Compression tester problems.

[Guest]

I picked up this compression tester kit from Harbor Freight:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95187

I got my engine warmed up, got the tester installed on cyl. #1, and noticed that the o-ring was not sealing, it was squishing around like jelly. Seems the o-rings that come with the kit are NOT the high-temp variety.

I tried using the fitting without the o-ring, but wasn't able to get it cranked down enough to prevent pressure from escaping.

I was contemplating wrapping up the threads on the fitting with teflon tape. Good/bad idea?

Suggestions? Solutions?

Thanks in advance.
Matt

[gearhead13]

teflon tape? bad idea. How do you get it back out after??
All 0-rings squish out when tightened too much. Just tighten it enough for a seal but not have it squish out, there is a fine line.

[wkmpt]

Okay, teflon tape is right out.

When I was attempting to check compression, using just enough pressure to seat the o-ring, it sounded like there was pressure squeaking past the o-ring. Is that normal?

[tkent02]

Okay, teflon tape is right out.

When I was attempting to check compression, using just enough pressure to seat the o-ring, it sounded like there was pressure squeaking past the o-ring. Is that normal?

No usually it can get tight enough to seal without being too tight for the o ring to seal.
Try vasoline on the o ring?

Or get a stiffer o ring.

[blowerbike]

install a plug washer on it..snug and test.

[Dogma]

Okay, teflon tape is right out.

When I was attempting to check compression, using just enough pressure to seat the o-ring, it sounded like there was pressure squeaking past the o-ring. Is that normal?

I had the same thing happen. I successfully got compression readings without the o-ring. I have no idea if this activity was the cause of the compression tester fitting jamming in the threads on the way out. The compression washer from an old spark plug might help you get a better seal instead of the o-ring.

As a matter of gland seal design (o-rings) I'm quite surprised that compression tester fittings don't capture the OD of the o-ring, and instead rely on the elasticity and friction of the rubber against the metal. On that note, it might be a good idea to make sure that the head and fitting are clean, dry, free of oil, etc. if you want to keep trying to use the o-ring. Or, wrap the fitting and o-ring with a few wraps of sturdy tape (corded packing tape?) to support the OD of the o-ring. A hose clamp would be more durable, but I'm not sure it would fit in among the head's cooling fins.

Hope that helps.

Edit: on closer reading, I see Blowerbike already suggested the washer from a spark plug. I understand he's pretty experienced in these matters. I'd go with that.

[wkmpt]

Update.

Okay. I got the o-ring to stay in place by wrapping some aluminum tape just past edge of the o-ring. Once tightened down, the tape 'scrunched up' a bit (don'tcha love technical terms!) and really held the o-ring in place. Cool. I'm still going to try to get a spark plug compression washer for next time, though.

Ok, my compression was dead-even across the board at 120psi. Plug #1 was a bit carbon-fouled. Plugs #2&3 were carbon-fouled with a very slight oily sheen over about half of the outer ring of the spark plug. Plug #4 was carbon-fouled with the same oily sheen as #2&3, the only notable difference was that the electrode of the plug looked very clean and slightly brassy.

I'm assuming the carbon fouling is because I'm running rich. Unsure about the oily part, though, and the clean electrode puzzles me.

Posting pics of the plugs shortly.

[TheCafeKid]

Let the plugs dry. If they stay "Wet" looking and dark, then its oil. Gas will evaporate rather quickly and leave a chalky, fluffy or ashy residue if you're simply rich. If the bike hasnt been run in a while, its not out of the realm of possibility that its going to let some oil passed the rings and valve seals. Get it running, dont worry about compression untill you run it for a while, and "re-break in" the motor..

[wkmpt]

Plug#1

Plug#2

Plug#3

Plug#4