Compression test results

[VW]

My compression test results were 1-120, 2-120, 3-115, 4-115. What does this mean in terms of my engine(1600DP) life? How would I test the other MAIN aspects of the engine(bottom end, etc.)?

Bugster

[74baja1915]

well that looks like they are with'in specs
Do you have a problem with the motor?
as long as they are not to different from eachother like 1-120 2-100 3-120 4 -90
then your compression is good

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If its not broke don't fix it, but if it can be made better by all means do it!

[ANT]

Those numbers are great. The thing to understand about compressions tests is that you're not so much looking for a specific pressure (to a certain degree you are...) but what you really want to find out if how the cyliders compare to each other.

In a perfect world they'd all be the same, capeesh?
-ANT

[Marc]

Does it run hot or make any unusual noises?
Does the oil pressure light ever come on for more than a second or so when you come to a stop after a long freeway trip?
Yank the crank back and forth to see how much endplay it has. Around .004" is great, .006" is OK, more is cause for concern. Pop off the valvecovers and grope the valvesprings, see how much you can wobble the valves in the guides. Should be barely detectable. What do the insides of the valvecovers & oil filler look like? Scummy could just mean the t'stat isn't working, but hard black deposits take years to form so usually indicate high miles. Still curious? You can pull off the rockers and inspect the valve stem tips for excess wear, or use a strong light and a mirror to peer into the chambers and see what kind of deposits are on the piston tops (dry light tan is good, wet black is bad). You could see if the head nuts are tight by checking the lower ones with a torque wrench (I'd check at 18 lb-ft for 8mm studs and 25 for 10mm) - if any move be sure to recheck the valve adjustment when you reinstall the rockers. There are other ways to get an impression of an engine's condition without any major surgery, but how does one describe smells, etc. in writing?
The compression numbers themselves can't tell you what the compression was when the motor was new (i.e. what the compression ratio is, whether or not the cam is stock) and variation from one gauge to the next is common, so your numbers don't tell us anything except that all 4 cylinders are approximately as good at pumping air, and that you should be using W8AC plugs if you're pretty sure it's a stock engine.
What letter(s) does the engine serial number start with? There are some that are known to be problematic.

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"For every complex problem, there is a solution that is simple, neat, and wrong." --H.L. Mencken
`67, 69, `77 Beetles, `73 II (Type I engine), `86 Audi 5000s, etc. etc.
Independent VW specialist shop manager/unit repairman 1978-1991
Lots of good links in my Yahoo! Briefcase
http://briefcase.yahoo.com/marcvellat

[VW]

Whoa, what a reply! The engine was a new mexican or brazilian engine. I'm guessing it's had about 40000-50000 miles put on it over it's life. My engine runs fine, I just wanna be prepared for engine failure if it's in the near future thats all(maybe paranoia). Now then, pulling on the crank pulley is a good way to check bottom end? Which way to I push/pull it? Up and down, right and left, in and out, all of the above?

Thanks for the replies!

[aussiebug]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by VW:
<B>Whoa, what a reply! The engine was a new mexican or brazilian engine. I'm guessing it's had about 40000-50000 miles put on it over it's life. My engine runs fine, I just wanna be prepared for engine failure if it's in the near future thats all(maybe paranoia). Now then, pulling on the crank pulley is a good way to check bottom end? Which way to I push/pull it? Up and down, right and left, in and out, all of the above?

Thanks for the replies!</B><HR></BLOCKQUOTE>

Grab the engine pulley and push/pull it fore and aft - what you are looking for is freeplay ALONG the cranksahft. Too much (any more than about .006") and the bearing saddles inside the engine are starting to wear. When that gets REALLY bad the bearing shells will spin, and you can probably say goodbuy to that case - if caught and rebuilt before it becomes a major problem an align-bore will usually fix the problem.

A fresh 1600 (nicely run-in) should give 130 or more psi. Your compression figures are fine for a partly worn engine - the main thing to watch for is more than 10psi worst to best - that would indicate one cylinder on the way out (and probably more following close behind).

The general rule is, once any cylinder gets below 100psi, it's time to start planning a rebuild. It's will probably run OK for some time with low psi, but it's telling you it needs work. I had one engine still running quite happily with 100, 100, 90 and 45 - no oil burning, just a little sluggish. The increasing fuel consumption was the first major sign.

Once compression drops you can sometimes find out the cause (either valves not sealing or rings not sealing). Do a test and measure the compression. Then squirt about 10cc of oil into the plug hole and do the test again. If the pressure goes up a little, the rings are the likely problem (oil provides a temporary seal), but if there is no improvement, the valves are suspect. Might help determine if you want to rebuild just the heads, or need to go further.

Hopefully all that is still a few years away for your engine.

Give it a regular oil changes and tune-ups (there are procedures on my site below) and it should keep you going for a long time yet.




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Rob
Rob and Dave's aircooled VW pages
Repair and Maintenance for the home mechanic
http://www.geocities.com/aussiebug1970/

[VW]

The engine's fine, I was just curious about the engine life.

Thanks guys

[rich2481]

check end play but you are asking a open question, hell anytime you have a used engine who knows the life span, could run for years, could blow up tomorrow, how do you check that, I dont know

[Marc]

Mexican motors are built with a low compression ratio to allow them to tolerate Pemex regular - could be yours never had over 120 when it was new. The main thing I'd be concerned about at 50K is that the odds of an exhaust valve breaking start climbing from here. If you preemptively did a valve job now, just to get new exhaust valves in there, you'd probably also clean, hone & rering the pistons/cylinders but shouldn't need to do much else. You could get well over 100K on the original valves, though (do ya feel lucky?) so you might decide to let it go and see. By around 120K, there's little point in doing anything short of a complete overhaul. Once in a great while a broken valve will damage more than just the head & piston, so there is a degree of risk beyond the inconvenience. You need to decide based upon your budget and what you need/use the car for. If it's your only transpo and a week in a rental car is out of the question, or you're going on a long cross-country trip beyond the range you'd want to tow it home from, you may want to do the work now. Otherwise, you may as well see how long it'll go with regular maintenance. Always note exactly how tight any exhaust valve is found at adjustment time and jot it down in a record. The only warning you'll ever get that an exhaust valve is getting ready to break is that it will be found getting tighter as the stem starts to neck down.
Now, say you go to 80-100K and decide for whatever reason that you can't trust it anymore...in addition to the work that you might have gotten away with at 50K, now the pistons aren't quite worth re-ringing, the rod bearings aren't quite good enough to make it another 50K and the cam & lifters are starting to show wear, so there will be a decision tree then as well (patch it and see if it'll make it to 120K OR do a valve job, new P&Ls, rod bearings, etc. without splitting the case which should guarantee another 50K, but when you go to rebuild it completely your pistons are already half-worn-out OR break down and do the complete overhaul a little bit early).
The point I'm trying to make here is that there is usually more than one "correct" decision about when to repair an engine, and more often than not the individual's transportation & financial situation can have as much to do with it as the engine's condition. A competent & ethical shop will explain the options once they know what they have to work with rather than just offer a one-size-fits-all exchange longblock solution. (The mileage numbers used above are fairly typical overall, but can vary with conditions/driving style/etc. - I just used them as aids to try to illustrate the point, so don't nobody start flaming me about how their engine has 300,000 original on it. My own car has close to 500K on its 3rd engine and 2nd trans, and the 2nd engine is still a runner - but 120K is more often than not at least "twilight time" for most people's Type I engines).

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"For every complex problem, there is a solution that is simple, neat, and wrong." --H.L. Mencken
`67, 69, `77 Beetles, `73 II (Type I engine), `86 Audi 5000s, etc. etc.
Independent VW specialist shop manager/unit repairman 1978-1991
Lots of good links in my Yahoo! Briefcase
http://briefcase.yahoo.com/marcvellat

[Hollywood241]

I'm running a 1915 with a 110 cam and I'm running like 100 compression on all the valves is that good?