HELP!! low compression on 4 cyl. in Dallas

[1975yellowBSPZ]

My new-to-me 75 auto-x 280z with l28 was burning some oil when I drove it back from houston. I just got around to checking the compression and it doesn't look good. Anyone know anything I can do other then a rebuild or put new rings in? any tricks? I am currenly running some high deterent oil tru it to see if maybe carbon was causing the rings to stick/ and to clean up the lower end due to the blow by. I broke the bank to buy it. I chked the cyl compression and I was getting 120, 20, 80, 120, 20,10 from front to rear!! The service manual says to test if the issue is with the lower end or upper end to put oil in the plug hog and test compression - it it is much higher its in the rings?lower end - if not its valves/upper end. It trippled at least in all of the cyl. so its def rings or cyl. I don't have an engine stand or much in the way of tools. Is there any way to avoid changing the rings at this point, or anyone in dallas who whould be willing to do this type of work cheap? Can this be done with the engine in the car?

It looks like at this rate I'm going to miss this years auto-x season alltogether and I don't feel comfortable with my own abilities to rebuild this whole engine myself, any leads, thought, or words of wisdom would be greatly appreciated.

Bryan W

[texasz]

I'm in the same boat, I will certainly miss this year's autox season all together and maybe part of next as well. See this thread for the kind of info and responses I got: http://www.classiczcars.com/forums/showthread.php?s=&threadid=7922

Maybe we should have a big engine rebuild party here in Texas for all of us who have to do this and don't really know quite what we're doing yet. You know, get together in a big shop with a couple skilled people to assist us...some pizza and beer...some tunes...lots of cursing...

[Gav240z]

you can pickup a second hand engine pretty cheap there's always one or 2 advertised. Since you know how to check compression etc you should be able to get a hold of a decent one for a low amount of $$$.

That way you can rebuild the engine you have in your own time and learn something new .

You could always sell that engine again later.

Just a thought.

[beandip]

With the compression that you gave there is no doubt the engine needs a rebuild. there should only be a few lbs. difference from ont cylinder to another . the 120 is low to start with. Start looking around , I picked up a '82zx engine complete with injection headers and alternater as well as starter, that had been rebuilt with a milled head and street cam . 35K miles on it for $500.00 . So start looking around . It's going to cost you at least twice that much to do a rebuild, a good one , on your engine. Head and all.

[mwz]

Is it just burning oil or does it run poorly? With readings that low, I would think it would just barely be running, and very badly. If it's running OK, I would re-check those readings...maybe it's not as bad as it seemed. Just a thought.

[dalt]

If you decide to change engines check with jerry at all z car specialists in fort worth. You should be able to get a decent engine for around 150 or so.If interested send a pm and I will give the details.

[ZmeFly]

with readings like that how in the hell did you get it home.

id adjust your valves into spec and just for shytes and giggles check it again, something doesnt seem right.

good luck with any choice you make, if the reading stay true to what they are now, you will need a total rebuild and or find yourself a donor engine

[LanceM]

I find it interesting that your low readings are in pairs for the most part. Putting oil in and increasing your readings does indicate rings but can be a fooler sometimes. Typically low paired cylinders indicate a bad head gasket/warped head/cracked block, alowing one cylinder to leak into another. I would be very tempted to pull the head and look inside, it would be only an afternoons work and a couple of gaskets. With readings down to 20 that cylinder should either have a ridge like a clif at the top or look like someone took a grinder to it!! This would also give you a chance to see if the engine is worth rebuilding, if the cylinder walls are tore up you would be better off finding a newer better block to start with.

You can change rings with the engine in the car, no fun but it can be done.

I too wonder how you got it home with readings like that, I'm suprized that it runs at all

[1975yellowBSPZ]

update:

I have a lower? milage 77 L28 sitting on my garage floor next to the stand it will go onto, next to my car.

I don't have compression readings on the engine, and my guess s that this cannot be done on the stand, I don't have a compressor for leakdown test

My current L28 is still in the car and I can unplug the #6 cyl and it runs about the same as with it plugged in. Still Drives ok(!?)

If the 77 motor checks out to be solid (any ideas as to how to check it while its out of the car would be smashing (I guess I'll have to load it up and take it somewhere?) I would not be opposed to putting it in the car and rebuilding the sick 75 engine as need arises, I really do need to get some other things done to the car prior to autox season (tires/wheels/struts/helmet/coilovers?/etc)

any thoughts, condolences, words of wisdom for what I'm soon to embark on, and anyone it dallas with ideas or a small compresser and a leakdown kit that would like to stop by and help me checkout this engine would be a friend for life

Bryan W

[LanceM]

Here's a link to a homemade leak down tester

http://www.xs11.com/tips/misc/misc3.shtml

Perhaps you know someone who has a compessor you could borrow? Looking at the leakdown tester I would say that the air volume required is extreamly low, perhaps one of those 12V ones for blowing up tires would be enough to get the job done without a big outlay of $ and be useful later on. Or another thought is a small air tank, they are not that expensive and you could fill it at a gas station as required.

Here's a wild thought, since you'll have it on a stand with the flywheel off you can't use a starter, how about a 1/2" drill driving a socket on the front of the crank? With all of the plugs out and checking the compression on just one cylinder at a time I bet the drill would turn it fast enough. Take a cheap 3/8" extention and cut off the ratchet end so it will go in the drill, 3/8 to 1/2 adapter and plug on your 27mm socket and go! Know anybody with a 1/2" drill?

If the engine is complete and ready to drop in, carbs, starter, fan, etc, something I've done and falls into the highly not recommended catagory is bolt it to a couple of hunks of 6 x 6 with a chunk under the back to hold the flywheel off the ground. Hot wire the ignition, stick the line from the fuel pump in a gallon can and use jumper cables to start it up. If you are going to run it very long a garden hose shoved in the bottom inlet works fine, but makes a mess Great way to check for bad spark plug wire

Like I said this falls into the "don't try this at home kids" catagory but is a way to see if it will run. The neighbors will love the sound of that short stack exhaust I must say though when I did this it was a duration test, wired the throttle wide open, no water, and let it go. I didn't think it was ever going to quit, gotta love them Datsun engines! Don't flame me too bad here, that was 25-30 years ago, there were plenty of them around then....

OK, ya done run me out of ways to check it without putting it in a car or tearing it down..... who knows maybe one of them might really work!

[texasz]

Here's a link to my thread where I was trying to do the same thing. Basically I found that you can not do a compression test with the engine out of the car like this. I tried with a drill, did not turn...I tried with an impact wrench, did not turn...I tried with a socket wrench with a LONG handle (3' logn!) and that didn't produce good results either.

Running the car in the manner that LanceM described is down right SCARY!!! Please don't try this, it's a bit nuts! Sorry LanceM, I know we all do stupid things when we are young (I certainly have) but this one is a bit out there. :stupid: Glad nothing happened to you. By the way, how long did the engine run?

[LanceM]

Yes scary and nuts, like I said "don't try this at home"

It didn't make it through the gallon of gas before it froze up. Man was it screaming though, had to be running 12K + with WOT and no load! And it ran for what seemed like a long time, we figured it would just over rev and blow, when it didn't we ah, sort of started running It didn't blow either, at least nothing sticking out anywhere, it just stopped, dead in an instant. We never looked but always figured we spun some of the main bearings. Ah to be young and wild again, well ok, maybe not

So Texasz, your experiance shows that the only thing to do is a leakdown test if it is on a stand. Probably the best test anyway since the results are more specific if there are problems that need to be figured out.