I have an '87 Toyota Corolla FX16 with the 4AGE DOHC engine, and fuel injection. It’s a long time piddle project. I think I’ve had the car for 14 years. Not so long ago, mileage wise, I had the engine rebuilt w/30 over higher compression pistons. The shop gave me back an assembled short block, and I installed all the rest of the stuff. The car seemed to run OK, but due to having to swap out the
(broken) correct transmission for one that would fit, I got a large change in gear ratios. 80 mph used to be 4k. With the new transmission it was 3.2k. Brought the mileage up from 30 to 36 mpg, but that is not the point of the car. It’s intended to be a fun toy. I noticed the plugs getting a carbon coat. Over the course of the years I acquired a pair of Tomei cams and some higher volume injectors. I assembled these into a spare head (you would not believe the amount of spare parts I have). I finally located a correct close-ratio transmission. I assembled it with the new transmission and the new head. I used a three layer steel head gasket, torqued it down in three passes, waited 15 minutes and torqued it again. It ran great for about 50 miles, and then rough and then no start. I checked compression. 1,3 and 4 had about 90#. 2 had 150#. Stock compression is 185#. I checked the timing most carefully- the marks on the crank pulley and the key on the crank, the knock marks on the cams, the tension of the belt. Same results on retest. I dribbled some oil in the cylinders and got 1-185, 2-300, 3-185, 4-185. Can anybody give me a reasonable reason for these results other than cylinder/piston/ring problem?
This is a long post. I apologize, but I tried to put in all facts I believed pertinent. Thanks for your thoughts.
Your numbers from #2 sound fishy. Like there is somthing IN there that should not be. The rest sure seem like bad rings. My first thought is did you check piston to valve clearance before installing the head? High lift cams with high compression pistons can mean valve contact…but your compression test would not be as it is. The wet test would still be bad.
You need to pull the head an find out what is going on inside.
BTW… Your performance loss was not wide ratio vs close ratio trans, it was the final drive ratio that killed your acceleration.
I’d’ve heard a piston hitting a valve. The 4age is a non-interference engine, and these cams have been used by others with this model engine. I just would like to believe the block and the machine shop are not the problem, but wishing doesn’t change much. If it’s not the head, and I don’t believe it is, then it’s out of my hands, because I don’t have the place and equipment to pull the engine. There is such a thing as coincidence, but the fact that these things happened closely in time has me wondering if I’m missing something obvious.
Correct about the ratio. Just put that in there in case it had some bearing on engine wear.
300 PSI? I think you injected too much oil for the “wet” compression test. That is not a good test method anyway. A cylinder leak down test, while more time consuming will prove what is leaking.
Multi-layer steel head gaskets require perfect mating surfaces, composite head gaskets are more forgiving. Was your replacement cylinder head resurfaced?
Valid questions. I know I put too much oil in. It was more slobber than dribble. However, after a few minutes I retested the low-reading bores and the compression had dropped to 120#.
I have had problems with composite gaskets blowing out. The cylinder head on the engine prior to this event had been surfaced and I used a steel gasket on it. This particular head I checked with a square. It may not have been perfect. However, is there a situation where a bad head gasket will give these readings? I can’t reason my way to it, but I’m certainly willing to be educated. There may be 11 different things going on here, and here I’m trying to get it answered with one reason. It’s cold, I don’t have a garage, and I’d like to have a plan before I tear into it.
None of this matters since you ran this block successfully until you installed a head with performance cams. You can’t assume there is clearance, you must PROVE there is enough clearance between the pistons and valves. Building performance engines is not a guess…I’ve been there, I’ve broken that, expensive lesson.
A few more thoughts now that I’ve had some time to think about it…
The new head and cams on the rebuilt high compression block with too little clearance between the pistons and valves… Not actually touching the pistons when cold… BUT
The engine warms up, the revs come up as you drive it, the rods stretch a little at higher revs, the pistons rock a little, the valves heat up, enlarge and start to just touch the pistons. The contact nibbles away at the aluminum piston tops shedding chips throughout the bores damaging the ring seal. 50 Miles later, compression is lost and the engine acts like the rings are worn out…but the valves still seal. The cause was inadequate clearance. A compression test shows the rings are shot…but not WHY the rings are shot.
I think the piston tops will show you the answer. If you had a boroscope to look down the spark plug holes, I think you’d see the marks on the pistons tops.
Who rebuilt that block? Unless you dumped a pint of oil into the cylinders the compression going from 90 to near 200 points to a ring problem and/or cylinder bore problem.
That bore problem could even be due to a poor crosshatch hone.
And I agree with Mustangman about the head/cam. You need to compare the stock lift/duration against the lift/duration on the performance cams.
OK, I tried the borescope. Unfortunately, the end of the scope is rigid for about 3 inches, so I couldn’t see the cyl walls. I could see the indents for the valve, and they looked good, but nothing I’d take to court. Off with its head.
This is a pint size engine, each cylinder is 397 cc, the combustion chamber is 42 cc (with stock compression ratio), that is 1.4 fluid ounces. If you add 1 ounce of oil to the cylinder it will greatly increase the compression readings and oil won’t seep past the MLS head gasket like air will.
Just curious, is this the famous AE86 or the not so famous AE82 body?
As for the engine, it was a popular swap to put an 4AGE on to Tercel 4WD wagon, but the transmissions were not made to handle the torque from them. To me that was a waste to have all that torque that you could not use. I put a 4AC in mine with a Weber.
One trick to insure that you have the proper piston to valve clearance is to assemble the head and block without the head gaskets, and without the head bolts, but put a layer of play-do on top of the head. Then slowly turn the engine over at least two times.
When you lift off the heads, you can tell if you have enough clearance. BTW, often with these on line forums, people will tell you about their success with those aftermarket parts but seldom are they used in the exact combination you used them in.
Also at some point, when you add high lift, long duration cams, high compression pistons, thinner head gaskets and shave the head, that non interference engine becomes an interference engine. I know that the 4AC with a Paradise Cam becomes an interference engine despite what some may say.