reading from your pics.
Just like doing a plug chop you need to hold the throttle/engine at a constant speed to get a reliable plug reading.
All pics show is that there may, I stress, there may be an oil blow by in L.H piston. ( R.H. on engine)

Bernhard said:

With a leaking head gasket you might not be able to diagnose a reliable reading from your pics.
Just like doing a plug chop you need to hold the throttle/engine at a constant speed to get a reliable plug reading.
All pics show is that there may, I stress, there may be an oil blow by in L.H piston. ( R.H. on engine)

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Im pretty sure oil on the left hand cylinder at least. (left hand in photo - right hand on bike)

including the bright shiny golden colour ?

And is there a witness mark in the inlet valve pocket on the right hand (in photo) piston ?

I suspect you might be able to get a valve plus a small animal down the valve guides on this engine

johnm said:

I suspect you might be able to get a valve plus a small animal down the valve guides on this engine

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Definitely a lot of oil burning going on there.
Seals on the top of the guides still intact and doing their job ?

Commando engines are long stroke engines, the rings don't last forever either.

And some pistons were a little keen to smear metal over the rings if lube got a little scanty, taking away the spring function of the rings - and thus its ring sealing ability...

Ugh! I don't want to pull the head off right away again. How does one check the valve guides? I never took the head apart before.

The rings are new and micced with the bite 40 over and 5 thou clearance..

Good thing is I can get this thing apart in an afternoon and not trash my tank and stuff in the process. If I need to pull it apart I will do it again without hesitation!

After annealing the gasket and reinstalling it is not leaking so far after 15 or so miles. Just part of the concern that may be overshadowed by my rings or/and valve guides...

Should I run these pics up to my mechanic that rebuilt the head?? He's a good guy that does a lot of high end work and is recommended by bibbiani...

A leak down test might reveal a leak or might not. Show your mechanic but in mean time just run it as normal which it likely is and only worry if it leaks very soon again. Your crowns are not that excessive at all and the even coated one looks great actually. I do know that a first 100 miles or so can lull ya into thinking that was that...

hobot said:

A leak down test might reveal a leak or might not. Show your mechanic but in mean time just run it as normal which it likely is and only worry if it leaks very soon again. Your crowns are not that excessive at all and the even coated one looks great actually. I do know that a first 100 miles or so can lull ya into thinking that was that...

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well as long as im not getting oil on my leg or waiting for a tow truck on the road i am happy. I do balance the love for tinkering in the garage with actually riding. I really want to learn the mechanics of working on these things much more than to just ride it around though hahah

It took me long enough but it is more satisfying when there are no myteries left in you Commando. I had about 4-5000 miles initially on Trixie nice and tight, but missed some initial retorque on 1000+ mile trip which weeped some then cracks in the carb boots to eat rings til smoking and fouling show stopper. I re-ringed, and re annealed beyond cherry into the orange yellow, which makes gasket so soft its hard to keep from handling distorting, to get ~1000 mile then weeping to leaking again mess and drips off after a ride. Ugh. I hope its just a over used gasket. Barrel and head surfaces checked and indexed in past and no over heating or over reving damage. May just be carb boot leaks again, only takes one or two rides across THE Grit to eat rings. Got Krank PCV but can't keep up any more. Nothing for it but dig in again base gasket up and secure carb boots better and see what happens. If I could stay below 70's on easy throttle its not much, some spittle on side covers and films here and there, but a Combat can get the best of ya in place like the Ozarks, so a mess on return but tingling for hours afterwards.

Rode her couple hours 100 miles yesterday after a month of too cold. One step on starts, after the smoke of wet sump cleared in a minute or so. After ya get one gone through just ride em till something stops ya then fix it and repeat till the end.

Yup!! You said it!! If you look at the pictures thread you can see a pic of her in the mojave dry lakebed as well as one from new mobs ranch at the top of Angeles crest. The other day we went to the lakebed and the next day to the crest. When I got home I had to wipe a couple drops off my fins and a few off my side panel. Irritati. Enough to tear down and anneal!! But she's a runner !! Hopefully the future holds more me hank al experience for me. I want to know his big inside out and really get it running well whatever it takes!!

Hi,

as long as it doesn't smoke and you have a proper idle, I won't do anything.

Ralf

If your using it on the steet and not pushing it then Id just run it.

But I still dont understand your ignition timing comment.

Valve guides/seals in the left cyll are bad. The right one doesn't actually look all that bad - could be rich running because it looks to have a "dryer" consistency as opposed to the obvious oil of the other, but hard to tell from the pic.

The rocker arm geometry in the head on these engines seem to vary considerably. Some of the rockers impart considerable sideways pressure to the valve which can cause relatively raped stem/guide/seal wear. I had one rocker that barely hit the top of the valve until I put in some shims to center it.

Certainly, as suggested, you can run it as long as you want. But If it was me and if it was convenient - hey, it's WINTER! - I'd pull the head and replace the valves/guides/seals and then check/adjust the rocker arm geometry. Yes, I'm that confident that they are bad. NOTE that contrary to popular belief, oil can be pulled into the combustion chamber via the exhaust valve guides as well via the venturi effect of the exh gasses leaving the cylinder. Modern engines use seals on both int and ext valves though the ints are by far the bigger culprit.

Before you pull the head off again, buy yourself a new cylinder base gasket and a set of rings. With that much oil burning , you should see smoke from the exhaust. If it happens only after you use engine braking the guides are probably leaking, and the vacuum is pulling oil past the valve stem. If that much oil is getting past the guides, I would do a head job on it. If it happens all the time, the problem is in the barrels. The colour of the crown on the RHS is too black, you should get the jetting right . Don't be so lazy, do you want to end up like me - trying to keep the urge going at age 71 ?

ludwig said:

hobot said:

Piston crown photo, what's it showing?..

Click to expand...

What is showing is a reminder to ALLWAYS use a composite head gasket on a road bike .
annealing , quenching , silk wire , silver spray , goop ... jesus ...

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+1 on that. There's only one brand of composite I trust and that is Victor Reinz. Fit dry, 3 torque intervals and its done, no leaks, no problems.

ML said:

ludwig said:

hobot said:

Piston crown photo, what's it showing?..

Click to expand...

What is showing is a reminder to ALLWAYS use a composite head gasket on a road bike .
annealing , quenching , silk wire , silver spray , goop ... jesus ...

Click to expand...

+1 on that. There's only one brand of composite I trust and that is Victor Reinz. Fit dry, 3 torque intervals and its done, no leaks, no problems.

Click to expand...

I think next time I will go iwth the composite one. I am not quite sold on the copper yet but it isnt leaking at the moment. I was hoping the oil and crap was due to the copper gasket failing.

I hope you have better luck than Trixie on the 'composite' Flamering substitutes for the older kind with more robust rings rather than crimped foil and an adhesive on study paper like material rather than dry less dense paper filler. Not even the same silvery grey neither. Let us know what shows up and how well it holds up as I'm still in market for Flamering just don't want to be the tester prover evaluator of their de-evolution no more. The more I reflect this gasket area the more I think i should just go w/o a gasket and use unwaxed floss or real cotton or silk thread and Hylomar and diddle Trixie's Combat valve train correct once and for all.

I'm using Andover composite gaskets since 30+ years, not racing and not gearing by 750 for 160 mph . No issue with them. it's not something that need to be proved tested evaluated.
I can understand that racer want to be able to reuse gasket but if you intend to ride your bike and not remove the head for a monthly check go to the composite gasket .

Copper for me , anneal , grease lightly , pull down three times , sorted , no bits of gasket blowing out even if it does leak ,which i've never had with copper .

So now Im going to be guilty of admitting to " do what I say not do what I do "

I use composite on my road bike and copper on my race bike.

Composite because it has always worked for me provided you carefully follow the retorquing procedure.

but to follow the retorquing procedure you need a minimum of 2 preferably three running and cooling cycles.

Which is never going to happen on a race bike !!!

On my race bike 99 % of the time its finished 5 minutes before it goes in the van. I start it and run it.

When I get to the circuit I get to tech ispection first and then use the time before first practice to retorque.

Then go out and go for it.

I make sure the gasket is good, the gasket is annealed, use copper coat and all the fasteners are in good condition - I havent had a gasket problem in 12 years of racing.

What should Mr Ice tea do ?

90 % of Commandos probably look like this inside.

They have maybe 45 bhp at the rear wheel and everyone is happy.

Unless you are wanting to set some sort of record I would ride it.

When I started racing I had 25 years of road riding and I thought my bikes worked just fine. But going racing they lasted about 5 minutes before engine failure. If you raced this engine it would be lucky to finish a meeting and it would be dead slow. (Based on the not yet explained story about ignition timing and the rich right cylinder and maybe a valve hitting the piston pocket etc)

But on the road it will probably go for years.

Id just ride it.

Well I'm gonna retorque again and ride it for a little while maybe through the summer but you better believe I will have this head off again! I love tinkering with the damn thing and I will be curious to see what it looks like after riding on this gasket for a while.

So far no leaks so something right must have happened during the process.

Frustrating though I have to wait three weeks till I can go for a spin. I noticed a busted spoke on rear rim yesterday so the wheels going back to buchanans for a look.. Then I leave to Singapore Saturday

Life gets in the way too much!