Compression Testing Questions

[87Superdupra]

So I have to test my engine and I'm not sure if I'm doing it right. TSRM said to Pull all spark Plugs, Pull Fuel pump fuse, block throttle open and test one at a time. When I try to start it it sounds like the starter just winding out. How do I do this correctly?
Also I just realized that I was sold one different size spark plug and did not catch it, it has been installed for a while. The regular size park plugs do not screw in anymore. What kind of a pain in the ass am I looking at on that front?

 

[koulee]

Wow, one different size spark plug...

I would get that taken care of first before attempting to compression test the motor.

 

[87Superdupra]

So How do I get that taken care of? Does that mean a new head? I compression tested the motor by the way and it looks like
1 80 (What the Fuck!??)
2 Comp Tester no longer screws in here.
3 160
4 158
5 160
6 160
Now I wanted to comp test my engine origonally becuase I was told my car was idling on 5 cylinders and My cyl number 5 spark plug was BLACK. My friend told me to first pull the spark plug wire while the engine was running and see if that made a difference. So I did...Cyl. 5 is not firing, but has good compression. When I pulled Cyl. 1 Plug out the engine chugged and slowed down (obviously firing!). Why is Cyl.1 Firing so little compression and Cyl. 5 is not?

 

[supra90turbo]

Yeah it's gonna sound like the starter is just winding out. Are you getting a reading on the gauge? It's gonna pump the gauge up to the highest point that the cylinder can compress the air to. Let it go about 3 revolutions, stop. Write down the number and go down the line. ::edit:: never mind...

How do you not notice when you're installing a spark plug that's too big?
If its big enough that it's to the point that the threads in the head are junk, then you must've really been muscling that thing in...

You should be able to helicoil the hole back to the stock size.

 

[87Superdupra]

Okay How do I "Helicoil" the plug back in? Second, It was the first time I had changed plugs on this relitivley new to me car Plus the plugs came in one box all the same part numbers, everything the exact same except for the width:3d_frown: . My friend was handin me plugs and I just tightened them down. Could a Cylinder fire with such low compression( 80 lbs)?

 

[starscream5000]

I find that amazing, never heard of someone trying to put a bigger spark plug than would fit into a head, and actually making it fit! That person needs to stay away from cars IMO.
Edit: How much larger was that plug?

 

[87Superdupra]

I find that amazing, never heard of someone trying to put a bigger spark plug than would fit into a head, and actually making it fit! That person needs to stay away from cars IMO.

Don't waste my time talkin shit. The damn plug is a very close in size and has Identical numbers to that of all of the other plugs printed all over it. Also I must not know my own strength becuase It was not hard to tighten it in there...AT ALL. Just trying to fix my mistake anybodys advice is appreciated. Not familiar with this helicoil method, what is it?

 

[billspreston01]

the wrong spark plug is bad, but there have been many cars I've worked on in my life where the spark plug (of the right size) was cross threaded. To try and make sure you don't have this problem again I would suggest:

1) never-seze (anti seaze...whatever) on the THREADS (don't make a mess)
2) use a spark plug socket (if you have one....I would get one, it's easier)
3) put the socket on a 6" extension and put the spark plug in BY HAND (aka: without the ratchet/breaker bar/torque wrench...whatever you're using). You should be able to get it almost all the way in that way. If it's not going in easy use a small ratchet but don't apply a ton of pressure. If it's taking anything more than a minimal amount of pressure then something is wrong and you probably need to clean the threads, you have it cross threaded, or it's the wrong size.
4) torque them down to the proper spec.

do a search for "helicoil". A lot of people (including me) use them for the exhaust mani studs since they like to strip out a lot.

Drill the hole bigger, tap it a bigger size, and then install a 'helicoil' looks kinda like a spring. the outside has the threads that you just tapped, and the inside has the threads that you need to get the spark plug, stud, screw, bolt whatever in there.

If/when you try this, you're gonna get a LOT of aluminum shavings down into your cylinder so you'll probably have to take the head off to do it.
Add 1tbsp of oil to cyl 1 and compression test again. If the number goes up then it's probably piston rings. if it doesn't change then you've got a) REALLY bad rings or b) valve stuck open, melted....whatever.

 

[JustAnotherVictim]

Okay How do I "Helicoil" the plug back in? Second, It was the first time I had changed plugs on this relitivley new to me car Plus the plugs came in one box all the same part numbers, everything the exact same except for the width:3d_frown: . My friend was handin me plugs and I just tightened them down. Could a Cylinder fire with such low compression( 80 lbs)?

Search Helicoil you'll find what you need, you'll have to remove the head to do it or else you'll blow a piston.
Yes a cylinder can fire low compression.
How did you not notice the spark plug? Spark plugs should slide in no problem.

 

[starscream5000]

Don't waste my time talkin shit. The damn plug is a very close in size and has Identical numbers to that of all of the other plugs printed all over it. Also I must not know my own strength becuase It was not hard to tighten it in there...AT ALL. Just trying to fix my mistake anybodys advice is appreciated. Not familiar with this helicoil method, what is it?

No disrespect intended, I just thought that the spark plug was like WAY larger than the stockers. If you helicoil it you would prob have to pull the head due to metal shavings.

 

[IJ.]

If it had the same numbers it was the same plug it's just a stripped plughole.........

If you go helicoil be very careful NOT to let anything drop into the plug hole while tapping, get some High Temp wheel bearing grease and put some in the Tap grooves to catch the swarf.

Tap a full turn remove the tap clean it add some grease then tap another turn repeating until it's done, be extra careful when screwing the Coil in to make sure it's square and I have NFI how you're going to break the drive tang off without dropping it in the cylinder...

I guess what I'm trying to convey here is I wouldn't helicoil a head on a motor, I'd do it on a bench so I could cleanup and make sure the coil isn't hanging into the chamber pretending to be a glowplug..

 

[johnathan1]

What did you mean byt "compression tester would not screw into #2"? Is it stripped out, or are the threads in the head too big? If it's because the threads are too big, then maybe you could just insert a helicoil that is the same size as the spark plug you put into it, and go back to stock size? Or maybe just use the same plug for now, until you can fix it? How was compression with the oversized plug in?

 

[souprat]

^^dont always like to read the thread do ya?

yeah 80 psi=no good. if it were me i would look into that first to see if teh engine is worth fixing. for example if its something in the head causing such bad compression(burned/stuck valve) than i would pull the head and fix that and also do the helicoil while i was there. but if your rings are toast then i would start sourcing a motor. or whip out the 'ol credit card and prepare for a build.

 

[johnathan1]

^^dont always like to read the thread do ya?

I DID read the whole thread. I was just trying to offer some help! Sorry, if I made anyone mad...jeez.

 

[mrnickleye]

I DID read the whole thread. I was just trying to offer some help! Sorry, if I made anyone mad...jeez.

Well...you made me sssoooo mad, that I'm going to bed !!!!!!:icon_evil Right after this info.......

But...souprat is correct about 80 psi problem. Sounds like you have a burnt valve (the most common 'low-compression' cause). You'll probably end up pulling the head and sending it to the machine shop, so they can repair the sparkplug holes too.

Also, back in the day, at Toyota for 4 years, I had to helicoil many stripped sparkplug holes. I did this right on the cars, with no later problems.

Previous hack mechanics messed them up by removing the plugs (tuneup ?) when the engine was still too hot, or crossthreading the new ones. The aluminum swells up, and the threads get very tight on the plug. Over tightening them will tear the threads right out.



Have the cylinder at the top dead center, then....
Do the helicoil dry, and then use a small diameter(but as big as will go into the hole) & slightly flexible hose attached to a strong shopvac, and vacuum out the cylinder. I used a clear hose from hardware store.

Cut the end of the hose at a slight angle so it won't sit flat on a surface. This allows vacuum air to flow and not 'suck' to the piston.:biglaugh:

You could / should also have a friend hold the hose beside the drill and tap to help keep as little as possible from falling into the hole.:biglaugh:

 

[billspreston01]

OR you could just check the threads on the spark plug and if you do have 1 different plug, try and figure out what it's for...and from now on buy 5 supra plugs and 1 xxxx plug haha. Just make sure it's the same as the other 5 with different threads.

 

[Boss302]

if it is the same part# on the plug it was just crossed threaded i would bet my life on it cause think if it's too big of a thread even a little its not gonna go in try threading a 10mm by 1.50 thread into a 10mm by 1.25 its a VERY small difference in size but it's huge in effect cause it will thread for a bit till it gets past the tip then it won't thread anymore try just re-tapping the original hole first before you make a bigger one. thats my opinion.

 

[87Superdupra]

I searched the plug and everynumber is the same on the plug its just noticeably wider when all the plugs are laid out.:dunno:

 

[IJ.]

If that is the case get the plug company to pay for the repairs...