Guys I just did a compression check on my motor and it had 145 across the board. I just installed this motor a few weeks ago, purchased it from soshin but I am not able to drive it because the body is in pieces. Anyway the reason I did a compression check is because I am getting blue smoke out the tail pipe, the weird thing is not all the time. I tried pouring oil down each cylinder and number one and four cylinders stayed the same, numbers 2 and 3 went up to 155(I may have put a little too much oil in, not sure if that would matter). I checked the plugs and they look good and did a vacuum test and it came out with about 21psi of vacuum at idle with a steady needle. The motor is a 91 zc dohc. Any ideas, bad rings?

 

145 is just a number and it could be high or low depending on the guage you used or if you did the test correctly (ie-disable the fuel system first). The most important thing when doing a test like you did isn't the actual number so much as it's how consistent the numbers are. In that sense you seem to be good. A motor that old could have worn rings, it could also have a headgasket issue between cylinders 2-3, it could have worn valve guides, valve seals etc especially if it has never been rebuilt. It might be worth lifting the head off it to take a look and freshen things up.

 

Thanks, I wish I did that when the motor was on a stand. I looked at the cylinder walls when I had the oil pan off with a flash light and they looked good, no scoring. I had to replace all the injectors because they were clogged so yeah the motor has been sitting for awhile. Soshin runs some kind of chemical in it to keep it from rusting. I was also thinking maybe the piston rings were sticking from sitting so long.
I guess my next test will be a leakdown test.

 

How exactly did you perform the test? Our motors are aluminum, so they expand when they get hot. You should warm the motor up to opperating temp, then do the test. Dont let any fuel get in the cylinders. Hold it at wide open throttle, and crank it over for about 10 seconds. That will give you an accurate reading.

 

145 seems low to me, regardless of correct/incorrectly doing the test. I would say worn rings or valve seals.

 

[QUOTE=1998GsRIntegra;44064426]How exactly did you perform the test? Our motors are aluminum, so they expand when they get hot. You should warm the motor up to opperating temp, then do the test. Dont let any fuel get in the cylinders. Hold it at wide open throttle, and crank it over for about 10 seconds. That will give you an accurate reading.[/QUOT

I did the test exactly as you described, maybe a little less than 10 seconds. I also thought the compression was low and sometimes I noticed the compression needle would drop slowly so I went out and bought a new gauge and my reading were a lot better, 195 to 200 across the board! I also picked up a leak down tester and will be doing that this weekend. I am thinking maybe the smoke is related to my valve stem seals because if you look in the exhaust ports on the head you can see oil around the top of the valves where they come out of the valve guides. What do you guys think?

 

As 1998GsRIntegra has described

Warm the car up to operating temp
Hold the throttle wide open
Crank for 10 seconds on each cyl.. you can count the cranks if you listen, this should give you about 9-11 cranks per cyl.

 

Blue smoke means oil leaking into the combustion chamber. There is only a few ways oil can get into the chamber: either bad piston rings, bad valve seal, or even a bad valve guide.
Bad compression rings (piston rings) will give you lower than normal compression.

 

Doing a compression test to check oil consumption is a myth that keeps spreading. The oil control rings on the piston control oil, not the compression rings. The compression rings only seal compression, they do not control oil. You could take the oil control rings off the piston and run a compression check and it would be higher than originally due to the oil entering the cylinder. Valve guide seals don't seal anything but oil anyway plus they are outside of the cylinder so they don't show up either.

If your PCV system is OK then there really is only two ways to get oil into the cylinder to be burned. Either the valve guides are not sealing due to excessive valve guide clearance or faulty seals or the oil control rings are faulty or stuck in their ring land due to carbon/varnish build up.

The valve guide seals themselves can get dried out and brittle and not seal but more commonly on a higher mileage engine that has been beat on the valve guide to valve stem clearance is excessive which wipes out the seal as the valve stem rocks around in the guide. Putting new seals on valve guides that are excessively worn is only a temporary repair and the new seals will be destroyed in short order.

Generally you can diagnose your oil consumption problem with a simple test. The problem with this test is if you have a catalytic converter it may mask the problem and you will have no smoke out the exhaust. If you have a cat it is better to do this test when the engine is dead cold so the cat hasn't had time to heat up. If you can install a test pipe in place of the cat that is even better. Get on a road where you can do full throttle blasts in 2nd or 3rd gear up to redline. Get the car moving and put it in 3rd gear and at about 2000 rpm put the accelerator all the way to the floor up until redline. If the engine smokes while you are accelerating you have faulty or stuck oil control rings. Then, after you have gotten to redline let your foot off the gas but leave it in gear so you are engine braking. If it smokes while decelerating then you are getting oil past your valve guides due to wear or faulty seals.

The reason accelerating causing the rings to pass oil is something called 'pumping' when there is excess oil on the cylinder walls because the oil control rings are not doing their job. As the engine is under load, the gas pressure (when you are decelerating there isn't much pressure in the cylinder) and motion of the piston physically pumps oil from below the rings to above the rings and into the cylinder. There are holes or slots on the piston behind the oil control ring land where oil can drain through and back to the crankcase. These holes or slots are not present on the compression ring lands. The thin oil control rings physically scrapes the oil off the cylinder wall and out these holes or slots.

Oil is consumed through the valve guides on deceleration because you have the throttle slammed shut and the engine rpm is high. This cause very low pressure (high vacuum) in the intake port at the outlet of the valve guide. the oil is 'sucked' through the valve guide due to the higher pressure in the crankcase. Oil doesn't go through the valve guides during acceleration because the pressure in the intake port and the crankcase are approximately equal at WOT (Wide Open Throttle).

 

^^^ This man knows his stuff^^^

Mr. Tucker, Do you ever plan on building a honda engine? Id like to see what you could create.

 

I haven't built a Honda engine in years but I got into this site when I was into Honda's (still am it's just not what I'm driving). I get my engine fix at work. I work on vehicles like this:



I'm tuning this car, when it was built it was only built to win car shows so I needed to do some modifications to get it to run right. We work on a lot of extremely high end cars like Porsche, Ferrari, Lamborghini, Bugatti, etc. We do mods on those cars too.

Check out our shop:
http://www.canepa.com/about/tour_1/index.html

I spent 4 years at Dinan Engineering, the BMW tuner as an engineer.

I'm teaching a class called High Performance Engine Preparation starting in April at DeAnza College in Cupertino, Ca. I'm going to announce it on this site when it gets closer to the start of the class.

 

i want your job.

 

That would only be like a 110 mile commute each way, send in an app.

 

^WOW...Now that's a shop!

I'd give both nuts to work there.

 

Hey i know this is a 2 year old thread but ita worth a shot. Ok so I got a similar issue. I got my gsr motor rebuilt just recently and i havent even ran it due to my issues. So the desk with it is that I have a surging idle along with oil leaking, and its coming out of my exhaust ports and on all cylinders but number 4. I took the header off and there's plenty of oil in the chambers and also on the spark
Plugs. Should i still do the process u recommended since the motor has not been broken in. And i had machine work done on my head and block but idk if maybe they did somethin wrong on the head like not replace valve stem seals. Thanks