Low compression 30,000 miles after rebuild 4g37 1.8 sohc

[91-talon-tsi]

I recently purchased a 94 eclipse base with the 1.8 sohc 4g37. There's been 5 owners including myself. The third previous owner had rebuilt the block after the engine had overheated and caused the pistons to swell and slightly scar the cylinder walls.

The rebuild consisted of honed cylinders, crankshaft turned, NPR piston rings, ACL rod and main bearings and all new gaskets. From what I found out, the previous owner who had the block rebuilt used the "motoman" method to break the engine in.

I changed the oil about 100 miles ago and the oil already has a faint gas smell to it as if there's some blow by. However, I have read that slight blow by is to be expected even with a brand new engine.

The thing is, I did a compression test today with a rental OEM brand compression tester from autozone. I warmed the engine up to operating temperature. Shut it down, pulled the MPI fuse, disconnected the distributor and fuel injectors, pulled all the plugs and tested one cylinder at a time with the throttle wide open. The results were 120psi across the board.

I'm having a hard time finding what the compression should be on a healthy 1.8 4g37, but I read somewhere that it's supposed to be 185 psi and 135 psi is the service limit. If that's the case, then how is my engine already at 120 psi when it was just rebuilt 36,000 miles ago ?

Could this be due to the fact that he just rebuilt the bottom end only and did not rebuild the cylinder head ? Should I rebuild the cylinder head and would it be safe to do so since the bottom end rebuild already has 36,000 miles on it ? Could it be due to the "motoman" break in method ? I'm really disappointed with these test results

 

[Wrenchit]

Did you put a squirt of oil in one cylinder at a time and then check the compression?

 

[turboglenn]

I recently purchased a 94 eclipse base with the 1.8 sohc 4g37. There's been 5 owners including myself. The third previous owner had rebuilt the block after the engine had overheated and caused the pistons to swell and slightly scar the cylinder walls.

The rebuild consisted of honed cylinders, crankshaft turned, NPR piston rings, ACL rod and main bearings and all new gaskets. From what I found out, the previous owner who had the block rebuilt used the "motoman" method to break the engine in.

Or at least that's what you were "TOLD", i've been witness to 4 personally and heard of a 5th engine locally sold by a "large import shop" (i won't name since i'mbeing subpeonad to court as witness on 3 of the tear downs) and all of then were just old junk yard motors in decent shape with ARP head studs and fresh felpro gaskets

There were even receipts saying "forged pistons" Eagle rods, etc..etc... Idon't look forward to having to testify against someone who was once a friend and i sitll have no hard feelings for, but i was there in another shop for 2 of them almost immediately after they were instlaled and the people had issues, met the other guy on here and witnessed what he had to show for his money, and yet there's 2 more here in nebraska that bought "built engines" fromthe same guy

Never believe what a stranger selling you something says, check for yourself..when i buy engines i tell them let me pull the pan and head and if i don't want the engine afterwards i'll pay for and install the new gaskets.. that will turn the bullshaattters away usually, and a good personw ill agree to it, buti know you bought a whole car. I probably woulda done compression and stuff on it first but then again i was a mechanic most of my life and still do it when lack of pain permits me to


even if you put oil in it, that's still a bad sign, just proves it's rings.. are you holding the throttle wide open when testing??that makes a big difference...also, check cam and crank alignment , if the guy got the belt on a tooth off it will make a HUGE compression difference too.. With my degreed settings i get 185 per cylinder on mine, and with them "0" or straight up i get like 165-160...

you should have at least 150psi per cylinder with timing correct and throttle open while turning the key until the gauge stops climbing (the right way to test it)


OH, and since getting a crappy smoking low comp engine on my BRANB NEW motorcycle with only 4 miles on when i got it from doing a real "easy break in" I now do EVERYTHING motoman style almost, i just use 4 cycles steadily getting more andmore into boost and revs each lasting 20 minutes with cool downs and inspections between,(if you read the books for testing on SAE engine/drivetrain) you'll learn why methods have changed and why more pressure from boost and engien breaking helps seat rings and why older machining styles and toolls needed that long and easy break in........... i've written it at least 15 times if you wanna search but i can't type anymorei'mtired

 

[bryanwheat]

With the 4 cylinders being so close to each other i'd suspect a bad tester or maybe you didn't do the test right.

 

[91-talon-tsi]

A fellow dsmer who's a member on here and other dsm forums had the rebuild done. I saw pics of the rebuild on another dsm forum, so I know it did in fact have a rebuild done. I adjusted the ignition timing back to 5* BTDC with the timing terminal grounded. It was slightly off until I adjusted it. I'll have to check the valve timing to make sure it's not off at all.

 

[DSM1G90]

Here's a site for 4G37 owners: http://www.dsm1eights.org
But with a small NT motor as the 4G37 135's for comp tests isn't too bad.

My little yellow 1G with the 1.8L with 204K miles still reads 125 to 132 across. But motor has weak valve seals -puffs good after sitting overnight.