Not sure what Happened, but here ya go.... - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Hotrodding Basics
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 05-14-2013, 07:33 PM
Member
 
Last photo:
Join Date: Feb 2004
Location: N Ga.
Posts: 384
Wiki Edits: 0

Thanks: 7
Thanked 21 Times in 19 Posts
Not sure what Happened, but here ya go....

I tried to post this as new thread, but somehow it ended up as reply to one of my own threads, totally unrelated. ???

Anyway, Burned exhaust valve. Cast iron seat, Stainless valve, leaded fuel.
Low compression engine (~8.5-1). Compression on that cylinder was 41. Should have been at least 70, the others were 75+. Leakdown proved it to be exhaust valve.
I have an idea as to the cause. But I want to hear from someone else.
I'll post the findings as soon as I find them.
Attached Thumbnails
Click image for larger version

Name:	DSCN6017[1].JPG
Views:	155
Size:	123.5 KB
ID:	74019  

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 05-14-2013, 07:48 PM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 60
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 598 Times in 547 Posts
Wazzit (type of engine, etc.)?

70 is still low if you're talking psi.

Valve adjusted too tight will overheat/burn/warp an exhaust valve due to insufficient seat time...
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 05-14-2013, 08:12 PM
Richiehd's Avatar
JS-70
 
Last photo:
Join Date: Jun 2011
Location: Jupiter FL
Posts: 913
Wiki Edits: 0

Thanks: 229
Thanked 66 Times in 58 Posts
Quote:
Originally Posted by cobalt327 View Post
Wazzit (type of engine, etc.)?

70 is still low if you're talking psi.

Valve adjusted too tight will overheat/burn/warp an exhaust valve due to insufficient seat time...
.
Agreed.
but possibly A vacuum leak on that one cylinder . How many miles on this motor?

Is this a test?
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 05-15-2013, 05:21 PM
Member
 
Last photo:
Join Date: Feb 2004
Location: N Ga.
Posts: 384
Wiki Edits: 0

Thanks: 7
Thanked 21 Times in 19 Posts
70 is good using a differential pressure guage. 80 psi is about the max that a person can keep the crank from turning. so holding 70/80 is pretty good. It's a leakdown test, you can listen where the air is escaping, and determine what's wrong.
In this particular case it's a 360 cubic inch aircraft engine. Has 550 hours since rebuild. (should have gone over 2000 hours)
Found the trouble to have been caused by a combo of two things. #1 leaded fuel, and #2 valve guides on the tight side, but still within allowance.
Lead buildup on the valve stem, caused stickin' valve, thus causing burned valve. (note the discolored stuff on the intake valve That's lead)
That's ok because he can get a complete cylinder assembly New from the engine manufacturer, including new piston, and rings, for about $1100 +/- a few bucks.
Now just exactly how izzit that lead is supposed to prevent valve troubles?
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 05-15-2013, 07:41 PM
Registered User
 
Last photo:
Join Date: Apr 2007
Location: Seattle, Wa
Posts: 7,088
Wiki Edits: 0

Thanks: 4
Thanked 539 Times in 455 Posts
Quote:
Originally Posted by st3gamefarm View Post
70 is good using a differential pressure guage. 80 psi is about the max that a person can keep the crank from turning. so holding 70/80 is pretty good. It's a leakdown test, you can listen where the air is escaping, and determine what's wrong.
In this particular case it's a 360 cubic inch aircraft engine. Has 550 hours since rebuild. (should have gone over 2000 hours)
Found the trouble to have been caused by a combo of two things. #1 leaded fuel, and #2 valve guides on the tight side, but still within allowance.
Lead buildup on the valve stem, caused stickin' valve, thus causing burned valve. (note the discolored stuff on the intake valve That's lead)
That's ok because he can get a complete cylinder assembly New from the engine manufacturer, including new piston, and rings, for about $1100 +/- a few bucks.
Now just exactly how izzit that lead is supposed to prevent valve troubles?
A low compression, air cooled, valve sticking airplane motor and your surprised by a burnt valve?

Lead in fuel was found to prevent seat erosion. But, it also contributes to sticking valves by both gumming up the lower part of the guide and stem as well as by contaminating the oil which gets into the upper guide. Add that to typical hotter valve temps of an air-cooled engine vis-a-vis a liquid cooled with a little tight guide clearance and you've got a recipe for a sticking valve. Then add to that an airplane motor, like a boat motor, works a lot harder than the typical car motor. Take off power, everything its got till you’re a up a ways, climb power, almost everything its got till you get to altitude which might be a while, cruise power what 60-70 percent of everything's its got till you throttle back for descent. If you operated the typical car engine that way it would be junk and a couple months.

Is this low lead av gas or something else? And I guess with such a low compression motor why lead at all?

Bogie
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 05-16-2013, 05:48 PM
Member
 
Last photo:
Join Date: Feb 2004
Location: N Ga.
Posts: 384
Wiki Edits: 0

Thanks: 7
Thanked 21 Times in 19 Posts
Quote:
Originally Posted by oldbogie View Post
A low compression, air cooled, valve sticking airplane motor and your surprised by a burnt valve?
Never said I was surprized by that, happens all the time.

Quote:
Lead in fuel was found to prevent seat erosion. But, it also contributes to sticking valves by both gumming up the lower part of the guide and stem as well as by contaminating the oil which gets into the upper guide. Add that to typical hotter valve temps of an air-cooled engine vis-a-vis a liquid cooled with a little tight guide clearance and you've got a recipe for a sticking valve. Then add to that an airplane motor, like a boat motor, works a lot harder than the typical car motor. Take off power, everything its got till you’re a up a ways, climb power, almost everything its got till you get to altitude which might be a while, cruise power what 60-70 percent of everything's its got till you throttle back for descent. If you operated the typical car engine that way it would be junk and a couple months.
We understand all that. But given the higher temps, one would think the lead would be scavenged better.

Quote:
Is this low lead av gas or something else? And I guess with such a low compression motor why lead at all?

Bogie
Running 100LL. Which contains more lead than old leaded premium car gas.
The only reason for running it in the 8.5:1 engines is that the STC to allow car gas, specifies that it must contain exactly 0% alcohol, and must be tested for it (simple to do), But that's not readilly available just anywhere any more.
Apparently lead is the only approved antiknock compound approved by th' manufacturer.
What prompted this thread, was the fact that a friend carried a set of 289 ford heads in to be worked. And the guy at the shop told him that If he didn't install hardened seats, or run lead additive in the fuel, he could not warrenty against burned valves within 10k-12k miles.
Airplane engines running mid grade unleaded, (alcohol free) have none of these problems, like sticky valves, fouled plugs, grey goo in the oil, sticky grey stuff on the underneath, etc.
Most all of them have hardened seats of one kind or other.
With a bore and stroke of 5.125"(bore) and 4.375" (stroke) and a ratio of 8.5:1 the actual compression using an automotive typ compression tester, is pretty high, (plugs pulled, turning with starter, 3 rounds) about 145-150.
I would expect it to be higher when idling at ~600 rpm.

Anyway, why would someone reccomend using lead additive, to prevent burned valves, when lead deposits, cause the sticky/burned valve trouble.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 05-17-2013, 12:36 AM
Semper Gumby
 
Last photo:
Join Date: Feb 2007
Location: Vancouver, BC
Posts: 335
Wiki Edits: 2

Thanks: 166
Thanked 201 Times in 163 Posts
One of the "everyone knows that" areas of "common knowledge' (which means "usually wrong") is that the lead was the lubricant for the exhaust valve. (oil would be burned off due to the temps of the valve) so only lead would do the job to provide a "babbit bearing" sorta lube for the valve stem and for the actual valve as it rises out of and sets back into the seat.

Tetraethyl lead was a main component in raising the octane of gas from the abysmal levels of pre-WWII to the stuff that hi-po engines could actually use.

When lead was abolished from gas in the 70's, many engines experienced valve recession and some also had greatly increased wear on valve stem guides and so the "common knowledge" came about.

I assume this is a Lycoming IO-360? (The one I owned for a while in a PA-28 was the 150 hp version and only needed 80/87 fuel) As I recall, the 100LL usually lead-fouled the plugs something fierce, but was a compromise fuel supposedly better than the (then common) 100/140
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 05-17-2013, 08:25 PM
Member
 
Last photo:
Join Date: Feb 2004
Location: N Ga.
Posts: 384
Wiki Edits: 0

Thanks: 7
Thanked 21 Times in 19 Posts
Quote:
Originally Posted by Dave57210 View Post
One of the "everyone knows that" areas of "common knowledge' (which means "usually wrong") is that the lead was the lubricant for the exhaust valve. (oil would be burned off due to the temps of the valve) so only lead would do the job to provide a "babbit bearing" sorta lube for the valve stem and for the actual valve as it rises out of and sets back into the seat.

Tetraethyl lead was a main component in raising the octane of gas from the abysmal levels of pre-WWII to the stuff that hi-po engines could actually use.

When lead was abolished from gas in the 70's, many engines experienced valve recession and some also had greatly increased wear on valve stem guides and so the "common knowledge" came about.

I assume this is a Lycoming IO-360? (The one I owned for a while in a PA-28 was the 150 hp version and only needed 80/87 fuel) As I recall, the 100LL usually lead-fouled the plugs something fierce, but was a compromise fuel supposedly better than the (then common) 100/140
O-360, not IO-360. (not fuel injected) The 150 hp in your Cherokee would have been an O-320. Actually, had this engine been an I0, the valve probably would not have been sticking as much. Due to better fuel metering.
The point that I was trying to make is to not fall into the OWT of lead in your fuel being beneficial to your engine. It is not, and never will be.
They quit makin' 80 octane avgas back in the very early '70s. An I haven't seen th' green stuff in as many years. so 100LL is all ya get, Some places offer mogas, but it's not legal to run it without the STc, and not all engines can get it, and in some cases, while you can get the STC, compliance is cost prohibitive. In some cases the STC is a simple matter of buying the paperwork, and a logbook entry. In other cases, it's all that plus extra fuel pumps, and different hoses, etc. And in other cases, it's not even available.
Nowadays, it's a moot point due to the alcohol in car gas. Which is a huge no-no in aircraft.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 05-18-2013, 01:40 PM
T-bucket23's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Engine basic condition - how to check Last photo:
Join Date: Aug 2005
Location: Massachusetts
Age: 57
Posts: 5,362
Wiki Edits: 26

Thanks: 9
Thanked 145 Times in 128 Posts
Loose spark plug can also cause burnt valves. allows cold outside are to be sucked into the cylinder which causes some thermal issues and leans the mixture way out.
__________________
Artificial Intelligence is no match for Natural Stupidity



Chet
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 05-18-2013, 02:15 PM
vinniekq2's Avatar
Registered User
 
Join Date: Jun 2012
Location: BC,Canada
Age: 56
Posts: 8,640
Wiki Edits: 0

Thanks: 364
Thanked 858 Times in 820 Posts
If its carbed(o-360) then how is the mixture set? is the E.G.T. guage accurate and in what cylinder?Has there been any mods to the cowl? The rear cylinders can run hotter.If the aircraft is a homebuilt like a lancair/glassair then over heating of the rear cylinders can be attributed to many things under the cowl.
not enough information about the plane and how the EGT is monitored. Long x country trips may need multiple adjustments to make up for air temp and angle of attack as fuel burns off. also humidity,of carb heat was left turned on,,,,,,,,
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 05-18-2013, 07:33 PM
Member
 
Last photo:
Join Date: Feb 2004
Location: N Ga.
Posts: 384
Wiki Edits: 0

Thanks: 7
Thanked 21 Times in 19 Posts
This is a normally aspirated Lyc, o-360. installed in a certified aircraft. Leaned IAW Manufacturer specs.
No EGT gauge. Due to the rising cost of fuel, leaning has become a "must do" kind of thing.
Had it been an IO-360, it could have been run "lean of peak" which would have done a better job of scavenging the lead, and not caused the fouling which led to the sticky/burned valve.
For those not familiar with "lean of peak" operations. The object of the game, is to lean the mixture untill the EGT peaks, (highest temp) then continue to lean untill it drops, by some amount (between 10 and 20 degrees). Problem is that carburetted engines, can't do that. There will be one cylinder running way rich, and one cylinder running way lean, and the others falling somewhere between, and one of those will be right at peak. With fuel injection, (port, not TB) you can get an even fuel flow to all cyls. Then you can successfully run LOP. Cars do it with a computer, and myriad sensors, piston single aircraft do it with a knob on the insrument panel, and an EGT gauge. Generally, once you reach your cruising altitude, you lean the fuel mixture untill the EGT gauge reaches it's highest temp, then continue to lean, untill the temp falls back down by some number of degrees. As long as all cylinders are running within a few degrees of each other, all is well.
Problem is with a carburetted engine, you cannot get all cylinders running at the same temp, so you must run them all rich. (some richer than others) Generally the ones that present the worst lead fouling problems are the ones running the coolest. Not running hot enough to burn off (scavenge) the lead, and the lead gets deposited in places that it does not need to be, such as valve stems.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 05-18-2013, 08:13 PM
vinniekq2's Avatar
Registered User
 
Join Date: Jun 2012
Location: BC,Canada
Age: 56
Posts: 8,640
Wiki Edits: 0

Thanks: 364
Thanked 858 Times in 820 Posts
why would there be no EGT guage? without an EGT there can only be a guess as to exhaust temp(s)
I ask a gain what type of A/C? cowls can cause cooling issues.If your comments were directed at me?
(For those not familiar with "lean of peak" operations.)I do understand and thats why I asked where the EGT sensor was located.
Is this your A/C? lots of the A/C engines still use sodium cooled exhaust valves.also if run at higher altitudes,the engine does not run very hot at all,for obvious reasons: sub zero temps and 40% loss of power or more
Reply With Quote Quick reply to this message

Recent Hotrodding Basics posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
What happened Henry Highrise Hotrodders Site Suggestions and Help 30 09-20-2012 09:26 PM
What happened? 47 Coupe Body - Exterior 9 12-21-2008 08:52 AM
What Happened? NAIRB Electrical 4 12-09-2004 04:40 PM
So what really happened? 1meancuda Hotrodders' Lounge 31 07-27-2004 01:19 AM
What happened while I was gone? Cruiseomatic Hotrodders' Lounge 5 02-05-2004 09:09 PM


All times are GMT -6. The time now is 06:46 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.