: Expected Cylinder Compression Values



nebulosity
08-01-13, 01:05 PM
Does anyone know what the expected cylinder compression values are for an '84 deville (4.1L)? I can't seem to find it in my shop manual.

Right now, one of the biggest problems with my Caddy is the serious lack of power; I can't seem to get it to go faster than 30 or 35 mph, and it's acceleration is really slow. I've been doing a bit of research on possible causes, and I know the compression in one of my cylinders was really not good, but I sort of expected that even still, I should be able to get it running well enough so that I can go have it emissions tested and licensed to give me time to plan more expensive and time consuming repairs.

So I got to thinking... what if the compression in my engine really wasn't satisfactory and is the major contributor to lack of power? Here are the compression test results we got last fall.

Cyl #1: 115psi
Cyl #3: 105psi
Cyl #5: 60psi
Cyl #7: 100psi
Cyl #2: 120psi
Cyl #4: 120psi
Cyl #6: 80psi
Cyl #8: 115psi

Relative to the highest values, Cylinder 5 is really crappy, cylinder 6 isn't much better, and I'm not sure what they're ACTUALLY supposed to be. I know I'm going to need an engine rebuild, but I really NEED to be able to get it licensed to give me more time to work on it (save money, make a plan, find a shop or do it myself, etc).

csbuckn
08-01-13, 01:51 PM
Its not really the numbers, it's the difference between them. There shouldn't be more then like 20% difference or something like that. Unfortunately, yours doesn't look too good with a 50% difference in one cylinder.

outsider
08-01-13, 01:51 PM
According to this post: http://www.cadillacforums.com/forums/ht4100-4-1-4-5-4/28786-pulled-plugs-compression-test-pics.html

Should be between 140 and 160.

I (thankfully) do not have any ht4100 engines so I can't tell you for sure but that sounds more inline with what I would expect.

nebulosity
08-01-13, 01:58 PM
According to this post: http://www.cadillacforums.com/forums/ht4100-4-1-4-5-4/28786-pulled-plugs-compression-test-pics.html

Should be between 140 and 160.

I (thankfully) do not have any ht4100 engines so I can't tell you for sure but that sounds more inline with what I would expect.

Thanks for helping me find that post! I forgot about the ht4100 forum. I need to visit there more.

Kinda sounds like I really need new rings...... :(

----------


Its not really the numbers, it's the difference between them. There shouldn't be more then like 20% difference or something like that. Unfortunately, yours doesn't look too good with a 50% difference in one cylinder.

Yeah. I wonder how much my power is affected by the differences in compression in the cylinders.

You know, I'll have to do another test when I get the Caddy back (unless the guys at the shop decide to do it). It was my first compression test -- I'm assuming you can't really do them wrong, right? o__O

cadillac kevin
08-01-13, 02:23 PM
Sounds like you have a 6 cylinder ht4100....not good.

nebulosity
08-01-13, 02:29 PM
Sounds like you have a 6 cylinder ht4100....not good.

Yeahh. :( i just don't have a driveway to be able to fix it. we'll see what Larry's (the shop) says.

Aztec ETC ECS
08-01-13, 05:01 PM
Kinda sounds like I really need new rings...... :(
More likely valve leaks. Put compressed air into the plug hole with the valves closed.
Take the air cleaner & oil cap off and listen for air. TB or exhaust- valves. Oil fill- rings.

I've seen engines w/broken rings have more than 80lbs.

nebulosity
08-01-13, 05:11 PM
I've seen engines w/broken rings have more than 80lbs.

Interesting... so if the valves are good, how does a mechanic determine whether the rings are a problem? By the fact that the compression is low and the valves are good?


More likely valve leaks. Put compressed air into the plug hole with the valves closed.
Take the air cleaner & oil cap off and listen for air. TB or exhaust- valves. Oil fill- rings.

Okay, I'll see about trying that (if the shop doesn't get to it first). Do weak lifters cause the valves not to seal properly? Or does a valve train that needs adjustment cause valves not to close properly? Or do valves warp over time? I'll do some research using google in the mean time.

j2rossit
08-01-13, 05:25 PM
The old school trick to confirm bad rings is to squirt some heavy oil into the the cylinder and redo the compression test. If the number on that cylinder jumps up, then the rings are bad.

nebulosity
08-01-13, 05:27 PM
The old school trick to confirm bad rings is to squirt some heavy oil into the the cylinder and redo the compression test. If the number on that cylinder jumps up, then the rings are bad.

Just like the lifter test we did. :)

WAIT....... do you think valves not sealing as they should would be the reason why I had wayyyyyy too much pressure in my valve cover???

Aztec ETC ECS
08-01-13, 05:34 PM
No, lifters wont do it. Either the valve or seat is N/G.
This exhaust valve came out of my 455:
http://i1259.photobucket.com/albums/ii547/AztecETCECS/valve.jpg

It's not impossible for worn rings to do it though. The air test will tell you.

nebulosity
08-01-13, 05:37 PM
No, lifters wont do it. Either the valve or seat is N/G.
This exhaust valve came out of my 455:

OUCH. :( How did that happen?


It's not impossible for worn rings to do it though. The air test will tell you.

Okay, thanks. :)

Aztec ETC ECS
08-01-13, 05:39 PM
WAIT....... do you think valves not sealing as they should would be the reason why I had wayyyyyy too much pressure in my valve cover???
Another clue. That would be blow-by past the rings.

nebulosity
08-01-13, 05:42 PM
Another clue. That would be blow-by past the rings.

Is piston ring failure a typical occurrence of engines at 89k miles? o.O

Aztec ETC ECS
08-01-13, 05:43 PM
OUCH. :( How did that happen?
Hard to tell for sure. The seat probably leaked first, causing the valve to burn

----------


Is piston ring failure a typical occurrence of engines at 89k miles? o.O
No, but the 4100's had their share of problems.

nebulosity
08-01-13, 05:45 PM
No, but the 4100's had their share of problems.

I kinda had a feeling. :/

I just hope the engine will hold up long enough to pass an emissions test to get it licensed... I don't have more than $1200 to dump into this engine, and no driveway to do a rebuild if it turns out to be bad rings. :(

Aztec ETC ECS
08-01-13, 05:51 PM
Oh, CA still has emissions for an '84.
NY is safety only pre-'96.
Good luck.

nebulosity
08-01-13, 05:53 PM
Oh, CA still has emissions for an '84.
NY is safety only pre-'96.

Yeah, California is really ridiculous about emissions. :/


Good luck.

Thanks. :)

If it turns out I need a rebuild, I wonder if I could have my shop pull the engine and give it to me to rebuild in my garage....... then I could bring it back to them and have them put it in. o.o........ hmm. That could be a back up plan.

The Ape Man
08-01-13, 06:50 PM
More likely valve leaks. Put compressed air into the plug hole with the valves closed.
Take the air cleaner & oil cap off and listen for air. TB or exhaust- valves. Oil fill- rings.

I've seen engines w/broken rings have more than 80lbs.

Add to that maybe some intake valves aren't even opening due to a flat camshaft.

nebulosity
08-01-13, 06:55 PM
Add to that maybe some intake valves aren't even opening due to a flat camshaft.

By "flat," how flat do you mean? I took a video of my valve train while cranking it over, and only one had a problem moving because of the lifter, but after we added oil, it worked almost perfectly. o_O

Given that the valves were moving, I know that the camshaft lobes aren't flat. It's possible they could be worn, but I didn't actually measure it to know. :/


http://www.youtube.com/watch?v=qZZW2H6ECEw

The Ape Man
08-01-13, 07:08 PM
Cool video! Reminds me of the Woodstock movie.

Has that lifter started working?

The reason I say camshaft lobe is they used to go flat on HT-4100s when coolant would mix with the engine oil. Yes it looks like you still had a good lobe when the video was shot.

nebulosity
08-01-13, 07:21 PM
Has that lifter started working?

Yep. It starts working after it pumps up with oil. :)

----------

OH! Wait a minute!!

When I took those compression measurements, that was BEFORE I knew the timing sprocket was stripped. Could the compression measurements be bad because the valves and piston were not running at the right time???

Those compression measurements are probably meaningless!!! I could have good compression, right?? I need to do a new compression test........

The Ape Man
08-01-13, 08:23 PM
Yep. It starts working after it pumps up with oil. :)

----------

OH! Wait a minute!!

When I took those compression measurements, that was BEFORE I knew the timing sprocket was stripped. Could the compression measurements be bad because the valves and piston were not running at the right time???

Those compression measurements are probably meaningless!!! I could have good compression, right?? I need to do a new compression test........

The cam timing should effect all cylinders in a similar manner.

nebulosity
08-01-13, 09:32 PM
The cam timing should effect all cylinders in a similar manner.

Only if the timing chain and sprockets stayed in the same relationship throughout each cylinder test, and I can almost guarantee you it was slipping all over the place. Look.... you can see that it really has a hard time grabbing..


http://www.youtube.com/watch?v=dJElwzFkCW0

csbuckn
08-01-13, 10:23 PM
The compressed air in the spark plug hole is probably the best way to tell what's going on in the cylinders. Easy to do and accurate too.

greencadillacmatt
08-01-13, 10:27 PM
^cs is the guy to listen to. :worship:

+1 for the air test.

Aztec ETC ECS
08-02-13, 09:02 AM
^cs is the guy to listen to. :worship:

+1 for the air test.
Who suggested the air test? :hmm:

csbuckn
08-02-13, 09:54 AM
More likely valve leaks. Put compressed air into the plug hole with the valves closed.
Take the air cleaner & oil cap off and listen for air. TB or exhaust- valves. Oil fill- rings.

I've seen engines w/broken rings have more than 80lbs.

I DID! See? Lol

j2rossit
08-02-13, 10:12 AM
When you do the air test, it's a good idea to open the radiator cap and watch for bubbles (if so, then the head gasket is suspect).

----------

Bad head gaskets are what the HT-4100 is notorious for. It never crossed my mind until now. How does the oil look? is there any smoke out the back?

deVille33
08-02-13, 10:18 AM
Cadillac valve systems are not adjustable, but lifter failure or oil passage blockage will cause that valve to perform below it's desired capacity. The 368, relative to the 425, should run much farther than 89K. It sounds like this engine was poorly maintained or abused or both. Without the ability to do these tests yourself, you will have to rely on your mechanic for the outcome.

cadillac kevin
08-02-13, 10:23 AM
Cadillac valve systems are not adjustable, but lifter failure or oil passage blockage will cause that valve to perform below it's desired capacity. The 368, relative to the 425, should run much farther than 89K. It sounds like this engine was poorly maintained or abused or both. Without the ability to do these tests yourself, you will have to rely on your mechanic for the outcome.

It's a 4100, not a 368. 89k is a long time for one (if its original).

j2rossit
08-02-13, 10:37 AM
The 4100 was notorious for spontaneously grenading itself due to overheating, wearing out the oil pump, and spinning cam bearings. If you were able to avoid these problems, they can last a very long time. I would not say that 89k is when the engine is worn out. They tended to fail catastrophically. That is why I would suggest trying to source a used GM replacement crate engine and drop that in instead of rebuilding the original if it turns out this isn't a simple top end repair.

Aztec ETC ECS
08-02-13, 12:01 PM
More likely valve leaks. Put compressed air into the plug hole with the valves closed.
Take the air cleaner & oil cap off and listen for air. TB or exhaust- valves. Oil fill- rings.

I've seen engines w/broken rings have more than 80lbs.I DID! See? Lol
:lildevil: Good forgery! ^^^
I couldn't have done it better myself. :histeric:

----------


It's a 4100, not a 368. 89k is a long time for one (if its original).
I like how they canted the valves for better flow & more HP. :rolleyes:

nebulosity
08-02-13, 03:17 PM
When you do the air test, it's a good idea to open the radiator cap and watch for bubbles (if so, then the head gasket is suspect).

----------

Bad head gaskets are what the HT-4100 is notorious for. It never crossed my mind until now. How does the oil look? is there any smoke out the back?

Just black smoke when it was running rich. The shop said they did a test for the head gasket and said it's fine.... I'll still be doing the test you suggested though. :)

----------


It's a 4100, not a 368. 89k is a long time for one (if its original).

89k is a long time for an original??? As an engineer I find that sooooo so sad (and embarrassing for the engineers). :(

----------


The 4100 was notorious for spontaneously grenading itself due to overheating, wearing out the oil pump, and spinning cam bearings. If you were able to avoid these problems, they can last a very long time. I would not say that 89k is when the engine is worn out. They tended to fail catastrophically. That is why I would suggest trying to source a used GM replacement crate engine and drop that in instead of rebuilding the original if it turns out this isn't a simple top end repair.

Thanks for the advice. I'd prefer to do a crate engine, but I'm not sure how California would feel about a non-original engine in this car. I need to post a thread and ask if anyone in California has successfully swapped engines and passed emissions. :(

----------


I like how they canted the valves for better flow & more HP. :rolleyes:

Valves are canted in which engine? What does that mean exactly ("canted")?

j2rossit
08-02-13, 03:29 PM
I'm not talking about putting in a non-original motor, it's still an HT-4100, just one that they made after 1985 to answer all the warranty replacements they were footing the bills for. Since it's a production engine made as a direct replacement for the one in your car it should have no impact whatsoever on emission laws. Only a true HT-4100 enthusiast can tell the difference without checking the numbers anyway (some extra cross bracing and the valve covers were different but that's only if the valve covers weren't swapped with the originals). Since these engines were produced for the dealership warranty swaps I don't buy that California didn't allow Caddy to honor their warranties and put replacement engines in.

cadillac kevin
08-02-13, 03:36 PM
Below are californias swap laws....pretty much, the engine has to be newer than the car, have all emissions equipment, OBD if equipped, working CEL, and has to be california certified (so you can't buy an engine from outside CA because it didn't meet CA certification when new). Pretty much, CA sucks for hot rodders (which confuses me how so cal is still seen as a hot rodders paradise.) I bet you could put a LT1 or LSx motor in and have it pass though.....they should meet all the requirements as long as you install the factory harness/ computer.
You also cannot install performance parts on engines (WTF....not sure how they could tell though.)
http://www.bar.ca.gov/80_barresources/07_autorepair/engine_change_guidelines.html

nebulosity
08-02-13, 03:39 PM
I'm not talking about putting in a non-original motor, it's still an HT-4100, just one that they made after 1985 to answer all the warranty replacements they were footing the bills for. Since it's a production engine made as a direct replacement for the one in your car it should have no impact whatsoever on emission laws. Only a true HT-4100 enthusiast can tell the difference without checking the numbers anyway (some extra cross bracing and the valve covers were different but that's only if the valve covers weren't swapped with the originals). Since these engines were produced for the dealership warranty swaps I don't buy that California didn't allow Caddy to honor their warranties and put replacement engines in.

I know, and I'm not exactly sure how California works, but I'm assuming they match the VIN number to the engine number, and they probably want to see that it's the engine that came with the car. I can imagine that they've seen a lot of DeVille's with HT4100 replacements since that engine had so many problems, so maybe they'd be okay with it (and I see your point about dealership warranty swaps, so you're probably right). What I really need to do is talk to someone at the DMV or an emissions referee about what I *can* do. At this point, I'm just guessing.

----------


Below are californias swap laws....pretty much, the engine has to be newer than the car, have all emissions equipment, OBD if equipped, working CEL, and has to be california certified (so you can't buy an engine from outside CA because it didn't meet CA certification when new). Pretty much, CA sucks for hot rodders (which confuses me how so cal is still seen as a hot rodders paradise.) I bet you could put a LT1 or LSx motor in and have it pass though.....they should meet all the requirements as long as you install the factory harness/ computer.
You also cannot install performance parts on engines (WTF....not sure how they could tell though.)
http://www.bar.ca.gov/80_barresources/07_autorepair/engine_change_guidelines.html

Wow! Thanks for the URL. I don't think I came across that link when I was looking up engine swaps. Yeah, California sucks (now you know why I'm paranoid, lol). I'll read through it.

Thanks again. :D

Aztec ETC ECS
08-02-13, 03:43 PM
Valves are canted in which engine? What does that mean exactly ("canted")?
In the 4100. It means offset or twisted(not in a row next to each other) a few degrees to improve airflow, like a big block Chevy or Ford. But the 4100 was not exactly the same performer.

lacville78
08-02-13, 03:47 PM
[/COLOR]

89k is a long time for an original??? As an engineer I find that sooooo so sad (and embarrassing for the engineers). :([COLOR="Silver"]

----------



You have to see this video! Cadillac was proud of how they designed that engine in the 80s. Remember H.T. Stands for "High Tech" haha.


http://www.youtube.com/watch?feature=player_detailpage&v=U89CpaKojlw

j2rossit
08-02-13, 03:48 PM
In the 4100. It means offset or twisted(not in a row next to each other) a few degrees to improve airflow, like a big block Chevy or Ford. But the 4100 was not exactly the same performer.

Not when compared to a big block.
But for it's time it was the best performance out of a 250 around and got (gets) great mileage. Their goal when producing the engine was to get the performance of a big block out of a tiny small-block.

Aztec ETC ECS
08-02-13, 03:53 PM
Not when compared to a big block.
But for it's time it was the best performance out of a 250 around and got (gets) great mileage. Their goal when producing the engine was to get the performance of a big block out of a tiny small-block.
They should have went right to the 4.9.

cadillac kevin
08-02-13, 06:11 PM
Not when compared to a big block.
But for it's time it was the best performance out of a 250 around and got (gets) great mileage. Their goal when producing the engine was to get the performance of a big block out of a tiny small-block.
They got the smoothness of a big block and good mileage right on it, they just forgot the power part.

The Ape Man
08-02-13, 06:25 PM
The HT-4100 was never intended to be used in RWD cars that weighed 4000 lbs. The fitment and imlementation is a compromise. They are more difficult to remove and replace than any other GM engine found in RWD Cadillacs.

They did a little better in lighter cars and were later refined into pretty fair powerplants.

----------


Only if the timing chain and sprockets stayed in the same relationship throughout each cylinder test, and I can almost guarantee you it was slipping all over the place. Look.... you can see that it really has a hard time grabbing..


http://www.youtube.com/watch?v=dJElwzFkCW0

That's a different story. The cam is changing relatively to the crank all the time. Never mind.

j2rossit
08-03-13, 02:10 PM
Since you've got the whole front end apart, don't even think of putting the original water pump back on. And if you do end up pulling the motor or sourcing one for a swap, change the oil pump when it's out.

nebulosity
08-03-13, 03:26 PM
Since you've got the whole front end apart, don't even think of putting the original water pump back on. And if you do end up pulling the motor or sourcing one for a swap, change the oil pump when it's out.

Don't worry, it has a new water pump on it. :) I'll be sure to change the oil pump if we go that far with repairs.

BigCadMan_1
08-04-13, 01:04 AM
And the HT4100 song go's on & on!!

j2rossit
08-04-13, 04:53 PM
And the HT4100 song go's on & on!!

:histeric: And who, might I ask, just worked out a deal on an 85 eldorado with the HT-4100? :wave:
but Mike's got you setup with a crate engine so :thumbsup:

BigCadMan_1
08-04-13, 06:03 PM
Hey Jon I've paid my HT4100 dues! I know these engines better then most & that's nothing I'm barging about either! With that said some people will just have to learn the hard way. I only made the deal for Mike's 85 Eldo because I know the providence of the car AND it's coming with a GM Good-Wrench crate engine as you pointed out. At this point in my life I would never buy or even entertain the idea of buying another 4.1 equipped Cadillac for anything more the current scrap value.....I don't care how clean the car! The problem with Cadillac people like us is most of the time we don't learn our lesson & end up with another lawn ornament 2 or 3 times before we get disciplined & not make the same mistake for a 3th or 4th time!

j2rossit
08-04-13, 06:13 PM
I wish you all the luck with that project. I know you got your stuff together and I'm happy to see another caddy saved from the wrecker.:2thumbs: