A spark plug extender? WTF for?

JLT · Post by **JLT** » Sat Jan 24, 2009 11:21 pm

Hi, all.

As a few of you know, something bad happened to my engine as I was traveling to BBB. It had all the earmarks of a burned valve ... lotsa noise, lower power, vibration. I'd done a compression test the weekend before, and the results were 140-140-130-140.

I pulled the engine out of the bus today to find out what went wrong, and when I pulled out the number one spark plug, this is what I saw. The upper plug is a normal plug (#4 in this case) and below it is what was in the number one socket:

As you see, it looks like an extension or extender ... in this case, an extender with a muckin' great hole burned into the side of it. The hole shows up nicely when I rotate the plug:

In all my years working on VWs, I have NEVER seen one of these things before, and I can't for the life of me figure out what it was supposed to accomplish except for maybe making the spark plug a little easier to get into the socket. Was there supposed to be some virtue in putting the spark plug electrodes an inch or so farther from the piston head? Was it supposed to prevent burned valves? Considering the dramatic failure mode of the part, I'm not surprised that I haven't seen one before, but why was it in there in the first place?

As it is, I'm tempted to just liberate the spark plug from the "extender" and screw it back into the head to see if it holds compression, but there's a little bit of aluminum at the base of the extender that must have come off the head threads, and since I've got the damn engine out anyway, I might as well take the heads off and see what the domes look like. (I hear my father saying "If you go looking for trouble, son, you're bound to find it.")

Has anybody else come across this sort of gizmo? Do you know the PO might have installed it?

vdubyah73 · Post by **vdubyah73** » Sun Jan 25, 2009 6:39 am

Is it one of those plugs for an engine that burns oil? Helps keep it from fouling?

vwlover77 · Post by **vwlover77** » Sun Jan 25, 2009 7:35 am

I have never seen one, but a little web searching supports Bill's suggestion that it's supposed to prevent the plug from getting fouled by oil.

Does your engine burn oil? Since you've got it out, maybe you can do a leakdown test to see if the rings are bad (before you pull the head!)

JLT · Post by **JLT** » Sun Jan 25, 2009 12:10 pm

vwlover77 wrote:I have never seen one, but a little web searching supports Bill's suggestion that it's supposed to prevent the plug from getting fouled by oil.

Does your engine burn oil? Since you've got it out, maybe you can do a leakdown test to see if the rings are bad (before you pull the head!)

I thought leak-down tests are only informative when the engine is warm. How does one do it with a cold engine? Just screw in the compression tester and hand-crank it a couple of times?

vwlover77 · Post by **vwlover77** » Sun Jan 25, 2009 1:32 pm

A leakdown test is done with an air compressor to supply pressurized air to the cylinder with a special tester like this one from Harbor Freight.

http://www.harborfreight.com/cpi/ctaf/d ... mber=94190

It tells you the general health of each cylinder by how much of the input pressure is lost through leaky rings or valves. You can tell by listening at the intake, exhaust, and crankcase vent where the leakage is occuring.

You turn the engine to get each cylinder at top-dead center (and hold it there so the compressed air doesn't push the piston down) and then perform the test. No need for a warm engine or to turn it over with the starter.

JLT · Post by **JLT** » Sun Jan 25, 2009 2:24 pm

vwlover77 wrote:A leakdown test is done with an air compressor to supply pressurized air to the cylinder with a special tester like this one from Harbor Freight.

http://www.harborfreight.com/cpi/ctaf/d ... mber=94190

Ah. Since I don't have access to an air compressor, I guess I won't be able to use it. But since the compression was good all around until the gizmo blew, I'd assume that the rings, etc. were working as they should have been.

bus71 · Post by **bus71** » Sun Jan 25, 2009 4:28 pm

It looks like the extension used to check compression on some gauge set-ups. You are supposed to remove it, then replace plug.

vwlover77 · Post by **vwlover77** » Sun Jan 25, 2009 5:22 pm

JLT wrote: Ah. Since I don't have access to an air compressor, I guess I won't be able to use it. But since the compression was good all around until the gizmo blew, I'd assume that the rings, etc. were working as they should have been.

Was your engine burning and/or consuming oil??

Colin, would worn valve guides show up in a compression test? I'm guessing not, yet they could allow oil to be drawn into the cylinder to foul the plug, yes?

Or, maybe the PO just hated changing that one plug and installed the extender as a convenience????

JLT · Post by **JLT** » Sun Jan 25, 2009 5:41 pm

bus71 wrote:It looks like the extension used to check compression on some gauge set-ups. You are supposed to remove it, then replace plug.

You get the prize.

And I get the booby prize.

I should have added that the compression tester was new, and that I was using it for the first time. The vital clue was that it was cylinder #1. What's the first cylinder you check for compression?

As I look on the Harbor Freight web site at a picture of my compression tester, I discover to my chagrin that it shows the extension firmly screwed into place at the end. Then I look at the compression tester itself, nestled quietly in my tool box, and

AAAAAAAAAAAAAARRRRRRRRRRRRRRRRGGGGGGGGGGGGGHHHHHH

I never notice that the tester hose was a little shorter after I did #1.

I think I will hang that extension from my rear-view mirror, or at least keep it in the tool tray where I can see it from time to time. It will keep me humble.

JLT · Post by **JLT** » Mon Jan 26, 2009 6:13 pm

One last thing on this thread:

The #1 spark plug didn't survive the ordeal. But a friend who sold her bus found some Bosch W7A spark plugs in her garage and gave them to me. I know that the heat range is different from the W8As that I have now, but can they be used in a 1600 dual port? What are the advantages/disadvantages of using the W7As?

Post by **Amskeptic** » Mon Jan 26, 2009 9:08 pm

JLT wrote:One last thing on this thread:

The #1 spark plug didn't survive the ordeal. But a friend who sold her bus found some Bosch W7A spark plugs in her garage and gave them to me. I know that the heat range is different from the W8As that I have now, but can they be used in a 1600 dual port? What are the advantages/disadvantages of using the W7As?

Type 4 plugs normally cannot be used in a Type 1 engine due to the longer thread reach.
I will be blowing away the chitchat on this thread.
Colin

regis101 · Post by **regis101** » Mon Jan 26, 2009 9:35 pm

The W8AC is physically different than the W8CC. His is a 71

I was looking for the colored chart about thread, reach etc but found this.

http://landiss.com/boschplugs.htm

The A and C have different reach.

JLT · Post by **JLT** » Fri Apr 03, 2009 8:29 am

I was over at the Kombi Haus in Sacramento yesterday, and one of the mechanics told me that when he was changing somebody's spark plugs, he found an unusually high one. You guessed it ... that somebody left the compression tester extender in the cylinder head, the same as I did. Fortunately, he didn't try to drive it twenty miles.

I felt a little better about it then.

The moral of the story is that if you're using a new compression tester, be sure that all of it comes out.

Itinerant Air-Cooled

Itinerant Air-Cooled

A spark plug extender? WTF for?

A spark plug extender? WTF for?

A follow-up of sorts