Compression test Qs

[BlackVert]

1. The directions say to hook up a battery charger so it cranks the same way every time. I just got a charger and it has 3 settings: 2A, 6A for charging, and 75A for starting. Which setting should I use?

2. To disable the spark, can I just disconnect the middle wire on the distributor cap?

3. A guy on corral said the test results can tell you if it is valve guides or not. How?

:SNSign:

 

[HISSIN50]

Chris, you're stuck with me posting on your thread again.

1). I'd use 6 amps.

2). I suppose you could (I haven't done it like that - perhaps others have) because I dont like for the coil to have no where to dissipate the energy it produces.


3). When you do the dry and then wet test, that can suggest to you how the rings are doing (the comparison is what allows this). I suppose the Corral guy figured that deductively the valve guides were what is left as the source of leakage (if wet and dry are the same), which I disagree with. That would be where the leakdown test comes into play - it allows you to pinpoint the source of issues in the motor much better.

You can have decent compression numbers but the leakdown is disappointing. But in your case, we're not really lookin for finding out exactly how the engine is sealing, but rather finding what the issue is with your car (so it runs well - you can make a leakdown tester at your leisure if you desire once it runs better). In other words, the comp. test should provide adequate data for this situation.

Do have the motor be hot. It's not as critical on a hypereutectic-slugged mill as it is on forged (coefficient of expansion) but it's more accurate when hot.

Good luck bud.

 

[BlackVert]

Chris, you're stuck with me posting on your thread again.

1). I'd use 6 amps.

2). I suppose you could (I haven't done it like that - perhaps others have) because I dont like for the coil to have no where to dissipate the energy it produces.


3). When you do the dry and then wet test, that can suggest to you how the rings are doing (the comparison is what allows this). I suppose the Corral guy figured that deductively the valve guides were what is left as the source of leakage (if wet and dry are the same), which I disagree with. That would be where the leakdown test comes into play - it allows you to pinpoint the source of issues in the motor much better.

You can have decent compression numbers but the leakdown is disappointing. But in your case, we're not really lookin for finding out exactly how the engine is sealing, but rather finding what the issue is with your car (so it runs well - you can make a leakdown tester at your leisure if you desire once it runs better). In other words, the comp. test should provide adequate data for this situation.

Do have the motor be hot. It's not as critical on a hypereutectic-slugged mill as it is on forged (coefficient of expansion) but it's more accurate when hot.

Good luck bud.

It is an honor to have you post on my threads. You always provide great info.

1. OK 6A it is

2. So how would you disable the ignition then?

3. Got it.

To be warmed up, can i just let it idle for like 5 minutes?

 

[urban96]

might wanna pull the fuse for the fuel pump too so the injectors dont squirt

 

[Therian]

It is an honor to have you post on my threads. You always provide great info.

1. OK 6A it is

2. So how would you disable the ignition then?

3. Got it.

To be warmed up, can i just let it idle for like 5 minutes?

Chris...

I agree with JT...75A is overkill...I'd prefer 12A, but 6A will do the job easily.

I usually pull the fuel pump harness in the trunk to ensure that the engine doesn't start...pulling the fuse works just as well

I usually start the car, rev it to 2000rpm and keep it there for a minute and a half...that will warm it up sufficiently

 

[BlackVert]

Actually, it is 12A, I forgot that I got the better charger.

It sure is a pain working around these damn equal length headers, especially when they are hot

 

[bill302]

click on link below,heres some good info on compression testing...
http://www.pumaracing.co.uk/comp.htm

 

[BlackVert]

3 hours later ...

#1: 135 dry, 135 wet
#2: 155 dry
#3: 140 dry
#4: 160 dry
#5: 146 dry
#6: 160 dry
#7: 145 dry
#8: 165 dry

ok, now what? do i need to do the others wet too?

 

[HISSIN50]

I wouldnt bother with wet numbers if this is a stock bottom end - the dry [absolute] numbers look decent (I expected a bit of spread since you were forced induction). I dont see the spread causing an issue. That's more spread than one wants to see but your issue would seem to be elsewhere.

I'll re-read the other thread to see if something jumps out.

It took some time but now you know you got decent compression - that's big.

 

[BlackVert]

yes it is a stock bottom end.

so the bottom end may not need a rebuild after all? that would be excellent.

fwiw, plugs 1-7 all look like they are covered with some light colored powder. plug #8 has what looks like oil on it. i'll take pics tomorrow if anyone wants to see them.

 

[BlackVert]

so i should have a leak-down test done then to see if the oil is coming through the valves?

or what should i do next to figure out where the oil is coming from?

i am also going to replace my pcv valve and try to figure out if there is a splash plate on the underside of the lower.

 

[HISSIN50]

Chris, I forgot - thank you for the kind thoughts in an earlier post. I feel the same way about almost everyone on here who replies to my questions too !

I might be missing the boat a bit but my couple thoughts...............

A leakdown test is great to check the condition of overall sealing in a motor - it's awesome to do before bolting on a blower to make sure it can take the extra cylinder pressure.

Now you had something go haywire and start making chitty noises. Without hearing it and just being there (it's hard enough to diagnose stuff like that in the flesh), it's hard to say what it could be or where I'd start. But for an issue like that, I dont think a leakdown test is going to help.

On your Corral thread, people saw your compression numbers but perhaps didnt know the underlying reason for checking compression, so they mentioned doing a leakdown test (I would have too, if you simply were wondering how the motor's sealing up, absent knowing of an underlying issue for the testing).

I think you had a ticking/pinging noise but it wasnt like detonation (it wasn't knocking, was it)?

My next step might be to drain oil and check for bad things in it. If you can cut open the filter, that's not a bad idea. I'd do that if you think a hard part took a dump.

If you think a rocker or something let go, well, I'd check that up top.

It's been a couple days since I read your thread and I just got back in from working outside for hours, so I'm a little dingier (word?) than normal. Grady and the other wise folk might have some better ideas for ya. I just start checking everything that I can think of (that isnt a royal pain to do) to look for clues.

Does it still make noise (like when you warmed it up for the comp. test)?

Good luck and bump Chris.

EDIT: I'm not sure I'd look at the oil control as being the issue if you've been drinking oil for a bit now and didnt have the pinging issues. I would certainly address that at some point, but it might not be a primary cause of the noise (though excessive oil in the chambers can cause detonation..............).....

 

[BlackVert]

Chris, I forgot - thank you for the kind thoughts in an earlier post. I feel the same way about almost everyone on here who replies to my questions too !

I might be missing the boat a bit but my couple thoughts...............

A leakdown test is great to check the condition of overall sealing in a motor - it's awesome to do before bolting on a blower to make sure it can take the extra cylinder pressure.

Now you had something go haywire and start making chitty noises. Without hearing it and just being there (it's hard enough to diagnose stuff like that in the flesh), it's hard to say what it could be or where I'd start. But for an issue like that, I dont think a leakdown test is going to help.

On your Corral thread, people saw your compression numbers but perhaps didnt know the underlying reason for checking compression, so they mentioned doing a leakdown test (I would have too, if you simply were wondering how the motor's sealing up, absent knowing of an underlying issue for the testing).

I think you had a ticking/pinging noise but it wasnt like detonation (it wasn't knocking, was it)?

My next step might be to drain oil and check for bad things in it. If you can cut open the filter, that's not a bad idea. I'd do that if you think a hard part took a dump.

If you think a rocker or something let go, well, I'd check that up top.

It's been a couple days since I read your thread and I just got back in from working outside for hours, so I'm a little dingier (word?) than normal. Grady and the other wise folk might have some better ideas for ya. I just start checking everything that I can think of (that isnt a royal pain to do) to look for clues.

Does it still make noise (like when you warmed it up for the comp. test)?

Good luck and bump Chris.

EDIT: I'm not sure I'd look at the oil control as being the issue if you've been drinking oil for a bit now and didnt have the pinging issues. I would certainly address that at some point, but it might not be a primary cause of the noise (though excessive oil in the chambers can cause detonation..............).....

thanks again.

what is the difference between pinging and knocking? I always thought they were the same ... it did sound sort of like a knock ... ?

i have only heard the noise when near (and at) WOT; ie - when the engine is working really hard.

and i still haven't gotten my new plugs back in. my old plugs were (are) 2 ranges cooler, still from my blower days. i got new ones today and a gap measurer; i hope to get them in tonight.

 

[HISSIN50]

Pinging is generally a lighter noise. To my ears (which have seen too many years of riding loud bikes with no helmet, and my old roadster with sidepipes), it's pretty much like the old analogy of 'marbles rattling in a glass jar'. It's a high pitched sound.

Knocking generally comes from the piston down. In your case, it'd probably be rod knock. That's where you can look in your oil for metal. Bad rod clearnances generally shows up as low oil pressure on a hot motor (pressure is resistance to flow, and excessive rod clearances lead to a lack of resistance, ergo a lack of pressure. Especially when oil is less viscous [hot]).

A knock is a deeper sound than pinging/detonation/pre-ignition.

 

[BlackVert]

That makes sense. I wouldn't be surprised at all if that is what it is. Would bad rod clearances also provide an explanation for the massive smoking I had the other night at 3/4-full throttle?

That sort of problem sounds like something that would require the bottom end to be rebuilt. Yes/No?

 

[BlackVert]

the plugs:

They were in with the KB. And I have driven the car a couple hundred miles with them after I took the KB off. IIRC, they are 1 range colder than stock

#4 broke when i was taking it out.

#7 is newer than the others because it broke when i was replacing my spark plug wires about 2 months ago.

#8 has oil on it, unlike the others.

what can you tell, if anything, from them?

 

[urban96]

if you think your sucking oil in the PCV you could put in one of those air/oil filters that many people here run (myself included)

you can make one for about $15 worth of parts. a husky air/oil seperator from home depot (9-$10) the little barbs (dunno if thats the right term for em) ($2) and some vaccume hose

 

[HISSIN50]

I can't make out the pic real well in terms of shading. Are the electrodes really as white as they appear (to me)?

We like to see more of a brownish/tan........ But I wonder if the background isnt screwing me up.

Any more info on how it ran while you warmed it up for the testing or more info on the noise it was making.............?? Some of the smart folks like Grady might have some ideas if we heard more.

I'd almost say to just run a breather or two for a bit to see how that affects things. Is the line from the oil filler to the CAI oilly inside? If it is, that's a clue that the PCV is overwhelmed.

Random thoughts.
Good luck.

 

[94-302-vert]

It does look like there is material depositing itself onto the plugs in that picture. Is that an accurate statement?

 

[BlackVert]

just pulled the #8 plug after maybe 250 miles max and it is covered with oil, again. my problem is definately there. i'm working on pulling the heads to have a look at the cylinder wall