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excessive mag drop & warm cyl.

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bwalker11(at)charter.net
Guest

Posted: Fri Apr 28, 2006 4:18 am Post subject: excessive mag drop & warm cyl.

Last July just before OSH I got water in the ignition  wires on my regular 52. After various methods  of drying out the wires, I ended up fouling the champions, so I replaced them  with the Chinese plugs.  ran well with good mag checks but I immediately  noticed a little higher cylinder head temps at various power  settings.  After a few months, I began to experience mag checks  in excess of 3 percent. mag checks degraded to 5 or 6 percent drop on both mags  but the engine ran smooth.  I changed out the ignition harness and  plugs with the kit from Dennis, checked timing, point gaps, and plug  gaps.  The engine starts easy, runs smooth, and develops 100 percent RPM,  but I still get a 5 percent mag drop during a static run up whether before  or after a flight, and cylinder head temps are still 10 to 20 degrees higher  than normal during all phases of operation.  Also compression checked over  70/80 on all cylinders.  I have not measured the valve clearances lately, I  suppose I could have an exhaust valve not opening completely. Any Ideas, anyone ?   Dennis?

  

 Wild Bill

dsavarese(at)elmore.rr.co
Guest

Posted: Fri Apr 28, 2006 4:43 am Post subject: excessive mag drop & warm cyl.

Bill,

 Just a couple of questions first -

 -What did you use to set TDC when you checked/set the  timing?

 -What did you set the timing to?  The spec is 14-16  degrees BTDC as measured at the propeller flange.

 -When you found what degree the points opened with the mag  timing box, did you check to see if the rotor was pointing DIRECTLY at the  scribed mark on the mag boss?

 - When was the last time the mag caps/distribution caps were  replaced?  The condition of the contacts on both the rotor and cap can make  a difference.

 - Have you tried swapping the mags from left to right to see  if the 5% mag drop follows the mag swap?

 - Has anyone made any fuel flow adjustments on the  carburetor?

 - Are you certain you do not have any intake leaks  particularly around the intake gland nuts and their rubber seals which  could cause lean operation and higher CHT's?

  

 Dennis

  

 [quote]   ---

bwalker11(at)charter.net
Guest

Posted: Fri Apr 28, 2006 5:19 am Post subject: excessive mag drop & warm cyl.

 

 [quote]   ---

JBernier(at)dart.org
Guest

Posted: Fri Apr 28, 2006 8:35 am Post subject: excessive mag drop & warm cyl.

Bill

I found it far more accurate to find TDC by making a tool out of an old spark plug. Hollow out the ceramic center, all of the ceramic, and force a steel rod down the center so that it extends beyond the point were the piston would miss it. You determine this distance with the same screw driver. Measure the distance that the screw driver travels into the cylinder at the same angle as the plug would travel when the piston is near TDC. Add about 0.5 inches to the distance. Affix the rod to this distance in the plug by measuring from the flat contact point. You should round the end of the rod so it doesn't nick the piston. I used JB Weld to hold it in place. Be certain that when you rotate the plug that the rod stays centered.  Pull the piston back down by reversing the prop direction, counter clockwise. Insert the new plug and finger tighten. Bring the piston back up in contact with the plug. Slowly. Once this is established read the degrees on the prop hub with a digital level. (They cost about $100 on the internet and well worth it.) Find the angle on the opposite side of the piston travel. Same technique, only with the piston traveling in the opposite direction. You will have to remove the plug, bring the piston beyond TDC, replace the plug, bring the piston back toward TDC until it touches the plug. Measure this angle using the same place on the prop hub. Determine the difference and divide it by 2. Add this to the original measurement for an accurate TDC. To find the advanced angle that the mags need to be set at just add this to your calculated TDC angle. Always set the piston in this position by moving the prop from well before TDC to the determined angle, prop turning in normal rotation. Clockwise as you face it.

It's more work but very accurate.

BTW,  As long as you set the final prop angle by moving it clockwise, prop lash will not be a factor. If you move it counter clockwise it will be a factor and your final piston position will be wrong. 

Good luck.

Jim B 



 	  Quote: 	
		  >> bwalker11(at)charter.net 04/28/06 8:18 AM >>>


	


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BitterlichMG(at)cherrypoi
Guest

Posted: Fri Apr 28, 2006 12:17 pm Post subject: excessive mag drop & warm cyl.

The suggestions for finding TDC and setting timing accurately have already been given and are very good obviously.  What I believe is significant is that both Mags have equal drop, and as they drop increased, they stayed equal through-out the process.  One thing I can say from direct observation and that is, the more advanced the engine timing is, the less the mag drop, and... a retarded engine runs hot.  Just the opposite of what makes sense. So... maybe it IS timing.    

Valve Lash.  There is just no question that valve lash drifts considerably in one year.  In other words, I strongly suspect you have a valve lash issue simply by the statement that you have not adjusted them in awhile.  What is "awhile" ??  I run my engine very hard, and have gotten into the habit of checking them every 6 months or so.  I've also seen a dramatic change in valve lash going from hot to cold.  Opinions vary on how to set lash... most people say: "Medium Warm".   I'd like to hear what Dennis has to say about that personally.  I have measured lash when the engine is HOT HOT HOT... and then have let it go stone cold and have measured it again.  I was agog.... it is a HUGE difference.  Since lash can impact generated power by a LOT... I lean towards setting them HOT.  Of course, it is then hard to set them all the same!  Setting them dead cold at least gets them all the same... assuming the change with heat is linear on all cylinders.  What do you have to say about this Dennis, or anyone else for that matter?    

Mark  

N50YK  

  

     

--

cpayne(at)joimail.com
Guest

Posted: Fri Apr 28, 2006 12:29 pm Post subject: excessive mag drop & warm cyl.

>Bill

 	  Quote: 	
		  I found it far more accurate to find TDC by making a tool out of an old spark plug.

 >
	


 >

 Arrggg!  You guys need to do it right! Either use a 14MM American Time-Rite or the calibrated Russian built dial indicator. Measure *exact* degrees directly off the crank on #4 and set your mags using a "buzz box" synchronizer, with lights of course. Set a 6" rule across the rotor when lining up the firing lead....or use a laser line like I do.

  

 A couple hundred bucks spent on the right tools will more than be compensated with a smooth running engine. Or, find someone with the tools and knowledge to do it for you.

  

 Craig Payne

 Obsessive-Complusive Tuner (OCT)

rvfltd(at)televar.com
Guest

Posted: Fri Apr 28, 2006 12:48 pm Post subject: excessive mag drop & warm cyl.

There have  been several NIB Time Rites on Ebay lately.  I bought one (at) 285.00, great  value as they are over $400.00 new.  There is one or two of them offered at  this time.

  

 

Always Yakin,

Doug Sapp  [quote]   --

viperdoc(at)mindspring.co
Guest

Posted: Fri Apr 28, 2006 5:26 pm Post subject: excessive mag drop & warm cyl.

Makes since to measure the valve lash warm to hot. The engine actually expands with heat. If you measure the circumference of the engine around the baffle pads or even over the valve covers when it is cold and then when it is hot, you will find it has increased in size by 2 inches. If you do not believe me talk to the Kimball's at Kimball's enterprises. They found that out doing custom cowlings for there aircraft that used the M-14.

 Doc

  

 



  

 [quote] ---

Steve Dalton

Joined: 27 Jan 2006
Posts: 8

Posted: Sat Apr 29, 2006 4:31 am Post subject: Re: excessive mag drop & warm cyl.

 	  Quote: 	
		  Last July just before OSH I got water in the ignition wires on my?regular?52. After various methods of drying out the wires, I ended up fouling the champions, so I replaced them with the Chinese plugs.? ran well with good mag checks but I immediately noticed a little higher cylinder head temps at various power settings.?? 	




Ski replaced his Champions with the Russian plugs and his CHT was noticably higher.  The Champions seem to run cold.  That's one reason why they foul so easily at idle.  MMO does help this.   



 	  Quote: 	
		  After?a few months, I began to experience mag checks in excess of 3 percent. mag checks degraded to 5 or 6 percent drop on both mags but?the engine ran smooth.? I changed out the ignition harness and plugs?with the kit from Dennis, checked timing, point gaps, and plug gaps.? The engine starts easy, runs smooth, and develops 100 percent RPM, but I still get a 5 percent mag drop during a static?run up whether before or after a flight, and cylinder head temps are still 10 to 20 degrees higher than normal during all phases of operation. 	




Sounds like the problem developed long after the plug swap, and replacing the harness and plugs did not help.  Because BOTH mags drop equally, it would seem to be a timing problem, ie, you timed them both the same...but wrong.  The higher temps could just be due to hotter plugs than the cold Champions.  Please keep us posted on your fix.



What did you find to be the problem with the TD engine at Sun & Fun?  Hope you're up and running soon.



Steve

dsavarese(at)elmore.rr.co
Guest

Posted: Sat Apr 29, 2006 4:43 am Post subject: excessive mag drop & warm cyl.

If I'm not mistaken, the M14 manual says to set the valve lash  cold.  Spec is .3 mm (.012"), with a tolerance of .25 mm (.010") to .35 mm  (.014").  If one sets the valve clearance slightly on the loose side, say  closer to the .35, that may help with the non-linear metal expansion and provide  overall adequate valve clearances.  As we all know, too tight equals burned  valves.   A couple of key points when checking the valve  clearance:

 1 - be sure to release the lifter spring pressure by pressing  down on the rocker arm adjuster nut and then insert the feeler gauge between the  roller and valve.

 2 - never measure the gap going with the roller.  Always  measure the gap at 90 degrees to the roller for a more accurate  measurement

 3 - a standard feeler gauge with the end slight bent is  typically too long and binds on the valve spring washer when feeling the  measurement.  It is best to shorten the bent end of the feeler gauge to  about 1/2" so it no longer will bind on the valve spring washer when inserted  perpendicular to the roller.

  

 One final thing to check of course would be leaking intake  gland nuts or intake tube collars, which cause lean cylinders.  Immediately  after shutting down, use a laser temperature sensor to measure the heat on each  cylinder.  Always measure at the exact same point on each cylinder, such as  just below the base of the spark plug.   Look for significant  differences in cylinder heat.    You may also be able to move the  probes from the rear plug of #4 to possibly #3 cylinder.  Then see what you  get for CHT.

  

 Just my 2 cents worth -

 Dennis

   

 [quote]   ---

bwalker11(at)charter.net
Guest

Posted: Sun Apr 30, 2006 6:30 am Post subject: excessive mag drop & warm cyl.

Steve,



Same problem with the TD as with my other Yak, water in the ignition wire 

housing.  The rubber sleeves that go to the front plugs will trap water even 

after you  take apart the lower section of the plug caps and drain the 

wires. After taking the harness apart and draining it about four times, I 

got tired of fooling with them and put new wires and plugs on the plane on 

Tuesday after SNF - took about six hours literally - "in the field".  Runs 

great now!  I'll let you know about the fix on the other plane when it 

happens.



By the way, I think the moisture is more of a problem on the older ignition 

wires, even the wire insulation was moist after I pulled it out of the 

harness.  I have'nt seen this problem on the wires Robert has been getting 

from Jill - he had replaced his lower wires - pulled them back through the 

original harness.  We flew through the same rain at the same time and he 

did'nt have a problem.



BW

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