M7 Turbo: Lead deposits all over pistons?

[jgw50]

LONG post, here's a summary, read the whole story and input if you dare!

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2005 M7 Turbo
6 lbs of boost
Running 100LL avgas premix 40:1

sandpaper looking soft gooey deposits all over the tops of both my pistons, can be removed with a q-tip and is the exact same color as my old lead fishing weights.

A/F readings:

Idle: 14.5
Mid range, no boost 13.5-15.5 (cant get the lean out)
Top end on 6 lbs of boost: 11.5-12

THE QUESTION: Are they lead deposits, are they bad, should I go leaner to get temps hotter to burn the lead out, anyone else ran into this?

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The Long story:

SO, I love the laydown motor and being able to take the powervalves out and check my "wash" after every ride.

Before my last ride I noticed a slight even sandblasted look all over the top of my piston. Even "blasting" all over the piston surface with no visable carbon on top of the piston, therefore no wash. I thought I was so lean that I was detonating, eroding the piston.

So, I thought I was detonating so I cranked the boondocker box way up to get her to run fatter, seemed to run 95% as good as before running similar A/F's but BD numbers about 4-10 numbers higher.

After that ride I looked at the pistons again and the "blasting" was worse, so I decided to stick a q-tip down there and woulden't you know, the "blasting" came right off.

The gunk was built up in little balls and peaks all over the pistons and when I took the q-tip out, it had cleaned the top of the piston, and the gunk looked like really really soft lead.

So, is this normal? Am I running so rich that the piston cant get hot enough to burn the TEL with the bromide? The sled seems to rip great and not too rich, but it seems like I would be totally safe leaning it out? There was a little of the lead stuff on the side of the piston that I could see throught the powervalve slot, can this cause siezure?

If you read all of that GOOD FOR YOU, and THANKS!

 

[Polarisrocks]

100LL is probably has one of the lowest lead contents of any of the leaded higher octain fuels. Try running some sunoco 112 unleaded and see if it goes away, its spendy though

 

[jgw50]

Anyone running racegas have similar gunk on their pistons?

 

[sledrush]

Yea I run 110 and get the same thing.

 

[Dano702]

I have a new sled , with all of its time on Sunoco at 10 lbs . I have been meaning to get the borescope down a hole . I will get back with you .

 

[monster7]

Anyone running racegas have similar gunk on their pistons?

Yes, VP C12....

TM7 10-14 psi

Same thing!

 

[jgw50]

Alright, good to know i'm not alone at least! I cranked my boost up to 9 lbs today for a ride and leaned out a little on boost. Got some whiteish brownish powder in my exhaust outlet.

I'm going to inspect the pistons sometime in the next couple of days, but from what i've read, if your combustion temps are above 900 degrees, there is bromine or bromide in the gas which is supposed to burn up the lead.

We'll see!

 

[Backcountry]

Greyish gummy deposits in an engine is also a sign of a coolant leak.

The whitish brownish powder in the exhaust outlet is normal and a sign of a decent tune...

 

[jgw50]

no coolant losses on my machine.

After reading a ton on these two stroke turbo's I prepared myself for watching every little thing every ride, constantly tuning the BD box, and wasting a lot of good days on having a machine that wouldent work.

Before every ride I check all boost fittings, coolant hoses/level, clutches, belt clearance, all exhaust bolts / fittings, and fuel pressure.

After every ride I take the powervalves out and inpspect the pistons as well as I can, check plugs, and look everything over. No problems so far.


To date i've got 250 miles on my sled, probably spent a total of 30 minutes dinking with the BD box (over 4 rides), and havent had any problems. This thing is awesome and much less finicky than everyone else without a turbo would have had me believe.

That being said i'm still new to this and think I can get bit in the butt any day now, but for the time being, I am one happy turbo two stroke rider! I've even got the money for a turbo nytro, but the M7 is just too much fun, and seems reliable enough.

 

[mtn mike on boost]

Greyish gummy deposits in an engine is also a sign of a coolant leak.

The whitish brownish powder in the exhaust outlet is normal and a sign of a decent tune...

agreed!!!!light brown residue a-ok

 

[FATLIP]

Did you switch to race gas or are you running the 100LL yet? I was thinking about trying some 100LL on my boosted poos but dont want troubles. The price diff around me is $3.50/gal for the two. Anyone have any input?

 

[speeddemon]

heck with only 6psi u might as well run unleaded pump gas !
mike

 

[hatchers]

i thought a A/F reading of 12.5 to 13 was the ideal?

11.5 seems rich, my sled gains another 15MPH track speed going from 12.2-12.8 A/F

 

[jgw50]

Yeah, i've since turned boost up to 9lbs (7000 - 10000 feet elevation) and turned AFR's to 12-12.5 and now I don't get the deposits on my pistons and she's got a lot more power too!

Still running avgas and loving it. I did some quick air density / charge temp calculations and I feel safe running the 9 lbs on 100ll. I also really like the advantage of having very consistant fuel. The avgas always is within the spec and is tested by the FAA. I havent touched my BD box for 3 rides, and dont really anticipate messing with it again!

I've been pulling my powervalves and pipe after every ride to check out stuff (mainly for detonation and wash) and have not found any problems so I will continue on 9lbs for a while.

I've heard that the reeds really start to tear up after 10psi and I don't want to start eating belts either!

 

[hatchers]

good to hear

my belt looks great, but i must keep an eye on oil funk and clean the DD area as needed

my oil res under the turbo would leak when the sled rolled over, last night i took everything apart and replaced both o-rings. The as shipped bottom o-ring looked like it had some rub wear.....weird! and the top o-ring was too big IMO. Also, the bottom o-ring is not 15% more then the depth of the o-ring groove????