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viperdoc(at)mindspring.co
Guest

Posted: Sat Jun 11, 2011 8:01 pm Post subject: Detonation

All,

I have an enigma with my 50. Changed the #1 and #3 cylinders after finding I had a compressions in the 30’s on those two cylinders. All others were 76 to 78’s. Tried staking them to no avail. Found that I had a bad valve guide on #1 and a leaking valve on #3. Replaced them with two rebuild cylinders with new pistons that included oversize rings. After reinstallation of the cylinders have developed a detonation that was severe enough to stake the elements on the fore and aft NGK spark plugs down onto the electrode effectively grounding them out. Figured it was caused by an induction leak after getting advice from the local gerus. Replaced the intake seals on the  intake tubes. Found I had the #1 seal leaking. Anyway runup was uneventful.  On lift off had a single misfire but climb out was uneventful. Inflight mag check at 70% and 700 mmHg was 3% on both mags. Pushing the power up to 100% for 3 to 5 seconds rewarded me with a  misfire followed by an irregular running engine. Pulling the RPM back to 70% smoother it out. Landing was uneventful as was the runup for Sumping the engine. After shutting down did a laser temp check that showed the #1 as the hottest cylinder at 145 deg C. all of the others were in the 120’s except for #6. It was 75 deg C.  Pulled the plugs on 6 and found the element closed down onto the electrode similar to the previous runup where the elements were closed on the #1, #1 and #4 cylinders. The elements on those plugs looked like they had been hammered down. OAT at 3500 ft was 85 deg.F.  CHT on #4 was 180 and Oil temp was 58 deg C. right at the bottom of the yellow arc when the detonation began. Surface temp was 95 deg F. 

So, do I still have an induction leak leaning it out or what? The first time, the #1, #3 and #4 front and rear plug were effectively grounded out after the detonations occurred during runup at 70%. Put another set of new plugs in gapped at 25/1000ths which is where the plugs are set from the factory. When the initial round of detonation occurred, I had new plugs in also but they were gapped at 20/1000ths. Remember #1 and #3 were the cylinders replace in which their intake tubes had their gaskets / Seals replaced. 

What am I missing? I’m about ready to pull the new cylinders off and start over! 

Doc

  [quote][b]

pfstelwagon(at)earthlink.
Guest

Posted: Sat Jun 11, 2011 10:52 pm Post subject: Detonation

I have seen ground electrodes blown off the spark  plugs from detonation but never hammered down.  I have seen plugs hammered  down from parts (screws etc.) in the cylinders.  In a normally aspirated  engine the parts can move from cylinder to cylinder, but I don't see how that  would happen in a supercharged engine.  Could be detonation but it would be  a severe case.

  

 CJ6-A  N23021 

  [quote][b]

dsavarese0812(at)bellsout
Guest

Posted: Sun Jun 12, 2011 5:29 am Post subject: Detonation

I believe severe detonation would cause damage to the piston as has been 

seen in many internal combustion engines with aluminum pistons, which 

the M14 has.   The parts you mention, wouldn't there be evidence of 

these parts in the combustion chamber upon inspection with a bore scope?



Dennis



On 6/12/2011 1:49 AM, Frank Stelwagon wrote:

 	  Quote: 	
		   I have seen ground electrodes blown off the spark plugs from 

 detonation but never hammered down.  I have seen plugs hammered down 

 from parts (screws etc.) in the cylinders.  In a normally aspirated 

 engine the parts can move from cylinder to cylinder, but I don't see 

 how that would happen in a supercharged engine.  Could be detonation 

 but it would be a severe case.

 CJ6-A  N23021

 *

 *

viperdoc(at)mindspring.co
Guest

Posted: Sun Jun 12, 2011 6:37 am Post subject: Detonation

Frank,

I thought the same thing immediately after the event. I bore scoped the cylinders looking for errant valve fragments, keepers, or any other metal fragments of unknown etiology. Even put a flexible magnet in the cylinders. Nothing was found. Inspected the piston heads. There was some pitting similar to coarse 200 grit sandpaper. Pretty well scanned all of the piston head as well as looked at the valve seats, the plugs in the cylinder and the airstart valve. Nothing found in the cylinders and no holes in the piston.

Off to the airport to pull the intake tubes to look for possible holes in them. Will recheck the collars again. 

Doc

 

From: owner-yak-list-server(at)matronics.com [mailto:owner-yak-list-server(at)matronics.com] On Behalf Of Frank Stelwagon

Sent: Sunday, June 12, 2011 1:50 AM

To: yak-list(at)matronics.com

Subject: Re: Detonation

 

I have seen ground electrodes blown off the spark plugs from detonation but never hammered down.  I have seen plugs hammered down from parts (screws etc.) in the cylinders.  In a normally aspirated engine the parts can move from cylinder to cylinder, but I don't see how that would happen in a supercharged engine.  Could be detonation but it would be a severe case.



 



CJ6-A  N23021 

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talew(at)bellsouth.net
Guest

Posted: Sun Jun 12, 2011 7:01 am Post subject: Detonation

Are you sure you installed the correct heat range plugs ? This sounds an interference problem .

 Terry



 

   From: Roger Kemp M.D. <viperdoc(at)mindspring.com>

To: yak-list(at)matronics.com

Sent: Sun, June 12, 2011 10:34:08 AM

Subject: RE: Re: Detonation



    

Frank, 

I thought the same thing immediately after the event. I bore scoped the cylinders looking for errant valve fragments, keepers, or any other metal fragments of unknown etiology. Even put a flexible magnet in the cylinders. Nothing was found. Inspected the piston heads. There was some pitting similar to coarse 200 grit sandpaper. Pretty well scanned all of the piston head as well as looked at the valve seats, the plugs in the cylinder and the airstart valve. Nothing found in the cylinders and no holes in the piston. 

Off to the airport to pull the intake tubes to look for possible holes in them. Will recheck the collars again.  

Doc 

    

From: owner-yak-list-server(at)matronics.com [mailto:owner-yak-list-server(at)matronics.com] On Behalf Of Frank Stelwagon

Sent: Sunday, June 12, 2011 1:50 AM

To: yak-list(at)matronics.com

Subject: Re: Detonation



 

   

I have seen ground electrodes blown off the spark plugs from detonation but never hammered down.  I have seen plugs hammered down from parts (screws etc.) in the cylinders.  In a normally aspirated engine the parts can move from cylinder to cylinder, but I don't see how that would happen in a supercharged engine.  Could be detonation but it would be a severe case.

  

 

  

CJ6-A  N23021 

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dsavarese0812(at)bellsout
Guest

Posted: Sun Jun 12, 2011 8:05 am Post subject: Detonation

The plugs are correct Terry.  It's the same automotive plugs we've all 

been using for years.  1/2" reach.  Actually the same length as the 

original Russian plugs.

Dennis



On 6/12/2011 9:59 AM, T A LEWIS wrote:

 	  Quote: 	
		   Are you sure you installed the correct heat range plugs ? This sounds 

 an interference problem .

 Terry



 ------------------------------------------------------------------------

 *From:* Roger Kemp M.D. <viperdoc(at)mindspring.com>

 *To:* yak-list(at)matronics.com

 *Sent:* Sun, June 12, 2011 10:34:08 AM

 *Subject:* RE: Re: Detonation



 Frank,



 I thought the same thing immediately after the event. I bore scoped 

 the cylinders looking for errant valve fragments, keepers, or any 

 other metal fragments of unknown etiology. Even put a flexible magnet 

 in the cylinders. Nothing was found. Inspected the piston heads. There 

 was some pitting similar to coarse 200 grit sandpaper. Pretty well 

 scanned all of the piston head as well as looked at the valve seats, 

 the plugs in the cylinder and the airstart valve. Nothing found in the 

 cylinders and no holes in the piston.



 Off to the airport to pull the intake tubes to look for possible holes 

 in them. Will recheck the collars again.



 Doc



 *From:*owner-yak-list-server(at)matronics.com 

 [mailto:owner-yak-list-server(at)matronics.com] *On Behalf Of *Frank 

 Stelwagon

 *Sent:* Sunday, June 12, 2011 1:50 AM

 *To:* yak-list(at)matronics.com

 *Subject:* Re: Detonation



 I have seen ground electrodes blown off the spark plugs from 

 detonation but never hammered down.  I have seen plugs hammered down 

 from parts (screws etc.) in the cylinders.  In a normally aspirated 

 engine the parts can move from cylinder to cylinder, but I don't see 

 how that would happen in a supercharged engine.  Could be detonation 

 but it would be a severe case.



 CJ6-A  N23021



 *    *

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 *http://www.matronics.com/Navigator?Yak-List*

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 ist" rel=nofollow target=_blank>http://www.matronics.com/Navigator?Yak-         -Matt Dralle,

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kregg(at)balancemyprop.co
Guest

Posted: Sun Jun 12, 2011 10:07 am Post subject: Detonation

Doc.  When you get a chance call me (at) 408.836.5122.  I may be able to help.



Kregg Victory



Sent from my Samsung Epicâ„¢ 4G



"Roger Kemp M.D." <viperdoc(at)mindspring.com> wrote:



 	  Quote: 	
		  Frank,



I thought the same thing immediately after the event. I bore scoped the

cylinders looking for errant valve fragments, keepers, or any other metal

fragments of unknown etiology. Even put a flexible magnet in the cylinders.

Nothing was found. Inspected the piston heads. There was some pitting

similar to coarse 200 grit sandpaper. Pretty well scanned all of the piston

head as well as looked at the valve seats, the plugs in the cylinder and the

airstart valve. Nothing found in the cylinders and no holes in the piston.



Off to the airport to pull the intake tubes to look for possible holes in

them. Will recheck the collars again. 



Doc



 



From: owner-yak-list-server(at)matronics.com

[mailto:owner-yak-list-server(at)matronics.com] On Behalf Of Frank Stelwagon

Sent: Sunday, June 12, 2011 1:50 AM

To: yak-list(at)matronics.com

Subject: Re: Detonation



 



I have seen ground electrodes blown off the spark plugs from detonation but

never hammered down.  I have seen plugs hammered down from parts (screws

etc.) in the cylinders.  In a normally aspirated engine the parts can move

from cylinder to cylinder, but I don't see how that would happen in a

supercharged engine.  Could be detonation but it would be a severe case.



 



CJ6-A  N23021

tjyak50

Joined: 31 May 2007
Posts: 81
Location: Phoenix, AZ

Posted: Mon Jun 13, 2011 5:45 am Post subject: Re: Detonation

There is about a mile of clearance from the top of the piston to the plug in those hemi-heads.



Are you running 100LL or some other fuel?  Detonation simply from being lean with stock compression ratio at low power on good 100LL seems unlikely to me.  If you had really bad gas maybe another story.



Mechanical "FOD" of some type?  Something small enough to get past the intake grate and sucked into the compressor then slung out to various cylinders causing plug damage, pitting, valve damage and intake backfires due to the valve stuck open?



Airborn mag check:  the big thing you are checking for is smoothness.  The prop gov will maintain the selected RPM so any rpm variation you might see is different from the ground mag check when the prop is fixed pitch on the low-pitch stops.  



Please keep us posted.



TJ

Yak 50 

www.airpowerinsurance.com

viperdoc(at)mindspring.co
Guest

Posted: Mon Jun 13, 2011 1:48 pm Post subject: Detonation

Running 100 LL with MMO all the time.

Concur with airborne mag thoughts

Found the #3 intake had 20/1000ths space along the edge of the trumpet when

I loosened the collar. The intake tube had been knocked off the wing by a

curious George milling around while I was working asking the usual torrid of

useless questions coming from a none round motor driver of spam cans at the

EAA meeting in my hanger. So at the least, I had an air leak on #3. Have

left the intake drain on #4,5, and 6 open before with this kind of BS. But

will that cause the plugs to be tapped down on #1, #3, and #4 the first time

I experienced the misfire. Then after changing all the plugs, scoping the

cylinders, rechecking the valve lash, replacing the supercharger intake

seals on #1 and #3 ( the replaced cylinders), the monster raises its' head

on #6??!!! Both fore and aft plugs were tapped down onto the element.

Still have not pulled the mag caps and checked the rotor/cap for arching nor

have I gotten to check the points and the rivet in the base plate. That is

next. 

Ran her up yesterday for about 10 mins to 80% with what felt like a normal

rumbling M-14. Have not strapped her down and pushed it up to 100% yet. A

few more things before I go there.

Scoping the effected cylinders did not reveal any foreign bodies, valves

with chips of cracks on them, no bright areas around the valve seat lip

suggestive of burning and there was, as you said, a boat load of clearance

between the piston and plugs.

And...the epic #$%^&*(at) saga continues!

Doc



--

tjyak50

Joined: 31 May 2007
Posts: 81
Location: Phoenix, AZ

Posted: Mon Jun 13, 2011 1:57 pm Post subject: Re: Detonation

Pull an intake tube from a lower jug and look into the blower wheel.  See if you can see any FOD hanging in the tube or near the sticky bottom.

Check the blower wheel and see if any garbage?



An interesting saga.  



100LL fuel with a 6.3:1 compression ratio at low power and low rpm on a relatively cool day is not a detonation prone machine.

viperdoc(at)mindspring.co
Guest

Posted: Mon Jun 13, 2011 4:57 pm Post subject: Detonation

Great  idea. I can gingerly bore scope it to. Just have keep the curious

jokers away from the prop when doing that!

Too damned hot to keep the hanger door closed the entire time! We're having

a central AZ summer only with HUMIDITY!

Doc



--

tjyak50

Joined: 31 May 2007
Posts: 81
Location: Phoenix, AZ

Posted: Mon Jun 13, 2011 9:08 pm Post subject: Re: Detonation

Remember:  NEVER pull just one spark plug.  Always remove at least all front or rear plugs.  If you only remove one and pull the prop through then you come back to that cylinder the engine will zip past the zero compression jug and surprise the shit out of you and risk serious injury.  Never pull just one plug if you move the prop.



Hope this all helps amigo.



Tj

viperdoc(at)mindspring.co
Guest

Posted: Tue Jun 14, 2011 5:43 am Post subject: Detonation

Generally all the plugs were pulled each time to replace them. The prop was not ,moved buy me when I only had the plugs out of #6 after finding it to be the cold one after the last flight ( test fight). 

Thanks for the help and advise.

Doc



Sent from my iPad



On Jun 14, 2011, at 12:08 AM, "tjyak50" <tomjohnson(at)cox.net> wrote:



 	  Quote: 	
		   

 

 Remember:  NEVER pull just one spark plug.  Always remove at least all front or rear plugs.  If you only remove one and pull the prop through then you come back to that cylinder the engine will zip past the zero compression jug and surprise the shit out of you and risk serious injury.  Never pull just one plug if you move the prop.

 

 Hope this all helps amigo.

 

 Tj

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=342930#342930

talew(at)bellsouth.net
Guest

Posted: Tue Jun 14, 2011 7:18 am Post subject: Detonation

Doc ,

I did not read that you you checked the ign. timing . 

If one mag is advanced too far you have a source for detonation .

Terry 



---

mark.bitterlich(at)navy.m
Guest

Posted: Tue Jun 14, 2011 8:35 am Post subject: Detonation

I have found that when I have people standing around asking questions

when I work on something, I invariably will FU... excuse me... will

invariably mess it up.   When you are putting your hands on something as

important as an aircraft engine, get everyone that is not directly

involved OUT OF THE HANGAR.  Sometimes their feelings will get hurt:

"HEY WE JUST WANT TO WATCH AND LEARN!"   Tough banouchee's!  Kick them

the heck out.  This is not an EAA event,  it is an aircraft engine

repair and there is no room for distractions.  



I have made the same mistake myself and have paid the price.  Now.... so

have you.  Time for us all to learn from it. 



As to your engine:  My 40 years of working on military aircraft have

taught me one thing.  If something is not working, it is almost ALWAYS

related to where humans recently laid their hands.  You just changed two

cylinders.  The engine was running just fine before you did that.  Now

it is not running well and it is doing something weird.  You did not

touch the mags... leave them alone.  Do not change the gap on the plugs

from what worked before.  If it worked before, it should work now.

Don't go changing anything that has ALWAYS worked before.  



This engine has a common intake fed by a blower.  This intake then has

individual intake tubes that feed up to individual cylinders.  If you

have a bad leak on any one intake, that leak has the capability to

impact the mixture to ALL of the cylinders.  Remember that an intake

leak can go BOTH DIRECTIONS.  If you have the engine developing less

manifold pressure than what outside ambient air pressure is, then the

leak can be air going in, and not fuel mixture going out.   The motor

has a blower, so at some settings and at some altitudes, stuff can come

out and at other settings "stuff" can come in.  



So it is really down to one of two things: 



1.  Something came apart and is rattling around inside.  Which seems

unlikely unless some idiot let a wrist pin cap fall off as the cylinder

was installed.  (This has happened before).  If this happened, you would

see metal in the filter by now.  



2.  There is some kind of bad intake leak.  Fix that.  If you can't find

any leaks, look some more.  If you still can't find any, get someone

else to come look.  



3.  Don't touch the mags.  They did not just pick this moment in time to

switch to some kind of ultra advanced condition unless you found them

LOOSE to begin with.  



4.  Borescope anything and everything you want to.  Always a good idea.

Just my two cents. 



Mark Bitterlich

  



--

tjyak50

Joined: 31 May 2007
Posts: 81
Location: Phoenix, AZ

Posted: Tue Jun 14, 2011 9:17 am Post subject: Re: Detonation

I second Marks comments.  Looky-loos with random ideas are distracting.

Looky-loos with random ideas spread thousands of miles away on the internet?  -Priceless!



The odd thing is how your spark plug electrodes got physically damaged.

What force physically smashed them down against the center thing?



Was it a ricochet?

Or a blast front?



Pictures would be neat.

Tj

82-2308

talew(at)bellsouth.net
Guest

Posted: Tue Jun 14, 2011 9:40 am Post subject: Detonation

tjyak50 ,

On my engine I have had to move and or remove the mags several times while

working on the plug wires , engine mounts and the generator . It is possible

that the mags ,or a mag , was moved to remove the cylinders and the associated

pistons.

Looky-Loo

Terry Lewis



---

viperdoc(at)mindspring.co
Guest

Posted: Tue Jun 14, 2011 10:03 am Post subject: Detonation

Agree with all said. Your comments bring peace of mind. I plan to run her up

again maybe this afternoon but not if ambient temp is 100 F as predicted. 

I am looking, as you said, at what changed. What changed is two new

cylinders. I found that the paper seal that Jill supplies for the intake

gasket was too thick and that the trumpet end of the intake on #3 had a gap

of 20/1000ths wide on about 1/4 of its diameter. I replaced the intake tubes

with newer ones off my other engine in the back that I am slowly rebuilding.

I replaced the rubber supercharger intake seals with new ones from Jill. I

still have to pull all the plugs and re-gap them...again. I plan to pull all

the valve covers and check the lash one more time. 

As you said, I'm going to bore scope it again since she was run up Sunday

afternoon. I thought about pulling a lower intake tube to look at the

underside of the supercharger turbine...but you know...given a little time

to think one can imagine all sorts of bad shit.

As far as I know the rags plugging the intake ports on the accessory case

were not screwed with and hopefully nothing was dropped in there. That could

cause a valve to stick.

I have drained oil out of her twice now from the nose case sump. I have run

a magnet through it and have strained it through a mesh cloth. Nothing but

carbon fragments found in very small amounts. I'm using the 4 micron mesh

that is used to catch kidney stones. Some Viruses can't pass through that

shit. If it is there I should catch it. 

This is freeking weird...I hate damned Zebras!

Doc 



--

viperdoc(at)mindspring.co
Guest

Posted: Tue Jun 14, 2011 10:20 am Post subject: Detonation

Tj,

Your comments are priceless...and appreciated also. Blast front vs. glow

plug secondary to the heat build-up in the cylinder essentially weakening

the element.  Don't know. Will try to take some pixs of the plugs...maybe

this afternoon...have too many alligators in my office right now...

Did not take the mags or the generator off to change the cylinders or the

intake tubes. Did take the #1, #2 and #3 exhaust stacks off though. They are

not leaking  from what I can tell.

Doc



--

dsavarese0812(at)bellsout
Guest

Posted: Tue Jun 14, 2011 12:32 pm Post subject: Detonation

The mags were not removed or moved because I removed the cylinders for 

Doc.  In fact, I have never, ever removed mags to remove cylinders before.

Dennis



A. Dennis Savarese

334-285-6263

334-546-8182 (cell)

Skype: Yakguy1

www.yak-52.com

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