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View Full Version : NON Celica- compression question



anachranerd
11-24-2009, 05:56 PM
Hey all,

So I rebuilt this escort engine short block. New rings, rod and main bearings, honed cylinders. Installed the engine in the car. After I bolted it in, i filled it up with oil and decided to run compression checks before i hooked up the rest of the crap.

So, on a cold engine, with a full battery charge, I got 120-110-110-120. Specs say 175-200 on this engine. Seems a little low. At least they are all close to each other.

So could the timing be off? Or is just low because the engine hasnt been run yet-hence piston rings arent fully seated yet? Could it be the cold? it was about 40F here last night.

extremeskillz
11-24-2009, 06:04 PM
My guess is the rings didn't seat correctly. I would give it a check!

anachranerd
11-25-2009, 12:00 AM
keep in mind, this hasnt been fired yet. all i did was crank it with the starter. the mani's arent on yet or anything.

im kinda wondering if it wont show full compression until its been fired and the rings have completely seated under load.

Luni
11-25-2009, 01:24 AM
Your compression readings will be low if the rings havent seated in.

So, Id double check my mechanical timing, and if everything is spot on like it should be, Id proceed with install, and break in.

And honestly, I recommend the more aggressive break in approach, as opposed to your traditional "baby it for 1000 miles" approach.

When I do an engine break in, I find a good stretch of road you can run through the gears in. Get into third gear around 2000 rpm. Floor it all the way up to around redline, and deccel back down letting the engine take the decel and pull vacuum, then accelerate a bit, shift into 4th, and do it again. Do this a couple times and then take it home, change the oil and filter.

I guess to back up, I always start a new engine and let it warm up to operating temp then change the oil. Then I take it out, perform the break in method I described, come home, change the oil again. For the first oil changes, during breakin, I use dino oil. Just regular ol Castrol GTX is what I roll.

Then Ill drive around on that oil for about 100 miles and change it again. Then finally Ill give that change 500-700 miles and change it again, and on that last change, is where Ill switch to synthetic.

Ive never had a problem with an engine Ive broken in that way.

Everyone has their own method of doing it. I was just sharing mine with you.

Grot
11-25-2009, 01:47 AM
Sorry to thread jack, but ima try that method on my GTS if i ever get her running.

I blew out an oil pump last time. Probably had nothing to do with my method though

anachranerd
11-25-2009, 05:41 PM
Thanks luni - i think we will use that method of break in.

rizin
11-26-2009, 02:15 AM
I am with you on this luni. I am going to break in my 5sgte how I normally drive.

alltracman78
11-26-2009, 03:12 AM
It's also not hot, compression specs are on a hot engine.

Also, if you're curious WHERE it's losing compression, do a leakdown test.
If it's the rings, run it and break it in, if it's the valves, the head work wasn't the greatest.

anachranerd
11-30-2009, 05:45 PM
Cool,, I will fire it up and see what happens. Too bad I got the whole thing together and no spark :( THink I either have a grounding issue or a short somewhere. booooo

mlwmlw
11-30-2009, 11:27 PM
If the oil didn't have time to get to the rings that might be it to. Sometimes if ya squirt a little bit of oil on the top of the pistons you can get higher readings.

Just an idea since you rebuilt the engine and maybe the oil hadn't traveled through all the passageways when you checked the compression
(at least for the 1st cylinder anyways)