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Cylinder Head & Short Block: 4G63 cams, valvetrain, pistons, rods, stroker kits, 6-bolt swaps, hybrids, etc. Read this Forum's Strict Guidelines.

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Old 01-11-2009, 09:36 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #1 (permalink)
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1G-specific

Low Compression after New Rings and Hone


91GSX won't start (see question at bottom):

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History(short version)-
Bought GSX for 500 with tranny but no motor.

Bought motor, cleaned it up and installed it. Car didn't start after months of trouble shooting took it to performance shop. After replacing relay and CAS, shop informed me that I was getting 30psi on each cylinder. ECU also checked out good.

Had car towed back home, pulled and tore apart engine down to block and had it inspected and hone by a machine shop. Block passed inspection and hone was complete. Took block home reassembled block with new piston and new crank bearing.

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Currently-
Car won't start, verified spark (can see it on plug), verified fuel-pump is coming on and fuel gauges state so; fuel on both sides of the rail (two gauges). Check compression 1-0, 2-60,3-60,4-60 after adding oil to the cylinders 1-90, 2-135, 3-150, 4-150. Of course still no start.

---------------------------------------------------------------------------------------------------------------------------

My questions is this:
Why am I getting such low compression if i just installed new rings?
And the head didn't appear to have any bent valves and the timing was dead on.

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Old 01-11-2009, 10:15 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #2 (permalink)
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Well, there won't be a seal on the new rings if they haven't yet been broken in and seated..which requires the engine to be running, so i wouldn't worry TOO much about that (although they are still quite low) have you had the head cheacked out to make sure there's no bent valves or sticking valves?

DO you even get any popping or sputtering to show the engine is trying to start?

Who did the timing belt install and was it verified to be correct after installing it ( i.e. turning the motor 6 times to ensure everything lines back up) ?

give me a little more info nad hopefully i can give you a little more help
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Old 01-11-2009, 10:37 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #3 (permalink)
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Quote:
Originally Posted by turboglenn View Post
Well, there won't be a seal on the new rings if they haven't yet been broken in and seated..which requires the engine to be running, so i wouldn't worry TOO much about that (although they are still quite low) have you had the head cheacked out to make sure there's no bent valves or sticking valves?

DO you even get any popping or sputtering to show the engine is trying to start?

Who did the timing belt install and was it verified to be correct after installing it ( i.e. turning the motor 6 times to ensure everything lines back up) ?

give me a little more info nad hopefully i can give you a little more help
-If I keep trying to start it will that help seat the rings?

-No popping or sputtering; engine just turn over and over. I thought I was not getting spark until I pull the plugs an verified.

-Done the Timing belt; prior to putting the head on I put the number piston at TDC the install the head with the cams lined up correctly. Then installed a brand new belt. I turned the motor at least 10 times and everything seemed fine.

Last edited by man_of_saturn; 01-11-2009 at 10:38 AM. Reason: type
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Old 01-11-2009, 10:47 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #4 (permalink)
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.... have you had the head checked out to make sure there's no bent valves or sticking valves?...p[/QUOTE]


Head haven't been check professionally but I had pulled the valves and cleaned and checked them, head should be good, doesn't have any visible issues.
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Old 01-11-2009, 11:22 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #5 (permalink)
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Some more info needed. What did you have it bored to? What kind of pistons are you using? Who and how was the rings prepped? Are the rings installed properly? Did you make sure the head gasket was sealing and your valve seals are O.K.? is there fuel inside the cylinders?

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Old 01-11-2009, 11:53 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #6 (permalink)
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The valve seats may be out of round and not sealing properly. It happened to us when once large name in the DSM world went out of business and was desperate to get their last orders filled. They shipped our head with what our machinist said were "square" valve seats but there was no way to tell by visual inspection. It might be worth your while to get the head checked by a reputable machinist.


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Old 01-11-2009, 12:01 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #7 (permalink)
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Quote:
Originally Posted by BoredDSM View Post
Some more info needed. What did you have it bored to? What kind of pistons are you using? Who and how was the rings prepped? Are the rings installed properly? Did you make sure the head gasket was sealing and your valve seals are O.K.? is there fuel inside the cylinders?
Engine was only honed, no boring was done.

Stock pistons.

Rings were prepped by being soaked in 10/30 oil over night and applied to rings after groves were cleaned out.

Rings installed with gaps on opposite sides. Rings had no markings to determine up or down.

HG was good, used copper spray on the cometic.

Seals are good.

Little fuel inside the cylinders, would think they would be flooded or spew out of the downpipe.
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Old 01-11-2009, 12:16 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #8 (permalink)
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Did you properly gap the rings? Did you install the rings in the right order? You should check your piston to wall clearance before you had any motor work done. It also could be something in the head like Kahl stated.

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Old 01-11-2009, 12:58 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #9 (permalink)
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NO matter what you should be able to get some popping or sputtering if there's fuel and spark... one fo the 2 isnt' happening. I would say that your injectors might not be firing. Have you tried spraying a little starting fluid in? ( i don't really advise the use of starting fluid, but it can help to see if you're getting any fuel in the engine or not)

I would stop worrying about ring gap and such until you can get some sort of fuel igniting inside the engine (assuming you're comfortable with the engines mechanical state) otherwise you will be pulling it back apart just to verify and still might not make any progress on starting the engine. HAve you checked the MFI or MPI (can't remember what mitsu calls it) but the fuses and relays for the ignition and fuel injectors should be checked

Also, cranking the motor WILL NOT seat the rings, they need positive pressure from combustion to be pressed out with enough force to "seat in"

Just focus on getting it to start for now with the one condition that you're confortable with your engines mechanical state and teh repairs you did from the piston install to the timing belt...if you trust all of that, don't give up on checking things until you get it running... BTW DON"T be one of the guys that makes no changes and simply charges the battery over and over to only run it dead cranking a motor that won't start..you'll only cost yourself more money that way. If the motor is going to start you will hear some thing in the first 5-10 seconds of cranking. IF not, don't crank anymore until you've changed something

One thing that i'm not saying is "acceptable" but is proven is that even with only one good cylinder the motor will start and run (very rough, but it will still start) When i blew my 7 bolt there was 3 cylinders with the HG blown and it still ran and drove me back to the pit lane
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Old 01-11-2009, 01:08 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #10 (permalink)
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put a little oil in the cylinder’s, when you do a head gasket or new rings you tend to was the cylinder out , if you put some oil in the cylinder it jump the compression up enough to run you need about 90+ psi for a engine to run

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Old 01-11-2009, 01:24 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #11 (permalink)
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I'll take a look at the injectors and verify that their spraying fuel.
Thanks!
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Old 01-11-2009, 01:47 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #12 (permalink)
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The entire "oil in cylinders" fix is dubious at best. Yes, it will raise compression, but remember you're putting fluid into the combustion chamber, lowering the amount of space there is in it and therefore raising compression as well.


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Old 01-12-2009, 11:26 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #13 (permalink)
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Quote:
Originally Posted by man_of_saturn View Post
HG was good, used copper spray on the cometic.
...did you resuface the head/block to ensure a good seal on the cometic headgasket? MLS needs to have a flat head/block for good seal, otherwise your compression wont be dead on..

Ive seen people resurface their heads by wetsanding and wondering why there engines wont start
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