Cannot stress enough the importance of cleaning out a block

[RED-Z06 2,567]

After honing...

 

Just tore my M12 back down after 5hrs of running,developed a rattle, oil on the piston.  The skirts are severely worn especially on the thrust side (rear of the block), the rod shows no scoring but its dull which is indicative of abrasive presence.  Rings were in spec 5hrs ago but now. .019/.024/.110 top to bottom.  The oil was dark and streaks of silver..i ran a magnet through the oil as it drained and got no ferrous debris so its aluminum...rod and piston.

 

Live and learn...ill clean it more thoroughly this time but im thinking what got me was the valve box, i don't recall if i flushed it after honing and some grit could have been in there.

 

Skirt thickness in 3 spots on trailing side..0.085 0.081 0.085.  And on the thrust side..0.061 0.054 0.058

[Snoopy11 5,718]

Some people may call me crazy... I think that applies... yes...

 

But after grinding on block or anything of that nature, I pressure wash my block, and blow it out with my gas blower...

 

I make sure the block is extremely dry, sitting it out in the sun as well.

 

Just my "educated redneck" method...

 

Don

[ebinmaine 72,604]

[Snoopy11 5,718]

1 minute ago, ebinmaine said:

 

 

 

Along with a big, hawkin' ...dawmn it...

 

Don

Edited January 11, 2022 by Snoopy11

[RED-Z06 2,567]

I dunked the whole block into hot soapy water in a tub and used various brushes to scrub inside and out, cleaned the bore with a scotch pad and soap then water and rags..until it came out clean, then 150psi air.until dry.

 

 

[ebinmaine 72,604]

Likely was the smallest little piece of aluminum schmutz that you can imagine. Just sitting in a corner waiting to get rolled around the engine...

 

I can't speak from experience having never done a small engine on my own but I've had carburetors that needed to be cleaned out three or four times before they ran right. Rare. But it happens.

 

[Snoopy11 5,718]

1 minute ago, ebinmaine said:

Likely was the smallest little piece of aluminum schmutz that you can imagine. Just sitting in a corner waiting to get rolled around the engine...

 

I can't speak from experience having never done a small engine on my own but I've had carburetors that needed to be cleaned out three or four times before they ran right. Rare. But it happens.

 

I had a steel pushrod go down into the oil pan of a briggs v twin.

 

Thing got friggin' obliterated.

 

HOWEVER, no damage to the cam or anything else.

 

Just had to dig pieces out after disassembly.

 

Don't ask me why it happened, but all I know is that it does... and usually destroys the cam...

 

OH, uh, speaking of that, @RED-Z06... any damage to the cam lobes?

 

Don

[Maxwell-8 4,367]

1 minute ago, Snoopy11 said:

the cam lobes

and crank?

 

I am sorry for you. s*ucks having an engine "destroyed" that way

[Snoopy11 5,718]

Just now, Maxwell-8 said:

and crank?

Yeah, crank journal could get scorred... but generally the came lobes are more vulnerable and soft...

 

Don

[RED-Z06 2,567]

2 minutes ago, Snoopy11 said:

I had a steel pushrod go down into the oil pan of a briggs v twin.

 

Thing got friggin' obliterated.

 

HOWEVER, no damage to the cam or anything else.

 

Just had to dig pieces out after disassembly.

 

Don't ask me why it happened, but all I know is that it does... and usually destroys the cam...

 

OH, uh, speaking of that, @RED-Z06... any damage to the cam lobes?

 

Don

Not seeing any other wear, the bore somehow has no notable wear still showing my crosshatch infact.  I think if id changed the oil it could have easily run like this 50+ hours but...

[Snoopy11 5,718]

Just now, RED-Z06 said:

I think if id changed the oil it could have easily run like this 50+ hours but...

Maybe... throw some rings in it?

 

Don

[Snoopy11 5,718]

32 minutes ago, RED-Z06 said:

oil on the piston

Smoking through exhaust or coming out of breather?

 

Don

[RED-Z06 2,567]

Crank measures 1.4995

Rod measures 1.5005

 

Not enough to knock...both still in spec but at the outside limits of running spec.

[RED-Z06 2,567]

4 minutes ago, Snoopy11 said:

Smoking through exhaust or coming out of breather?

 

Don

Somehow not really...no breather smoke or excessive vapor, no smoke visible while running but it had used some

[RED-Z06 2,567]

9 minutes ago, Snoopy11 said:

Maybe... throw some rings in it?

 

Don

Ive got new piston, rings, rod...on the way

[Snoopy11 5,718]

2 minutes ago, RED-Z06 said:

Crank measures 1.4995

 

1 minute ago, RED-Z06 said:

Ive got new piston, rings, rod...on the way

Sounds like... maybe a new crank in order.

 

Just a matter of time.

 

Don

[Achto 29,391]

I will spend far more time cleaning an engine than I will cleaning an open wound. 

 

Instead of soap & water grab a few cans of brake cleaner. Hose it down, dry it off with a blow gun, repeat 3 or 4 times. To clean the bore, put motor oil on a clean rag and wipe the bore. Repeat this using a clean rag each time until the rag comes out just as clean as it was before scrubbing the bore. Yes, it will have oil on it but there should be no black residue. 

[RED-Z06 2,567]

35 minutes ago, Snoopy11 said:

 

Sounds like... maybe a new crank in order.

 

Just a matter of time.

 

Don

Still within new spec..i could buy a new one and it be 1.4995

[Achto 29,391]

3 hours ago, RED-Z06 said:

Crank measures 1.4995

Rod measures 1.5005

 

.001" clearance sound perfect to me. Common clearance is .0008 -  .001" per inch diameter of the crank pin. 

[RED-Z06 2,567]

3 minutes ago, Achto said:

 

.001" clearance sound perfect to me. Common clearance is .0008 -  .001" per inch diameter of the crank pin. 

Yeah that definitely wasnt my noise, there is scuffing on the rod big end though.  The piston took a beating

[Achto 29,391]

4 hours ago, RED-Z06 said:

After honing..

 

I know that you stated the piston ring end gap but what is your piston to cylinder clearance. Too great of clearance will cause piston slap or chatter. An egg shaped hole will also cause the same thing. Measure the bore in multiple spots, right all of you numbers down and see how strait the cylinder is. Measure the skirt on you new piston and figure out what you clearance is.

[RED-Z06 2,567]

1 minute ago, Achto said:

 

I know that you stated the piston ring end gap but what is your piston to cylinder clearance. Too great of clearance will cause piston slap or chatter. An egg shaped hole will also cause the same thing. Measure the bore in multiple spots, right all of you numbers down and see how strait the cylinder is. Measure the skirt on you new piston and figure out what you clearance is.

I probably should but, if its larger than spec im not going to have it punched out, just not worth it, im already to the point id have been ahead of the game to just pickup a used local M16 that ran for $200 and just swapped it on.  No doubt the bore has some wear from the contamination vs last week, but...it'd be well more than its worth to punch it 10 or 20 over.  It would cost 250+ for a local machine shop to bore it..been there with an M10S...700 in machining and parts for a 250 dollar engine.

[RED-Z06 2,567]

And they are great engines...no doubt, but when you look at what parts cost...if not for sketchy aftermarket stuff it wouldn't be worth doing.  Look at what a coil from stens would run retail vs dealer cost..

[RED-Z06 2,567]

Old piston across the thrust faces on the skirts...3.363"

 

New piston  3.369"

 

That represents the maximum new size and maximum wear specified limit...

 

6thou wear is probably my noise

[Achto 29,391]

Common clearance for a cast piston is .001 to .0015 per inch diameter. Hypereutectic pistons are tighter around .0005 per inch diameter. You are just outside the cast piston limits. It would probably be ok but may be noisy. You can get .003 over oem pistons, might be an option.

Or maybe go .010 over rings on the stock piston, file end gap for correct gap.

 

Did you put the balance gears back in when you built it the last time?

Edited January 12, 2022 by Achto